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Data show that since 2008 air pollution linked to carbon emissions has been on the decline and are now at 1995 levels. This is good news for concerns about global warming. What’s behind this trend? And will it continue? N.C. State University economist Mike Walden responds.

“Well … indeed it is good news, and again we want to understand why to try to ascertain whether it will continue into the future. Clearly one big factor has been the recession. During recessions people drive less, factories produce less, therefore they use less energy. And so one concern is that as the recession recedes and we get back economic growth, will these emission levels go up?

“But another big factor that researchers have found has been there’s been a switch in how we generate power, particularly electricity. We are seeing the country move away from coal, away from oil – and those tend to be … sources that pollute more – and moving to natural gas. And natural gas is much less polluting. For example, natural gas is half as polluting as coal.

“So that trend continues, even if we do see economic growth and more energy used on that basis. If we change the mix of fuels that we’re using, we could see perhaps this good news continue.”