John Sterman, Jay W. Forrester Professor in Computer Science Professor of System Dynamics Director, MIT System Dynamics Group
CAMBRIDGE, Mass., January 2010 — The current proposals under consideration in the negotiations to produce a global climate treaty are not only inadequate, they could lead to a catastrophic rise in global warming, according to MIT Sloan School of Management Professor John Sterman, who recently returned from the U.N. Summit in Copenhagen. A partner in ClimateInteractive.org, he helped create the C-ROADS climate policy simulation model and Climate Scoreboard that measure the long-term effects of various proposals for emissions reductions discussed at last month’s talks on the global climate.
“The good news is that the agreement adopted in Copenhagen affirms the goal of limiting warming to 2.0° C (3.6° F) above pre-industrial temperatures,” he says. “The bad news is that there is nothing in the agreement or in current proposals by individual nations that gets us anywhere close to that goal.”
According to the C-ROADS model, continuing business as usual would lead to an expected temperature increase of 4.8 °C (8.6 ° F). But even if all the commitments for emissions reductions made by individual nations at the conference were fully implemented, the expected rise in temperatures is still 3.9 °C (7.0 °F) above preindustrial levels, with potentially catastrophic consequences to ecosystems, the economy, and human welfare, says Sterman.
To stabilize atmospheric concentrations of greenhouse gases and limit these risks, Sterman says that global greenhouse gas emissions must peak before 2020 and then fall at least 80% below recent levels by 2050, continuing to drop by the end of this century until we have a carbon neutral economy. Doing so might limit the expected warming to the target of 2 °C (3.6 °F).
To understand why stabilizing atmospheric concentrations of CO2 requires emissions to fall, Sterman compares the atmosphere to a bathtub. He explains, “Everyone knows that if you fill your tub faster than it drains, the level of water in the tub will rise until it overflows. In exactly the same way, we are currently pouring carbon dioxide and other greenhouse gases into the atmosphere roughly twice as fast as they are being drained out.
To stabilize the concentration of CO2 and other greenhouse gases at a level that might prevent irreversible global warming, we need to cut emissions to the point where the flow into the bathtub -- the atmosphere -- is balanced by the flow out of the tub.”
However, the drains that remove carbon from the atmosphere may be clogging up. Carbon, says Sterman, is removed by oceans, forests, and other plants, but those resources are not unlimited. The more carbon removed by these “sinks,” the harder it is for them to take up additional carbon.
In addition, a number of “positive feedbacks” can further slow the removal of carbon from the atmosphere, constricting the drain from the tub. For example, global warming is already melting some permafrost in high latitudes, where large amounts of carbon previously were frozen. As the permafrost melts, carbon is released into the atmosphere as carbon dioxide and methane, leading to still more warming. “Nobody knows exactly at what point these feedbacks may cause irreversible warming, but the higher the concentration of carbon dioxide, the warmer it gets and the closer we are to the tipping point,” says Sterman.
The uncertainty about the impact of emissions means that cutting emissions enough to reach an expected warming of 2 °C (3.6 °F) would still leave a 50% chance that warming would be higher. He says, “A 50% chance of limiting warming to 2 °C is better than doing nothing, but who thinks playing Russian roulette with half the chambers loaded is a good gamble? To limit the chance that warming will exceed 2 °C by 2100 to no more than a 5% chance, emissions would have to fall even farther and faster. That's still like playing Russian roulette with 1 in 20 chambers loaded. Who would play that game, especially when the gun is pointed not at our heads but at our children’s?”
While the need to reduce emissions is urgent, Sterman notes that it is becoming cheaper each year to cut emissions by using alternative sources of energy such as solar and wind as well as by investing in efficiency, which can have economic benefits. Studies show as much as 12 billion tons of greenhouse gas emissions could be eliminated every year, profitably, by insulating buildings, eliminating incandescent lights, driving hybrid cars, and increasing the efficiency of electronics, he says.
Sterman adds, “In the end, it comes down to public support. We have to change the way we use energy and support policies that will enable those changes to occur. Science is no longer the bottleneck to action. We need to focus on social and political change.”
The C-ROADS climate policy model is a joint project of MIT, the Sustainability Institute, and Ventana Systems.