One year ago, 195 countries agreed a pact to limit global warming. Although there was — and remains — doubt over whether the commitments that were made would be enough to limit warming to the extent the signatory countries professed they wanted, the pact was hailed as "historic, durable and ambitious." Certainly, it was necessary, coming as the planetary warning signs were flashing bright red. As the ink dried on the agreement's signatures, 2015 was about to succeed 2014 as the warmest year on record – a title it would lose to 2016.

With the combination of international action and overwhelming evidence, it felt as if the tide of climate denialism – the determined rearguard action by anti-science and pro-fossil fuel politicians and their kinfolk to assert that global warming didn't exist — had been finally turned back. Twelve months later, the landscape looks entirely different.

After the Paris accord was reached, Dana Nuccitelli, a climate blogger for Skeptical Science and The Guardian, actually wrote a piece about how the deniers had lost. "At the time, I thought the Paris accords were basically the death knell for the climate denial industry," he told Seeker. "After all, climate denial is based entirely on opposition to climate solutions and policies, and the whole world had agreed that such solutions and policies were necessary. Then, less than a year later, the world's largest historical carbon polluter elected a president who had promised to use his power to undermine the Paris accords and undo all the progress his predecessor had made in finally curbing the country's contribution to global warming. I did not see this climate denial rebound coming, and I find it both depressing and alarming."

Indeed, on Jan. 20, the United States will inaugurate a president who has tweeted that climate change is a hoax perpetuated by the Chinese; and, although he has subsequently claimed that was a joke, his actions and statements since then have hardly challenged the view that he refuses to acknowledge the veracity of climate science. Sure, he told the New York Times that he was "keeping an open mind" on the subject and on the issue of whether to do withdraw from the Paris accords; and he met with Al Gore and Leonardo DiCaprio. But his incoming White House Chief of Staff Reince Priebus subsequently stated that Trump "has his default position [on climate science], which most of it is a bunch of bunk."

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This is the science of Joseph Fourier, who discovered the greenhouse effect in the 1820s; of John Tyndall, who established the role of carbon dioxide in that greenhouse effect in 1859; of Svante Arrhenius, who postulated the climatic impacts of changing levels of CO2 in 1896; of countless scientists, working on theoretical models and in the field across the globe, whose research is producing mountains of data and information every day.

Virtually all of that data and information is easily accessible to anyone who has interest in looking at it. Yet, according to Ben Carson, "there are a lot of people who say 'overwhelming science,' but then when you ask them to show the overwhelming science they never can show it." Carson, Trump's former rival for the Republican nomination, has now been put forward by the president-elect as the secretary for Housing and Urban Development; and he is far from the only putative cabinet member to express anything from skepticism to outright hostility toward climate science.

Attorney-General designee Jeff Sessions, for example, said in 2003 that, "I believe there are legitimate disputes about the validity and extent of global warming," adding that, "Carbon dioxide does not hurt you. We have to have it in the atmosphere. It is what plants breathe" — the latter parts of which are not untrue but spectacularly miss the point. Incoming CIA Director Mike Pompeo has called the Paris agreement a "radical climate change deal" — and not in a good way. Interior Secretary nominee Ryan Zinke and Energy Secretary designate Rick Perry have both described climate science as unproven; while Scott Pruitt, the Oklahoma attorney general whom Trump has tapped to run the Environmental Protection Agency, has stated that "Scientists continue to disagree about the degree and extent of global warming and its connection to the actions of mankind."

In this context, the nominee for Secretary of State, Rex Tillerson might appear to be a relative moderate, given that he has at least acknowledged the need for a carbon tax and issued a statement of support for the Paris accords — except that he did so while at the helm of ExxonMobil, which has pushed to open up the Arctic to oil drilling and which fostered climate skepticism despite commissioning studies in the 1970s and 1980s that showed conclusively that climate change is real.

It has left some climate scientists — such as Michael Mann of Penn State University, the creator of the famous 'Hockey Stick' graph, who has been subjected to numerous forms of harassment and intimidation — fearing "an era of McCarthyist attacks on our work and our integrity." Mann wrote in the Washington Post: "It's easy to envision, because we've seen it all before. We know we could be hauled into Congress to face hostile questioning from climate change deniers. We know we could be publicly vilified by politicians. We know we could be at the receiving end of federal subpoenas demanding our personal emails. We know we could see our research grants audited or revoked."

Mann and others are concerned, also, for the policy implications of climate denial in the executive branch. "We are afraid that four (possibly eight) years of denial and delay might commit the planet to not just feet, but yards, of sea level rise, massive coastal flooding (made worse by more frequent Katrina and Sandy-like storms), historic deluges, and summer after summer of devastating heat and drought across the country," he wrote.

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What, then, could and should climate scientists be doing to continue making the case for the reality of climate change?

"Lawmakers respond to their voters, so we need to convince voters about the urgency of tackling climate change," Nuccitelli said. "I think bipartisan grassroots organizations like Citizens' Climate Lobby (CCL) are better suited for this, although they can use assistance from scientists. CCL has found that many, perhaps most Republican lawmakers are aware of the threats posed by climate change and the need to do something about it, but they're lacking the public support to take action. We need grassroots organization to change that political climate.

"Climate communication has vastly improved over the past several years. Thanks to resources like the Debunking Handbook, scientists and communicators are now much better at debunking myths without reinforcing them. Unfortunately, there's also a strong flow of misinformation coming from certain biased sources, counteracting much of the efforts made by the scientific community and science communicators. To stem the influence of those biased sources, we need to make climate misinformation societally unacceptable."

Some scientists are concerned about what's been called a "post-truth" environment, in which wide swaths of the country refuse to acknowledge facts that threaten their worldview, that view all sources of information as equally valid, and that thing nothing should be considered factual, even — or especially — if it comes from a reputable source or news organization.

This "post-truth" society is "a problem we're struggling with, and I don't think it's one that scientists can solve," said Nuccitelli. "A post-fact world is a difficult environment for scientists, whose currency is evidence and facts. The good news is that a recent survey found that even conservative Republicans support climate policies (carbon taxes, regulation or both), by a wide margin. They also strongly support clean energy, and a plurality of conservative Republicans even support international climate agreements like the Paris accords. They view climate change as a low priority, but there isn't a strong ideological opposition to the solutions underpinning climate denial. So there's hope that things can shift.

"Climate scientists will still have to help debunk the climate science misinformation and myths that are likely to become prevalent over the next few years. But I think they'll also have to step out of their comfort zones and engage with the public more directly on a personal level, identifying with various groups as a "trusted source" the way Katharine Hayhoe does with evangelicals. Most Americans never meet any scientists, and it's hard to be swayed by people we don't meet."

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One of the challenges with which many scientists struggle, however, is leaving those comfort zones that Nuccitelli mentions, and the extent to which they feel able to speak publicly, not just about their research, but about the implications of that research. Another Trump adviser, Bob Walker, derided much climate research, without any apparent irony, as being "heavily politicized." That can intimidate some scientists. But it did not prevent approximately 500 attendees of the American Geophysical Union conference in San Francisco staging a 'Stand Up for Science' rally earlier this month.

"We don't want to be here," said one of those present, Harvard's Naomi Oreskes. "We want to be doing the work we were trained and educated to do, which is science... but we are at a moment in history where we have to stand up."

At the same time, however, Nuccitelli said that it is wrong to expect scientists to carry the entire burden.

"I think we need to ask more of the general public," he said. "The scientists have done their principal job of identifying and communicating the threats posed by human-caused climate change. We [the public and the policymakers we've elected] haven't done enough to act on that information, and in fact in this year's election we've started to go backward. We need more activism from the public, to demand that our leaders take action to address the tremendous threats climate change poses."

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