New research from last week 31/2012
Posted by Ari Jokimäki on August 6, 2012
If you prefer new peer-reviewed science over non-peer-reviewed PR papers, this is the post for you. Apart from scientists themselves, peer-reviewers, and journal editors, you are the first people on Earth to know about the things presented below.
Tree-ring proxies can provide reliable indicators of temperature variability even in rapidly warming climate
Abstract: “Northwestern North America has one of the highest rates of recent temperature increase in the world, but the putative ‘divergence problem’ in dendroclimatology potentially limits the ability of tree-ring proxy data at high latitudes to provide long-term context for current anthropogenic change. Here, we reconstruct summer temperatures from a Picea glauca maximum latewood density (MXD) chronology that shows a stable relationship to regional temperatures and spans most of the last millennium at the Firth River in northeastern Alaska. We estimate that the warmest epoch in the last nine centuries occurs during the late 20th century, with average temperatures over the last thirty years of our reconstruction (1973 to 2002 CE) approximately 1.3 ± 0.4°C warmer than the long-term preindustrial mean (1100 to 1850 CE), a change associated with rapid increases in greenhouse gases. Prior to the late 20th century, multidecadal temperature fluctuations covary broadly with changes in natural radiative forcing. Our findings emphasize that tree-ring proxies can provide reliable indicators of temperature variability even in a rapidly warming climate.”
Citation: Kevin J. Anchukaitis, Rosanne D. D’Arrigo, and Laia Andreu-Hayles, David Frank and Anne Verstege, Ashley Curtis, Brendan M. Buckley, Gordon C. Jacoby, and Edward R. Cook, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00139.1.
Global coverage for carbon dioxide measurements from satellites
Abstract: “We present an analysis of the global mid-tropospheric CO2 retrieved for all-sky (clear and cloudy) conditions from measurements by the Atmospheric Infrared Radiation Sounder on board the Aqua satellite in 2003-2009. The global data coverage allows us to identify the set of CO2 spatial patterns and their time variability by applying the Principal Component Analysis and the Empirical Mode Decomposition. The first, dominant pattern represents 93% of the variability and exhibits the linear trend of 2 ± 0.2 ppm/year, as well as annual and interannual dependencies. The single-site record of CO2 at Mauna Loa compares well with variability of this pattern. The first principal component is phase-shifted relative to the Southern Oscillation indicating a causative relationship between the atmospheric CO2 and the ENSO. The higher-order patterns show regional details of CO2 distribution and display the semi-annual oscillation. We also compare the CO2 distributions with the distribution of two major characteristics of air transport: the vertical velocity and potential temperature surfaces at the same height. In agreement with modeling, CO2 concentration closely traces the potential temperature surfaces (isentropes) in mid and high latitudes. However its vertical transport in the tropics, where these surfaces are mostly horizontal, is suppressed. Our results are in agreement with the previous results on annual and interannual CO2 time variability obtained by using the network flask data. This knowledge of the global CO2 spatial patterns can be useful in climate analyses and potentially in the challenging task of connecting CO2 sources and sinks with its distribution in the atmosphere.”
Citation: Alexander Ruzmaikin, Hartmut H. Aumann, and Thomas S. Pagano, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00223.1.
Southeast Australia autumn rainfall reduction might be due to poleward shift of ocean-atmosphere circulation
Abstract: “Since the 1950s, annual rainfall over southeast Australia (SEA) has decreased considerably with a maximum decline in the austral autumn season (March-May), particularly from 1980 onwards. The understanding of SEA autumn rainfall variability, the causes and associated mechanisms for the autumn reduction remain elusive. As such, a new plausible mechanism for SEA autumn rainfall variability is described, and the dynamics for the reduction are hypothesised. Firstly, there is no recent coherence between SEA autumn rainfall and the Southern Annular Mode, discounting it as a possible driver of the autumn rainfall reduction. Secondly, weak trends in the subtropical ridge intensity (STRI) cannot explain the recent autumn rainfall reduction across SEA, even though a significant relationship exists between the ridge and rainfall in April and May. With a collapse in the relationship between the autumn STRI and position in recent decades, a strengthening in the influence of the post-monsoonal winds from north of Australia has emerged, as evident by a strong post-1980 coherence with SEA pressure and rainfall. From mid-late autumn, there has been a replacement of a relative wet climate in SEA with a drier climate from northern latitudes, representing a climate shift that has contributed to the rainfall reduction. The maximum baroclinicity, as indicated by Eady growth rates, shifts polewards. An associated poleward shift of the dominant process controlling SEA autumn rainfall further enhances the reduction, particularly across southern SEA. This observed change over the past few decades is consistent with a poleward shift of the ocean and atmosphere circulation.”
Citation: Wenju Cai and Tim Cowan, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00035.1.
Satellite records have only recently reached sufficient length to detect trends in cloudiness
Abstract: “Satellite drift is an historical issue affecting the consistency of those few satellite records capable of being used for studies on climate time-scales. Here we address this issue for the PATMOS-x/AVHRR cloudiness record, which spans three decades and eleven disparate sensors. A two-harmonic sinusoidal function is fit to a mean diurnal cycle of cloudiness derived over the course of the entire AVHRR record. We validate this function against measurements from GOES sensors, finding good agreement, and then test the stability of the diurnal cycle over the course of the AVHRR record. It is found that the diurnal cycle is subject to some inter-annual variability over land, but that the differences are somewhat offset when averaged over an entire day. The fit function is used to generate daily-averaged time-series of ice, water and total cloudiness over the Tropics, where it is found that the diurnal correction affects the magnitude and even sign of long-term cloudiness trends. A statistical method is applied to determine the minimum length of time required to detect significant trends, and we find that only recently have we begun generating satellite records of sufficient length to detect trends in cloudiness.”
Citation: Michael J. Foster, Andrew Heidinger, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00666.1.
It’s not internal variability, it’s not unknown forcing, it’s mankind
Abstract: “Global-scale variations in the climate system over the last half of the 20th Century, including long-term increases in global-mean near-surface temperatures, are consistent with concurrent human-induced emissions of radiatively-active gases and aerosols. However, such consistency does not preclude the possible influence of other forcing agents, including internal modes of climate variability or unaccounted for aerosol effects. To test whether other unknown forcing agents may have contributed to multi-decadal increases in global-mean near-surface temperatures from 1950-2000, data pertaining to observed changes in global-scale sea-surface temperatures and observed changes in radiatively-active atmospheric constituents are incorporated into numerical global climate models. Results indicate that the radiative forcing needed to produce the observed long-term trends in sea-surface temperatures—and global-mean near-surface temperatures—is provided predominantly by known changes in greenhouse gases and aerosols. Further, results indicate that less than 10% of the long-term historical increase in global-mean near-surface temperatures over the last half of the 20th century could have been the result of internal climate variability. In addition they indicate that less than 25% of the total radiative forcing needed to produce the observed long-term trend in global-mean near-surface temperatures could have been provided by changes in net radiative forcing from unknown sources (either positive or negative). These results, which are derived from simple energy balance requirements, emphasize the important role humans have played in modifying the global climate over the last half of the 20th Century.”
Citation: Bruce T. Anderson, Jeff R. Knight and Mark A. Ringer, Jin-Ho Yoon, Annalisa Cherchi, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00645.1.
Observations of climate feedbacks over 2000-2010 and comparisons to climate models
Abstract:“Feedbacks in response to climate variations during the period 2000-2010 have been calculated using reanalysis meteorological fields and top-of-atmosphere flux measurements. Over this period, the climate was stabilized by a strongly negative temperature feedback (~ −3 W/m2/K); climate variations were also amplified by a strong positive water vapor feedback (~ +1.2 W/m2/K) and smaller positive albedo and cloud feedbacks (~ +0.3 and +0.5 W/m2/K, respectively). These observations are compared to two climate model ensembles, one dominated by internal variability (the control ensemble) and the other dominated by long-term global warming (the A1B ensemble). The control ensemble produces global average feedbacks that agree within uncertainties with the observations, as well as producing similar spatial patterns. The most significant discrepancy was in the spatial pattern for the total (shortwave + longwave) cloud feedback. Feedbacks calculated from the A1B ensemble show a stronger negative temperature feedback (due to a stronger lapse-rate feedback), but that is cancelled by a stronger positive water vapor feedback. The feedbacks in the A1B ensemble tend to be more smoothly distributed in space, which is consistent with the differences between ENSO climate variations and long-term global warming. The sum of all of the feedbacks, sometimes referred to as the thermal damping rate, is −1.15±0.88 W/m2/K in the observations, −0.60±0.37 W/m2/K in the control ensemble. Within the control ensemble, models that more accurately simulate ENSO tend to produce thermal damping rates closer to the observations. The A1B ensemble average thermal damping rate is −1.26±0.45 W/m2/K.”
Citation: A. E. Dessler, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00640.1.
Simulating the effects of methane disaster scenario
Abstract: “Decadal timescale responses of climate and the global carbon cycle to warming associated with rapid increases in atmospheric methane from a massive methane release from marine sedimentary methane hydrates are investigated with a coupled climate-carbon cycle model. A 1000-fold methane increase (from <1 to 1000 ppmv) causes surface air temperatures to increase with a global warming of >6°C within 80 years. The amount of carbon stored in the land biosphere decreases by >25%. This is mostly due to a large decrease in tropical net primary production during the first few years (~−40%), which is caused by a decrease in photosynthesis and an increase in plant maintenance respiration with the early warming of ~3°C, leading to tropical forest dieback (>20%) and the largest decrease in vegetation carbon of >50% (~80% of the decrease in global vegetation carbon). The decrease in global land carbon is also partly due to forest diebacks (mainly boreal forest dieback by heat stress) at northern middle latitudes. In contrast, vegetation increases by >50% at northern high latitudes because of the amelioration to warm and wet conditions. Sensitivity experiments show that the warming of >6°C consists mainly of >5°C by the 1000-fold atmospheric methane and an additional increase of 1°C by the atmospheric CO2 increase due to the land CO2 release, and that the CO2 fertilization of land plants prevents further warming of 1°C by limiting the atmospheric CO2 increase. The large decrease in land biomass estimated in this study suggests a critical situation for the land ecosystem or agricultural production especially in the tropics.”
Citation: Atsushi Obata and Kiyotaka Shibata, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00533.1.
Extracting seasonal climate information from Antarctic ice cores
Abstract: “As part of the United States’ contribution to the International Trans-Antarctic Scientific Expedition (ITASE), a network of precisely dated and highly resolved ice cores was retrieved from West Antarctica. The ITASE dataset provides a unique record of spatial and temporal variations of stable water isotopes (δ18O and δD) across West Antarctica. We demonstrate that, after accounting for water vapor diffusion, seasonal information can be successfully extracted from the ITASE cores. We use meteorological reanalysis, weather station, and sea ice data to assess the role of temperature, sea ice, and the state of the large-scale atmospheric circulation in controlling seasonal average water isotope variations in West Antarctica. The strongest relationships for all variables are found in the cores on and west of the West Antarctic Ice Sheet Divide and during austral fall. During this season positive isotope anomalies in the westernmost ITASE cores are strongly related to a positive pressure anomaly over West Antarctica, low sea ice concentrations in the Ross and Amundsen Seas, and above normal temperatures. Analyses suggest that this seasonally distinct climate signal is due to the pronounced meridional oriented circulation and its linkage to enhanced sea ice variations in the adjacent Southern Ocean during fall, both of which also influence local to regional temperatures.”
Citation: Marcel Küttel, Eric J. Steig, Qinghua Ding, Andrew J. Monaghan and David S. Battisti, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1460-7.
Abrupt climate changes in Northern hemisphere during MWP but not during LIA
Abstract: “We investigate the occurrence of abrupt changes in a total of 35 different proxy records from the extra-tropical Northern Hemisphere for the last ~1,500 years. The proxy records include ice-core δ18O, speleothem, tree ring width/density, marine sediment and lake sediment records with annual, sub-decadal or decadal resolutions. The aim is to explore the spatio–temporal distribution of abrupt climate changes using a kink point analysis technique. A clustering of warm kink points (the kink points with the highest temperatures) around AD 1000 appears corresponding to the Medieval Warm Period and indicates a geographically widespread temperature peak at that time. Kink points around AD 1000 are somewhat more numerous on higher latitudes than on lower latitudes. There are some tendencies for the coldest kink points (the kink points with the lowest temperatures) to be clustered in the ninetenth century, but they are generally more unevenly spaced in time than the warm peaks around AD 1000. The relative lack of kink points detected during the 1500 s–1700 s, likely the coldest part of the Little Ice Age, implies that this cold period was relatively stable and without abrupt events. A possible cluster of kink points on lower latitudes in the early ninth century is also found. No clear difference in the timing of kink points between the different proxy types can be observed.”
Citation: István Matyasovszky and Fredrik Charpentier Ljungqvist, Theoretical and Applied Climatology, 2012, DOI: 10.1007/s00704-012-0725-8.
Warming of 2K impacts Europe economy only moderately but 4K warming impact is clearly negative
Abstract: “This paper evaluates the impacts of climate change to European economies under an increase in global mean temperature at +2 °C and +4 °C. It is based on a summary of conclusions from available studies of how climate change may affect various sectors of the economies in different countries. We apply a macroeconomic general equilibrium model, which integrates impacts of climate change on different activities of the economies. Agents adapt by responding to the changes in market conditions following the climatic changes, thus bringing consistency between economic behaviour and adaptation to climate change. Europe is divided into 85 sub-regions in order to capture climate variability and variations in vulnerabilities within countries. We find that the impacts in the +2 °C are moderate throughout Europe, with positive impacts on GDP in some sub-regions and negative impacts down to 0.1 per cent per year in others. At +4 °C, GDP is negatively affected throughout Europe, and most substantially in the southern parts, where it falls by up to 0.7 per cent per year in some sub-regions. We also find that climate change causes differentiations in wages across Europe, which may cause migration from southern parts of Europe to northern parts, especially to the Nordic countries.”
Citation: Asbjørn Aaheim, Helene Amundsen, Therese Dokken, Taoyuan Wei, Global Environmental Change, 2012, http://dx.doi.org/10.1016/j.gloenvcha.2012.06.005.
Aerosols cause solar dimming so rice yields decrease despite of warming climate
Abstract: “The impacts of climate change on crop yield have increasingly been of concern. In this study, we investigated the impacts of trends in sunshine duration (S) and maximum temperature (T max) on rice yields in Jiangsu Province at both the provincial and county level during the period from 1980 to 2008. The results showed that although S and T max both were positively correlated with rice yields, the combined impacts of the decreasing trend of S (0.37 h/decade) and the increasing trend of T max (0.34 °C/decade) in August caused a reduction of 0.16 t ha−1 in rice yields (approximately 1.8 %) in Jiangsu Province, and the trend of S had played a dominant role in the yield losses. Further analyses suggest that the increasing concentration of aerosols from rapid economic development in Jiangsu Province has caused a significant solar dimming at least since 1960, making mitigations and adaptation measurements on regional haze impact imperative. Our study provides a prototype for detecting negative feedback on agricultural production caused by intensified anthropogenic activities that aim only to create rapid economic development.”
Citation: Jiabing Shuai, Zhao Zhang, Xiaofei Liu, Yi Chen, Pin Wang and Peijun Shi, Regional Environmental Change, 2012, DOI: 10.1007/s10113-012-0332-3.
Analysis of aerosol and ozone forcing between 1850 and 2100
Abstract: “Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at −0.15 W m−2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0.41 W m−2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4.5 and RCP6.0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060–2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8.5 and RCP2.6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2.6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8.5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with −0.34 and −0.28 W m−2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8.5, 4.5 and 2.6 scenarios. While for RCP6.0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between −12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed −3 W m−2.”
Citation: Sophie Szopa, Y. Balkanski, M. Schulz, S. Bekki, D. Cugnet, A. Fortems-Cheiney, S. Turquety, A. Cozic, C. Déandreis and D. Hauglustaine, et al., Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1408-y.
Western North American tree populations already lag behind their optimal climate niche
Abstract: “An important criticism of bioclimate envelope models is that many wide-ranging species consist of locally adapted populations that may all lag behind their optimal climate habitat under climate change, and thus should be modeled separately. Here, we apply a bioclimate envelope model that tracks habitat of individual populations to estimate adaptational lags for 15 wide-ranging forest tree species in western North America. An ensemble classifier modeling approach (RandomForest) was used to spatially project the climate space of tree populations under observed climate trends (1970s to 2000s) and multi-model projections for the 2020s, 2050s and 2080s. We find that, on average, populations already lag behind their optimal climate niche by approximately 130 km in latitude, or 60 m in elevation. For the 2020s we expect an average lag of approximately 310 km in latitude or 140 m in elevation, with the most pronounced geographic lags in the Rocky Mountains and the boreal forest. We show that our results could in principle be applied to guide assisted migration of planting stock in reforestation programs using a general formula where 100 km north shift is equivalent to approximately 44 m upward shift in elevation. However, additional non-climatic factors should be considered when matching reforestation stock to suitable planting environments.”
Citation: Laura K. Gray and Andreas Hamann, Climatic Change, 2012, DOI: 10.1007/s10584-012-0548-8.
Arctic Ocean contributes to Arctic amplification by losing heat to atmosphere when sea ice retreats
Abstract: “The heat budget of the upper Arctic Ocean is examined in an ensemble of coupled climate models under idealised increasing CO2 scenarios. All of the experiments show a strong amplification of surface air temperatures but a smaller increase in sea surface temperature than the rest of the world as heat is lost to the atmosphere as the sea-ice cover is reduced. We carry out a heat budget analysis of the Arctic Ocean in an ensemble of model runs to understand the changes that occur as the Arctic becomes ice free in summer. We find that as sea-ice retreats heat is lost from the ocean surface to the atmosphere contributing to the amplification of Arctic surface temperatures. Furthermore, heat is mixed upwards into the mixed layer as a result of increased upper ocean mixing and there is increased advection of heat into the Arctic as the ice edge retreats. Heat lost from the upper Arctic Ocean to the atmosphere is therefore replenished by mixing of warmer water from below and by increased advection of warm water from lower latitudes. The ocean is therefore able to contribute more to Arctic amplification.”
Citation: Tim Graham and Michael Vellinga, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1454-5.
How Little Ice Age showed up in Antarctica?
Abstract: “Increasing paleoclimatic evidence suggests that the Little Ice Age (LIA) was a global climate change event. Understanding the forcings and associated climate system feedbacks of the LIA is made difficult by the scarcity of Southern Hemisphere paleoclimate records. We use a new glaciochemical record of a coastal ice core from Mt. Erebus Saddle, Antarctica, to reconstruct atmospheric and oceanic conditions in the Ross Sea sector of Antarctica over the past five centuries. The LIA is identified in stable isotope (δD) and lithophile element records, which respectively demonstrate that the region experienced 1.6 ± 1.4 °C cooler average temperatures prior to 1850 AD than during the last 150 yr and strong (>57 m s−1) prevailing katabatic winds between 1500 and 1800 AD. Al and Ti concentration increases of an order of magnitude (>120 ppb Al) are linked to enhanced aeolian transport of complex silicate minerals and represent the strongest katabatic wind events of the LIA. These events are associated with three 12–30 yr intervals of cooler temperatures at ca. 1690 AD, 1770 AD and 1840 AD. Furthermore, ice core concentrations of the biogenic sulphur species MS− suggest that biological productivity in the Ross Sea polynya was ~80% higher prior to 1875 AD than at any subsequent time. We propose that cooler Antarctic temperatures promoted stronger katabatic winds across the Ross Ice Shelf, resulting in an enlarged Ross Sea polynya during the LIA.”
Citation: Rhodes, R. H., Bertler, N. A. N., Baker, J. A., Steen-Larsen, H. C., Sneed, S. B., Morgenstern, U., and Johnsen, S. J.: Little Ice Age climate and oceanic conditions of the Ross Sea, Antarctica from a coastal ice core record, Clim. Past, 8, 1223-1238, doi:10.5194/cp-8-1223-2012, 2012.
CLASSIC OF THE WEEK: Chamberlin (1898)
Abstract: No abstract. Quote from the beginning of the article: “THE virtues of carbon dioxide are in inverse ratio to the sinister reputation which “a little knowledge” and a narrow homocentric point of view have given it. As a constituent of the atmosphere it is as necessary to the maintenance of life as oxygen because it is the food of plants and they in turn are the food of animals. Its peculiar competency to retain the heat of the sun renders it a decisive factor in the maintenance of that measurable constancy and geniality of temperature upon which the existence of life depends. It is a leading agency in the disintegration of crystalline rock and is a necessary factor in other geologic changes. It is an essential link in a chain of vital processes which involve all the constituents of the atmosphere. Inherently it may be no more necessary to these processes, save in its thermal nature, than is oxygen, but being the minimum factor in the atmosphere it becomes regulative and decisive, because variations in it affect the whole cycle of processes dependent on it, while similar variations in the major constituents may have no appreciable effect.”
Citation: T. C. Chamberlin, The Journal of Geology, Vol. 6, No. 6 (Sep. – Oct., 1898) (pp. 609-621).
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