As delegates from 195 countries work diligently in Paris to hash out an international deal to tackle climate change, their work relies on the huge consensus of climate science that shows the world is headed for a dangerous future if greenhouse gas emissions are not curtailed. But back home in the United States, historically the biggest carbon emitter of all, climate science gets a much rockier reception. In fact, climate scientists find themselves and their work regularly under attack.

Not only are there organized efforts like Lamar Smith's House science committee issuing subpoenas and striving to discredit scientists, but harassment and hate mail arrives every day via the Internet. Their work has found itself in the crosshairs of a political ideology that has an ugly side.

InsideClimate News spoke to nearly a dozen climate scientists and communicators about the harassment they face. For them, death threats, sexist remarks, claims of fraud, bomb threats, letters laced with powdery substances, references to rape and Nazis have become almost standard. According to emails shared with ICN, messages range from derisive ("I hope your mental illness gets better") to downright threatening ("YOU ARE GOING TO HANG SOON!").

Katharine Hayhoe of Texas Tech University, who does outreach with evangelical Christians, says she can receive up to 200 emails and letters a day following a media appearance, telling her she's a fraud and a liar, threatening her family and challenging her religious views. People have also shown up unannounced and agitated at her office to confront her about her scientific views.

"One email I got said something like, 'I hope your child sees your head in a basket after you've been guillotined for all the fraud you climate scientists have been committing,'" Hayhoe said.

"There are people who become dedicated to following you, who have Google alerts set up on your name, who stalk your Twitter and Facebook accounts, who essentially make a career out of ridiculing and vilifying you," Hayhoe said.

An example of a hate message directed at a climate scientist and obtained by ICN.

While fervent public mistrust of established science is not unique to climate change (the anti-vaccination movement is another prominent example), the level of cruelty of climate harassment is alarming, and is also largely a U.S. phenomenon.

A recent poll by the Pew Research Center shows that only 45 percent of Americans—compared to 54 percent of people worldwide (and nearly 100 percent of working U.S. climate scientists)—believe climate change is a serious problem. Among Republicans, that percentage falls to 20 percent.

Another recent study, by PNAS, showed that the campaigns funded by fossil fuel companies to sow doubt about climate science have been remarkably effective in shaping public opinion in the U.S.

"This is more like politics, with nasty ads that often tell lies or half-truths, distort records," said Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Co. But unlike many politicians, "scientists don't have a superPAC to fight the claims. This is the new reality for us. Scientists moving into the realm of climate science need to be aware of this. Unfortunately, this is the new world we have to live in."

An example of a hate message directed at a climate scientist and obtained by ICN.

This phenomenon isn't unique to scientists either. Journalist Seth Borenstein, who covers climate science for the Associated Press, frequently gets harassed on social media. "Why can't we put these dangerous eco-terrorists in prison, or better yet, just execute them!" one Twitter user wrote in September, tagging Borenstein in the post.

The harassment gets scarier when it isn't contained to the Internet.

A few weeks after a local California magazine published a story about Benjamin Santer, an atmospheric scientist at Lawrence Livermore National Laboratory, the researcher got a knock on his front door at 10 p.m. By the time he answered it, there was a dead rat on his doormat and a yellow Hummer was speeding away from the house, its driver yelling profanity out the window. Santer's young son was upstairs at the time.

Michael Mann, a climate researcher at Penn State University, was left a suspicious looking package with a white powdery substance at his office. The FBI later determined it was cornmeal. Mann and nine other climate scientists also had their names, bios and for some pictures posted on the White Nationalist web forum Stormfront.org, a group whose members have been linked to the hate crime murders of nearly 100 people across the globe.

An example of a hate message directed at a climate scientist and obtained by ICN.

Harassment can be particularly jolting for young scientists, Trenberth said. Most science graduate programs offer some sort of media training, but they largely focus on how to effectively talk to journalists, not how to deal with a barrage of hate mail from the public that follows that interaction. For someone just a few years out of their PhD, an onslaught of personal threats and questions to their scientific credibility is disturbing and confidence-shaking. As a result, young scientists often retreat to the ivory tower to focus solely on research, rather than continue to engage with the public, said Trenberth.

Researchers told InsideClimate News that when they were dealing with the first wave of climate-related harassment in the 1990s and early 2000s, they found themselves ill-equipped to deal with the torrent of attacks. Over the years, however, they have set up informal support networks to fight back.

An example of a hate message directed at a climate scientist and obtained by ICN.

In 2011, Mann and other researchers set up the Climate Science Defense Fund, a nonprofit that helps scientists defend themselves against politically motivated legal actions. The organization helps scientists find pro bono representation and raises funds to assist with legal costs.

"When I find myself with younger climate scientists who are subject to similar harassment, nasty emails, letters to superiors, I try to convey...[that] there's an infrastructure," Mann said.

Even with that help, hate mail and harassment takes a toll on scientists—and science. Researchers spend time and resources addressing denialists' debunked claims in a way the scientific community has never done before, according to a study published in May in the peer-reviewed journal Global Environmental Change. They also often downplay future climate risks to avoid being labeled an "alarmist" by climate contrarians, concluded the same study.

It can also take a toll on personal lives and relationships. And for some, the fear of being attacked, ridiculed or investigated remains years after the hate mail stops.

Hayhoe has found herself snapping at her son during particularly intense periods of attack. "That shouldn't be happening, it shouldn't be affecting my personal life," Hayhoe said. "As scientists we need to take a step back and ask, what toll is this having on me, on my professional work and on my personal life?"

Many of the researchers InsideClimate News spoke with said they have taken steps to protect themselves and their families from hate mail and harassment. Some have unlisted home addresses and phone numbers. Others have arranged that any mail or visitors get filtered through a central office at work, such as the headquarters of their university department.

"Some things are worth fighting for," said Santer, who has been the target of harassment since the mid-1990s. "A clear public understanding of the nature and causes of climate change is worth fighting for.

"If you are doing science that people care about, that is relevant, there will be pushback," he added. "You will receive not only justified or unjustified scientific criticism, but you will encounter attacks on your integrity, your character and your motives. You need to be prepared for them. They are the price of doing what we do. But it is important to remember they are just background noise."

The world needs more researchers talking about global warming right now, not less, climate scientists and communicators said.

"If you work in string theory or big bang cosmology, do great work inside the ivory tower. That's fine," said Hayhoe. "But when you are doing work on something like cancer, Ebola or climate change, there's an urgency. People are being harmed today. If we keep our results to ourselves, that's lives lost."

Ultimately, these attacks haven't stymied the flow of new climate research being published or the suring up of the scientific consensus for human-driven global warming. Many of the researchers InsideClimate News spoke with considered stepping out of the public eye at some point in their career, but in the end, none did.

"I am not looking back in anger," said Santer. "I really do think the main lesson I've learned through all this is wow, I get to come into work every day and learn something new about this incredible planet on which we live. That is an extraordinary privilege."