New research from last week 51/2012
Posted on 24 December 2012 by Ari Jokimäki
Merry christmas to all climate science fans! What would be better way to spend christmas than to read brand new climate research. That you find below a plenty.
Subtropical forests are threatened by their lack of resilience against long-term climate change
Abstract:"Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought-induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of China's forested land. In the present study, we describe how the monsoon evergreen broadleaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broadleaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long-term climate change."
Citation: Guoyi Zhou, Changhui Peng, Yuelin Li, Shizhong Liu, Qianmei Zhang, Xuli Tang, Juxiu Liu, Junhua Yan, Deqiang Zhang, Guowei Chu, Global Change Biology, DOI: 10.1111/gcb.12128.
Seabirds as sources of nitrous oxide and methane
Abstract: "In this study, tundra N2O and CH4 fluxes were measured from one seabird sanctuary (SBT) and two non-seabird colonies (NST-I and NST-II) in Ny-Ålesund (79°55′N, 11°56′E), Svalbard during the summers of 2008 and 2009. N2O and CH4 fluxes from SBT showed large temporal and spatial variations depending on the intensity of seabird activity. High seabird activity sites showed large N2O and CH4 emissions while low N2O and CH4 emissions, even CH4 uptake occurred at medium and low seabird activity sites. Overall the mean fluxes were 18.3 ± 3.6 μg N2O m−2 h−1 and 53.5 ± 20.3 μg CH4 m−2 h−1 from tundra SBT whereas tundra NST-I and NST-II represented a relatively weak N2O source (8.3 ± 13.2 μg N2O m−2 h−1) and strong CH4 sink (−82.8 ± 22.3 μg CH4 m−2 h−1). Seabird activity was the strongest control of N2O and CH4 fluxes compared with soil temperature and moisture, and high N2O and CH4 emissions were created by soil physical and chemical processes (the sufficient supply of nutrients NH4+–N, NO3−–N, total nitrogen, total phosphorus and total carbon from seabird guano, seabird tramp and appropriate water content) related to the seabird activity. Our work suggests that tundra ecosystems impacted by seabird activity are the potential “hotspots” for N2O and CH4 emissions although these sources have been largely neglected at present. Furthermore the combination of seabird activity and warming climate will likely further enhance N2O and CH4emissions from the High Arctic tundra."
Citation: Zhu, R., Q. Chen, W. Ding, and H. Xu (2012), Impact of seabird activity on nitrous oxide and methane fluxes from High Arctic tundra in Svalbard, Norway, J. Geophys. Res., 117, G04015, doi:10.1029/2012JG002130.
Area change of glaciers in the Canadian Rocky Mountains, 1919 to 2006
Abstract: "Glaciers in the Canadian Rocky Mountains constitute an important freshwater resource. To enhance our understanding of the influence climate and local topography have on glacier area, large numbers of glaciers of different sizes and attributes need to be monitored over periods of many decades. We used Interprovincial Boundary Commission Survey (IBCS) maps of the Alberta–British Columbia (BC) border (1903–1924), BC Terrain Resource Information Management (TRIM) data (1982–1987), and Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) imagery (2000–2002 and 2006) to document planimetric changes in glacier cover in the central and southern Canadian Rocky Mountains between 1919 and 2006. Over this period, glacier cover in the study area decreased by 590 ± 70 km2 (40 ± 5%), 17 of 523 glaciers disappeared and 124 glaciers fragmented into multiple ice masses. Glaciers smaller than 1.0 km2 experienced the greatest relative area loss (64 ± 8%), and relative area loss is more variable with small glaciers, suggesting that the local topographic setting controls the response of these glaciers to climate change. Small glaciers with low slopes, low mean/median elevations, south to west aspects, and high insolation experienced the largest reduction in area. Similar rates of area change characterize the periods 1919–1985 and 1985–2001; −6.3 ± 0.6 km2 yr−1 (−0.4 ± 0.1% yr−1) and −5.0 ± 0.5 km2 yr−1 (−0.5 ± 0.1% yr−1), respectively. The rate of area loss, however, increased over the period 2001–2006; −19.3 ± 2.4 km2 yr−1 (−2.0 ± 0.2% yr−1). Applying size class-specific scaling factors, we estimate a total reduction in glacier cover in the central and southern Canadian Rocky Mountains for the period 1919–2006 of 750 km2(30%)."
Citation: Tennant, C., Menounos, B., Wheate, R., and Clague, J. J.: Area change of glaciers in the Canadian Rocky Mountains, 1919 to 2006, The Cryosphere, 6, 1541-1552, doi:10.5194/tc-6-1541-2012, 2012.
Measurement methods affect the observed global dimming and brightening
Abstract: "Surface incident solar radiation (G) determines our climate and environment. G has been widely observed with a single pyranometer since the late 1950s. Such observations have suggested a widespread decrease between the 1950s and 1980s (“global dimming”), i.e., at a rate of -3.5 W m−2 per decade (or -2% per decade) from 1960 to 1990. Since the early 1990s, the diffuse and direct components of G have been measured independently and a more accurate G was calculated by summing these two measurements. Data from this summation method have suggested that G has increased at a rate of 6.6 W m−2 per decade (3.6% per decade) from 1992 to 2002 (“brightening”) at selected sites. The brightening rates from these studies were also higher than those from a single pyranometer. In this paper, we used 17 years (1995-2011) parallel measurements by the two methods from nearly 50 stations to test whether these two measurement methods of G provide similar long-term trends. Our results show that although measurements of G by the two methods agree very well on a monthly time scale, the long-term trend from 1995 to 2011 determined by the single pyranometer is 2-4 W m−2 per decade less than that from the summation method. This difference of trends in the observed G is statistically significant. The dependence of trends of Gon measurement methods uncovered here has an important implication for the widely reported “global dimming” and “brightening” based on datasets collected by different measurement methods, i.e., the dimming might have been less if measured with current summation methods."
Citation: Kaicun Wang, Robert E. Dickinson, Qian Ma, John A. Augustine, and Martin Wild, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00482.1.
High-resolution bioclimate map of the world
Abstract: "Aim: To develop a novel global spatial framework for the integration and analysis of ecological and environmental data. Location: The global land surface excluding Antarctica. Methods: A broad set of climate-related variables were considered for inclusion in a quantitative model, which partitions geographic space into bioclimate regions. Statistical screening produced a subset of relevant bioclimate variables, which were further compacted into fewer independent dimensions using principal components analysis (PCA). An ISODATA clustering routine was then used to classify the principal components into relatively homogeneous environmental strata. The strata were aggregated into global environmental zones based on the attribute distances between strata to provide structure and support a consistent nomenclature. Results: The global environmental stratification (GEnS) consists of 125 strata, which have been aggregated into 18 global environmental zones. The stratification has a 30 arcsec resolution (equivalent to 0.86 km2 at the equator). Aggregations of the strata were compared with nine existing global, continental and national bioclimate and ecosystem classifications using the Kappa statistic. Values range between 0.54 and 0.72, indicating good agreement in bioclimate and ecosystem patterns between existing maps and the GEnS. Main conclusions: The GEnS provides a robust spatial analytical framework for the aggregation of local observations, identification of gaps in current monitoring efforts and systematic design of complementary and new monitoring and research. The dataset is available for non-commercial use through the GEO portal (http://www.geoportal.org)."
Citation: Marc J. Metzger, Robert G. H. Bunce, Rob H. G. Jongman, Roger Sayre, Antonio Trabucco, Robert Zomer, Global Ecology and Biogeography, DOI: 10.1111/geb.12022.
Last Glacial Maximum based climate sensitivity estimate is 2.5C with high probability of being under 4C
Abstract:"We investigate the relationship between the Last Glacial Maximum (LGM) and climate sensitivity across the PMIP2 multi-model ensemble of GCMs, and find a correlation between tropical temperature and climate sensitivity which is statistically significant and physically plausible. We use this relationship, together with the LGM temperature reconstruction of Annan and Hargreaves (2012), to generate estimates for the equilibrium climate sensitivity. We estimate the equilibrium climate sensitivity to be about 2.5°C with a high probability of being under 4°C, though these results are subject to several important caveats. The forthcoming PMIP3/CMIP5 models were not considered in this analysis, as very few LGM simulations are currently available from these models. We propose that these models will provide a useful validation of the correlation presented here."
Citation: Hargreaves, J. C., J. D. Annan, M. Yoshimori, and A. Abe-Ouchi (2012), Can the Last Glacial Maximum constrain climate sensitivity?, Geophys. Res. Lett., 39, L24702, doi:10.1029/2012GL053872.
Observed acidification trends in North Atlantic water masses
Abstract: "The lack of observational pH data has made it difficult to assess recent rates of ocean acidification, particularly in the high latitudes. Here we present a time series that spans over 27 yr (1981–2008) of high-quality carbon system measurements in the North Atlantic, which comprises fourteen cruises and covers the important water mass formation areas of the Irminger and Iceland Basins. We provide direct quantification of acidification rates in upper and intermediate North Atlantic waters. The highest rates were associated with surface waters and with Labrador Sea Water (LSW). The Subarctic Intermediate and Subpolar Mode Waters (SAIW and SPMW) showed acidification rates of −0.0019 ± 0.0001 and −0.0012 ± 0.0002 yr−1, respectively. The deep convection activity in the North Atlantic Subpolar Gyre injects surface waters loaded with anthropogenic CO2 into lower layers, provoking the remarkable acidification rate observed for LSW in the Iceland Basin (−0.0016 ± 0.0002 yr−1). An extrapolation of the observed linear acidification trends suggests that the pH of LSW could drop 0.45 units with respect to pre-industrial levels by the time atmospheric CO2 concentrations reach ~775 ppm. Under circulation conditions and evolution of CO2 emission rates similar to those of the last three decades, by the time atmospheric CO2reaches 550 ppm, an aragonite undersaturation state could be reached in the cLSW of the Iceland Basin, earlier than surface SPMW."
Citation: Vázquez-Rodríguez, M., Pérez, F. F., Velo, A., Ríos, A. F., and Mercier, H.: Observed acidification trends in North Atlantic water masses, Biogeosciences, 9, 5217-5230, doi:10.5194/bg-9-5217-2012, 2012.
In addition to ozone layer, Montreal Protocol protects also Earth's hydroclimate
Abstract:"The 1987 Montreal Protocol regulating emissions of chlorofluorocarbons (CFCs) and other ozone depleting substances (ODSs) was motivated primarily by the harm to human health and ecosystems arising from increased exposure to ultraviolet-B (UV-B) radiation associated with depletion the ozone layer. It is now known that the Montreal Protocol has helped reduce radiative forcing of the climate system since CFCs are greenhouse gases (GHGs), and that ozone depletion (which is now on the verge of reversing) has been the dominant driver of atmospheric circulation changes in the Southern Hemisphere in the last half century. In this paper we show that the Montreal Protocol also significantly protects the Earth’s hydroclimate. Using the Community Atmospheric Model, version 3 (CAM3), coupled to a simple mixed layer ocean, we demonstrate that in the ‘World Avoided’ (i.e. with CFC emissions not regulated), the subtropical dry zones would be substantially drier, and the middle and high latitude regions considerably wetter in the coming decade (2020-29) than a world without ozone depletion. Surprisingly, we find that these changes are very similar, in both pattern and magnitude, to those caused by projected increases in GHG concentrations over the same period. We further show that, by dynamical and thermodynamical mechanisms, both the stratospheric ozone depletion and increased CFCs contribute to these changes. Our results imply that, as a consequence of the Montreal Protocol, changes in the hydrological cycle in the coming decade will be only half as strong as what they otherwise would be."
Citation: Yutian Wu, Lorenzo M. Polvani, Richard Seager, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00675.1.
Possible link between previous autumn sea ice cover and northern Eurasia winter precipitation
Abstract:"This paper examines the impacts of the previous autumn sea ice cover (SIC) on the winter Northern Hemisphere annular mode (NAM) and winter precipitation in Eurasia. The coherent variations among the Kara–Laptev autumn SIC, winter NAM and Eurasian winter precipitation appear after the year 1982, which may prove useful for seasonal prediction of winter precipitation. From a physical point, the Kara–Laptev SIC and sea surface temperatures (SST) anomalies develop in autumn and remain in winter. Given that winter NAM is characterized by an Arctic–midlatitude seesaw centered over the Barents Sea and Kara–Laptev seas, it is closely linked to the Arctic forcing that corresponds to the Kara–Laptev sea ice increase (reduction) and the associated surface temperature cooling (warming). Moreover, based on both model simulations and observations, the diminishing Kara–Laptev Sea ice does induce positive SLP anomalies over high latitude Eurasia in winter, which is accompanied by a significant surface warming in northern Eurasia and cooling south of the Mediterranean. This SAT anomaly pattern facilitates increases of specific humidity in northern Eurasia with a major ridge extending southward along the East Asian coast. As a result, the anomalous Eurasian winter precipitation has a more zonal band structure."
Citation: Fei Li and Huijun Wang, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00380.1.
The continuously increasing minimum temperature of Oahu - hot nights at Hawaii
Abstract:"We examined trends in minimum and maximum temperatures in the Oahu during the period of past 39 (1969–2007) and 25 (1983–2007) years. We found a strong spatial and temporal variability in the temperature trends on Oahu. During the past 39 years, island-wide minimum temperature has increased by 0.17 °C/decade and shows a considerable variability in trends at individual location. There was no detectable trend found in maximum temperature over the same time period. The year 1983 was identified as the change point in the island-wide minimum temperature. During the recent 25 years annual and summer maximum temperature showed a decline while minimum temperature continued to increase. Trend in diurnal temperature range (DTR) shows a decline during the past 39 years with a stronger decreasing trend during the recent 25 years. The trend in DTR for Oahu is much higher compared to the global DTR trend indicating a rapid warming in minimum temperature. Extreme temperature indices show a general warming during the past 39 years. There has been significant increase in tropical and warm nights at the two urban stations. Maximum temperature generally followed the Pacific Decadal Oscillation (PDO) except the period when there is an increase in Hawaii Rainfall Index (HRI). In contrast, minimum temperature showed better agreement with HRI compared to the PDO, at least up until 1999 after which it showed an increase. Despite the relative cooling in PDO during the recent decade an increase in minimum temperature can be attributed to a decline in HRI."
Citation: Mohammad Safeeq, Alan Mair, Ali Fares, International Journal of Climatology, DOI: 10.1002/joc.3629.
Other studies from last week
Global CFC-11 (CCl3F) and CFC-12 (CCl2F2) measurements with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS): retrieval, climatologies and trends - Kellmann et al. (2012) [FULL TEXT]
CLASSIC OF THE WEEK: Man's Inadvertent Modification of Weather and Climate
Abstract:No abstract. First paragraph: "Man may be changing his weather. And if he is, the day may come when he will either freeze by his own hand or drown. The delicate balances within the atmosphere and the history of climatic change in the past suggest that through his inadvertent actions he may be driving the atmosphere either to a disastrous ice age - or as bad - to a catastrophic melting of the ice caps. Either may literally be possible, but it depends on just what he is doing to the atmosphere. He does not know for sure."
Citation: Bull. Amer. Meteor. Soc., 51, 1043–1048, doi: http://dx.doi.org/10.1175/1520-0477(1970)0512.0.CO;2.
This is a cross-post from AGW Observer. About this series. 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.