AGW Observer

Observations of anthropogenic global warming

New research from last week 14/2012

Posted by Ari Jokimäki on April 9, 2012

We only have 10 new papers this week but they are diverse. Himalayan glaciers, global temperature record, European growing season, bioenergy, Australia snow cover, ancient ocean acidification, marine boundary layer cloud feedbacks, ocean temperature measurements, stratospheric air, and solar activity proxies are all subjects that get treated with new research articles this week. Remember that 1960 Keeling paper where he announced that atmospheric carbon dioxide concentration is increasing? As the classic of the week we bring you a paper from that same issue of Tellus, where it is estimated based on ocean carbon dioxide uptake that carbon dioxide from fossil fuel burning should increase the atmospheric concentration.


Potential solar activity proxy from 10Be in lake sediments

10Be in lacustrine sediments – a record of solar activity? – Mann et al. (2012)

Abstract: “Concentrations and fluxes of cosmogenic 10Be in three varved lake sediments covering the last 100 years were determined to investigate their suitability to record past solar activity. The 10Be signal in lake sediments is composed of a component reflecting the radionuclide production in the atmosphere and a component related to the subsequent transport into the sediment. In order to separate these two components we applied singular-spectrum analysis (SSA). The extracted patterns in concentrations and depositional fluxes were compared to 10Be records from polar ice cores and to the solar modulation potential derived from neutron monitor data. In the transport component we discovered the existence of a long-term trend in the 10Be concentrations, which can be attributed to the redox cycle of both lakes. In the production component we found a similar pattern as in the NGrip ice core. A cross correlation analysis yielded a significant negative correlation between the 10Be production component and the solar modulation potential. 10Be lags the production on average by 1.5 years which corresponds to the expected transport time from the atmosphere to the Earth’s surface. Hence, we conclude that varved lake sediments are potentially suitable to study the solar activity of the past. However, one should be aware that various mechanisms may mask the 10Be signal in the sediment.”

Citation: M. Mann, J. Beer, F. Steinhilber, M. Christl, Journal of Atmospheric and Solar-Terrestrial Physics, http://dx.doi.org/10.1016/j.jastp.2012.03.011.


How old is stratospheric air?

Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period – Stiller et al. (2012) [FULL TEXT]

Abstract: “An extensive observational data set, consisting of more than 106 SF6 vertical profiles from MIPAS measurements distributed over the whole globe has been condensed into monthly zonal means of mean age of air for the period September 2002 to January 2010, binned at 10° latitude and 1–2 km altitude. The data were analysed with respect to their temporal variation by fitting a regression model consisting of a constant and a linear increase term, 2 proxies for the QBO variation, sinusoidal terms for the seasonal and semi-annual variation and overtones for the correction of the shapes to the observed data set. The impact of subsidence of mesospheric SF6-depleted air and in-mixing into non-polar latitudes on mid-latitudinal absolute age of air and its linear increase was assessed and found to be small. The linear increase of mean age of stratospheric air was found to be positive and partly larger than the trend derived by Engel et al. (2009) for most of the Northern mid-latitudes, the middle stratosphere in the tropics, and parts of the Southern mid-latitudes, as well as for the Southern polar upper stratosphere. Multi-year decrease of age of air was found for the lowermost and the upper stratospheric tropics, for parts of Southern mid-latitudes, and for the Northern polar regions. Analysis of the amplitudes and phases of the seasonal variation shed light on the coupling of stratospheric regions to each other. In particular, the Northern mid-latitude stratosphereis well coupled to the tropics, while the Northern lowermost mid-latitudinal stratosphere is decoupled, confirming the separation of the shallow branch of the Brewer-Dobson circulation from the deep branch. We suggest an overall increased tropical upwelling, together with weakening of mixing barriers, especially in the Northern Hemisphere, as a hypothetical model to explain the observed pattern of linear multi-year increase/decrease, and amplitudes and phase shifts of the seasonal variation.”

Citation: Stiller, G. P., von Clarmann, T., Haenel, F., Funke, B., Glatthor, N., Grabowski, U., Kellmann, S., Kiefer, M., Linden, A., Lossow, S., and López-Puertas, M.: Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period, Atmos. Chem. Phys., 12, 3311-3331, doi:10.5194/acp-12-3311-2012, 2012.


Correcting biases in XBT based ocean temperature measurements

Empirical correction of XBT data – Hamon et al. (2012) [FULL TEXT]

Abstract: “We use a collocation method between XBT and CTD/OSD (Ocean Station Data including bottle cast and low resolution CTD) from WOD2005 to statistically correct the XBT fall rate. An analysis of the annual median bias on depth shows that it is necessary to apply a thermal correction, a second order correction on the depth as well as a depth offset representing measurement errors during XBT deployment. We separated data in several categories: shallow and deep XBTs and below or above 10°C of vertically averaged ocean temperatures (in the top 400m). We also processed separately XBT measurements in the western Pacific between 1968 and 1985 due to large regional biases. The estimated corrections deviate from other published estimates with some large variations in time of both linear and curvature terms in the depth corrections, and less time variation of the temperature correction for the deep XBTs. This analysis of heat content derived from corrected XBTs provides at first order a similar variability to other estimates from corrected XBTs and MBTs. It shows a fairly prominent trend in 0-700m ocean heat content of 0.39.1022J/year between 1970 and 2008.”

Citation: M. Hamon, G. Reverdin, and P.-Y. Le Traon, Journal of Atmospheric and Oceanic Technology 2012, doi: http://dx.doi.org/10.1175/JTECH-D-11-00129.1.


Negative feedback from cloud water amount and positive feedback from cloudiness reduction in marine boundary layer

Marine boundary-layer cloud feedbacks in a constant relative humidity atmosphere – Rieck et al. (2012)

Abstract: “The mechanisms that govern the response of shallow cumulus, such as found in the trade-wind regions, to a warming of the atmosphere in which large-scale atmospheric processes act to keep relative humidity constant are explored. Two robust effects are identified. First, and as is well known, the liquid-water lapse-rate increases with temperature and tends to increase the amount of water in clouds, making clouds more reflective of solar radiation. Second, and less well appreciated, the surface fluxes increase with the saturation specific humidity which itself is a strong function of temperature. Using large-eddy simulations we show that the liquid-water lapse-rate acts as a negative feedback: a positive temperature increase driven by radiative forcing is reduced by the increase in cloud water and hence cloud albedo. However, this effect is more than compensated by a reduction of cloudiness associated with the deepening and relative drying of the boundary layer, driven by larger surface moisture fluxes. Because they are so robust these effects are thought to underlie changes in the structure of the marine boundary layer as a result of global warming.”

Citation: Malte Rieck, Louise Nuijens, and Bjorn Stevens, Journal of the Atmospheric Sciences 2012, doi: http://dx.doi.org/10.1175/JAS-D-11-0203.1.


Trying to detect ancient ocean acidification

Recognising ocean acidification in deep time: An evaluation of the evidence for acidification across the Triassic-Jurassic boundary – Greene et al. (2012)

Abstract: “While demonstrating ocean acidification in the modern is relatively straightforward (measure increase in atmospheric CO2 and corresponding ocean chemistry change), identifying palaeo-ocean acidification is problematic. The crux of this problem is that the rock record is a constructive archive while ocean acidification is essentially a destructive (and/or inhibitory) phenomenon. This is exacerbated in deep time without the benefit of a deep ocean record. Here, we discuss the feasibility of, and potential criteria for, identifying an acidification event in deep time. Furthermore, we investigate the evidence for ocean acidification during the Triassic-Jurassic (T-J) boundary interval, an excellent test case because 1) it occurs in deep time, beyond the reach of deep sea drilling coverage; 2) a potential trigger for acidification is known; and 3) it is associated with one of the ‘Big Five’ mass extinctions which disproportionately affected modern-style invertebrates. Three main criteria suggest that acidification may have occurred across the T-J transition. 1) The eruption of the Central Atlantic Magmatic Province (CAMP) and the associated massive and rapid release of CO2 coincident with the end-Triassic mass extinction provide a suitable trigger for an acidification event (full carbonate undersaturation in the surface ocean is possible but improbable). 2) Tentative evidence for a global paucity of carbonate across the end-Triassic mass extinction versus the adjacent stratigraphy is consistent with a predicted sedimentary response to acidification. 3) The end-Triassic mass extinction was particularly selective against acid-sensitive organisms (more so than perhaps any other extinction event) and temporarily eliminated coral reefs. Therefore multiple lines of evidence are consistent with a T-J ocean acidification event within our current resolution to recognise such events in deep time. The conclusion that the end-Triassic extinction was influenced by acidification implies that short-term acidification perturbations may have long-term effects on ecosystems, a repercussion that has previously not been established. Although anthropogenic emissions are more rapid than any event in the geologic record, events such as the T-J can serve as partial analogues for the present anthropogenic carbon release. Since the T-J was such a pronounced crisis for both modern-style marine invertebrates and scleractinian reefs, it is of particular interest in terms of informing projections about the effects of modern ocean acidification.”

Citation: Sarah E. Greene, Rowan C. Martindale, Kathleen A. Ritterbush, David J. Bottjer, Frank A. Corsetti, William M. Berelson, Earth Science Reviews, http://dx.doi.org/10.1016/j.earscirev.2012.03.009.


Observational record of Australia snow cover

Satellite based observations for seasonal snow cover detection and characterisation in Australia – Bormann et al. (2012)

Abstract: “A new daily snow cover dataset was developed using Moderate resolution Imaging Spectroradiometer (MODIS) Level-1B products for the Australian alpine region over the period 2000–2010 at 500 m resolution. The dataset has been evaluated during clear-sky conditions using snow detection estimates derived from Landsat Thematic Mapper (TM) data and has been compared to the MOD10_L2 snow cover products. The ability to customise the snow detection threshold is one of the benefits of developing the Melt Area Detection Index (MADI) approach for regional conditions. The dataset provides a new satellite based observational record that may be used to characterise spatial and temporal development of Australian snow cover extent and duration. The new snow cover observations provide insight into snow characteristics in this region where significant declines in snow cover extent, season duration and a shift towards earlier snow melt date are observed. Shifts towards early season melt dates are observed for snow at 1580 m and above. This includes areas which are pertinent to snow recreation activities in the region. Season length declines are attributed to earlier seasonal snowmelt rather than later season onset and may be linked to observed warming trends in the area. The MODIS based approach can be applied to other regions and other sensors to assist in evaluating snow modelling efforts and improve water resource management and snow hydrology based investigations.”

Citation: Kathryn J. Bormann, Matthew F. McCabe, Jason P. Evans, Remote Sensing of Environment, Volume 123, August 2012, Pages 57–71, http://dx.doi.org/10.1016/j.rse.2012.03.003.


Large-scale production of bioenergy from forest biomass is neither sustainable nor GHG neutral

Large-scale bioenergy from additional harvest of forest biomass is neither sustainable nor greenhouse gas neutral – Schulze et al. (2012)

Abstract: “Owing to the peculiarities of forest net primary production humans would appropriate ca. 60% of the global increment of woody biomass if forest biomass were to produce 20% of current global primary energy supply. We argue that such an increase in biomass harvest would result in younger forests, lower biomass pools, depleted soil nutrient stocks and a loss of other ecosystem functions. The proposed strategy is likely to miss its main objective, i.e. to reduce greenhouse gas (GHG) emissions, because it would result in a reduction of biomass pools that may take decades to centuries to be paid back by fossil fuel substitution, if paid back at all. Eventually, depleted soil fertility will make the production unsustainable and require fertilization, which in turn increases GHG emissions due to N2O emissions. Hence, large-scale production of bioenergy from forest biomass is neither sustainable nor GHG neutral.”

Citation: Ernst-Detlef Schulze, Christian Körner, Beverly E. Law, Helmut Haberl, Sebastiaan Luyssaert, GCB Bioenergy, DOI: 10.1111/j.1757-1707.2012.01169.x.


Changes in the timing in European growing season differ regionally

Combining satellite derived phenology with climate data for climate change impact assessment – Ivits et al. (2012)

Abstract: “The projected influence of climate change on the timing and volume of phytomass production is expected to affect a number of ecosystem services. In order to develop coherent and locally effective adaptation and mitigation strategies, spatially explicit information on the observed changes is needed. Long-term variations of the vegetative growing season in different environmental zones of Europe for 1982–2006 have been derived by analysing time series of GIMMS NDVI data. The associations of phenologically homogenous spatial clusters to time series of temperature and precipitation data were evaluated. North-East Europe showed a trend to an earlier and longer growing season, particularly in the northern Baltic areas. Despite the earlier greening up large areas of Europe exhibited rather stable season length indicating the shift of the entire growing season to an earlier period. The northern Mediterranean experience a growing season shift towards later dates while some agglomerations of earlier and shorter growing season were also seen. The correlation of phenological time series with climate data shows a cause-effect relationship over the semi natural areas consistent with results in literature. Managed ecosystems however appear to have heterogeneous change pattern with less or no correlation to climatic trends. Over these areas climatic trends seemed to overlap in a complex manner with more pronounced effects of local biophysical conditions and/or land management practices. Our results underline the importance of satellite derived phenological observations to explain local nonconformities to climatic trends for climate change impact assessment.”

Citation: E. Ivits, M. Cherlet, G. Toth, S. Sommer, W. Mehl, J. Vogt, F. Micale, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.03.010.


Analysis of quasiperiodic 50-80 year oscillation in global temperature record

Quasiperiodic climate variability with a period of 50–80 years: Fourier analysis of measurements and Earth System Model simulations – Henriksson et al. (2012)

Abstract: “We examine an oscillation of global mean temperature with a period of about two thirds of a century. We find evidence for the oscillation both in the instrumental temperature record and in an Earth System Model millennium simulation without external forcing. There is also evidence for the oscillation in the Central England Temperature record, the longest instrumental record available. Our method is based on a discrete Fourier transform with varying starting point and length of time window. This method allows us to make a quantitative estimate of the contribution of an oscillation to global mean temperature, to track the phase evolution of the oscillation and to compare measurement and model results. The multidecadal oscillation could provide part of the explanation both for near-constant global mean temperatures in recent years despite warming by rising concentrations of greenhouse gases and for declining global mean temperature in the 1950s and 1960s alongside with the explanation of aerosol cooling. Quantitative estimates of the contribution of the oscillation to global mean temperature vary between ±(0.03–0.17) K. For the instrumental temperature record, our results indicate an amplitude of 0.03 K presently if the IPCC model average represents the effect of external forcings well, and (0.08–0.17) K when using simple linear and quadratic fits for detrending. For the millennium simulation, the amplitude of the oscillation is (0.05–0.06) K, but could be underestimated as compared to reality if external forcing acts to globally synchronize multidecadal variability. The role of the Atlantic Multidecadal Oscillation (AMO) in the model is discussed. The AMO has a spatial temperature distribution similar to earlier literature results and is more correlated with the global oscillation when external forcing is included.”

Citation: S. V. Henriksson, P. Räisänen, J. Silén and A. Laaksonen, Climate Dynamics, DOI: 10.1007/s00382-012-1341-0.


Himalayan glaciers have gotten smaller and glacial lakes bigger

Responses of glaciers and glacial lakes to climate variation between 1975 and 2005 in the Rongxer basin of Tibet, China and Nepal – Wu et al. (2012)

Abstract: “This research presents an evaluation of glacier recession and glacial-lake expansion in the Rongxer basin in the Mount Qomolangma National Reserve of central Himalaya. Changes in glacier and glacial-lake surface areas in the Reserve between 1975, 1992 and 2005 have been estimated using remote sensing and GIS techniques that have integrated field data from 2009, 1:50,000 scale topographic maps, ASTER satellite data from 2009, and Landsat MSS/TM images in 1975, 1992 and 2005. By 2005, the glacier surface area had declined from 596.52 to 451.58 km2 with a total area loss of 144.94 km2, and glacial lakes had increased from 3.55 to 7.87 km2, an increase of 121.69 %. The volume of glaciers was reduced by 69.99 km3 from 1975 to 2005. The observed changes in the extent of glaciers are in line with the observed atmospheric warming in the Rongxer basin. Records from the Tingri station and Nyalam station have revealed warming during the ablation season since the 1970s at a rate of 0.03–0.04 °C a−1 in the northern and central Rongxer basin. At higher elevations in the study area, represented by the Tingri and Nyalam meteorological stations, the summer warming was accompanied by negative anomalies in annual precipitation since the 1970s, likely enhancing glacier retreat and glacial lake expansion.”

Citation: Shan-shan Wu, Zhi-jun Yao, He-qing Huang, Zhao-fei Liu and Gao-huan Liu, Regional Environmental Change, DOI: 10.1007/s10113-012-0302-9.


CLASSIC OF THE WEEK: Kanwisher (1960)

pCO2 in Sea Water and its Effect on the Movement of CO2 in Nature – Kanwisher (1960) [FULL TEXT]

Abstract:“A method is described for measuring pCO2 in sea water. A gas phase is analyzed continuously by infrared absorption for CO2 while it is equilibrated gently with the water in a countercurrent column. It has been used to determine the changes in pCO2 produced by variations of temperature and total CO2. Partial pressure shows large changes for small increments in these two independant variables. These properties of sea water are useful in estimating the movement of CO2 between the atmosphere and oceans. It appears, for instance, that most of the fossil fuel CO2 released by man has been effective in increasing the percentage of this gas in air.”

Citation: John Kanwisher, Tellus, Volume 12, Issue 2, pages 209–215, May 1960, DOI: 10.1111/j.2153-3490.1960.tb01302.x.


When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

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