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  • 1
    Publication Date: 2008-05-10
    Description: The Amazon rainforest plays a crucial role in the climate system, helping to drive atmospheric circulations in the tropics by absorbing energy and recycling about half of the rainfall that falls on it. This region (Amazonia) is also estimated to contain about one-tenth of the total carbon stored in land ecosystems, and to account for one-tenth of global, net primary productivity. The resilience of the forest to the combined pressures of deforestation and global warming is therefore of great concern, especially as some general circulation models (GCMs) predict a severe drying of Amazonia in the twenty-first century. Here we analyse these climate projections with reference to the 2005 drought in western Amazonia, which was associated with unusually warm North Atlantic sea surface temperatures (SSTs). We show that reduction of dry-season (July-October) rainfall in western Amazonia correlates well with an index of the north-south SST gradient across the equatorial Atlantic (the 'Atlantic N-S gradient'). Our climate model is unusual among current GCMs in that it is able to reproduce this relationship and also the observed twentieth-century multidecadal variability in the Atlantic N-S gradient, provided that the effects of aerosols are included in the model. Simulations for the twenty-first century using the same model show a strong tendency for the SST conditions associated with the 2005 drought to become much more common, owing to continuing reductions in reflective aerosol pollution in the Northern Hemisphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cox, Peter M -- Harris, Phil P -- Huntingford, Chris -- Betts, Richard A -- Collins, Matthew -- Jones, Chris D -- Jupp, Tim E -- Marengo, Jose A -- Nobre, Carlos A -- England -- Nature. 2008 May 8;453(7192):212-5. doi: 10.1038/nature06960.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Engineering, Computing and Mathematics, University of Exeter, Exeter EX4 4QF, UK. p.m.cox@exeter.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18464740" target="_blank"〉PubMed〈/a〉
    Keywords: Aerosols/*analysis ; Atlantic Ocean ; Carbon Dioxide/analysis ; Disasters/history/*statistics & numerical data ; *Ecosystem ; Environmental Pollution/*statistics & numerical data ; *Greenhouse Effect ; History, 20th Century ; History, 21st Century ; *Models, Theoretical ; Pacific Ocean ; Probability ; Rain ; Seasons ; South America ; Temperature ; Trees/*physiology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2009-05-02
    Description: Global efforts to mitigate climate change are guided by projections of future temperatures. But the eventual equilibrium global mean temperature associated with a given stabilization level of atmospheric greenhouse gas concentrations remains uncertain, complicating the setting of stabilization targets to avoid potentially dangerous levels of global warming. Similar problems apply to the carbon cycle: observations currently provide only a weak constraint on the response to future emissions. Here we use ensemble simulations of simple climate-carbon-cycle models constrained by observations and projections from more comprehensive models to simulate the temperature response to a broad range of carbon dioxide emission pathways. We find that the peak warming caused by a given cumulative carbon dioxide emission is better constrained than the warming response to a stabilization scenario. Furthermore, the relationship between cumulative emissions and peak warming is remarkably insensitive to the emission pathway (timing of emissions or peak emission rate). Hence policy targets based on limiting cumulative emissions of carbon dioxide are likely to be more robust to scientific uncertainty than emission-rate or concentration targets. Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO(2)), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 degrees C above pre-industrial temperatures, with a 5-95% confidence interval of 1.3-3.9 degrees C.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Allen, Myles R -- Frame, David J -- Huntingford, Chris -- Jones, Chris D -- Lowe, Jason A -- Meinshausen, Malte -- Meinshausen, Nicolai -- England -- Nature. 2009 Apr 30;458(7242):1163-6. doi: 10.1038/nature08019.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, University of Oxford, OX1 3PU, UK. myles.allen@physics.ox.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19407800" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere/*chemistry ; Benchmarking ; Carbon/*analysis ; Carbon Dioxide/*analysis ; Computer Simulation ; *Greenhouse Effect ; History, 18th Century ; History, 19th Century ; History, 20th Century ; History, 21st Century ; Human Activities/history ; Industry/history ; *Models, Theoretical ; *Temperature ; Time Factors ; Uncertainty
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2013-02-08
    Description: The release of carbon from tropical forests may exacerbate future climate change, but the magnitude of the effect in climate models remains uncertain. Coupled climate-carbon-cycle models generally agree that carbon storage on land will increase as a result of the simultaneous enhancement of plant photosynthesis and water use efficiency under higher atmospheric CO(2) concentrations, but will decrease owing to higher soil and plant respiration rates associated with warming temperatures. At present, the balance between these effects varies markedly among coupled climate-carbon-cycle models, leading to a range of 330 gigatonnes in the projected change in the amount of carbon stored on tropical land by 2100. Explanations for this large uncertainty include differences in the predicted change in rainfall in Amazonia and variations in the responses of alternative vegetation models to warming. Here we identify an emergent linear relationship, across an ensemble of models, between the sensitivity of tropical land carbon storage to warming and the sensitivity of the annual growth rate of atmospheric CO(2) to tropical temperature anomalies. Combined with contemporary observations of atmospheric CO(2) concentration and tropical temperature, this relationship provides a tight constraint on the sensitivity of tropical land carbon to climate change. We estimate that over tropical land from latitude 30 degrees north to 30 degrees south, warming alone will release 53 +/- 17 gigatonnes of carbon per kelvin. Compared with the unconstrained ensemble of climate-carbon-cycle projections, this indicates a much lower risk of Amazon forest dieback under CO(2)-induced climate change if CO(2) fertilization effects are as large as suggested by current models. Our study, however, also implies greater certainty that carbon will be lost from tropical land if warming arises from reductions in aerosols or increases in other greenhouse gases.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cox, Peter M -- Pearson, David -- Booth, Ben B -- Friedlingstein, Pierre -- Huntingford, Chris -- Jones, Chris D -- Luke, Catherine M -- England -- Nature. 2013 Feb 21;494(7437):341-4. doi: 10.1038/nature11882. Epub 2013 Feb 6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉College of Engineering, Mathematics and Physical Science, University of Exeter, Exeter EX4 4QF, UK. p.m.cox@exeter.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23389447" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon Cycle/*physiology ; Carbon Dioxide/analysis/*metabolism ; Cell Respiration ; *Climate Change ; *Models, Theoretical ; Photosynthesis ; Rain ; Temperature ; Trees/*metabolism ; *Tropical Climate ; Uncertainty
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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