Wondering why Congress doesn't pass more environmental legislation? The poor economy probably has a lot to do with it. A new study finds that U.S. senators are far less likely to take green votes when the unemployment rate in their state is high.

(Virginia Mayo/AP)

That's plausible enough. Recent research by Matthew Kahn and Matthew Kotchen found that public support for action on climate change tends to drop when unemployment rises. If people are worried about losing their jobs, it's a lot harder to focus on how high the oceans will rise decades from now.

But no one had really looked at whether this phenomenon affects members of Congress as well. And it appears to. Grant Jacobsen of the University of Oregon took a look at the voting records of 296 senators between 1976 and 2008. He then checked the local unemployment rate in each senator's state, and matched them up to the "green scores" that were given to each senator by the League of Conservation Voters.

The result? "A one point increase in the [state] unemployment rate leads to a statistically significant 0.48 point decline in the LCV score of the average senator."

This was true for senators in both parties, although conservatives saw a steeper decline. Incumbent Republicans saw their green scores fall by 0.83 percentage points, on average, for every one-point rise in local unemployment. Incumbent Democrats saw their scores fall by an average of 0.29 points.

Jacobsen also tried to figure out what would happen if unemployment hadn't risen throughout this period. He estimated that if each state had stayed at its lowest observed unemployment rate, "then the proportion of [Senate] votes taking the environmentally favorable outcome would have increased from 36% to 41%."

Now obviously there's more going on with these votes than just the economy. Ideology also matters, as do local interests. For instance, North Dakota has an extremely low unemployment rate right now, thanks to an oil and gas boom, but neither of its current senators — John Hoeven (R) and Heidi Heitkamp (D) — are rushing to sponsor climate-change bills. But the study does suggest that, at the margins, Congress is more likely to vote in favor of green legislation when the economy is booming.

Further reading:

— That all said, it's worth noting that there's a lot the Obama administration can do on climate change without Congress, particularly by crafting EPA carbon regulations for existing power plants.

Here's one proposal from the Natural Resources Defense Council to do so, which would cut U.S. carbon-dioxide emissions an extra 10 percent by 2025. Note that the EPA is legally required to issue some sort of rules here, though no one knows how stringent they'll end up being.