An MIT analysis of climate risk indicates that even moderate carbon-reduction policies now can substantially lower the risk of future climate change.
But global emissions need to be cut quickly if the world is to avoid a temperature rise of more than two degrees Celsius above the pre-industrial level. Without prompt action, says MIT, extreme changes could soon become much more difficult, if not impossible, to control.
The US needs to meet its emissions targets, the rest of the developed world must match them, and China and other large developing countries must follow suit with only a decade or two delay.
The new study examined the effects of four different versions of possible emissions-reduction policies.
It used the MIT Integrated Global Systems Model, a detailed computer simulation of global economic activity and climate processes that has been developed and refined since the early 1990s. The research involved hundreds of runs of the model. Each run used slight variations in input parameters, selected so that each run had about an equal probability of being correct based on present observations and knowledge.
This approach gives a more realistic assessment, said Mort Webster, assistant professor of engineering systems. "One of the common mistakes in the literature," he says, "is to take several different climate models, each of which gives a 'best guess' of temperature outcomes, and take that as the uncertainty range. But that's not right. The range of uncertainty is actually much wider."
One interesting finding is that even relatively modest emissions-control policies can have a big impact on the odds of the most damaging climate outcomes.
For example, under the strongest of the four policy options, the average projected outcome was a 1.7 degrees C reduction of the expected temperature increase in 2100, but for the most extreme projected increase (with five percent probability of occurring) there was a 3.2 degree C reduction. And that's especially significant, the authors say, because the most damaging effects of climate change increase drastically with higher temperature, in a very non-linear way.
Mort Webster, assistant professor of engineering systems, warned that public discussion over climate change policies gets framed as a debate between the most extreme views on each side. "The world is ending tomorrow, versus it's all a myth," he said. "Neither of those is scientifically correct or socially useful."
"It's a tradeoff between risks," he says. "There's the risk of extreme climate change but there's also a risk of higher costs. As scientists, we don't choose what's the right level of risk for society, but we show what the risks are either way."