Two degrees -- that value has long been the guideline for international climate policy. Were the increase in average global temperatures held below 2 degrees Celsius (3.6 degrees Fahrenheit), then drastic climate change and long-term irreversible damage -- like the melting of Greenland's glaciers -- could still be avoided. Or so it was thought.
But a new study by an international research team has determined that the two-degree goal is no longer achievable.
Even today's atmospheric levels of greenhouse gases such as carbon dioxide are high enough to cause a global increase in temperature of between 2 and 2.4 degrees Celsius. "Drastic and immediate" emissions reductions would be "impossible," the paper, which was presented in Brussels on Thursday, argues. The concentration of these gases will thus continue to increase in upcoming decades. The researchers write: "An overshoot of the atmospheric greenhouse gas concentrations needed to constrain global warming to 2 degrees Celsius is thus inevitable."
The paper is 39 pages long and includes among its 12 authors Nicolas Stern, a London-based environmental economist, and Hans-Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research. The "Synthesis Report" summarizes the results of the Climate Change Congress that took place in Copenhagen in March -- an event which included roughly 2,500 participants and over 1,400 papers.
The authors write that the report was peer reviewed a second time before publication. It reflects the current stage of climate research and will provide the basis for discussions at the United Nations Climate Change Conference in December regarding a new climate protection regime to take over once the Kyoto Protocol expires in 2012. Essentially, it is an update of the Fourth Assessment Report from 2007, which was written by the United Nations Intergovernmental Panel on Climate Change (IPCC). That report evaluated papers that are now four years old or older.
The new report doesn't just address the issue of carbon dioxide but also nitrous oxide, methane, and all other greenhouse gases present in the atmosphere as well. Climate researchers calculate their warming effects in "CO2 equivalents" so that they are able to operate with a standardized unit. The amount of greenhouse gases are measured in ppm or "parts per million." The concentration of such gases in the atmosphere was over 460 ppm CO2 equivalents in 2007. At 450 ppm, there is only a 50 percent chance that the temperature increase would stay under 2 degrees Celsius, according to the Copenhagen report, citing a recent study.
Humanity Should Settle on a Four Degree Increase
The global average temperature rose just under 0.8 degrees Celsius from 1850 to 2005. The current warming trend is 0.13 to 0.16 degrees per decade. In 2007, the IPCC assumed that the earth's average temperature could increase anywhere from 1.8 to 4.0 degrees Celsius by the end of this century -- depending on which strategy the international community adopts and by how much greenhouse gas emissions are reduced.
According to the current findings, the world is currently on track for the worst-case scenario -- the dynamics of climate change are already larger than feared.
To be on the safe side, people should adjust for a three, four or even five degrees of warming, PIK head Schellnhuber recommended in March at the Copenhagen congress. Should he be right, extreme weather resulting from rising global temperatures could be even more dramatic than assumed up until now.
In the past, the IPCC prepared an entire spectrum of possible emissions scenarios for this century. According to the new report, "some climate indicators are changing near the upper end of the range indicated by the projections or, as in the case of sea level rise, at even greater rates than indicated by IPCC projections." The report continues, "current estimates indicate that ocean warming is about 50 percent greater than had been previously reported by the IPCC."
Konrad Steffen, professor for Environmental Science at the University of Colorado in Boulder, explains what that means. "The forecast for the year 2100 probably needs to be revised at least by a meter or more," he says.
Schellnhuber, who is also a climate consultant for the German government, says he is worried "that we still aren't seeing a large portion of the unavoidable global warming." Dirt particles in the atmosphere, especially sulphate aerosols, have created a certain cooling effect and has prevented a stronger temperature increase at the moment. "If we were to ever install sulphur filters all over the world, then we would already be at 2.5 degree warming," the physicist said.
The new report paints a picture of rising sea levels -- fueled by rapidly melting polar ice caps -- for centuries. "Thus, the changes current generations initiate in the climate will directly influence our descendents long into the future. In fact, global average surface temperature will hardly drop in the first thousand years after greenhouse gas emissions are cut to zero."