The Copenhagen Diagnosis (2009), a report by 26 scientists from around the world, including 14 members of the Intergovernmental Panel on Climate Change, was released immediately before the beginning of the COP15 meeting of the UNFCCC in Copenhagen. The report is intended as an update to the IPCC 2007 Working Group 1 report. The report summarizes and highlights climate studies published since the (2006) close-off date for the IPCC report that the authors deemed most relevant to the COP15 negotiations in Copenhagen. It’s an excellent summary of the current state of climate science for students, including some very good responses to the skeptics on several important issues, including the argument that temperature increases are merely natural climatic variability, allegations that temperatures have been declining during the past decade, and responses to the argument that temperature increases precede increases in atmospheric concentrations of carbon dioxide.
The report is also, as the Guardian in the UK has characterized it, a bit of a “kick in the pants” to the IPCC, emphasizing that the climatic prognosis may be far grimmer than projected in AR4.
Among the key take-aways are the following:
- Concentrations of carbon dioxide are now more than 105 ppm above natural pre-industrial levels, and are potentially higher than at any time in the last 3-20 million years;
- New reseach and observations have led climate researchers to conclude that climate will lead to an atmosphere contining more water vapor, amplifying positive feedback mechanisms that contribute to accelerated rises in temperatures;
- Global cooling has not occured in the past decade; NASA’s global temperature data reveals temperatures increasing 0.19C per decade in the last decade, with past ten year trends (i.e. 1990-1999, 1991-2000, and so on) averaging between 0.17 and 0.34C per decade
- Increases in temperature are not attributable to changesin solar activity, with solar radiation almost constant over the past 50 years, with even a slight decrease over this period. Over the past three years, the sun’s brightness has reached an all-time low since satellite measurements began;
- Recent studies have confirmed observed trends of more hot extremes and fewer cold extremes; moreover, recent studies confirm likely further increases in precipitation extremes;
- The magnitude of feedback that may occur as permafrost melts is unknown, but may prove to be substantial; a recent study found strong observation evidence for acceleration of carbon emissions from warming of a peat bog overlying permafrost in Sweden. The recent increases in atmospheric concentrations of methane may also be linked to surface warming;
- Mass loss of glaciers and ice caps has increased considerably since the 1990s and now contributes about 1.2 millimeters per year to global sea level rise. the rate of loss from both Greenland and Antarctic ice sheets has also increased recently (with Greenland contributing as much as 0.7 millimeters per year to sea level rise, and Antarctica almost nearly as much) and there’s evidence that rate of ice discharge into the sea can occur far more rapidly than previously occurred;
- There is increasing evidence that the transition to an ice-free summer in the Arctic may occur abruptly because of amplifying feedbacks
- The threat of ocean acidification is becoming increasingly stark, with evidence of smaller shells during higher carbon dioxide conditions over the past 50,000 years, and projections that shells of some calcifiying species may begin to dissolve in the Arctic and Southern Ocean when atmospheric levels of carbon dioxide reach 450ppm, which would be around 2030 in a business as usual scenario
- Sea level has risen faster than expected and is likely to rise much more by 2100 than the 18-59 centimeter projections of the IPCC;
- The report identifies 9 potential “tipping points,” in which the the future state of the climatic system could be altered by a small change in forcing; these include the Arctic (Greenland ice sheet), Antarctic (West Antarctic ice sheet), Amazonia (potential tipping point resulting in dieback of up to 80% of the rainforest) and West Africa (potential disruption of the Sahel and West African Monsoon)
- Under a business as usual scenario, temperatures would reach 4-7C by 2100; even at the lower end of emissions (which will require very aggressive cuts in emissions), temperatures rise 2-3C by the century’s end;
- By 2050, it is likely that annual per capita emissons of carbon dioxide will have to be below 1 ton to avoid exceeding a 2C increase in temperatures.