We did not have to wait until 2000 to find these predictions were correct: by the 1980s, global warming became apparent in temperature measurements from weather stations around the world. In 1988, the Intergovernmental Panel on Climate Change (IPCC) was founded to analyze the issue in more detail, and in 1992 at the Earth Summit in Rio de Janeiro world leaders signed a historic treaty: the Framework Convention on Climate Change. Its goal: “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.”
Unfortunately, little has been achieved in the 17 years since then. In fact, carbon dioxide emissions from fossil fuels were almost 40 percent higher last year relative to 1990. And even the rate at which emissions are increasing is now three times higher than in the 1990s. Global temperatures had already risen by 0.5ºC above preindustrial levels by the early 1990s, and another 0.3ºC have been added to that since the Rio Earth Summit. And they keep rising.
Most countries now agree that global warming should be stopped at a maximum of 2ºC. But this has become an extremely tough challenge, as growth in greenhouse-gas emissions and atmospheric stocks accelerated in the years since Rio. That is why Copenhagen is so important: it may well be our last to address climate change before it addresses us.
Tyndall’s measurements 150 years ago showed that carbon dioxide traps heat and causes warming. And, 50 years ago, Keeling’s measurements showed that carbon dioxide levels are increasing. In the meantime, earth’s climate has been heating up, as predicted. How much more proof do we need before we act?
Stefan Rahmstorf is professor of physics of the oceans at Potsdam University and department head at the Potsdam Institute for Climate Impact Research.
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