Pictures of the Future    Spring 2007

Why Carbon Dioxide Emissions Need to be Cut in Half by 2050

Interview with Hans Joachim Schellnhuber

Prof. Hans Joachim Schellnhuber is Director of the Institute for Climate Impact Research in Potsdam. Schellnhuber, 56, was one of the first researchers to investigate the consequences of climate change. The physicist was also Research Director at the Tyndall Centre for Climate Change in Norwich (UK) from 2001 to 2005. The exceptional value of his work was officially recognized when the Queen named him "Honorary Commander of the Most Excellent Order of the British Empire" (CBE). German Chancellor Angela Merkel recently appointed Schellnhuber to serve as Advisor on Climate Issues to the Federal Government during Germany’s presidency of the EU Council and chairmanship of the G8 conference. The country assumes both roles this year.

In his report, British economist Sir Nicholas Stern warns that the world economy is in danger. Stern says the concentration of greenhouse gases in the atmosphere must be kept below 550 ppm if global warming is to be limited to a maximum of 2 to 3 °C. Do you agree?

Schellnhuber: Schellnhuber: Two to three degrees—that doesn’t sound like much, but it is. The temperature rise between the last ice age and the current temperate period was only five degrees, yet what a difference those five degrees have made for the world! But let me spell out in detail what the Stern Report says. Even if we meet the 550 ppm target, we will still face a 90-% probability of global warming of more than 2 °C. That’s pretty alarming. I would tighten Stern’s demand and stipulate an upper limit of 450 ppm. That way, there’s a 50-% probability that global warming will be limited to 2°C, although a 50-50 chance is not particularly reassuring either. Basically, to be sure of meeting the two-degree limit, we would have to cut emissions to below 400 ppm in the long term.

Why two degrees? Is that, so to speak, the point of no return if we are to get a handle on global warming?

Schellnhuber: It’s not a hard and fast line, but once we cross it, the damage becomes rapidly uncontrollable. The temperature of the planet would increase to a greater degree than at any other time during the last 20 million years—all within just one century. That would be a real roller-coaster ride for the earth, an unprecedented phenomenon.

Would global warming that significantly exceeded two degrees really have a dramatic impact?

Schellnhuber: Yes, it would. For a start, the sea ice in the Arctic and the ice on Greenland would melt completely, and the ice in the Antarctic would melt in part. In the long term, sea levels would rise enormously as a result. We’d have to evacuate practically all coastal areas; human civilization as we know it would have to be reinvented. What’s more, because of the direct CO₂ transfer from the atmosphere, the oceans would become more acidic, and marine life would also have to adapt. Second, the atmosphere would be more heavily laden with water vapor and energy, resulting in increasingly violent storms. Third, the variation in precipitation patterns would become more extreme, meaning even less rain in places where there is already little rainfall, and vice versa. Just one consequence of this would be increasing desertification. And fourth, because of the greater temperature difference between land and sea, Europe would face the prospect of a monsoon effect.

How much would it cost to meet the two-degree target?

Schellnhuber: According to Stern, we would have to invest around one percent of world GDP in order to limit global warming to between two and three degrees. His report relies heavily on model calculations produced by our institute as part of an international comparative project. We adopted new methods of economic analysis, because earlier studies on the costs of protecting the atmosphere, mainly originating in the U.S., were based on false premises. They barely took account of technological advances in the use of environmentally friendly energy sources and therefore came to an unrealistically high figure. According to our results, even the cost of sticking to the two-degree limit is less than one percent of global economic output. Stern has factored in a safety margin, making his calculation more pessimistic than ours.

And what would be the costs of doing nothing at all?

Schellnhuber: Schellnhuber: At least ten times higher than the costs of protecting the atmosphere, that is to say somewhere between ten and 20 % of world GDP.

What concrete measures can we take?

Schellnhuber: Essentially, the world’s energy system needs to be put on a new, low-carbon diet. That means, first of all, conserving energy and using it more efficiently, and, secondly, greatly increasing our use of renewable sources—including wind and solar power, and geothermal energy and biomass. By far the most cost-effective method here is simply to use less energy. The British town of Woking, for example, has reduced its CO₂ emissions by almost 80 % over the last ten years, saving a lot of money in the process. There’s tremendous potential here. For instance, thermal insulation for buildings, low-energy lights, low-consumption vehicles, and lots more. Developing renewable energy sources is, by comparison, more expensive, but it is imperative in the long term.

Are greater efficiency and renewable energy enough?

Schellnhuber: Not on their own. In particular, we’re going to have to use carbon sequestration. That means whenever carbon is combusted, the CO₂ must be captured rather than being emitted into the atmosphere. This is most effective in biomass power plants—that way, the net amount of carbon in the atmosphere is reduced. In addition, the operating life of existing nuclear power plants could be extended, since their associated dangers are low compared to those of global warming. On the other hand, their contribution to generating capacity cannot be boosted substantially without ramping up the industry to reprocess spent plutonium—or building thousands of new nuclear power plants. In my opinion, however, the gains from extending the operating life of nuclear facilities should be channeled into developing alternative energy sources.

Will industry cooperate in this reorientation of the world’s energy system?

Schellnhuber: Yes, if conditions are right. Governments must establish guidelines and set targets. I think it’s sensible for each country to draw up its own roadmap, and then to combine these into a kind of world road atlas. There’s no escaping the fact that we need to halve global CO₂ emissions by 2050, compared to 1990 levels. And industrial countries should really be reducing carbon emissions by 60 to 80 %, because they’ve produced much more CO₂ than developing countries.

How effective is emissions trading?

Schellnhuber: The concept calls for trade in emissions allowances, whereby the state deliberately ensures a stringent market. That’s fine, in principle, but it can’t remain an isolated measure. Important, too, is greater use of innovative technology, although it pays to remember that the biggest gains are always a result of reducing energy waste. London alone produces as much CO₂ as all of Portugal. Yet its increasing energy demand can be completely attributed to the increasing use of appliances that consume power when in standby mode. That can be changed, as every engineer knows.

What’s the short term roadmap?

Schellnhuber: 2007 and 2008 are decisive years, because the pressure will be on to develop a successor agreement to Kyoto. Then, over the next five to ten years, important decisions are going to have to be made regarding the modernization of a lot of power plants.

What can a global company like Siemens do about the climate challenge?

Schellnhuber: German companies have the strengths needed to cope with climate change. Don’t forget, people used to poke fun at Germans because of our concern for the environment. But our industry can help launch a new industrial revolution—and even post good earnings in the process—which will one day lead to a zero-emissions society. Invest now, and you’ll later have the advantage of being able to supply your technology to the major markets of the future, such as China and India.

Where does the U.S. fit into this equation? And do you think it will start to control its greenhouse emissions before it’s too late?

Schellnhuber: Countries like India and China, which are consuming increasing amounts of energy, will continue to point the finger at the U.S. as long as it fails to cut emissions. But I think there’s a good chance that policy in Washington will change following the presidential election in 2008. The U.S. probably won’t sign up to the Kyoto Protocol, but it could end up setting similar targets. The U.S. might change as Europe has. Here, many people didn’t want to recognize warming. They thought there would be another 50 years to go before the train would derail. But today I sense a growing interest among people in politics and business.

Has the Stern Report brought about a real sea change in opinion?

Schellnhuber: The way I see it, years of warnings from scientists have weakened those who argued that global warming was a fantasy. Now Stern has managed to tear down the last remaining walls of resistance by taking the facts and calculating their economic impact. His arguments will carry a lot of weight, because when it comes to politics, economic arguments are what counts.

                                                                  Interview conducted by Jeanne Rubner