With climate change, uncertainty is no-one’s friend

Uncertainty cuts both ways highlights University of Bristol's Stephan Lewandowsky - if your preferred estimate is at the low end of a range, you're neglecting similarly likely high end estimates. Image credit: University of Bristol

Uncertainty cuts both ways highlights University of Bristol’s Stephan Lewandowsky – if your preferred estimate is at the low end of a range, you’re neglecting similarly likely high end estimates. Image credit: University of Bristol

Waiting longer to act on climate change will cost us more than taking immediate action. It’s a message that’s getting louder and louder, repeated from many sides. In March it was stressed by US Secretary of State John Kerry. In April it was highlighted by the UN Intergovernmental Panel on Climate Change (IPCC)’s latest report. Last month it was underlined by Hank Paulson, treasury secretary under George Bush, hedge fund manager Tom Steyer, and former New York Mayor Michael Bloomberg. This week the Council of Economic Advisors, the agency advising President Obama on economic policy, joined in.

These messages could hardly be any clearer, but still some of us remain uncertain on the need to act. The best argument for waiting until we’re more certain to act is that if climate change turns out to be harmless, our efforts to fight it will be wasted. Even simple things like current weather are enough to sway our opinions, and when uncertain it’s always tempting to feel like we don’t need to do anything. But that’s the wrong reaction to uncertainty on climate change, according to psychologist Stephan Lewandowsky from the University of Bristol, UK.

The researchers have found that greater uncertainty over how much Earth warms in response to our CO2 emissions would actually raise forecasts of average damage costs from climate change. Greater uncertainty also means projections see it as more likely that steps to cut emissions won’t keep the world below warming levels governments have agreed we must avoid. So, if we are unsure whether we can slow the climate juggernaut down before we smash into the wall, we’re better off hitting the brakes earlier. As Stephan explained, ‘uncertainty is no one’s friend’.

Evidence is piling up against the economic argument for waiting to see if climate sensitivity is less than 1C per doubling of CO2. Image copyright Springer, see reference below.

Evidence is piling up against the economic argument for waiting to see if climate sensitivity is less than 1°C per doubling of CO2. Image copyright Springer, see reference below.

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Could climate’s crop impact catch us with our plants down?

The odds that yields of maize will fall by a tenth over the next 20 years have shortened from 1-in-200 to 1-in-10. Image copyright Raman Sharma used via Flickr Creative Commons license.

The odds that yields of maize will fall by a tenth over the next 20 years have shortened from 1-in-200 to 1-in-10. Image copyright Raman Sharma, used via Flickr Creative Commons license.

With the next two decades set to see a stronger increase in demand for food than the rest of the 21st century, declining harvests would cause some serious problems. Right now crop yields are growing, but could climate trends cause them to fall by a tenth, say, over the next 10-20 years?

That’s the question David Lobell from Stanford University in California and Claudia Tebaldi from the US National Center for Atmospheric Research in Boulder, Colorado have tried to answer. They find that if the world wasn’t warming, the chance of yields decreasing by a tenth over the next 20 years would be less than 1-in-200. However, climate change has made shrinking yields more likely, shortening the odds to a 1-in-10 chance for maize and a 1-in-20 chance for wheat.

“It was surprising to see how likely it is nowadays for climate trends to significantly cut into yield progress,” David told me. “It is still more likely than not that climate will be a slight drag on progress instead of a major factor. But we can’t rule out a major slowdown, and that means we should probably think through that type of scenario to figure out how to prepare for it.”

Such near-future climate forecasts are unusual, David underlined. “Longer periods allow the signal of climate change to become clearer compared to natural variability,” he explained. “But it may simply be that most of the initial questions about climate change were about the long timescales, to decide about questions related to energy choices and emissions. Now, a lot of questions are related about how to properly adapt to the changes happening now.”

What will happen to crops is central to David’s interests as associate director of Stanford’s Center on Food Security and the Environment. “I often get asked by governments or the private sector if climate change will threaten food supply in the next couple of decades, as if it’s a simple yes or no answer,” the scientist revealed. “This was especially true of a committee I recently served on focused on social stresses from climate change in the near-term. The truth is that over a 10 or 20 year period, it depends largely on how fast things warm, and we can’t predict that very precisely. So the best we can do is put odds on things.” Read the rest of this entry »