Mitt Romney said Tuesday in a questionnaire that “human activity contributes” to global warming, but that “unilateral” U.S. actions such as emissions regulations would not solve the issue.

Romney’s response to ScienceDebate.org’s question on climate change offered insight on a topic the GOP presidential candidate has shared little about.

Romney has pushed for increased government research funding for low-emission technologies — particularly nuclear energy — and decried President Obama’s push to regulate carbon emissions.

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“My best assessment of the data is that the world is getting warmer, that human activity contributes to that warming, and that policymakers should therefore consider the risk of negative consequences,” Romney said in his questionnaire response.

“Nowhere along the way has the President indicated what actual results his approach would achieve — and with good reason. The reality is that the problem is called Global Warming, not America Warming," added Romney.

The president also responded to the questionnaire, calling climate change "one of the biggest issues of this generation” and reiterating his support of clean-energy technologies.

He also touted many of the Environmental Protection Agency (EPA) emissions initiatives that Romney criticized, such as recently finalized fuel economy standards for cars and the first-ever proposed carbon emission standards for new coal-fired power plants.

Climate change has been a backburner issue on the presidential campaign trail, and an Obama aide recently hinted it would remain so.

Scant mention was made of climate change at last week’s Republican National Convention, and the list of Democratic National Convention speakers suggests it is unlikely the issue will receive prominence this week in Charlotte, N.C.

Last month former Vice President Al Gore Albert (Al) Arnold GoreCompromise, yes — but how? A pre-debate suggestion Trump-Biden debate: High risk vs. low expectations Interest in presidential election hits near-record high: poll MORE, a prominent climate advocate, criticized both candidates for steering clear of the issue.

In their questionnaire responses, Romney and Obama split sharply on the effectiveness of American efforts to stem global warming.

Obama touted his EPA and clean-energy policies as proof that the United States is setting an example for the international community. He also praised international accords with "all major developed and developing nations" on emission limits.

Romney, however, said such steps are ineffective so long as developing nations including China continue emitting greenhouse gases to keep their economies churning. He said U.S. regulatory actions would yield no net benefit to curbing global warming and would hurt the domestic economy.

"I believe we should pursue what I call a ‘No Regrets’ policy — steps that will lead to lower emissions, but that will benefit America regardless of whether the risks of global warming materialize and regardless of whether other nations take effective action," Romney said.

Congressional Republicans have been harsh critics of Obama’s emissions regulations, arguing they impose burdensome costs on business and will stifle economic growth.

Many Republicans also question the impact of human activity on global warming, with many outright rejecting that connection. Romney claimed there is a “lack of scientific consensus” on the extent of the human effects on global warming.

Most scientists agree humans have an effect on global warming. Between 97 and 98 percent of published climate researchers believe man-made climate change is real, according to an oft-cited 2010 study in the Proceedings of the National Academy of Sciences.

-- This story was updated at 4:18 p.m.