Environmental campaigners have long suspected that the over-representation of rural interests on Capitol Hill is at least partly responsible the USA's slow response to climate change, but a new study has now set out to determine the extent to which the influence of rural voters and lobbyists has put a brake on green legislation.

The study, presented at a conference last month by researchers from the department of political science at the University of California, found that the political system in the US was biased towards rural voters and thus made it much harder for administrations to pass climate legislation such as President Obama's proposed cap-and-trade bill.

The researchers compared contrasting environmental policies in the US and UK, and asked why countries that are similar in their cultural, political, and legal traditions have such a different approach to green legislation.

They concluded that imbalances in the US political system that give disproportionate power to rural voters lay at the root of the differences.

Under the US system, Senate seats are apportioned equally among the states, regardless of their population.

As a result the state with the smallest population, Wyoming, has two senators per million voters, while the most populous state, California, has 0.06 senators per million voters. Overall, the 21 smallest and generally most rural states have the population of California, but 42 senators compared to California's two.

The study argues that rural voters tend to be more opposed to environmental legislation, as they are more dependent on private vehicles for transportation and must travel longer distances for professional and personal purposes, while the observable externalities of gasoline consumption, such as local air pollution, and traffic congestion affect them less.

"In the United States, but not in England, the voters that are most harmed by high environmental taxes—rural voters—are systematically overrepresented in the political system," the report states. "These results are important because they show that political institutions—specifically, malapportioned legislatures—can shape environmental policy outcomes."

Consequently, successive US administrations have shied away from imposing potentially unpopular environmental policies such as higher fuel taxes. The report notes that while pre-tax gas prices in the US are slightly higher than in the UK, gas prices in the UK are almost three times higher at the pump.

Moreover, the study says the political imbalance in countries such as the US makes it less likely for them to ratify international climate change agreements – the USA never ratified the Kyoto protocol.

"In many of these cases, this institutional variation is the result of antiquated and idiosyncratic historical choices," says the report. "But the evidence points to an unintended consequence in the realm of environmental policy."

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