Lenton, the scientist from the University of Exeter, said he believes it comes down to political leadership, which helps to increase public confidence in the science, and to deter skeptics.
"Governments here [in the UK and Europe] have largely accepted ... that we've got to massively cut our carbon emissions and change our whole way of doing things by 2050," Lenton said. When climate scientists talk to politicians or to the public on climate dangers "one ends up preaching to the converted," he said of Europe.
The UK has pledged to cut emissions by at least 34 percent by 2020, and 80 percent by 2050. The government has funded climate science education at home and has even extended those efforts abroad. The Foreign and Commonwealth Office (FCO) gave about $20,000 to the U.S.-based Environmental Defense Fund to help fund a project to counter climate skepticism in the Texas State Legislature, the Guardian reported earlier this year.
The European Union, home to the world's largest carbon market, has promised a 20 percent reduction of emissions by 2020, and says it would increase that to 30 percent by 2020 if other major emitters agree to the same. Germany is undergoing an energy transformation on a massive scale to replace its retiring nuclear fleet with renewable power.
In contrast to Europe, climate policies in the United States are dead for the foreseeable future, and climate skepticism has become a tenet of Republican politics. GOP presidential nominee Mitt Romney has reversed his earlier position that human activities cause global warming. Even Barack Obama has steered clear of climate change, despite research showing that he would benefit from addressing it.
Lack of political leadership alone, however, doesn't explain the harassment in the United States.
Stephen Harper's Conservative government in Canada has pulled the country out of the Kyoto Protocol, the 1997 global treaty to reduce greenhouse emissions, and has appointed several climate skeptics to crucial federal scientific bodies, including the Natural Sciences and Engineering Research Council and the Canada Foundation for Innovation. Yet Canadians still have some of the world's strongest belief that global warming is happening—and harassment of scientists is not on the scale of its southern neighbor.
"We are generally left alone to do our work," said Bruno Tremblay, a climatologist at McGill University in Montreal, Canada. Tremblay said that unlike many conservative Americans, Canadians generally don't harness suspicions about the government overstepping its powers by trying to control carbon emissions and conserve energy, and in fact they encourage it. So the skeptics' message doesn't mesh with them, he said.
Abuse of Free Speech
Alan Leshner, chief executive officer of the American Association for the Advancement of Science, the world's largest scientific society, said he sees the attacks on scientists in the United States as "very disconcerting." Last year, AAAS released a statement condemning the harassment.
"The incidents reflect two unfortunate things," Leshner said in an interview, "we live in a society where ideologies trump our willingness to hear what science says, and in a country where free speech is so widely valued, people are being attacked."
The foreign scientists interviewed for this story generally agreed that religion and ideology play a bigger role in U.S. politics than they do in their own countries. "This inevitably means things are more about belief than about evidence in the U.S.," said Lenton of the University of Exeter.
According to a 2012 poll by Yale and George Mason Universities, Americans' climate change beliefs divide along party and ideological lines. Among those who said they were "alarmed" or "concerned" about global warming, more than two-thirds identified themselves as Democrat, Independent, or moderate or liberal. In contrast, less than 15 percent of Republicans or conservatives described themselves as alarmed or concerned.
Generally, the more conservative the Republican, the more likely they are to flat-out deny the existence of climate change. Former presidential candidate Rick Santorum, for instance, referred to the acceptance of global warming as a "pseudo-religion" in a column earlier this year for Red State.
Australia Steps Up Climate Efforts Amid Harassment
After the United States, the country with the most harassment by skeptics is Australia. Most speculate that's because the country is the largest exporter of coal in the world. Coal industry groups in Australia have sought to cast doubt on climate science and have lobbied against carbon emission limits. But political will for climate action has been strong enough to counter their opposition.
Last month Australia joined the EU and New Zealand in putting a price on carbon dioxide emissions, and will launch a carbon trading scheme in 2015.