completely online in Spiegel Online http://www.spiegel.de/spiegel/0, 1518,661308,00. html
For ten years the average global temperature rises to not continue. The climatologists speculate on how this trend can be explained. Is it the lack of sunspots? Or in unusual ocean currents?
At least in Copenhagen could play the weather. The Danish Meteorological Institute forecast for the climate conference in December temperatures one degree above the long-term average.
But otherwise it is far from global warming does not currently produces. The average temperature rise on Earth Since the beginning of the millennium no longer continues to increase. And this year it looks like a standstill.
ground to a halt climate change is just want to negotiate in advance that the world summit in the Danish capital, where thousands of politicians, civil servants, scientists, business leaders and environmental activists to a reduction in greenhouse gases. To many billion € to be haggled.
rose almost 30 years, the fever chart of planets sharply: from the seventies of the 20th Century until the late nineties to average 0.7 degrees Celsius. "Currently, however, the heat taken a break," said the meteorologist Mojib Latif of the Leibniz Institute of Marine Sciences, one of the most climate researchers in Germany. In view of the temperature curve, he speaks of a "plateau", a high-level stagnation, "There is no truth to quibble, we have to face."
Although the temperature down is likely to change anything in the long-term warming trend, but he feeds doubts about the predictive power of climate models - and is a political issue. For months, climate skeptics graze their web forums on the findings. Many climate researchers treat the temperature data, in the public domain as bashful as a teenager a love bite - and therefore damage their own credibility.
"It is not to deny that this one in our community The hottest topics. says Jochem Marotzke, Director at the Max Planck Institute for Meteorology in Hamburg, the climate modelers is to open: "We do not really know why this stagnation is happening now"
Just a few weeks ago. the UK's Hadley Centre for Climate Change the excitement with its latest calculations the average global temperature fanned: From 1999 to 2008, the world has warmed by 0.07 degrees Celsius, therefore only - and not those of 0.2 degrees Celsius in the still of the clear UN IPCC assumes. Calculate one forget the two natural climate events El Niño and La Niña out, then even a temperature trend of 0.0 degrees Celsius, the British ascertaining numerical Experts - that a halt.
The differences between individual regions of the world are huge: the Arctic recorded as an increase of nearly three degrees Celsius, which led to a dramatic melting of sea ice. But at the same time to cool large areas of North America, the Western Pacific and the Arabian peninsula from. Europe, including Germany, is still slightly in the positive range (see chart).
But some researchers do not admit the British calculations partout. "The warming continued falling in recent years," said Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research (PIK) defiant. With this view he is however, largely alone. The Hamburg Max Planck researchers Marotzke consider that it was, "I know of no serious colleague who would deny that in recent years is not getting warmer."
For the lay public are all the confusing messages: Why is so hard fought on climate change, although it currently does not become warmer? And how can it be that there appears among the researchers are not even a consensus on the development of temperatures, although these are yet measured the time?
517 weather stations include the global network. But any measurement is only a small dot on the large world map and have extrapolated using supercomputers for the region be. In addition, there are still many blind spots. The largest of these is the Arctic, where there are a massive area of only about 20 stations; climatologists speak of the "Arctic-hole".
Researchers at the Hadley Centre for the hole had simply used the global average, ignoring that it was in the Arctic have become significantly warmer, criticized Rahmstorf. But a NASA working group of the Goddard Institute for Space Studies in New York, which takes into account the special case in the Arctic is defined in Rahmstorf, for the past five years for a similar flat temperature curve as the British counterparts. Marotzke judges, therefore, Rahmstorf did it "argument from the curve taken.
Marotzke and Latif keep the run of researchers as Rahmstorf Black calculation even counterproductive. "We need the public to declare that the temperatures caused by greenhouse gases not rush from one record to another, but subject to natural fluctuations" said Latif dangerous it be seen to individual weather events such as a drought in Mali, or a hurricane, as examples of the already fully slamming climate change
Latif:.. "We have in the past might suggest too strongly that the development in a simple straight line always leads to the top. In fact, periods of stagnation . Or even cooling as normal "
climatologists are characterized by their computer models, a curve whose end point lies far in the future: By the end of the century, according to the forecast, will increase the average global temperature by around three degrees Celsius - unless . it is possible to drastically reduce greenhouse gas look like on the other hand the global climate in 2015, 2030 or 2050, no one knows for sure change
Besides the human impact and natural factors in climate processes on Earth. The currents of the ocean are subject to certain cycles, as is the activity of the sun. Also, large volcanic eruptions can dampen the temperature rise in the medium term. The eruption of Pinatubo in June 1991 as the world's temperature dropped by 0.5 degrees Celsius. Shall extend a cooler climate, the eruption phase, which began in the late eighties.
But the Pinatubo eruption is already too long ago. So which factor behind the current lame warming?
fact is: The sun is weakening. Its radiation activity is currently at a minimum - which is also evident from the low number of sunspots on its surface. After the calculation of NASA scientists led by David Rind, which was recently published in Geophysical Research Letters, is the reduced solar activity is the principle cause of the stagnant Warming.
ocean expert Latif, however typing more on the "Pacific decadal oscillation." This flow phenomenon in the Pacific can be more cold deep water to rise at the equator. The cooling effect on Earth's atmosphere is substantial.
With his team at the Leibniz Institute of Marine Sciences Latif worked as one of the first model to create medium-term forecasts for the next five to ten years. "We believe we ran there only gradually," says MPI expert Marotzke, also to a large-scale, the Federal Ministry of Research funded project starts.
consensus among researchers, however, about that it will eventually go with the temperatures likely to continue upwards. The prize question is: When it is getting warmer?
If the Pacific deep water is indeed the most important limiting factor should be to pause the climate change until the middle of next decade, says Latif. It is however, especially the sun, the cool, it could quickly become warmer again, for after all the experience, the solar activity would have to increase again in the coming years.
"And that could go with a real jolt," said Adam Scaife Hadley climatologist. Because of the natural cyclical warming then even those come through from the Man-made greenhouse effect to.
not only at conferences, the climate researchers argue passionately about when the temperatures are rising again. Even bet to be won, what will happen with the warming.
Rahmstorf is so sure to keep right in his predictions at the end that he bets out 2500 euros. "I will win," says the gloomy prophet of Potsdam.
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