How will climate change affect the world?
In a mere 200 years man has increased the CO2 in the atmosphere by 100 ppm (parts per million). This corresponds to the increase during the transition from a glacial to an interglacial period, which under natural conditions, however, would have taken several thousand years. Today, CO2 in the atmosphere is the highest it has been in the past several million years, and the emission in recent years was also higher than assumed by the IPCC report in its worst case scenarios. An interview with Prof. Peter Lemke, head of the Department of Climate Sciences at the Alfred Wegener Institute, who has contributed significantly to the IPCC reports.
If we actually succeed in massively reducing greenhouse gas emissions, how much will the global temperature increase by the end of the century?
In this case, we may succeed in limiting global warming to two degrees. This is the goal Europe has set itself, and it should be achievable with a concerted effort. However, even this relatively moderate increase in temperature means that a portion of the Greenland ice sheet will melt and almost all mountain glaciers, such as those in the Alps would disappear. In addition, the seawater will expand due to warming. All these factors combined, would cause a sea level rise of between 20 to 50 centimetres. The main reason why we cannot predict this more precisely is that we do not yet exactly know how the outlet glaciers of the Greenland and Antarctic ice sheets will react to increasing temperatures.
What will happen if global greenhouse gas emissions increase, rather than decrease in the coming decades?
In the past two years, the worldwide CO2 emissions have already increased more than assumed in worst-case scenarios of the final UN Intergovernmental Panel on climate Change (IPCC) report. If this continues, the climate would warm up four degrees, rather than by 2 degrees. Thus, the ice on Greenland, in the long run, will melt away entirely. By the year 2100 we can probably expect a sea level rise in access of one meter. After a few centuries, the sea level could even rise by up to seven meters. Coastal cities such as Bremerhaven, Mumbai or New York would have to be relocated or given up. Prior to this, we must be prepared for heat waves. If our models are correct, an unusually hot summer such as we experienced in 2003 would be considered normal within three decades, and within 60 years considered cool - if we continue emitting CO2 at the present rate.
Will climate change have a stronger impact in some areas more than in others?
All regions, which are already dry today, will become even drier, according to the climate scenarios. In contrast, the regions that are already wet today will receive even more rain. And, as we are currently already seeing, climate change is likely to be more pronounced in the northern latitudes than in lower latitudes. This is due to the fact that snow and ice cover in northern latitudes have already decreased in recent decades. The reason being that snow and ice are white and have the positive property of reflecting sunlight back into space. When these surfaces melt, dark areas become exposed and absorb the sun's energy more effectively. These zones thus heat up more rapidly and as a consequence, more ice melts. This feedback effect seems to be responsible for the observed temperature rise is in the Arctic over the past 50 years, which was twice as fast as the increase of the global average.
In the past, natural climate fluctuations such as the switching between warm and ice ages, prevailed. What role could these natural fluctuations play in the foreseeable future?
The natural climate system has produced, inter alia, ice ages, which caused dramatic changes, especially in the northern hemisphere. However, during the past eight ice ages, the CO2 concentration was always about 180 CO2 ppmv (parts per million by volume). In the warm periods, this value then increased to 280 CO2 ppmv. The duration of the transition between the CO2 minimum in a glacial and the CO2 maximum in an interglacial period is about 20,000 years. Currently we live in an interglacial period, however, we do not measure 280 CO2 molecules per million air molecules, but 385, which are due to anthropogenic greenhouse gas emissions. This means that we have released to the atmosphere as much CO2 as was recorded during the transition from a glacial to interglacial period. But, what took 20,000 years to change, we have now realized in only 200 years! That's what causes the real climate problem: Our climate system cannot cope with the rate at which we are releasing CO2 into the atmosphere.
How important is it to adapt now to projected climate change?
Since the beginning of industrialization, we have already caused a temperature rise of 0.7 degrees. Even if we were to stop emitting CO2 from one day to the next, global temperatures would continue to increase by the same amount during the coming decades. This constitutes an increase of 1.4 degrees. It means that we will have to adapt in any event. We will need to raise dikes and guard against heat waves and increased rainfall. We would also need to take preventive measures and change our energy production from fossil to renewable energy sources to mitigate climate change impacts.
What do you expect from the climate summit in Copenhagen?
I hope that countries like the US, but also the European countries will be prepared to strongly reduce greenhouse gas emissions. Experts estimate that it would cost one to two percent of the gross national product to introduce measures of prevention and adaptation to climate change. For Germany this would mean an annual budget of some 20 billion Euros, which sounds like a lot of money, but Germans annually spend a similar sum on garbage and sewage disposal. Shouldn’t climate protection be worth this much?
