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  • 1
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    Net carbon dioxide losses of northern ecosystems in response to autumn warming (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-01-04
    Description: The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring, with spring and autumn temperatures over northern latitudes having risen by about 1.1 degrees C and 0.8 degrees C, respectively, over the past two decades. A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity. These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future. Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn-to-winter carbon dioxide build-up, suggesting a shorter net carbon uptake period. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We use a process-based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In contrast, warming increases photosynthesis more than respiration in spring. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC degrees C(-1), offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Piao, Shilong -- Ciais, Philippe -- Friedlingstein, Pierre -- Peylin, Philippe -- Reichstein, Markus -- Luyssaert, Sebastiaan -- Margolis, Hank -- Fang, Jingyun -- Barr, Alan -- Chen, Anping -- Grelle, Achim -- Hollinger, David Y -- Laurila, Tuomas -- Lindroth, Anders -- Richardson, Andrew D -- Vesala, Timo -- England -- Nature. 2008 Jan 3;451(7174):49-52. doi: 10.1038/nature06444.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉LSCE, UMR CEA-CNRS, Batiment 709, CE, L'Orme des Merisiers, F-91191 Gif-sur-Yvette, France. slpiao@lsce.ipsl.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18172494" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere/chemistry ; Biomass ; Carbon Dioxide/analysis/*metabolism ; Cell Respiration ; *Ecosystem ; Fossil Fuels ; Geography ; Greenhouse Effect ; History, 20th Century ; History, 21st Century ; Oceans and Seas ; Photosynthesis ; Plant Transpiration ; Plants/metabolism ; Rain ; *Seasons ; Soil/analysis ; *Temperature ; Water/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Observed increase in local cooling effect of deforestation at higher latitudes (2011)
    Nature Publishing Group (NPG)
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    Publication Date: 2011-11-19
    Description: Deforestation in mid- to high latitudes is hypothesized to have the potential to cool the Earth's surface by altering biophysical processes. In climate models of continental-scale land clearing, the cooling is triggered by increases in surface albedo and is reinforced by a land albedo-sea ice feedback. This feedback is crucial in the model predictions; without it other biophysical processes may overwhelm the albedo effect to generate warming instead. Ongoing land-use activities, such as land management for climate mitigation, are occurring at local scales (hectares) presumably too small to generate the feedback, and it is not known whether the intrinsic biophysical mechanism on its own can change the surface temperature in a consistent manner. Nor has the effect of deforestation on climate been demonstrated over large areas from direct observations. Here we show that surface air temperature is lower in open land than in nearby forested land. The effect is 0.85 +/- 0.44 K (mean +/- one standard deviation) northwards of 45 degrees N and 0.21 +/- 0.53 K southwards. Below 35 degrees N there is weak evidence that deforestation leads to warming. Results are based on comparisons of temperature at forested eddy covariance towers in the USA and Canada and, as a proxy for small areas of cleared land, nearby surface weather stations. Night-time temperature changes unrelated to changes in surface albedo are an important contributor to the overall cooling effect. The observed latitudinal dependence is consistent with theoretical expectation of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle, the latter of which remains uncertain in climate models.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lee, Xuhui -- Goulden, Michael L -- Hollinger, David Y -- Barr, Alan -- Black, T Andrew -- Bohrer, Gil -- Bracho, Rosvel -- Drake, Bert -- Goldstein, Allen -- Gu, Lianhong -- Katul, Gabriel -- Kolb, Thomas -- Law, Beverly E -- Margolis, Hank -- Meyers, Tilden -- Monson, Russell -- Munger, William -- Oren, Ram -- Paw U, Kyaw Tha -- Richardson, Andrew D -- Schmid, Hans Peter -- Staebler, Ralf -- Wofsy, Steven -- Zhao, Lei -- England -- Nature. 2011 Nov 16;479(7373):384-7. doi: 10.1038/nature10588.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA. xuhui.lee@yale.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22094699" target="_blank"〉PubMed〈/a〉
    Keywords: Air/analysis ; *Altitude ; Atmosphere/analysis ; Biophysical Processes ; Canada ; Climate ; Conservation of Natural Resources ; Forestry ; Seasons ; *Temperature ; Trees/*growth & development ; United States
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-07-12
    Description: Terrestrial plants remove CO2 from the atmosphere through photosynthesis, a process that is accompanied by the loss of water vapour from leaves. The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon. Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange. We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various competing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong CO2 fertilization effect. The results suggest a partial closure of stomata-small pores on the leaf surface that regulate gas exchange-to maintain a near-constant concentration of CO2 inside the leaf even under continually increasing atmospheric CO2 levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon- and water-based economics of terrestrial vegetation, which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation-climate models.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keenan, Trevor F -- Hollinger, David Y -- Bohrer, Gil -- Dragoni, Danilo -- Munger, J William -- Schmid, Hans Peter -- Richardson, Andrew D -- England -- Nature. 2013 Jul 18;499(7458):324-7. doi: 10.1038/nature12291. Epub 2013 Jul 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA. tkeenan@oeb.harvard.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23842499" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere/chemistry ; Carbon Dioxide/*analysis ; *Ecosystem ; Plant Leaves/chemistry ; Trees/*chemistry ; Water/*analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    Keenan et al. reply (2014)
    Nature Publishing Group (NPG)
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    Publication Date: 2014-03-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keenan, Trevor F -- Hollinger, David Y -- Bohrer, Gil -- Dragoni, Danilo -- Munger, J William -- Schmid, Hans Peter -- Richardson, Andrew D -- England -- Nature. 2014 Mar 13;507(7491):E2-3. doi: 10.1038/nature13114.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biological Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia. ; USDA Forest Service, Northern Research Station, Durham, New Hamphire 03824, USA. ; Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, Ohio 43210, USA. ; Department of Geography, Indiana University, Bloomington, Indiana 47405, USA. ; School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA. ; Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen 82467, Germany. ; Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24622207" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon Dioxide/*analysis ; *Ecosystem ; Trees/*chemistry ; Water/*analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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