Climate models involve some of the most demanding computations of any simulations, and only a handful of institutes worldwide have the necessary supercomputers. The computers must run at full capacity for months to work their way through the jungle of data produced by coupled differential equations.All of this is much too complicated for politicians, who aren't terribly interested in the details. They have little use for radiation budgets and ocean-atmosphere circulation models. Instead, they prefer simple targets.
For this reason a group of German scientists, yielding to political pressure, invented an easily digestible message in the mid-1990s: the two-degree target. To avoid even greater damage to human beings and nature, the scientists warned, the temperature on Earth could not be more than two degrees Celsius higher than it was before the beginning of industrialization.
It was a pretty audacious estimate. Nevertheless, the powers-that-be finally had a tangible number to work with. An amazing success story was about to begin.
'Clearly a Political Goal'
Rarely has a scientific idea had such a strong impact on world politics. Most countries have now recognized the two-degree target. If the two-degree limit were exceeded, German Environment Minister Norbert Röttgen announced ahead of the failed Copenhagen summit, "life on our planet, as we know it today, would no longer be possible."
But this is scientific nonsense. "Two degrees is not a magical limit -- it's clearly a political goal," says Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research (PIK). "The world will not come to an end right away in the event of stronger warming, nor are we definitely saved if warming is not as significant. The reality, of course, is much more complicated."
Schellnhuber ought to know. He is the father of the two-degree target.
"Yes, I plead guilty," he says, smiling. The idea didn't hurt his career. In fact, it made him Germany's most influential climatologist. Schellnhuber, a theoretical physicist, became Chancellor Angela Merkel's chief scientific adviser -- a position any researcher would envy.
Rule of Thumb
The story of the two-degree target began in the German Advisory Council on Global Change (WBGU). Administration politicians had asked the council for climate protection guidelines, and the scientists under Schellnhuber's leadership came up with a strikingly simple idea. "We looked at the history of the climate since the rise of homo sapiens," Schellnhuber recalls. "This showed us that average global temperatures in the last 130,000 years were no more than two degrees higher than before the beginning of the industrial revolution. To be on the safe side, we came up with a rule of thumb stating that it would be better not to depart from this field of experience in human evolution. Otherwise we would be treading on terra incognita."
As tempting as it sounds, on closer inspection this approach proves to be nothing but a sleight of hand. That's because humans are children of an ice age. For many thousands of years, they struggled to survive in a climate that was as least four degrees colder than it is today, and at times even more than eight degrees colder.
Long article in der Spiegel on changing perceptions in the climate debate. Pretty even-handed. The above clip is just a small excerpt, RTWT.