In an effort to bring together the large amount of additional scientific knowledge on climate change that has been amassed since the IPCC AR4, the International Alliance of Reseach Universities( Australian National University, University of California – Berkeley, University of Cambridge, University of Copenhagen, ETH Zürich, National University of Singapore, University of Oxford, Peking University, The
University of Tokyo, Yale University) convened an international congress on climate change, which was held in Copenhagen from March 10-12, 2009. Most of the 2500 participants at the Congress were members of the climate science community, including many contributors to the last IPCC  report. The Congress’s Synthesis Report would be an excellent reading assignment for students. Among the Report’s most important conclusions:

• Ocean warming is about 50% greater than previously reported in the IPCC, and “given that the ocean stores so much heat, a change in ocean temperature, which reflects a change in the amount of heat stored in the ocean, is a better indicator of change in the climate than changes in air temperature;”
• The amplifying effects of vulnerable positive feedback mechanisms, most prominently, weakening of land and ocean sinks, are becoming increasingly clear. Under the IPCC’s A2 scenario, vulnerability of such sinks could amplify projected warming by 0.1-1.5C; the additional effects of accelerated methane and CO2 emissions from thawing permafrost is also potentially significant but not yet quantified;
• Sea levels are likely to rise 1 meter or more by 2100, i.e. slightly exceeding the upper level projections in AR4; the rate of sea level rise has accelerated since 1993, largely due to the growing contribution of ice loss from Greenland and Antarctica. The rapid reduction of Arctic sea ice has been a particularly dramatic development in the past few years also;
• Recent research already demonstrates substantial impacts from temperature increases to date, and there’s increasing evidence of the serious impacts if temperatures rise above the two degree Celsius “guardrail.” The study includes the revised IPCC “burnt embers” diagram, which indicates that many serious climatic impacts will be triggered at temperature levels below previously projected, including serious impacts on ecosystems and risks associated with extreme weather events, which will occur below the 2 degree C guardrail;
• Atmospheric levels of carbon dioxide are already at levels projected to increase temperatures between 2.0-2.4C; to limit the extent of overshoot of these levels, emissions should peak in the near future; if peak emissions are not reached until 2020, emissions reductions required to have a reason chance of remaining within the 2C “guardrail” would be a very daunting 5% annually;
• A 400 ppm CO2-equivalents target, about the same as today’s concentrations, is estimated to give a 75% chance of confining global warming to less than 2°C;
• The Report concludes on a hopeful note, concluding that technologies exist to reduce aggregate GHG emissions by more than 50% by 2050, and to near zero in some regions. The Report includes an excellent analysis of sectoral responses, including in the agricultural, renewable, and forest sectors. Additionally, the Report emphasizes the importance of transforming governance from a set of individual regimes to an integrated institutional architecture, and the need to focus on effectuating public behavioral change. The Report (and the accompanying panel reports) provide an excellent roadmap for building campaigns to effecuate transformative change in society.

The conclusions of this Report are both sobering; they demonstrate that as we’ve begun to resolve many of the uncertainties associated with future climate projections, the dice appear increasingly stacked against us, and somewhat hopeful, laying out a framework for addressing climate change that could help us avert many of the most serious potential consequences.

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