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Archive for August, 2009

Papers on the non-significant role of cosmic rays in climate

Posted by Ari Jokimäki on August 31, 2009

This list contains papers which show that cosmic rays don’t have significant role in recent climate change, so this list doesn’t contain the papers from Svensmark et al. or other papers symphatetic to the strong role for cosmic rays, but such papers and issues are discussed in papers below (see also Anti-AGW papers debunked section for some Svensmark et al. papers). The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

LATEST UPDATE (December 25, 2012): Laken et al. (2012) added.

A cosmic ray-climate link and cloud observations – Laken et al. (2012) “Despite over 35 years of constant satellite-based measurements of cloud, reliable evidence of a long-hypothesized link between changes in solar activity and Earth’s cloud cover remains elusive. This work examines evidence of a cosmic ray cloud link from a range of sources, including satellite-based cloud measurements and long-term ground-based climatological measurements. The satellite-based studies can be divided into two categories: (1) monthly to decadal timescale analysis and (2) daily timescale epoch-superpositional (composite) analysis. The latter analyses frequently focus on sudden high-magnitude reductions in the cosmic ray flux known as Forbush decrease events. At present, two long-term independent global satellite cloud datasets are available (ISCCP and MODIS). Although the differences between them are considerable, neither shows evidence of a solar-cloud link at either long or short timescales. Furthermore, reports of observed correlations between solar activity and cloud over the 1983–1995 period are attributed to the chance agreement between solar changes and artificially induced cloud trends. It is possible that the satellite cloud datasets and analysis methods may simply be too insensitive to detect a small solar signal. Evidence from ground-based studies suggests that some weak but statistically significant cosmic ray-cloud relationships may exist at regional scales, involving mechanisms related to the global electric circuit. However, a poor understanding of these mechanisms and their effects on cloud makes the net impacts of such links uncertain. Regardless of this, it is clear that there is no robust evidence of a widespread link between the cosmic ray flux and clouds.” Benjamin A. Laken, Enric Pallé, Jaša Čalogović and Eimear M. Dunne, J. Space Weather Space Clim. 2 (2012) A18, DOI: http://dx.doi.org/10.1051/swsc/2012018. [http://www.swsc-journal.org/articles/swsc/pdf/2012/01/swsc120049.pdf">Full text]

Solar irradiance, cosmic rays and cloudiness over daily timescales – Laken & Čalogović (2011) “Although over centennial and greater timescales solar variability may be one of the most influential climate forcing agents, the extent to which solar activity influences climate over shorter time periods is poorly understood. If a link exists between solar activity and climate, it is likely via a mechanism connected to one (or a combination) of the following parameters: total solar irradiance (TSI), ultraviolet (UV) spectral irradiance, or the galactic cosmic ray (GCR) flux. We present an analysis based around a superposed epoch (composite) approach focusing on the largest TSI increases and decreases (the latter occurring in both the presence and absence of appreciable GCR reductions) over daily timescales. Using these composites we test for the presence of a robust link between solar activity and cloud cover over large areas of the globe using rigorous statistical techniques. We find no evidence that widespread variations in cloud cover at any tropospheric level are significantly associated with changes in the TSI, GCR or UV flux, and further conclude that TSI or UV changes occurring during reductions in the GCR flux are not masking a solar-cloud response. However, we note the detectability of any potential links is strongly constrained by cloud variability.” Laken, B. A. and J. Čalogović(2011), Geophys. Res. Lett., 38, L24811, doi:10.1029/2011GL049764. [Full text]

Relationship of Lower Troposphere Cloud Cover and Cosmic Rays: An Updated Perspective – Agee et al. (2011) “An updated assessment has been made of the proposed hypothesis that “galactic cosmic rays (GCRs) are positively correlated with lower troposphere global cloudiness.” A brief review of the many conflicting studies that attempt to prove or disprove this hypothesis is also presented. It has been determined in this assessment that the recent extended quiet period (QP) between solar cycles 23–24 has led to a record high level of GCRs, which in turn has been accompanied by a record low level of lower troposphere global cloudiness. This represents a possible observational disconnect, and the update presented here continues to support the need for further research on the GCR-Cloud hypothesis and its possible role in the science of climate change.” Ernest M. Agee, Kandace Kiefer and Emily Cornett, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00169.1.

The contribution of cosmic rays to global warming – Sloan & Wolfendale (2011) “A search has been made for a contribution of the changing cosmic ray intensity to the global warming observed in the last century. The cosmic ray intensity shows a strong 11 year cycle due to solar modulation and the overall rate has decreased since 1900. These changes in cosmic ray intensity are compared to those of the mean global surface temperature to attempt to quantify any link between the two. It is shown that, if such a link exists, the changing cosmic ray intensity contributes less than 8% to the increase in the mean global surface temperature observed since 1900.” T. Sloan and A.W. Wolfendale, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.07.013. [Full text]

Cosmic ray effects on cloud cover and their relevance to climate change – Erlykin et al. (2011) “A survey is made of the evidence for and against the hypothesis that cosmic rays influence cloud cover. The analysis is made principally for the troposphere. It is concluded that for the troposphere there is only a very small overall value for the fraction of cloud attributable to cosmic rays (CR); if there is linearity between CR change and cloud change, the value is probably ~1% for clouds below ~6.5km, but less overall. The apparently higher value for low cloud is an artifact. The contribution of CR to ’climate change’ is quite negligible.” A.D. Erlykin, B.A. Laken and A.W. Wolfendale, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.03.001.

Cosmic rays and global warming – Erlykin et al. (2010) A brief review article. “Is global warming man made or is it caused by the effects of solar activity on cosmic rays as claimed by some? Here we describe our search for evidence to distinguish between these claims. … In our view the jury is back and the verdict is that cosmic rays and solar irradiance are not guilty for most of the Global Warming. Nevertheless, they could be responsible for a contribution and we look forward to future experiments such as CLOUD at CERN which should be able to quantify to what extent ionization plays a part in the production of aerosols, the precursors of cloud formation.” [Full text]

Sudden Cosmic Ray Decreases: No Change of Global Cloud Cover – Calogovic et al. (2010) “Here we report on an alternative and stringent test of the CRC-hypothesis by searching for a possible influence of sudden GCR decreases (so-called Forbush decreases) on clouds. We find no response of global cloud cover to Forbush decreases at any altitude and latitude.” [Full text]

Cosmic ray decreases and changes in the liquid water cloud fraction over the oceans – Laken et al. (2009) “Svensmark et al. (2009) have recently claimed that strong galactic cosmic ray (GCR) decreases during ‘Forbush Decrease (FD) events’ are followed by decreases in both the global liquid water cloud fraction (LCF) and other closely correlated atmospheric parameters. To test the validity of these findings we have concentrated on just one property, the MODIS LCF and examined two aspects: 1) The statistical chance that the decrease observed in the LCF is abnormal. 2) The likelihood of the observed delay (∼5 to 9 days) being physically connected to the FD events. On both counts we conclude that LCF variations are unrelated to FD events: Both the pattern and timing of observed LCF changes are irreconcilable with current theoretical pathways. Additionally, a zonal analysis of LCF variations also offers no support to the claimed relationship, as the observed anomaly is not found to vary latitudinally in conjunction with cosmic ray intensity.” [Full text]

Results from the CERN pilot CLOUD experiment – Duplissy et al. (2009) “During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the CLOUD1 experiment, whose aim is to study the possible influence of cosmic rays on clouds. … Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. … In conclusion, therefore, the experimental variables were not well enough controlled to exclude the presence of ion-induced nucleation on the basis of Fig. 7; it merely does not support the presence of strong contributions from this source.” [Full text]

On the correlation between cosmic ray intensity and cloud cover – Erlykin et al. (2009) “Various aspects of the connection between cloud cover (CC) and cosmic rays (CR) are analyzed. Most features of this connection viz. an altitude dependence of the absolute values of CC and CR intensity, no evidence for the correlation between the ionization of the atmosphere and cloudiness, the absence of correlations in short-term low cloud cover (LCC) and CR variations indicate that there is no direct causal connection between LCC and CR in spite of the evident long-term correlation between them. … The most significant argument against causal connection of CR and LCC is the anticorrelation between LCC and the medium cloud cover (MCC).” [Full text]

Atmospheric data over a solar cycle: no connection between galactic cosmic rays and new particle formation – Kulmala et al. (2009) “More than a decade ago, variations in galactic cosmic rays were suggested to closely correlate with variations in atmospheric cloud cover and therefore constitute a driving force behind aerosol-cloud-climate interactions. Later, the enhancement of atmospheric aerosol particle formation by ions generated from cosmic rays was proposed as a physical mechanism explaining this correlation. Here, we report unique observations on atmospheric aerosol formation based on measurements at the SMEAR II station, Finland, over a solar cycle (years 1996–2008) that shed new light on these presumed relationships. Our analysis shows that none of the quantities related to aerosol formation correlates with the cosmic ray-induced ionisation intensity (CRII). We also examined the contribution of ions to new particle formation on the basis of novel ground-based and airborne observations. A consistent result is that ion-induced formation contributes typically less than 10% to the number of new particles, which would explain the missing correlation between CRII and aerosol formation.” [Full text]

Can cosmic rays affect cloud condensation nuclei by altering new particle formation rates? – Pierce & Adams (2009) “In this paper, we present the first calculations of the magnitude of the ion-aerosol clear-air mechanism using a general circulation model with online aerosol microphysics. In our simulations, changes in CCN from changes in cosmic rays during a solar cycle are two orders of magnitude too small to account for the observed changes in cloud properties; consequently, we conclude that the hypothesized effect is too small to play a significant role in current climate change.”

On the possible connection between cosmic rays and clouds – Erlykin et al. (2009) “Various aspects of the connection between cloud cover (CC) and cosmic rays (CR) are analysed. We argue that the anticorrelation between the temporal behaviour of low (LCC) and middle (MCC) clouds evidences against causal connection between them and CR. Nevertheless, if a part of low clouds (LCC) is connected and varies with CR, then its most likely value averaged over the Globe should not exceed 20% at the two standard deviation level.” [Full text]

Solar activity and the mean global temperature – Erlykin et al. (2009) This study finds that the changes in the cosmic ray rate lags the changes in temperature. “The cyclic variation in the cosmic ray rate is observed to be delayed by 2–4 years relative to the temperature, the solar irradiance and daily sun spot variations suggesting that the origin of the correlation is more likely to be direct solar activity than cosmic rays. Assuming that the correlation is caused by such solar activity, we deduce that the maximum recent increase in the mean surface temperature of the Earth which can be ascribed to this activity is ~<14% of the observed global warming.” [Full text]

Cosmic rays, cloud condensation nuclei and clouds – a reassessment using MODIS data – Kristjánsson et al. (2008) “Averaging the results from the 22 Forbush decrease events that were considered, no statistically significant correlations were found between any of the four cloud parameters and GCR, when autocorrelations were taken into account.” [Full text]

Testing the proposed causal link between cosmic rays and cloud cover – Sloan & Wolfendale (2008) “A decrease in the globally averaged low level cloud cover, deduced from the ISCCP infrared data, as the cosmic ray intensity decreased during the solar cycle 22 was observed by two groups. The groups went on to hypothesize that the decrease in ionization due to cosmic rays causes the decrease in cloud cover, thereby explaining a large part of the currently observed global warming. We have examined this hypothesis to look for evidence to corroborate it. None has been found and so our conclusions are to doubt it. From the absence of corroborative evidence, we estimate that less than 23%, at the 95% confidence level, of the 11 year cycle change in the globally averaged cloud cover observed in solar cycle 22 is due to the change in the rate of ionization from the solar modulation of cosmic rays. “ [Full text]

Cosmic Rays and The Climate – Sloan (2008) Summarizes different views on the issue. “A number of papers and posters were presented at the ECRS on the subject of the relationship between cosmic rays (CR) and both the climate and the weather. I was asked by the organisers to attempt to summarise them.” [Full text]

Cosmic Rays and Global Warming – Sloan & Wolfendale (2007) “It has been claimed by others that observed temporal correlations of terrestrial cloud cover with `the cosmic ray intensity’ are causal. The possibility arises, therefore, of a connection between cosmic rays and Global Warming. If true, the implications would be very great. We have examined this claim to look for evidence to corroborate it. So far we have not found any and so our tentative conclusions are to doubt it. Such correlations as appear are more likely to be due to the small variations in solar irradiance, which, of course, correlate with cosmic rays. We estimate that less than 15% of the 11-year cycle warming variations are due to cosmic rays and less than 2% of the warming over the last 35 years is due to this cause.” [Full text]

Solar activity, cosmic rays, clouds and climate – an update – Kristjánsson et al. (2004) “Eighteen years of monthly averaged low cloud cover data from the International Satellite Cloud Climatology Project are correlated with both total solar irradiance and galactic cosmic ray flux from neutron monitors. When globally averaged low cloud cover is considered, consistently higher correlations (but with opposite sign) are found between low cloud variations and solar irradiance variations than between variations in cosmic ray flux and low cloud cover.” [Full text]

Pattern of Strange Errors Plagues Solar Activity and Terrestrial Climate Data – Damon & Laut (2004) “Links have been made between cosmic rays and cloud cover, first total cloud cover and then only low clouds, and between solar cycle lengths and northern hemisphere land temperatures. … Analysis of a number of published graphs that have played a major role in these debates and that have been claimed to support solar hypotheses shows that the apparent strong correlations displayed on these graphs have been obtained by incorrect handling of the physical data.” [Full text]

Solar activity and terrestrial climate: an analysis of some purported correlations – Laut (2003) “The last decade has seen a revival of various hypotheses claiming a strong correlation between solar activity and a number of terrestrial climate parameters: Links between cosmic rays and cloud cover, first total cloud cover and then only low clouds, and between solar cycle lengths and Northern Hemisphere land temperatures. These hypotheses play an important role in the scientific as well as in the public debate about the possibility or reality of a man-made global climate change. I have analyzed a number of published graphs which have played a major role in these debates and which have been claimed to support solar hypotheses. My analyses show that the apparent strong correlations displayed on these graphs have been obtained by an incorrect handling of the physical data.” [Full text]

Cosmic Rays, Clouds, and Climate – Carslaw et al. (2002) A review paper. “It has been proposed that Earth’s climate could be affected by changes in cloudiness caused by variations in the intensity of galactic cosmic rays in the atmosphere. This proposal stems from an observed correlation between cosmic ray intensity and Earth’s average cloud cover over the course of one solar cycle. Some scientists question the reliability of the observations, whereas others, who accept them as reliable, suggest that the correlation may be caused by other physical phenomena with decadal periods or by a response to volcanic activity or El Niño.” [Full text]

A new look at possible connections between solar activity, clouds and climate – Kristjánsson et al. (2002) “We present a re-evaluation of the hypothesis of a coupling between galactic cosmic rays, clouds and climate. We have used two independent estimates of low cloud cover from the International Satellite Cloud Climatology Project, covering 16.5 years of data. The cloud cover data are used in conjunction with estimates of galactic cosmic ray flux and measurements of solar irradiance. It is found that solar irradiance correlates better and more consistently with low cloud cover than cosmic ray flux does. The correlations are considerably lower when multichannel retrievals during daytime are used than retrievals using IR-channels only.” [Full text]

Some results relevant to the discussion of a possible link between cosmic rays and the Earth’s climate – Wagner et al. (2001) “However, the smoothed combined flux of 10Be and 36Cl at Summit, Greenland, from 20–60 kyr B.P. (proportional to the geomagnetically modulated cosmic ray flux) is unrelated to the corresponding δ18O and CH4 data (interpreted as supraregional climate proxies). (3) Furthermore, although a comparison of the incoming neutron flux with cloud cover in Switzerland over the last 5 decades shows a significant correlation at times during the 1980s and 1990s, this does not occur during the rest of the period.” [Full text]

Sunshine records from Ireland: cloud factors and possible links to solar activity and cosmic rays – Pallé & Butler (2001) “The importance of cosmic rays as a link between solar activity and climate was assessed from a study of the ISCCP-D2 satellite cloud factors and Irish sunshine data. Whilst these results confirmed the strong correlation between total cloud factor and cosmic rays over non-tropical oceans between 1984 and 1991 previously reported, it was found that this correlation did not hold in the subsequent period 1991-1994. Other work has established a link through specifically low cloud. Indirect evidence of cloud formation by cosmic rays from a variation in the sunshine factor following Forbush decreases, and over the sunspot cycle, was mostly negative. Although a dip at seven years past sunspot minimum is evident in the sunshine factor for all four sites and in most seasons, it is of marginal statistical significance.” [Full text]

Cloud cover variations over the United States: An influence of cosmic rays or solar variability? – Udelhofen & Cess (2001) “To investigate whether galactic cosmic rays (GCR) may influence cloud cover variations, we analyze cloud cover anomalies from 1900–1987 over the United States. … The cloud cover variations are in phase with the solar cycle and not the GCR.”

Is there a cosmic ray signal in recent variations in global cloudiness and cloud radiative forcing? – Kristjánsson et al. (2000) “In order to evaluate a recent hypothesis of a coupling between galactic cosmic rays, clouds, and climate we have investigated temporal variations in global cloudiness and radiative fluxes at the top of the atmosphere. … When the results are related to temporal variations in cosmic ray activity, we do not find support for a coupling between cosmic rays, total cloudiness, and radiative forcing of climate. … The net radiative effect of clouds during the period 1985–1989 shows an enhanced cooling effect despite a reduction in both total and low cloud cover. This contradicts the simple relationship between cloud cover and radiation assumed in the cosmic-ray-cloud-climate hypothesis.”

Are Cosmic Rays Influencing Oceanic Cloud Coverage – Or Is It Only El Niño? – Farrar (2000) “The monthly average (C2) cloud coverage data produced by the International Satellite Cloud Climatology Project (ISCCP) for the period of July 1986–June 1991 show strong global and regional cloud coverage variations associated with the El Niño of 1986–1987. The Pacific Ocean, in particular, shows strong regional variations in cloud coverage. These agree well with contemporaneous satellite observations of broadband shortwave infrared cloud forcing measured by the Earth Radiation Budget Experiment. Svensmark and Friis-Christensen (1997) noted a similarity between the shape of the timeseries curve of average cloud coverage fraction for mid- to low-latitude ocean-areas and the time series curve of cosmic ray flux intensity. They proposed a causal relationship – a `missing link’ for solar cycle influence on Earth climate. Further spatial and temporal analysis of the same ISCCP C2 data in this paper indicates that the cloud coverage variation patterns are those to be expected for the atmospheric circulation changes characteristic of El Niño, weakening the case for cosmic rays as a climatic forcing factor.”

Closely related

Testing the link between terrestrial climate change and Galactic spiral arm transit – Overholt et al. (2009) Tests the correlation of climate changes and Earth’s passage through spiral arms of the Milky Way. Possible climate effects largely relate to cosmic rays. “We re-examine past suggestions of a close link between terrestrial climate change and the Sun’s transit of spiral arms in its path through the Milky Way galaxy. These links produced concrete fits, deriving the unknown spiral pattern speed from terrestrial climate correlations. We test these fits against new data on spiral structure based on CO data that do not make simplifying assumptions about symmetry and circular rotation. If we compare the times of these transits with changes in the climate of Earth, the claimed correlations not only disappear, but we also find that they cannot be resurrected for any reasonable pattern speed.” [Full text]

Toward Direct Measurement of Atmospheric Nucleation – Kulmala et al. (2007) A paper on the results of SMEAR project which (among other activities) provides direct measurements of atmospheric nucleation. They find that ion-induced nucleation is not very important (ion-induced nucleation fraction is only 10 % of total nucleation at best). “We introduce an instrumental setup to measure atmospheric concentrations of both neutral and charged nanometer-sized clusters. By applying the instruments in the field, we come to three important conclusions: … (iii) neutral nucleation dominates over the ion-induced mechanism, at least in boreal forest conditions.”

For those interested in the SMEAR project results, see the presentation of Markku Kulmala in “Climate Change – Man Made?” seminar in Stockholm (2009) (click the “cosmic rays and climate change”, Kulmala’s presentation starts after Svensmark’s, about at 00:34:15).

There are plenty of papers which deal with this cosmic ray issue while concentrating solar forcing as a whole (for example a string of papers from Lockwood & Fröhlich). Many of those papers would belong to the list above, but I shall make a separate entry on them, and add link to that post here when I have made it (separate post is already on the works). UPDATE (September 3, 2009): Here is the link to the post about the Sun’s role.

Original claims of Svensmark et al. were based on the apparent correlation between the cosmic rays and an observed decreasing trend in ISCCP cloud cover data, but it has been found out that ISCCP trend was an artifact of satellite viewing geometry, so it seems that there is no observational basis for the original claim. [UPDATE (March 17, 2010): I have recently discussed about this here.] There are few papers discussing this, and I will give one of them below.

Arguments against a physical long-term trend in global ISCCP cloud amounts – Evan et al. (2007) “Here we show that trends observed in the ISCCP data are satellite viewing geometry artifacts and are not related to physical changes in the atmosphere. Our results suggest that in its current form, the ISCCP data may not be appropriate for certain long-term global studies, especially those focused on trends.” [Full text]

UPDATE (September 10, 2009): As it has been suggested that cosmic rays affect by changing the cloud cover, this is relevant here:
Papers on global cloud cover trends

Update history

UPDATE (January 2, 2012): Laken & Čalogović (2012) added and my opinion statement removed.
UPDATE (September 26, 2011): Agee et al. (2011) added.
UPDATE (August 16, 2011): Sloan & Wolfendale (2011) added.
UPDATE (April 27, 2011): Erlykin et al. (2011) added.
UPDATE (April 4, 2010): Farrar (2000) added, thanks to Paul Farrar for pointing it out, see the comment section below.
UPDATE (March 23, 2010): Erlykin et al. (2010) added, thanks to Pekka Pirilä for pointing it out (elsewhere).
UPDATE (February 23, 2010): Pallé & Butler (2001) added, thanks to Barry for pointing it out, see the comment section below.
UPDATE (February 8, 2010): Wagner et al. (2001) added.
UPDATE (January 8, 2010): Laken et al. (2009) added. Calogovic et al. (2010) added, thanks to PeterPan for pointing it out, see the comment section below. Kristjánsson et al. (2000), Udelhofen & Cess et al. (2001), Kristjánsson et al. (2002), Damon & Laut (2004), and Kristjánsson et al. (2004) added.
UPDATE (November 29, 2009): Duplissy et al. (2009) added.
UPDATE (October 26, 2009): Erlykin et al. (2009) added. Thanks to PeterPan for pointing it out, see the discussion section below. Update history section also added.
UPDATE (October 23, 2009): Overholt et al. (2009) and Pierce & Adams (2009) added. Thanks to PeterPan for pointing these out, see the discussion section below.
UPDATE (October 13, 2009): Kulmala et al. (2009) added.
UPDATE (October 8, 2009): I modified the text relating to the SMEAR project; I had misunderstood the bit about 1 % effect, so I left that part out and everyone can just check out Kulmala’s presentation and see what he says about that (thanks to Theo Kurtén for pointing this out).
UPDATE (October 7, 2009): Kulmala et al. (2007) and some more information on SMEAR project added (thanks to Theo Kurtén and Tuomas Helin for the information on this).

Posted in AGW evidence | 41 Comments »

Papers on 1500 year climate cycle

Posted by Ari Jokimäki on August 29, 2009

This list contains papers on the 1500 year cycle (the Dansgaard-Oeschger events and Bond events) that is evident in past climate records, especially in Northern Atlantic. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (January 7, 2010): Alley (2007) added.

On the Stochastic Nature of the Rapid Climate Shifts during the Last Ice Age – Ditlevsen & Ditlevsen (2009) “This observation is an important piece in the climate puzzle, because the fact that the climate is a no-memory process indicates that the transitions are noise induced and the mean residence time in one state indicates how stable that climate state is to perturbations. The possibility of a hidden periodic driver is also investigated. The existence of such a driver cannot be ruled out by the relatively sparse data series (containing only 21 onsets). However, because the record is fitted just as well by the much simpler random model, this should be preferred from the point of view of simplicity.” [Link to PDF]

Conceptual model for millennial climate variability: a possible combined solar-thermohaline circulation origin for the ~1,500-year cycle – Dima & Lohmann (2009) “In a conceptual model approach, we show that this millennial variability can originate from rectification of an external (solar) forcing, and suggest that the thermohaline circulation, through a threshold response, could be the rectifier. We argue that internal threshold response of the thermohaline circulation (THC) to solar forcing is more likely to produce the observed DO cycles than amplification of weak direct ~1,500-year forcing of unknown origin, by THC.” [Link to PDF]

Wally Was Right: Predictive Ability of the North Atlantic “Conveyor Belt” Hypothesis for Abrupt Climate Change – Alley (2007) A review paper. “Linked, abrupt changes of North Atlantic deep water formation, North Atlantic sea ice extent, and widespread climate occurred repeatedly during the last ice age cycle and beyond in response to changing freshwater fluxes and perhaps other causes. This paradigm, developed and championed especially by W.S. Broecker, has repeatedly proven to be successfully predictive as well as explanatory with high confidence. Much work remains to fully understand what happened and to assess possible implications for the future, but the foundations for this work are remarkably solid.” [Link to PDF]

The origin of the 1500-year climate cycles in Holocene North-Atlantic records – Debret et al. (2007) “These results reveal that the 1500-year climate cycles are linked with the oceanic circulation and not with variations in solar output as previously argued (Bond et al., 2001). In this light, previously studied marine sediment (Bianchi and McCave, 1999; Chapman and Shackleton, 2000; Giraudeau et al., 2000), ice core (O’Brien et al., 1995; Vonmoos et al., 2006) and dust records (Jackson et al., 2005) can be seen to contain the evidence of combined forcing mechanisms, whose relative influences varied during the course of the Holocene. Circum-Atlantic climate records cannot be explained exclusively by solar forcing, but require changes in ocean circulation, as suggested previously (Broecker et al., 2001; McManus et al., 1999).” [Link to PDF]

Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model – Braun et al. (2005) “Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard–Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of ~87 and ~210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation.” [Link to PDF]

Timing of abrupt climate change: A precise clock – Rahmstorf (2003) “Many paleoclimatic data reveal a ∼1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.” [Link to PDF]

Widespread evidence of 1500 yr climate variability in North America during the past 14 000 yr – Viau et al. (2002) “Times of major transitions identified in pollen records occurred at 600, 1650, 2850, 4030, 6700, 8100, 10 190, 12 900, and 13 800 cal yr B.P., consistent with ice and marine records. We suggest that North Atlantic millennial-scale climate variability is associated with rearrangements of the atmospheric circulation with far-reaching influences on the climate.”

Persistent Solar Influence on North Atlantic Climate During the Holocene – Bond et al. (2001) “A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic’s “1500-year” cycle.” [Link to PDF]

A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates – Bond et al. (1997) “Evidence from North Atlantic deep sea cores reveals that abrupt shifts punctuated what is conventionally thought to have been a relatively stable Holocene climate. During each of these episodes, cool, ice-bearing waters from north of Iceland were advected as far south as the latitude of Britain. At about the same times, the atmospheric circulation above Greenland changed abruptly. Pacings of the Holocene events and of abrupt climate shifts during the last glaciation are statistically the same; together, they make up a series of climate shifts with a cyclicity close to 1470 ± 500 years.” [Link to PDF]

Iceberg Discharges into the North Atlantic on Millennial Time Scales During the Last Glaciation – Bond & Lotti (1995) “High-resolution studies of North Atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years, much more frequently than the 7000-to 10,000-year pacing of massive ice discharges associated with Heinrich events. The calving cycles correlate with warm-cold oscillations, called Dansgaard-Oeschger events, in Greenland ice cores.”

Evidence for general instability of past climate from a 250-kyr ice-core record – Dansgaard et al. (1993) “Recent results from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades.”

Holocene climatic variations—Their pattern and possible cause – Denton & Karlén (1973) Apparently the first paper that noted this cycle, although according to their abstract, they identify a 2500 year cycle. “These results suggest that a recurring pattern of minor climatic variations, with a dominant overprint of cold intervals peaking about each 2500 yr, was superimposed on long-term Holocene and Late-Wisconsin climatic trends.”

Closely related

CO2 threshold for millennial-scale oscillations in the climate system: implications for global warming scenarios – Meissner et al. (2008) “The model shows two very different responses: for CO2 concentrations of 400 ppm or lower, the system evolves into an equilibrium state. For CO2 concentrations of 440 ppm or higher, the system starts oscillating between a state with vigorous deep water formation in the Southern Ocean and a state with no deep water formation in the Southern Ocean. … If the UVic ESCM captures a mechanism that is present and important in the real climate system, the consequences would comprise a rapid increase in atmospheric carbon dioxide concentrations of several tens of ppm, an increase in global surface temperature of the order of 1–2°C, local temperature changes of the order of 6°C and a profound change in ocean stratification, deep water temperature and sea ice cover.” [Link to PDF]

Posted in AGW evidence | 4 Comments »

Rising carbon dioxide concentration stops the glacial/interglacial cycle

Posted by Ari Jokimäki on August 24, 2009

I have seen claims from denialists that the past records of temperature from Antarctic ice cores show that we are heading towards an ice age. The reason for this claim can be seen from the temperature reconstruction made from the Vostok ice core deuterium profile. Details are given here which is where I also got the data for the graph presented in Fig. 1.

vostok_temp
Figure 1. Reconstructed temperature from Vostok ice core.

The claim suggests that the same is happening now that happened about 130000 years ago, and about 240000 years ago, and about 320000 years ago, that is, the temperature increased quickly and then also decreased quickly and it all happened seemingly in a cyclic process. However, the claim misses few things. First, let us see how high CO2 concentration was during the past 400000 years shown in Vostok temperature reconstruction. There’s also CO2 concentration measured from Vostok ice core. It is described here, and the data is also given there. I have made a graph out of the data, and it is presented in Fig. 2.

vostok_co2
Figure 2. CO2 concentration from Vostok ice core.

We find out that CO2 concentration varied between 180 and 300 ppm during the last 400000 years when glacial/intarglacial cycles were going on. The thing that the claim misses is that currently, the CO2 concentration is getting close to 400 ppm which is far more than anything during the past 400000 years. But, does it matter? Here we arrive to the second thing the claim misses.

If we look further back in time than Vostok ice core, we find out that glacial/interglacial cycle has not been always functional. There has been times when global temperature was continuously high for long periods of time (millions of years) without any glacial periods. During those times, also CO2 concentration has been high, much higher than it is today. Based on the knowledge of those past times, Royer (2006) has suggested that glaciation starts only when CO2 concentration decreases below 500 ppm. However, Royer cannot give very accurate limit, but only says that it is below 500 ppm. Above we saw that the maximum value of CO2 concentration were quite consistently 280-300 ppm during interglacial periods of recent 400000 years. Based on this, I would say that it matters that current CO2 concentration is far above the normal interglacial maximum. I cannot say for sure that we have already reached the below 500 ppm threshold Royer suggests, but I also don’t see any reasons to assume that the next glacial would be about to begin. At least the situation is currently heading towards the threshold.

Also, at any case, to change climate, you always need forcings to be such that a change can occur. This is the third thing the claim misses. Currently, there’s no forcing in sight that could turn things around. As Hansen et al. (2008) show, greenhouse gases have always (well, at least the last 65 million years) been the determining factor of where climate goes. Other forcings have only minor roles as initiators. (However, albedo changes can be very strong feedback, but is not usually considered as an initiator of climate changes because there would have to be some pre-existing cause to change the albedo.) Note also that Hansen et al. succesfully explain the glacial/interglacial cycle by greenhouse gas forcing with Earth’s orbital changes acting as the initiator. So, to see when the next ice age is going to start, we only need to see which way the greenhouse gases are pointing.

Currently, greenhouse gases are pointing towards warmer climate.

Posted in Climate claims | 18 Comments »

Papers on temperature trends in stratosphere

Posted by Ari Jokimäki on August 21, 2009

This list of papers contains observations of trends in temperature of Earth’s stratosphere. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (November 20, 2011): Wang et al. (2011) added.
UPDATE (August 21, 2010): Randel & Cobb (2008) was changed to Randel & Cobb (1994) and full text link was added to it. Full text link was added to Shine et al. (2006) and Ramaswamy et al. (2002).
UPDATE (September 11, 2009): Randel et al. (2009) added.

Construction of Stratospheric Temperature Data Records from Stratospheric Sounding Units – Wang et al. (2011) “In recognizing the importance of Stratospheric Sounding Unit (SSU) onboard historical NOAA polar-orbiting satellites in assessment of long-term stratospheric temperature changes and limitations in previous available SSU datasets, this study constructs a fully-documented, publicly-accessible, and well-merged SSU time series for climate change investigations. Focusing on methodologies, this study describes the details of data processing and bias corrections in the SSU observations for generating consistent stratospheric temperature data records, including 1) removal of the instrument gas leak effect in its CO2 cell; 2) correction of the atmospheric CO2 increasing effect; 3) adjustment for different observation viewing angles; 4) removal of diurnal sampling biases due to satellite orbital drift; and 5) statistical merging of SSU observations from different satellites. After reprocessing, the stratospheric temperature records are composed of nadir-like, gridded brightness temperatures that correspond to identical weighting functions and a fixed local observation time. The 27-year reprocessed SSU data record comprises global monthly and pentad layer temperatures, with grid resolution of 2.5° latitudes by 2.5° longitudes, of the mid-stratosphere (TMS), upper-stratosphere (TUS), and top-stratosphere (TTS), which correspond to the three SSU channel observations. For 1979-2006, the global mean trends for TMS, TUS, and TTS, are respectively -1.236±0.131, -0.926±0.139, and -1.006±0.194 K/decade. Spatial trend pattern analyses indicated that this cooling occurred globally with larger cooling over the tropical stratosphere.” Likun Wang, Cheng-Zhi Zou, and Haifeng Qian, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00350.1

An update of observed stratospheric temperature trends – Randel et al. (2009) “An updated analysis of observed stratospheric temperature variability and trends is presented on the basis of satellite, radiosonde, and lidar observations. … Temperature changes in the lower stratosphere show cooling of ∼0.5 K/decade over much of the globe for 1979–2007, with some differences in detail among the different radiosonde and satellite data sets. Substantially larger cooling trends are observed in the Antarctic lower stratosphere during spring and summer, in association with development of the Antarctic ozone hole. … Trends in the middle and upper stratosphere have been derived from updated SSU data, taking into account changes in the SSU weighting functions due to observed atmospheric CO2 increases. The results show mean cooling of 0.5–1.5 K/decade during 1979–2005, with the greatest cooling in the upper stratosphere near 40–50 km.” [Full text]

Understanding Recent Stratospheric Climate Change – Thompson & Solomon (2009) “The long-term, global-mean cooling of the lower stratosphere stems from two downward steps in temperature, both of which are coincident with the cessation of transient warming after the volcanic eruptions of El Chichón and Mount Pinatubo. … First, evidence is provided that shows the unusual steplike behavior of global-mean stratospheric temperatures is dependent not only upon the trend but also on the temporal variability in global-mean ozone immediately following volcanic eruptions. Second, the authors argue that the warming/cooling pattern in global-mean temperatures following major volcanic eruptions is consistent with the competing radiative and chemical effects of volcanic eruptions on stratospheric temperature and ozone. Third, it is revealed that the contrasting latitudinal structures of recent stratospheric temperature and ozone trends are consistent with large-scale increases in the stratospheric overturning Brewer–Dobson circulation.” [Full text]

Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling – Ramaswamy et al. (2006) “Observations reveal that the substantial cooling of the global lower stratosphere over 1979–2003 occurred in two pronounced steplike transitions. These arose in the aftermath of two major volcanic eruptions, with each cooling transition being followed by a period of relatively steady temperatures. … The anthropogenic factors drove the overall cooling during the period, and the natural ones modulated the evolution of the cooling.”

Global Change in the Upper Atmosphere – Laštovička et al. (2006) “The upper atmosphere is cooling and contracting as a result of rising greenhouse gas concentrations.”

A comparison of model-simulated trends in stratospheric temperatures – Shine et al. (2006) “Estimates of annual-mean stratospheric temperature trends over the past twenty years, from a wide variety of models, are compared both with each other and with the observed cooling seen in trend analyses using radiosonde and satellite observations. The modelled temperature trends are driven by changes in ozone (either imposed from observations or calculated by the model), carbon dioxide and other relatively well-mixed greenhouse gases, and stratospheric water vapour. … The modelled annual- and global-mean cooling of the upper stratosphere (near 1 hPa) is dominated by ozone and carbon dioxide changes, and is in reasonable agreement with observations.” [Full text]

Recent Stratospheric Climate Trends as Evidenced in Radiosonde Data: Global Structure and Tropospheric Linkages – Thompson & Solomon (2005) “In contrast to conclusions published in previous assessments of stratospheric temperature trends, it is demonstrated that in the annual mean the tropical stratosphere has cooled substantially over the past few decades.” [Full text]

Thermal and dynamical changes of the stratosphere since 1979 and their link to ozone and CO2 changes – Langematz et al. (2003) “It is suggested that the observed upper stratospheric temperature trends during the past two decades in low to middle latitudes are caused by radiative effects due to the O3 and CO2 changes, while the cooling of the polar stratosphere in winter is enhanced by changes in dynamical heating.”

Effects of ozone and well-mixed gases on annual-mean stratospheric temperature trends – Ramaswamy et al. (2002) “The effects of changes in ozone and well-mixed greenhouse gases upon the annual-mean stratospheric temperatures are investigated using a general circulation model and compared with the observed (1979–2000) trends. … …the simulated results are in reasonable quantitative agreement with the vertical profile of the observed global-and-annual-mean stratospheric cooling, and with the observed lower stratospheric zonal-and-annual-mean cooling. This affirms the major role of these species in the temperature trend of the stratosphere over the past two decades.” [Full text]

Stratospheric Temperature Trends: Observations and Model Simulations – Ramaswamy et al. (2001) “The stratosphere has, in general, undergone considerable cooling over the past 3 decades. … Simulations based on the known changes in species’ concentrations indicate that the depletion of lower stratospheric ozone is the major radiative factor in accounting for the 1979-1990 cooling trend in the global, annual-mean lower stratosphere (∼0.5 to 0.6 K/decade), with a substantially lesser contribution by the well-mixed greenhouse gases.” [Full text]

Stepwise changes in stratospheric temperature – Pawson et al. (1998) “There is a clear cooling over the 33 years considered. It is not well described by a linear trend because of the increased cooling since 1991.”

Coherent variations of monthly mean total ozone and lower stratospheric temperature – Randel & Cobb (1994) “The temperature trends derived here show significant cooling of the lower stratosphere over Northern Hemisphere (NH) midlatitudes in winter-spring and over Antartica in Southern Hemisphere (SH) spring; the overall space-time patterns are similar to those determined for ozone trends.” [Full text]

CLOSELY RELATED

Review of Mesospheric Temperature Trends – Beig et al. (2003) “There are a growing number of experimental results centered on, or consistent with, zero temperature trend in the mesopause region (80–100 km). The most reliable data sets show no significant trend but an uncertainty of at least 2 K/decade. On the other hand, a majority of studies indicate negative trends in the lower and middle mesosphere with an amplitude of a few degrees (2–3 K) per decade. In tropical latitudes the cooling trend increases in the upper mesosphere. … Quantitatively, the simulated cooling trend in the middle mesosphere produced only by CO2 increase is usually below the observed level. However, including other greenhouse gases and taking into account a “thermal shrinking” of the upper atmosphere result in a cooling of a few degrees per decade.” [Full text]

Posted in AGW evidence | 2 Comments »

Papers on changes in DLR

Posted by Ari Jokimäki on August 19, 2009

This list of papers contains evidence of changes in downward longwave radiation (DLR) caused by changing concentrations of greenhouse gases (GHG). The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (February 3, 2010): Allan (2000) and some links to GEBA added.
UPDATE (October 8, 2009): I replaced the link to Wang & Liang (2009). It was at the time of the writing of this list so new paper that it only appeared in a “papers in press” list, but now it has a proper link to abstract page (no PDF seems to be available for free, sorry).

Global atmospheric downward longwave radiation over land surface under all-sky conditions from 1973 to 2008 – Wang & Liang (2009) “The decadal variation in global Ld under both clear and cloudy conditions at about 3200 stations from 1973 to 2008 are presented. We found that daily Ld increased at an average rate of 2.2 Wm-2 from 1973 to 2008. The rising trend results from increases in air temperature, atmospheric water vapor and CO2 concentration.”

Combined surface solar brightening and increasing greenhouse effect support recent intensification of the global land-based hydrological cycle – Wild et al. (2008) “Here we present a first-order trend estimate for the 15-year period 1986–2000, which suggests that surface net radiation over land has rapidly increased by about 2 Wm-2 per decade, after several decades with no evidence for an increase. This recent increase is caused by increases in both downward solar radiation (due to a more transparent atmosphere) and downward thermal radiation (due to enhanced concentrations of atmospheric greenhouse-gases).” [Link to PDF]

The climatological record of clear-sky longwave radiation at the Earth’s surface: evidence for water vapour feedback? – Prata (2008) “Here long-term (more than 25 years) mean monthly profiles obtained from globally distributed land-based radiosonde stations are subjected to detailed radiative transfer computations and Fourier time-series analysis. The results indicate that over the period 1964-1990, there has been a global increase in the clear-sky longwave flux at the surface. The global trend is approximately +1.7 W m-2 per decade, and there is a strong latitudinal pattern, with greater increases occurring in the tropics and smaller increases at both poles. There are also concomitant increases in precipitable water and the patterns appear to be highly correlated with increases in F↓. Increases in CO2 with time were not included in the calculations and it is estimated that the radiative impact of changes in CO2 on the F↓ trend is ∼20% per decade. A simple model of the dependence of surface air temperature and precipitable water on the downwards clear-sky flux supports the notion that both variables are contributing to increases in F↓. It is suggested that increases in precipitable water represent a positive feedback on F↓.”

Measurements of the Radiative Surface Forcing of Climate – Evans & Puckrin (2006) “A comparison between our measurements of surface forcing emission and measurements of radiative trapping absorption from the IMG satellite instrument shows reasonable agreement. The experimental fluxes are simulated well by the FASCOD3 radiation code. This code has been used to calculate the model predicted increase in surface radiative forcing since 1850 to be 2.55 W/m2. In comparison, an ensemble summary of our measurements indicates that an energy flux imbalance of 3.5 W/m2 has been created by anthropogenic emissions of greenhouse gases since 1850. This experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming.” [Link to PDF]

Variability in clear-sky longwave radiative cooling of the atmosphere – Allan (2006) DLR is among the issues discussed in this paper, but it is measured only indirectly (very indirectly, actually, from measurements of column integrated water vapor and temperature measurements). [Link to PDF]

Comparison of clear-sky surface radiative fluxes simulated with radiative transfer models – Puckrin et al. (2004) “The surface fluxes of several important radiatively active gases, including H2O, CO2, CH4, N2O, O3, and the chlorofluorocarbons CFC11 and CFC12, were simulated with the radiation band models from the National Center for Atmospheric Research (NCAR) community climate model 3 (CCM3), the single-column community atmospheric model (SCAM), and the Canadian global climate model 3 (GCM3). These results were compared with the measured fluxes for a very cold winter day and with the simulated results for other standard atmospheres using the line-by-line radiative transfer model (LBLRTM). The comparison shows that the total surface radiative flux contributed by all the greenhouse gases combined is well simulated by the SCAM and GCM3 radiation band models.” [Link to PDF]

Radiative forcing – measured at Earth’s surface – corroborate the increasing greenhouse effect – Philipona et al. (2004) “Here we show that atmospheric longwave downward radiation significantly increased (+5.2(2.2) Wm-2) partly due to increased cloud amount (+1.0(2.8) Wm-2) over eight years of measurements at eight radiation stations distributed over the central Alps. … However, after subtracting for two thirds of temperature and humidity rises, the increase of cloud-free longwave downward radiation (+1.8(0.8) Wm-2) remains statistically significant and demonstrates radiative forcing due to an enhanced greenhouse effect.” [Link to PDF]

BSRN Longwave Downward Radiation Measurements Combined With GCMs Show Promise For Greenhouse Detection Studies – Wild & Ohmura (2004) Presents model simulations of DLR and some initial observational results. “First analyses of the available observational time series of LWD in the BSRN database show an overall increase over the past decade.” [Link to PDF]

The Surface Downward Longwave Radiation in the ECMWF Forecast System – Morcrette(2002) Compares model results of DLR to observations.

Downward longwave radiation in general circulation models: a case study at a semi‐arid continental site – Wild & Cechet (2002) Compares model results of DLR to observations.

Evaluation of Downward Longwave Radiation in General Circulation Models – Wild et al. (2001) Compares model results of DLR to observations.

Evaluation of Simulated Clear-Sky Longwave Radiation Using Ground-Based Observations – Allan (2000) “Surface observations from a tropical ocean and a subarctic land-based site are employed to evaluate the clear-sky surface downwelling longwave irradiance (SDL) simulated using the European Centre for Medium-Range Weather Forecasts reanalysis (ERA). Comparison of simulated clear-sky and observed all-sky SDL highlights coincident periods of irradiance variability on various timescales in both datasets.” [Link to PDF]

Longwave surface radiation over the globe from satellite data: An error analysis – Gupta et al. (1993) “Errors have been analysed for monthly-average downward and net longwave surface fluxes derived on a 5° equal-area grid over the globe using a satellite technique. … The errors in the TOVS-derived surface temperature, water vapour burden and cloud cover were estimated by comparing these meteorological parameters with independent measurements obtained from other satellite sources. Analysis of the overall errors shows that the present technique could lead to underestimation of downward fluxes by 5 to 15 Wm-2 and net fluxes by 4 to 12 Wm-2.”

Downward Longwave Irradiance at the Ocean Surface From Satellite Data: Methodology and in Situ Validation – Frouin et al. (1987) “The results indicate that the satellite methods perform similarly, with standard errors of estimate ranging from 21 to 27 W m−2 on a half-hourly time scale and from 16 to 22 W m−2 on a daily time scale. These errors correspond to 6 to 8% and 4 to 6% of the average measured values, respectively. When compared with techniques based on empirical formulas that employ conventional surface data, the satellite methods also exhibit similar standard errors of estimate. The satellite methods, however, are favored, since they are generally less biased and globally applicable.”

Estimation of daytime downward longwave radiation at the surface from satellite and grid point data – Schmetz et al. (1986) “A hybrid method is developed for the estimation of the daytime downward longwave radiation flux (DLF) at the surface. … The method is a first attempt to estimate the DLF at regional scales from satellite data on the cloud field and grid point analysis data on the thermodynamic field.”

Downward Longwave Radiation at the Surface from Satellite Measurements – Darnell et al. (1983) “A new technique is presented for generating downward longwave flux at the Earth’s surface from satellite meteorological data and a radiative transfer model The technique was tested by using TIROS-N data from 41 passes over a ground site covering a period of one month. Satellite-derived fluxes were compared with those measured by a ground-based pyrgeometer during each overpass. The standard error of the satellite-derived fluxes relative to the mean ground-measured values was found to be 6.5%.” [Link to PDF]

Closely related

Global Energy Balance Archive (GEBA) (“Proto-GEBA”), see also GCOS Switzerland GEBA page, especially this report.

Papers on atmospheric measurements of GHGs
Papers on changes in OLR due to GHG’s

Posted in AGW evidence | 1 Comment »

Papers on the albedo of the Earth

Posted by Ari Jokimäki on August 17, 2009

This list of papers contains observations of Earth’s albedo, concentrating especially on the possible changes in albedo. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (November 4, 2009): Loeb et al. (2007) and Loeb et al. (2007) added, thanks to John Cook for pointing them out, see the discussion section below.

Inter-annual variations in Earth’s reflectance 1999-2007 – Palle et al. (2008) Doesn’t find much trends in albedo, although emphasizes a brief 1.5 year long increase in reflectance. “In the common period, earthshine, CERES along with ISCCP-FD data show a trendless albedo. However, preceding CERES, earthshine and ISCCP-FD reflectances show a significant increase before flattening and holding the increase.” [Link to PDF]

Variability in global top-of-atmosphere shortwave radiation between 2000 and 2005 – Loeb et al. (2007) “The ground-based Earthshine data show an order-of-magnitude more variability in annual mean SW TOA flux than either CERES or ISCCP, while ISCCP and CERES SW TOA flux variability is consistent to 40%. Most of the variability in CERES TOA flux is shown to be dominated by variations global cloud fraction, as observed using coincident CERES and MODIS data. Idealized Earthshine simulations of TOA SW radiation variability for a lunar-based observer show far less variability than the ground-based Earthshine observations, but are still a factor of 4–5 times more variable than global CERES SW TOA flux results. Furthermore, while CERES global albedos exhibit a well-defined seasonal cycle each year, the seasonal cycle in the lunar Earthshine reflectance simulations is highly variable and out-of-phase from one year to the next.”

Multi-Instrument Comparison of Top-of-Atmosphere Reflected Solar Radiation – Loeb et al. (2007) “Observations from the Clouds and the Earth’s Radiant Energy System (CERES), Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) between 2000 and 2005 are analyzed in order to determine if these data are meeting climate accuracy goals recently established by the climate community. The focus is primarily on top-of-atmosphere (TOA) reflected solar radiances and radiative fluxes. … The results presented in this study are in stark contrast to those of Pallé et al. (2004, 2005) who claim to have observed a 6 Wm-2 increase in annual mean reflected solar radiation between 2000 and 2003 based on Earthshine measurements. … When the global monthly anomalies in CERES Terra SW TOA flux in Fig. 9b are averaged annually, the difference between the minimum and maximum yearly anomalies is 0.6 Wm-2, an order-of-magnitude smaller than the change found in the Earthshine data. Given the remarkable consistency shown here between data records from CERES, MODIS, MISR, SeaWiFS and ISCCP, none of these additional data records support a 6 Wm-2 change between 2000 and 2003.” [Link to PDF]

Comment on ‘‘A multi-data comparison of shortwave climate forcing changes’’ by Pallé et al. – Bender (2006) Gives a nice overview to different albedo measurement techniques while commenting on Pallé et al. work. [Link to PDF]

22 views of the global albedo—comparison between 20 GCMs and two satellites – Bender et al. (2006) Compares climate model simulations to real world observations of Earth’s albedo. “Discrepancies between different data sets and models exist; thus, it is clear that conclusions about absolute magnitude and accuracy of albedo should be drawn with caution.” [Link to PDF]

Changes in Earth’s Albedo Measured by Satellite – Wielicki et al. (2005) “The satellite data show that the last four years are within natural variability and fail to confirm the 6% relative increase in albedo inferred from observations of earthshine from the moon.” [Link to PDF]

Changes in Earth’s Reflectance over the Past Two Decades – Palle et al. (2004) “This proxy shows a steady decrease in Earth’s reflectance from 1984 to 2000, with a strong climatologically significant drop after 1995. From 2001 to 2003, only earthshine data are available, and they indicate a complete reversal of the decline.” [Link to PDF]

Earthshine and the Earth’s albedo: 2. Observations and simulations over 3 years – Pallé et al. (2003) “Since late 1998, we have been making sustained measurements of the Earth’s reflectance by observing the earthshine from Big Bear Solar Observatory. … We find that our precision, with steady observations since December 1998, is sufficient to detect a seasonal cycle.”

Earthshine and the Earth’s albedo: 1. Earthshine observations and measurements of the lunar phase function for accurate measurements of the Earth’s Bond albedo – Qiu et al. (2003) “We have been making sustained observations of the earthshine from Big Bear Solar Observatory in California since late 1998. We also have intermittent observations from 1994–1995. Here, we develop a modern method of measuring, instantaneously, the large-scale reflectance of the Earth.” [Link to PDF]

Estimate of top-of-atmosphere albedo for a molecular atmosphere over ocean using Clouds and the Earth’s Radiant Energy System measurements – Kato et al. (2002) “The shortwave broadband albedo at the top of a molecular atmosphere over ocean between 40°N and 40°S is estimated using radiance measurements from the Clouds and the Earth’s Radiant Energy System (CERES) instrument and the Visible Infrared Scanner (VIRS) aboard the Tropical Rainfall Measuring Mission satellite.”

Earthshine observations of the Earth’s reflectance – Goode et al. (2001) “Regular photometric observations of the moon’s “ashen light” (earthshine) from the Big Bear Solar Observatory (BBSO) since December 1998 have quantified the earth’s optical reflectance. We find large (∼5%) daily variations in the reflectance due to large‐scale weather changes on the other side of the globe. … However, we find seasonal variations roughly twice those of the simulation, with the earth being brightest in the spring.”

Global change and the dark of the moon – Flatté et al. (1992) This is largely a review article. “We have considered the possibility of using earthshine to measure the reflectance properties of the earth (albedo and phase function). Measurements of earthshine carried out by Danjon in 1926-33 show that even then the average albedo could be determined with a precision of +/- 0.01 and that both synoptic and seasonal variations could be observed clearly. We show that, after correction for wavelength dependence and the opposition effect in the lunar reflectance properties, Danjon’s visual albedo of 0.40 can be reconciled with the ERBE satellite Bond albedo of 0.30.” [Link to PDF]

Repetition of Danjon earthshine measurements for determination of long term trends in the earth’s albedo – Huffman et al. (1990) “The authors are investigating the possibility of determining whether changes have occurred in the albedo of the earth due to changes in cloud properties. The method is to reproduce as faithfully as possible the measurements of earthshine made by André Danjon during the period from 1926 to 1935 and continued by J. Dubois from 1940 to 1960. To this end a “cat’s eye” photometer similar to that used by Danjon has been constructed and data taking begun. Analysis for long term trends depends on understanding of geographic effects, seasonal variations, and 10 year variations in earthshine.”

Albedo, color, and polarization of the Earth – Danjon (1954), in The Earth as a Planet, edited by G. P. Kuiper. Presents early albedo measurements by earthshine.

The albedo of the planet Earth and of clouds – Fritz (1949) “The albedo of the whole earth is calculated to be 35 per cent, largely on the basis of Danjon’s visual lunar measurements. The calculations also give a value of about 0.50 for the average albedo of clouds, which is in better agreement with measurements than the currently accepted value.”

Sur l’albedo de la terre – Dubois (1947). (I haven’t found suitable link for this one but some details are given in Qiu et al., 2003, see above.) Presents early albedo measurements by earthshine.

Recherches sur la photométrie de la lumiére cendrée et l’albedo de la terre – Danjon (1928). (I’m not certain that the linked paper is correct, but both the name and the journal reference seem to be similar to what is given in Qiu et al., 2003, see above, they also give some details on this. See also Flatté et al., 1992 for details on this.) Presents early albedo measurements by earthshine.

Posted in AGW evidence | 6 Comments »

Papers on GHG role in historical climate changes

Posted by Ari Jokimäki on August 15, 2009

This list of papers contains evidence of important role of greenhouse gases in historical climate changes. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

See also papers on glacial terminations, which has lot of relevant papers to this list also.

UPDATE: (July 27, 2012): Lorius et al. (1990) added , thanks to Barry for pointing it out (see the comment section below).
UPDATE: (July 1, 2010): Ballantyne et al. (2010) added, thanks to J Bowers for pointing it out (see the comment section below).
UPDATE: (February 9, 2010): Doney & Schimel (2007) added.
UPDATE: (January 30, 2010): Halevy et al. (2009) added, thanks to Bob for pointing it out (see the comment section below).
UPDATE: (January 9, 2010): Cuffey & Vimeux (2001) added.
UPDATE: (October 12, 2009): Tripati et al. (2009) added.
UPDATE: (September 17, 2009): Shackleton & Pisias (1985) and Genthon et al. (1987) added.
UPDATE: (August 19, 2009): Hogg (2008), Scheffer et al. (2006), and Fischer et al. (1999) added.

Significantly warmer Arctic surface temperatures during the Pliocene indicated by multiple independent proxies – Ballantyne et al. (2010) “Here, we estimate mean annual temperature (MAT) based upon three independent proxies from an early Pliocene peat deposit in the Canadian High Arctic. Our proxies, including oxygen isotopes and annual ring widths (MAT = –0.5 ± 1.9 °C), coexistence of paleovegetation (MAT = –0.4 ± 4.1 °C), and bacterial tetraether composition in paleosols (MAT = –0.6 ± 5.0 °C), yield estimates that are statistically indistinguishable. The consensus among these proxies suggests that Arctic temperatures were ~19 °C warmer during the Pliocene than at present, while atmospheric CO2 concentrations were ~390 ppmv. These elevated Arctic Pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo. These results indicate that Arctic temperatures may be exceedingly sensitive to anthropogenic CO2 emissions.” [Full text]

Radiative transfer in CO2-rich paleoatmospheres – Halevy et al. (2009) “We examine the sensitivity of line-by-line results to three parameterizations of line and continuum absorption by CO2, all of which yield essentially identical radiation fluxes at low CO2 abundance. However, when applied to atmospheres containing 0.1–5 bars of CO2, appropriate for early Earth and Mars, the outgoing longwave radiation calculated with the three parameterizations differs by as much as 40 W m−2. … Despite these uncertainties, we conclude that early Mars probably required other infrared absorbers to reach super-freezing surface temperatures, while for the early Earth, this is not necessarily the case.” [Full text]

Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years – Tripati et al. (2009) “We use boron/calcium ratios in foraminifera to estimate pCO2 during major climate transitions of the last 20 million years (myr). During the Middle Miocene, when temperatures were ~3 to 6°C warmer and sea level 25 to 40 meters higher than present, pCO2 was similar to modern levels.”

Target Atmospheric CO2: Where Should Humanity Aim? – Hansen et al. (2008) Paper full of interesting discussion about past climate changes. “Paleoclimate data show that climate sensitivity is ∼3°C for doubled CO2, including only fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is ∼6°C for doubled CO2 for the range of climate states between glacial conditions and ice-free Antarctica.” [Full text]

Glacial cycles and carbon dioxide: A conceptual model – Hogg (2008) “Here I compare observed climate cycles with results from a simple model which predicts the evolution of global temperature and carbon dioxide over the glacial-interglacial cycle. The model includes a term which parameterises deep ocean release of CO2 in response to warming, and thereby amplifies the glacial cycle. In this model, temperature rises lead CO2 increases at the glacial termination, but it is the feedback between these two quantities that drives the abrupt warming during the transition from glacial to interglacial periods.” [Full text]

Linkages between CO2, climate, and evolution in deep time – Royer (2008) “Over the past 450 million years (Myr), CO2 was low when extensive, long-lived ice sheets were present (330–290 Myr ago and 35 Myr ago to the present day) and moderately high to high at other times. However, some intervals in Earth’s past fail to show any consistent relationship.” [Full text]

Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change – Fletcher et al. (2008) “Here, we present high-resolution records of Mesozoic and early Cenozoic atmospheric CO2 concentrations from a combination of carbon-isotope analyses of non-vascular plant (bryophyte) fossils and theoretical modelling. … Time-series comparisons show that these variations coincide with large Mesozoic climate shifts, in contrast to earlier suggestions of climate–CO2 decoupling during this interval. These reconstructed atmospheric CO2 concentrations drop below the simulated threshold for the initiation of glaciations on several occasions and therefore help explain the occurrence of cold intervals in a ‘greenhouse world’.”

The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems – Kürschner et al. (2008) “Here we present a CO2 record based on stomatal frequency data from multiple tree species. Our data show striking CO2 fluctuations of ≈600–300 parts per million by volume (ppmv). Periods of low CO2 are contemporaneous with major glaciations, whereas elevated CO2 of 500 ppmv coincides with the climatic optimum in the Miocene. Our data point to a long-term coupling between atmospheric CO2 and climate.” [Full text]

Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era – Came et al. (2007) A follow-up paper to Veizer et al. (2000, see below) that arrives to opposite conclusion than Veizer et al. (2000) “Our results indicate that tropical sea surface temperatures were significantly higher than today during the Early Silurian period (443–423 Myr ago), when carbon dioxide concentrations are thought to have been relatively high, and were broadly similar to today during the Late Carboniferous period (314–300 Myr ago), when carbon dioxide concentrations are thought to have been similar to the present-day value. Our results are consistent with the proposal that increased atmospheric carbon dioxide concentrations drive or amplify increased global temperatures.” [Full text]

Carbon and Climate System Coupling on Timescales from the Precambrian to the Anthropocene – Doney & Schimel (2007) A review paper. “Here we bring together evidence on the dominant climate, biogeochemical and geological processes organized by timescale, spanning interannual to centennial climate variability, Holocene millennial variations and Pleistocene glacial-interglacial cycles, and million-year and longer variations over the Precambrian and Phanerozoic. Our focus is on characterizing, and where possible quantifying, internal coupled carbon-climate system dynamics and responses to external forcing from tectonics, orbital dynamics, catastrophic events, and anthropogenic fossil-fuel emissions. One emergent property is clear across timescales: atmospheric CO2 can increase quickly, but the return to lower levels through natural processes is much slower. The consequences of human carbon cycle perturbations will far outlive the emissions that caused them.” [Full text]

CO2-forced climate thresholds during the Phanerozoic – Royer (2006) “Here, I compare 490 published proxy records of CO2 spanning the Ordovician to Neogene with records of global cool events to evaluate the strength of CO2-temperature coupling over the Phanerozoic (last 542 my). … A pervasive, tight correlation between CO2 and temperature is found both at coarse (10 my timescales) and fine resolutions up to the temporal limits of the data set (million-year timescales), indicating that CO2, operating in combination with many other factors such as solar luminosity and paleogeography, has imparted strong control over global temperatures for much of the Phanerozoic.” [Full text]

Positive feedback between global warming and atmospheric CO2 concentration inferred from past climate change – Scheffer et al. (2006) “Here we present an alternative way of estimating the magnitude of the feedback effect based on reconstructed past changes. Linking this information with the mid-range Intergovernmental Panel on Climate Change estimation of the greenhouse gas effect on temperature we suggest that the feedback of global temperature on atmospheric CO2 will promote warming by an extra 15–78% on a century-scale.” [Full text]

CO2 as a primary driver of Phanerozoic climate – Royer et al. (2004) “Here we review the geologic records of CO2 and glaciations and find that CO2 was low (1000 ppm) during other, warmer periods.” [Full text]

Cosmic Rays, Carbon Dioxide, and Climate – Rahmstorf et al. (2004) “Two main conclusions result from our analysis of [Shaviv & Veizer, 2003]. The first is that the correlation of cosmic ray flux (CRF) and climate over the past 520 Myr appears to not hold up under scrutiny. … Our second conclusion is independent of the first. Whether there is a link of CRF and temperature or not, the authors’ estimate of the effect of a CO2-doubling on climate is highly questionable.” [Full text]

High CO2 levels in the Proterozoic atmosphere estimated from analyses of individual microfossils – Kaufman & Xiao (2003) “Our results indicate that carbon dioxide was an important greenhouse gas during periods of lower solar luminosity, probably dominating over methane after the atmosphere and hydrosphere became pervasively oxygenated between 2 and 2.2 gigayears ago.” [Full text]

Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination III – Caillon et al. (2003) “The sequence of events during Termination III suggests that the CO2 increase lagged Antarctic deglacial warming by 800 ± 200 years and preceded the Northern Hemisphere deglaciation.”

Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric CO2 – DeConto & Pollard (2003) “The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary (34 million years ago) (refs 1–4) is one of the most fundamental reorganizations of global climate known in the geologic record. … According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition, relative to CO2 concentration.” [Full text]

Carbon dioxide and climate over the past 300Myr – Retallack (2002) “Large and growing databases on these proxy indicators support the idea that atmospheric CO2 and temperature are coupled. In contrast, CO2–temperature uncoupling has been proposed from geological time-series of carbon isotopic composition of palaeosols and of marine phytoplankton compared with foraminifera, which fail to indicate high CO2 at known times of high palaeotemperature. Failure of carbon isotopic palaeobarometers may be due to episodic release of CH4, which has an unusually light isotopic value (down to −110[promille], and typically −60[promille]δ13C) and which oxidizes rapidly (within 7–24 yr) to isotopically light CO2.” [Full text]

Covariation of carbon dioxide and temperature from the Vostok ice core after deuterium-excess correction – Cuffey & Vimeux (2001) “Here we incorporate measurements of deuterium excess from Vostok in the temperature reconstruction and show that much of the mismatch is an artefact caused by variations of climate in the water vapour source regions. Using a model that corrects for this effect, we derive a new estimate for the covariation of CO2 and temperature, of r2 = 0.89 for the past 150 kyr and r2 = 0.84 for the period 350–150 kyr ago. Given the complexity of the biogeochemical systems involved, this close relationship strongly supports the importance of carbon dioxide as a forcing factor of climate. Our results also suggest that the mechanisms responsible for the drawdown of CO2 may be more responsive to temperature than previously thought.”

Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozoic eon – Veizer et al. (2000) “Here we present a reconstruction of tropical sea surface temperatures throughout the Phanerozoic eon (the past 550 Myr) from our database of oxygen isotopes in calcite and aragonite shells. … But our data conflict with a temperature reconstruction using an energy balance model that is forced by reconstructed atmospheric carbon dioxide concentrations.”

Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica – Petit et al. (1999) “Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.” [Full text]

Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations – Fischer et al. (1999) “High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere.”

The ice-core record: climate sensitivity and future greenhouse warming – Lorius et al. (1990) “The prediction of future greenhouse-gas-induced warming depends critically on the sensitivity of Earth’s climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial–interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.” C. Lorius, J. Jouzel, D. Raynaud, J. Hansen & H. Le Treut, Nature 347, 139 – 145 (13 September 1990); doi:10.1038/347139a0. [Full text]

Vostok ice core: climatic response to CO2 and orbital forcing changes over the last climatic cycle – Genthon et al. (1987) “Vostok climate and CO2 records suggest that CO2 changes have had an important climatic role during the late Pleistocene in amplifying the relatively weak orbital forcing. The existence of the 100-kyr cycle and the synchronism between Northern and Southern Hemisphere climates may have their origin in the large glacial–interglacial CO2 changes.”

Atmospheric carbon dioxide, orbital forcing, and climate – Shackleton & Pisias (1985) “A 340,000-year record of benthic and planktonic oxygen and carbon isotope measurements from an equatorial Pacific deep-sea core are analyzed. The data provide estimates of both global ice volume and atmospheric carbon dioxide concentration over this period. The frequencies characteristic of changes in the earth-sun orbital geometry dominate all the records. Examination of phase relationships shows that atmospheric carbon dioxide concentration leads ice volume over the orbital bandwidth, and is forced by orbital changes through a mechanism, at present not fully understood, with a short response time. Changes in atmospheric CO2 are not primarily caused by glacial-interglacial sea level changes, which had been hypothesized to affect atmospheric CO2 through the effect on ocean chemistry of changing sedimentation on the continental shelves. Instead, variations in atmospheric CO2 should be regarded as part of the forcing of ice volume changes.”

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Papers on Palaeocene–Eocene Thermal Maximum

Posted by Ari Jokimäki on August 11, 2009

Recently there has been discussion on Palaeocene–Eocene Thermal Maximum (PETM) relating to recent paper in Nature Geoscience by Zeebe et al. (2009). Here is RealClimate article about the issue containing also a nice introduction to PETM. That lead me to compile this list of papers about PETM. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative. Here is a related list of links (mostly websites and news items) made by Oakden Wolf.

UPDATE (April 18, 2012): McInerney & Wing (2011) added. Thanks to Barry for pointing it out.

The Paleocene-Eocene Thermal Maximum: A Perturbation of Carbon Cycle, Climate, and Biosphere with Implications for the Future – McInerney & Wing (2011) “During the Paleocene-Eocene Thermal Maximum (PETM), ~56 Mya, thousands of petagrams of carbon were released into the ocean-atmosphere system with attendant changes in the carbon cycle, climate, ocean chemistry, and marine and continental ecosystems. The period of carbon release is thought to have lasted <20 ka, the duration of the whole event was ~200 ka, and the global temperature increase was 5–8°C. Terrestrial and marine organisms experienced large shifts in geographic ranges, rapid evolution, and changes in trophic ecology, but few groups suffered major extinctions with the exception of benthic foraminifera. The PETM provides valuable insights into the carbon cycle, climate system, and biotic responses to environmental change that are relevant to long-term future global changes." Francesca A. McInerney, and Scott L. Wing, Annual Review of Earth and Planetary Sciences, Vol. 39: 489-516 (Volume publication date May 2011), DOI: 10.1146/annurev-earth-040610-133431. [Full text]

Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming – Zeebe et al. (2009) “We conclude that in addition to direct CO2 forcing, other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Palaeocene–Eocene Thermal Maximum.” [Link to PDF]

Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison – Panchuk et al. (2008) “Possible sources of carbon that may have caused global warming at the Paleocene-Eocene boundary are constrained using an intermediate complexity Earth-system model configured with early Eocene paleogeography. … This pulse could not have been solely the result of methane hydrate destabilization, suggesting that additional sources of CO2 such as volcanic CO2, the oxidation of sedimentary organic carbon, or thermogenic methane must also have contributed.”

On the duration of the Paleocene-Eocene thermal maximum (PETM) – Röhl et al. (2007) “A detailed chronology was developed with nondestructive X-ray fluorescence (XRF) core scanning records on the scale of precession cycles, with a total duration of the PETM now estimated to be ∼170 ka.” [Link to PDF]

Reversed deep-sea carbonate ion basin gradient during Paleocene-Eocene thermal maximum – Zeebe & Zachos (2007) “Here we show that during the PETM, the deep-sea undersaturation was not homogeneous among the different ocean basins.” [Link to PDF]

Beyond methane: Towards a theory for the Paleocene–Eocene Thermal Maximum – Higgins & Schrag (2006) “However, the magnitude of the warming (5 to 6 °C [2],[3]) and rise in the depth of the CCD (> 2 km; [4]) indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis. Additional carbon sources associated with methane hydrate release (e.g. pore-water venting and turbidite oxidation) are also insufficient. We find that the oxidation of at least 5000 Gt C of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the PETM, for which there are several potential mechanisms.” [Link to PDF]

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum – Sluijs et al. (2006) “We show that sea surface temperatures near the North Pole increased from 18 °C to over 23 °C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming.” [Link to PDF]

An Ancient Carbon Mystery – Pagani et al. (2006) “About 55 million years ago, Earth experienced a period of global warming that lasted similar to 170,000 years. This climate event–the Paleocene-Eocene Thermal Maximum (PETM)–may be the best ancient analog for future increases in atmospheric CO sub(2). But how well do we understand this event?”

Extreme warming of mid-latitude coastal ocean during the Paleocene-Eocene Thermal Maximum: Inferences from TEX86 and isotope data – Zachos et al. (2006) “Here we present a record of sea surface temperature change across the Paleocene-Eocene boundary for a nearshore, shallow marine section located on the eastern margin of North America. The SST record, as inferred from TEX86 data, indicates a minimum of 8 °C of warming, with peak temperatures in excess of 33 °C. Similar SSTs are estimated from planktonic foraminifer oxygen isotope records, although the excursion is slightly larger.”

Rapid Acidification of the Ocean During the Paleocene-Eocene Thermal Maximum – Zachos et al. (2005) “These findings indicate that a large mass of carbon (»2000 x 109 metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.”

Deep-Sea Temperature and Circulation Changes at the Paleocene-Eocene Thermal Maximum – Tripati & Elderfield (2005) “Foraminiferal magnesium/calcium ratios indicate that bottom waters warmed by 4° to 5°C, similar to tropical and subtropical surface ocean waters, implying no amplification of warming in high-latitude regions of deep-water formation under ice-free conditions. Intermediate waters warmed before the carbon isotope excursion, in association with downwelling in the North Pacific and reduced Southern Ocean convection, supporting changing circulation as the trigger for methane hydrate release.”

A Transient Rise in Tropical Sea Surface Temperature During the Paleocene-Eocene Thermal Maximum – Zachos et al. (2003) “Using mixed-layer foraminifera, we found that the combined proxies imply a 4° to 5°C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.”

Methane oxidation during the late Palaeocene thermal maximum – Dickens (2000) “Important conclusions from this work are that massive CH4 release into any carbon reservoir will cause a negative delta 13C excursion, increased atmosphere pCO2, elevated global surface temperature, and pelagic carbonate dissolution, but that the timing and magnitude of these responses depends on the location of CH4 oxidation.”

Abrupt deep-sea warming, palaeoceanographic changes and benthic extinctions at the end of the Palaeocene – Kennett & Stott (1991) “A remarkable oxygen and carbon isotope excursion occurred in Antarctic waters near the end of the Palaeocene (~57.33 Myr ago), indicating rapid global warming and oceanographic changes that caused one of the largest deep-sea benthic extinctions of the past 90 million years.”

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Papers on ocean temperature

Posted by Ari Jokimäki on August 10, 2009

This list of papers contains evidence of the warming of the world ocean. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (September 24, 2012): Levitus et al. (2012) added. Thanks to Barry for pointing it out.
UPDATE (November 24, 2010): Lyman et al. (2010) added. Thanks to Anander for pointing it out, see the comment section below.
UPDATE (September 22, 2010): Roemmich & Gilson (2009) and Gregory et al. (2004) added.
UPDATE (September 12, 2010): Purkey & Johnson (2010) added.
UPDATE (April 24, 2010): Page updated. Some papers got new full text links and DiNezio & Goni (2010) was added.
UPDATE (November 19, 2009): Douglass & Knox (2009) added, thanks to Magnus W for pointing it out, see the comment section of “Papers on Earth’s radiation budget”.
UPDATE (October 11, 2009): von Schuckmann et al. (2009) and Church et al. (2009) added.

World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010 – Levitus et al. (2012) “We provide updated estimates of the change of ocean heat content and the thermosteric component of sea level change of the 0–700 and 0–2000 m layers of the World Ocean for 1955–2010. Our estimates are based on historical data not previously available, additional modern data, and bathythermograph data corrected for instrumental biases. We have also used Argo data corrected by the Argo DAC if available and used uncorrected Argo data if no corrections were available at the time we downloaded the Argo data. The heat content of the World Ocean for the 0–2000 m layer increased by 24.0 ± 1.9 × 1022 J (±2S.E.) corresponding to a rate of 0.39 W m−2 (per unit area of the World Ocean) and a volume mean warming of 0.09°C. This warming corresponds to a rate of 0.27 W m−2 per unit area of earth’s surface. The heat content of the World Ocean for the 0–700 m layer increased by 16.7 ± 1.6 × 1022 J corresponding to a rate of 0.27 W m−2 (per unit area of the World Ocean) and a volume mean warming of 0.18°C. The World Ocean accounts for approximately 93% of the warming of the earth system that has occurred since 1955. The 700–2000 m ocean layer accounted for approximately one-third of the warming of the 0–2000 m layer of the World Ocean. The thermosteric component of sea level trend was 0.54 ± .05 mm yr−1 for the 0–2000 m layer and 0.41 ± .04 mm yr−1 for the 0–700 m layer of the World Ocean for 1955–2010.” Levitus, S., et al. (2012), World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010, Geophys. Res. Lett., 39, L10603, doi:10.1029/2012GL051106. [Full text]

Robust warming of the global upper ocean – Lyman et al. (2010) “A large (~1023 J) multi-decadal globally averaged warming signal in the upper 300 m of the world’s oceans was reported roughly a decade ago and is attributed to warming associated with anthropogenic greenhouse gases. The majority of the Earth’s total energy uptake during recent decades has occurred in the upper ocean, but the underlying uncertainties in ocean warming are unclear, limiting our ability to assess closure of sea-level budgets, the global radiation imbalance and climate models. For example, several teams have recently produced different multi-year estimates of the annually averaged global integral of upper-ocean heat content anomalies (hereafter OHCA curves) or, equivalently, the thermosteric sea-level rise. Patterns of interannual variability, in particular, differ among methods. Here we examine several sources of uncertainty that contribute to differences among OHCA curves from 1993 to 2008, focusing on the difficulties of correcting biases in expendable bathythermograph (XBT) data. XBT data constitute the majority of the in situ measurements of upper-ocean heat content from 1967 to 2002, and we find that the uncertainty due to choice of XBT bias correction dominates among-method variability in OHCA curves during our 1993–2008 study period. Accounting for multiple sources of uncertainty, a composite of several OHCA curves using different XBT bias corrections still yields a statistically significant linear warming trend for 1993–2008 of 0.64 W m-2 (calculated for the Earth’s entire surface area), with a 90-per-cent confidence interval of 0.53–0.75 W m-2.” John M. Lyman, Simon A. Good, Viktor V. Gouretski, Masayoshi Ishii, Gregory C. Johnson, Matthew D. Palmer, Doug M. Smith & Josh K. Willis, Nature 465, 334-337 (20 May 2010) | doi:10.1038/nature09043. [Full text]

Warming of Global Abyssal and Deep Southern Ocean Waters Between the 1990s and 2000s: Contributions to Global Heat and Sea Level Rise Budgets – Purkey & Johnson (2010) “We quantify abyssal global and deep Southern Ocean temperature trends between the 1990s and 2000s to assess the role of recent warming of these regions in global heat and sea level budgets. We compute warming rates with uncertainties along 28 full-depth, high-quality, hydrographic sections that have been occupied two or more times between 1980 and 2010. We divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and estimate temperature trends in the 24 sampled basins. The three southernmost basins show a strong statistically significant abyssal warming trend, with that warming signal weakening to the north in the central Pacific, western Atlantic, and eastern Indian Oceans. Eastern Atlantic and western Indian Ocean basins show statistically insignificant abyssal cooling trends. Excepting the Arctic Ocean and Nordic seas, the rate of abyssal (below 4000 m) global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0.027 (±0.009) W m−2 applied over the entire surface of the Earth. Deep (1000–4000 m) warming south of the Sub-Antarctic Front of the Antarctic Circumpolar Current adds 0.068 (±0.062) W m−2. The abyssal warming produces a 0.053 (±0.017) mm yr−1 increase in global average sea level and the deep warming south of the Sub-Antarctic Front adds another 0.093 (±0.081) mm yr−1. Thus warming in these regions, ventilated primarily by Antarctic Bottom Water, accounts for a statistically significant fraction of the present global energy and sea level budgets.” Sarah G. Purkey and Gregory C. Johnson, Journal of Climate 2010, doi: 10.1175/2010JCLI3682.1. [Full text]

Identifying and Estimating Biases between XBT and Argo Observations Using Satellite Altimetry – DiNezio & Goni (2010) “A methodology is developed to identify and estimate systematic biases between expendable bathythermograph (XBT) and Argo observations using satellite altimetry. … The depth-dependent XBT-minus-Argo differences suggest a global positive bias of 3% of the XBT depths. The fact that this 3% error is robust among the different ocean basins provides evidence for changes in the instrumentation, such as changes in the terminal velocity of the XBTs. The value of this error is about the inverse of the correction to the XBT fall-rate equation (FRE) implemented in 1995, suggesting that this correction, while adequate during the 1990s, is no longer appropriate and could be the source of the 3% error. This result suggests that for 2000–07, the XBT dataset can be brought to consistency with Argo by using the original FRE coefficients without the 1995 correction.” [Full text]

The 2004–2008 mean and annual cycle of temperature, salinity, and steric height in the global ocean from the Argo Program – Roemmich & Gilson (2009) “The Argo Program has achieved 5 years of global coverage, growing from a very sparse global array of 1000 profiling floats in early 2004 to more than 3000 instruments from late 2007 to the present. Using nearly 350,000 temperature and salinity profiles, we constructed an upper-ocean climatology and monthly anomaly fields for the 5-year era, 2004–2008. A basic description of the modern upper ocean based entirely on Argo data is presented here, to provide a baseline for comparison with past datasets and with ongoing Argo data, to test the adequacy of Argo sampling of large-scale variability, and to examine the consistency of the Argo dataset with related ocean observations from other programs. The Argo 5-year mean is compared to the World Ocean Atlas, highlighting the middle and high latitudes of the southern hemisphere as a region of strong multi-decadal warming and freshening. Moreover the region is one where Argo data have contributed an enormous increment to historical sampling, and where more Argo floats are needed for documenting large-scale variability. Globally, the Argo-era ocean is warmer than the historical climatology at nearly all depths, by an increasing amount toward the sea surface; it is saltier in the surface layer and fresher at intermediate levels. Annual cycles in temperature and salinity are compared, again to WOA01, and to the National Oceanography Center air–sea flux climatology, the Reynolds SST product, and AVISO satellite altimetric height. These products are consistent with Argo data on hemispheric and global scales, but show regional differences that may either point to systematic errors in the datasets or their syntheses, to physical processes, or to temporal variability. The present work is viewed as an initial step toward integrating Argo and other climate-relevant global ocean datasets.” Dean Roemmich, and John Gilson, Progress In Oceanography, Volume 82, Issue 2, August 2009, Pages 81-100, doi:10.1016/j.pocean.2009.03.004. [Full text]

Changes in global upper-ocean heat content over the last half century and comparison with climate models – Church et al. (2009) Apparently an update to Domingues et al. (2008). “Here, we present updates of our previous estimates of global upper ocean heat content annual anomalies from 1961 to 2008. These updates will allow for spatial and instrumental biases in the historical data base and include improved upper-ocean heat content estimates from recent Argo data.”

Global hydrographic variability patterns during 2003–2008 – von Schuckmann et al. (2009) “Monthly gridded global temperature and salinity fields from the near-surface layer down to 2000 m depth based on Argo measurements are used to analyze large-scale variability patterns on annual to interannual time scales during the years 2003–2008. … Global mean heat content and steric height changes are clearly associated with a positive trend during the 6 years of measurements.” [Full text] Here is a related PDF-file from Mercator Ocean Quarterly Newsletter (von Schuckmann et al. section starts from page 3). See also the article relating to this paper by John Cook at SkepticalScience.

Ocean heat content and Earth’s radiation imbalance – Douglass & Knox (2009) “Earth’s radiation imbalance is determined from ocean heat content data and compared with results of direct measurements. Distinct time intervals of alternating positive and negative values are found: 1960–mid-1970s (−0.15), mid-1970s–2000 (+0.15), 2001–present (−0.2 W/m2), and are consistent with prior reports. These climate shifts limit climate predictability.” [Full text]

Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems – Levitus et al. (2009) “We provide estimates of the warming of the world ocean for 1955–2008 based on historical data not previously available, additional modern data, correcting for instrumental biases of bathythermograph data, and correcting or excluding some Argo float data. The strong interdecadal variability of global ocean heat content reported previously by us is reduced in magnitude but the linear trend in ocean heat content remain similar to our earlier estimate.” Addresses also the issues raised by Gouretski & Koltermann (2007). [Full text]

Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections – Ishii & Kimoto (2009) “In comparison with the previous temperature analysis, large differences are found in the present analysis as follows: the duration of large ocean heat content in the 1970s shortens dramatically, and recent ocean cooling becomes insignificant.” [Full text]

Improved estimates of upper-ocean warming and multi-decadal sea-level rise – Domingues et al. (2008) “Our ocean warming and thermal expansion trends for 1961–2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993–2003, which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors” [Full text]

In Situ Data Biases and Recent Ocean Heat Content Variability – Willis et al. (2008) “Two significant instrument biases have been identified in the in situ profile data used to estimate globally integrated upper-ocean heat content. A large cold bias was discovered in a small fraction of Argo floats along with a smaller but more prevalent warm bias in expendable bathythermograph (XBT) data. These biases appear to have caused the bulk of the upper-ocean cooling signal reported by Lyman et al. between 2003 and 2005.” [Full text]

How much is the ocean really warming? – Gouretski & Koltermann (2007) “Using bias-corrected XBT data we argue reduces the ocean heat content change since the 1950s by a factor of 0.62. Our estimate of the ocean heat content increase (0–3000 m) between 1957–66 and 1987–96 is 12.8·1022 J.” [Full text]

Simulated and observed variability in ocean temperature and heat content – AchutaRao et al. (2007) “For all major ocean basins, there was good agreement between the simulated and observed sampling distributions of OHC changes on 2-, 5-, and 10-year time scales (see SI Figs. 6–8). … Our analysis shows that the cooling found by Lyman et al. is spurious. At least five lines of evidence support this conclusion.” [Full text]

Isolating the signal of ocean global warming – Palmer et al. (2007) “We present a new analysis of millions of ocean temperature profiles designed to filter out local dynamical changes to give a more consistent view of the underlying warming. Time series of temperature anomaly for all waters warmer than 14°C show large reductions in interannual to inter-decadal variability and a more spatially uniform upper ocean warming trend (0.12 Wm−2 on average) than previous results.”

Is the World Ocean Warming? Upper-Ocean Temperature Trends: 1950–2000 – Harrison & Carson (2007) “Where there are sufficient observations for this analysis, there is large spatial variability of 51-yr trends in the upper ocean, with some regions showing cooling in excess of 3°C, and others warming of similar magnitude.” [Full text]

Recent cooling of the upper ocean – Lyman et al. (2006) Reports an apparent cooling of the oceans after 2003, but later it turned out to be a problem in observations (See Willis et al., 2008 given above). [Full text]

Anthropogenic Warming of the Oceans: Observations and Model Results – Pierce et al. (2006) “Comparing the observations with results from two coupled ocean–atmosphere climate models [the Parallel Climate Model version 1 (PCM) and the Hadley Centre Coupled Climate Model version 3 (HadCM3)] that include anthropogenic forcing shows remarkable agreement between the observed and model-estimated warming.” [Full text]

Penetration of Human-Induced Warming into the World’s Oceans – Barnett et al. (2005) “A warming signal has penetrated into the world’s oceans over the past 40 years. The signal is complex, with a vertical structure that varies widely by ocean; it cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models.” [Full text]

Warming of the world ocean, 1955–2003 – Levitus et al. (2005) “During 1955–1998 world ocean heat content (0–3000 m) increased 14.5 x 1022 J corresponding to a mean temperature increase of 0.037°C at a rate of 0.20 Wm-2 (per unit area of Earth’s total surface area).” [Full text]

Simulated and observed decadal variability in ocean heat content – Gregory et al. (2004) “Previous analyses by Levitus et al. [2000] (“Levitus”) of ocean temperature data have shown that ocean heat content has increased over the last fifty years with substantial temporal variability superimposed. The HadCM3 coupled atmosphere–ocean general circulation model (AOGCM) simulates the Levitus trend if both natural and anthropogenic forcings are included. In the relatively well-observed northern hemisphere upper ocean, HadCM3 has similar temporal variability to Levitus but, like other AOGCMs, it has generally less variability than Levitus for the world ocean. We analyse the causes of this discrepancy, which could result from deficiencies in either the model or the observational dataset. A substantial contribution to the Levitus variability comes from a strong maximum around 500 m depth, absent in HadCM3. We demonstrate a possibly large sensitivity to the method of filling in the observational dataset outside the well-observed region, and advocate caution in using it to assess AOGCM heat content changes.” Gregory, J. M., H. T. Banks, P. A. Stott, J. A. Lowe, and M. D. Palmer (2004), Geophys. Res. Lett., 31, L15312, doi:10.1029/2004GL020258.

Warming of the World Ocean – Levitus et al. (2000) “The heat content of the world ocean increased by ~2 × 1023 joules between the mid-1950s and mid-1990s, representing a volume mean warming of 0.06°C. This corresponds to a warming rate of 0.3 watt per meter squared (per unit area of Earth’s surface).” [Full text]

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Papers on Antarctic temperature trends

Posted by Ari Jokimäki on August 8, 2009

This is a list of papers about temperature trends in Antarctic. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (November 28, 2010): Schneider et al. (2006), van den Broeke (2000), and Shuman & Stearns (2001) added.
UPDATE (November 9, 2009): Milliken et al. (2009) added to “closely related” section, thanks to John Cook for pointing it out (see the comment section below).
UPDATE (September 14, 2009): Chapman & Walsh (2007) added, thanks for “Curious” for pointing this paper to me (see the comments section below).

Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year – Steig et al. (2009) “Here we show that significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, an area of warming much larger than previously reported.” [Full text] [Correction]

Attribution of polar warming to human influence – Gillett et al. (2008) “We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence.” [Full text]

Recent variability and trends of Antarctic near-surface temperature – Monaghan et al. (2008) “The subtle shift toward warming during the past 15 years raises the question of whether the recent trends are linked more closely to anthropogenic influences or multidecadal variability.” [Full text]

A Synthesis of Antarctic Temperatures – Chapman & Walsh (2007) “Monthly surface air temperatures from land surface stations, automatic weather stations, and ship/buoy observations from the high-latitude Southern Hemisphere are synthesized into gridded analyses at a resolution appropriate for applications ranging from spatial trend analyses to climate change impact assessments. … Trends calculated for the 1958–2002 period suggest modest warming over much of the 60°–90°S domain. All seasons show warming, with winter trends being the largest at +0.172°C decade−1 while summer warming rates are only +0.045°C decade−1. The 45-yr temperature trend for the annual means is +0.082°C decade−1 corresponding to a +0.371°C temperature change over the 1958–2002 period of record.” Chapman, William L., John E. Walsh, 2007, J. Climate, 20, 4096–4117. doi: 10.1175/JCLI4236.1. [Full text]

Antarctic temperatures over the past two centuries from ice cores – Schneider et al. (2006) “We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high-resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti-phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental Southern Hemisphere (SH) mean temperature record and the reconstruction suggests that at longer timescales, temperatures over the Antarctic continent vary in phase with the SH mean. Our reconstruction suggests that Antarctic temperatures have increased by about 0.2°C since the late nineteenth century. The variability and the long-term trends are strongly modulated by the SH Annular Mode in the atmospheric circulation.” Schneider, D. P., E. J. Steig, T. D. van Ommen, D. A. Dixon, P. A. Mayewski, J. M. Jones, and C. M. Bitz (2006), Geophys. Res. Lett., 33, L16707, doi:10.1029/2006GL027057. [Full text]

Antarctic atmospheric temperature trend patterns from satellite observations – Johanson & Fu (2006) “We show good agreement between satellite-inferred temperature trends and radiosonde observations. It is illustrated that the Antarctic troposphere has cooled in the summer and fall seasons since 1979,… It is shown that significant tropospheric warming prevails during Antarctic winters and springs, but we also find significant winter cooling over half of East Antarctica.” [Full text]

Significant Warming of the Antarctic Winter Troposphere – Turner et al. (2006) “The data show that regional midtropospheric temperatures have increased at a statistically significant rate of 0.5° to 0.7°Celsius per decade over the past 30 years. … The available data do not allow us to unambiguously assign a cause to the tropospheric warming at this stage.” [Full text]

Antarctic climate change during the last 50 years – Turner et al. (2005) “The Reference Antarctic Data for Environmental Research (READER) project data set of monthly mean Antarctic near-surface temperature, mean sea-level pressure (MSLP) and wind speed has been used to investigate trends in these quantities over the last 50 years for 19 stations with long records. Eleven of these had warming trends and seven had cooling trends in their annual data (one station had too little data to allow an annual trend to be computed), indicating the spatial complexity of change that has occurred across the Antarctic in recent decades.” [Full text] [Erratum]

A further assessment of surface temperature changes at stations in the Antarctic and Southern Ocean, 1949-2002 – Jacka et al. (2004) “The data are studied in four groupings: coastal Antarctica (excluding the Antarctic Peninsula), inland Antarctica, the Antarctic Peninsula and the Southern Ocean/Pacific Ocean islands. We find that within each of these four groupings the average trend indicates warming.”

Recent Rapid Regional Climate Warming on the Antarctic Peninsula – Vaughan et al. (2003) “We discuss the significance of [recent rapid regional] warming in one area, the Antarctic Peninsula. Here warming was much more rapid than in the rest of Antarctica where it was not significantly different to the global mean. We highlight climate proxies that appear to show that [recent rapid regional] warming on the Antarctic Peninsula is unprecedented over the last two millennia, and so unlikely to be a natural mode of variability.”

Climate change (Communication arising): Recent temperature trends in the Antarctic – Turner et al. (2002) “Doran et al. claim that there has been a net cooling of the entire continent between 1966 and 2000, particularly during summer and autumn. We argue that this result has arisen because of an inappropriate extrapolation of station data across large, data-sparse areas of the Antarctic.”

Antarctic climate cooling and terrestrial ecosystem response – Doran et al. (2002) “Although previous reports suggest slight recent continental warming, our spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn.” [Full text]

Decadal-Length Composite Inland West Antarctic Temperature Records – Shuman & Stearns (2001) “Decadal-length, daily average, temperature records have been generated for four inland West Antarctic sites by combining automatic weather station (AWS) and satellite passive microwave brightness temperature records. These records are composites due to the difficulty in maintaining continuously operating AWS in Antarctica for multiyear to multidecade periods. Calibration of 37-GHz, vertical polarization, brightness temperature data during periods of known air temperature by emissivity modeling allows the resulting calibrated brightness temperatures (TC) to be inserted into data gaps with constrained errors. By the same technique, but with reduced constraints, TC data were also developed through periods before AWS unit installation or after removal. The resulting composite records indicate that temperature change is not consistent in sign or magnitude from location to location across the West Antarctic region. Linear regression analysis shows an approximate 0.9°C increase over 19 yr at AWS Byrd (0.045 yr−1 ±0.135°C), a 0.9°C cooling over 12 yr at AWS Lettau (−0.078 yr−1 ±0.178°C), a 3°C cooling over 10 yr at AWS Lynn (−0.305 yr−1 ±0.314°C), and a 2°C warming over 19 yr at AWS Siple (0.111 yr−1 ±0.079°C). Only the Siple trend is statistically significant at the 95% confidence level however. The temperature increases at Siple and possibly Byrd are suggestive of a broader regional warming documented at sites on the Antarctic Peninsula. The cooling suggested by the shorter records in the vicinity of the Ross Ice Shelf is consistent with results recently reported by Comiso and suggests that significant regional differences exist. Continued data acquisition should enable detection of the magnitude and direction of potential longer-term changes.” Shuman, Christopher A., Charles R. Stearns, 2001, J. Climate, 14, 1977–1988. [Full text]

Variability and Trends in Antarctic Surface Temperatures from In Situ and Satellite Infrared Measurements – Comiso (2000) “The surface air temperatures observed from stations in Antarctica have been shown to have predominantly positive trends that are as high as 0.5°C decade−1 along the Antarctic Peninsula. To evaluate whether the trends are caused by a local or large-scale phenomenon in the Antarctic region, surface temperatures inferred from infrared satellite data from 1979 to 1998 have been analyzed in combination with data from 21 stations that have long record lengths. The surface temperatures derived from infrared data are coherent spatially and temporally and are shown to agree well with Antarctic station data with a correlation coefficient of 0.98 and a standard deviation of about 3°C. The trend analysis on station data yielded on the average 0.012 ± 0.008°C yr−1 and −0.008 ± 0.025°C yr−1 for the 45- and 20-yr record, respectively. The latter reasonably agrees with the trend of −0.042 ± 0.067°C yr−1 inferred from the satellite 20-yr record. The 20-yr record length is shown to be about the minimum length required for a meaningful trend analysis study. However, interannual fluctuations of the temperatures are large and the 95% confidence level for the satellite trends ranges from −0.177 to 0.094°C yr−1 for the Antarctic ice sheet. Nevertheless, the observed cooling is intriguing, especially since it is compatible with the observed trend in the sea ice cover. In the sea ice regions, the northernmost positions of the ice edge are shown to be influenced by alternating warm and cold anomalies around the continent. The pattern of these anomalies is consistent with that of the Antarctic circumpolar wave but with predominantly mode-3 instead of mode-2 wave as reported previously.” Comiso, Josefino C., 2000, J. Climate, 13, 1674–1696. [Full text]

On the Interpretation of Antarctic Temperature Trends – van den Broeke (2000) “Determining the rate of atmospheric warming in Antarctica is hampered by the brevity of the temperature records (<50 years), which still contain signals of decadal circulation variability in the Southern Hemisphere. In this note it is demonstrated that Antarctic warming trends have been regionally modified by slow circulation changes and associated changes in sea-ice cover: decadal weakening of the semiannual oscillation since the mid-1970s has limited the meridional heat exchange between Antarctica and its surroundings, so that warming trends have leveled out since then. In contrast, northerly circulation anomalies in combination with decreased sea-ice cover have regionally enhanced low-level warming, for instance in the region of the Antarctic Peninsula. Based on this knowledge, the authors propose a background Antarctic warming trend of 1.30 ± 0.38°C (century)−1, representative of the period 1957–95.” van den Broeke, Michiel R., 2000, J. Climate, 13, 3885–3889. [Full text]

Closely related

High-resolution Holocene climate record from Maxwell Bay, South Shetland Islands, Antarctica – Milliken et al. (2009) “The highest resolution Holocene sediment core from the Antarctic Peninsula to date was collected during the first SHALDRIL cruise (NBP0502). … This high-resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat. … There is no evidence for an early Holocene climatic reversal, as recorded farther south at the Palmer Deep drill site. Minimum sea-ice cover and warm water conditions occurred between 8.2 and 5.9 ka. From 5.9 to 2.6 ka, there was a gradual cooling and more extensive sea-ice cover in the bay. After 2.6 ka, the climate varied slightly, causing only subtle variation in glacier grounding lines. There is no compelling evidence for a Little Ice Age readvance in Maxwell Bay. The current warming and associated glacial response in the northern Antarctic Peninsula appears to be unprecedented in its synchroneity and widespread impact.”

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