Five years after Donald Trump's infamous "hoax" tweet, in which he called climate change a fiction developed by the Chinese, the president, again on Twitter, reacted to a recent cold snap by saying "we could use a little bit of that good old Global Warming"—this, at the tail end of a year that was the United States' third warmest on record.

Trump's musings have gone from fringe fantasy to official obfuscation, enshrining a denialism that runs through the core of his administration, from the top down.

Yet signs are beginning to surface that suggest this refusal to accept even the basics of climate science may come up against their limits.

Last year, the administration signed off on a comprehensive, government-wide update of the mainstream science that clearly says humans have contributed to atmospheric warming.

Then there were rumblings that Scott Pruitt's "red team, blue team" review of climate science could be put on ice. That could stymie calls to overturn the "endangerment finding" that authorizes climate action under the Clean Air Act.

Finally, climate hawks in the Senate are rallying to defeat Trump's proposed appointment of Kathleen Hartnett White, who considers carbon dioxide the "gas of life," as head of the Council on Environmental Quality.

Still, the pervasive culture of denialism within the administration has enabled the rollback or attempted rollback of dozens of regulations meant to protect public health, safety and the environment through an astonishingly speedy assault that has demoralized EPA workers and prompted hundreds to flee the agency.

Here, briefly, a sampling of statements by Trump's top lieutenants about what climate scientists have said is the greatest existential threat to humanity:

Vice President Mike Pence: "Claims of catastrophic consequences in global warming are not reflective of the majority of the opinions even among IPCC (Intergovernmental Panel on Climate Change) scientists."

Secretary of State Rex Tillerson: "The increase in greenhouse gas concentrations in the atmosphere are having an effect. Our ability to predict that effect is very limited."

EPA Administrator Scott Pruitt: "I would not agree that [carbon dioxide] is a primary driver to the global warming that we see."

Secretary of Energy Rick Perry, when asked whether carbon dioxide is the main driver of climate change: "No. Most likely the primary control knob is the ocean waters and this environment that we live in." He also called climate change "one contrived phony mess."

Secretary of Agriculture Sonny Perdue: "... we don't know definitively in my opinion what is causing climate change."

Nominee to lead the Council on Environmental Quality Kathleen Hartnett White: "An invisible, harmless trace gas in the Earth's atmosphere, CO2 is a plant food."

Action has accompanied the words. The administration has scrubbed government websites of climate change-related information, effectively purged advisory boards of qualified scientists and replaced them with scientists from regulated industries, is attempting to roll back the Obama administration's Clean Power Plan, has moved to reverse fuel economy standards and is attempting to withdraw from the landmark 2015 Paris climate agreement.

Denial Seeps Into Agencies, Trump Voters' Views

Beyond policy changes, there's an attempted cultural shift, a less obvious effect that is permeating the consciousness of voters.

According to an October poll by the Yale Program on Climate Change Communication and the George Mason University Center for Climate Change Communication, seven in 10 registered American voters, or 72 percent, think global warming is happening, barely changed from 2008. On the other hand, only 37 percent of conservative Republicans think global warming is occurring—13 percentage points lower than in 2008 and, significantly, nine points lower than one year ago, shortly after Trump's election.

The tenor of the administration is likely seeping into government agencies, too, in more or less obvious ways.

"These folks set the tone of the conversation both within the agencies and outward, toward the public," explained Michael Oppenheimer an atmospheric scientist at Princeton University and a coordinating author of the IPCC. "Although many career employees will continue their work as before, the signal from above will be 'you are wasting your time' at best or 'keep it up and your career will be in danger' at worst. This is bound to slow progress on science and reverse progress on policy, as is already happening."

Attacking the Endangerment Finding

Still, the real prize for the administration is going to prove difficult.

The "endangerment finding"—the EPA's foundational conclusion that forms the basis of greenhouse gas regulations—is directly in the crosshairs of the administration and its staunchest allies in the fossil fuel industry and Congress.

Recently, Pruitt said he would hold a public "red team, blue team" exercise to challenge the basis for the finding and the broader scientific consensus on climate change. The concept, Pruitt has said, is to provide an "objective" debate on climate change and carbon dioxide, with mainstream scientists on one side and climate skeptics on the other. Scientists have completely trounced the concept, noting that the scientific consensus around climate change, embodied in sweeping government reports, is already robustly peer-review and has been through a "red team, blue team" process already.

Unfortunately for those who want to dismantle the endangerment finding, there's the most recent National Climate Assessment's Climate Science Special Report, released this fall, which affirmed that human-caused emissions of greenhouse gases are the primary driver of climate change. The report, mandated by law, requires the administration to sign off on it. And while many critics of the administration worried about possible tinkering with the findings in the report, its conclusions were unvarnished.

That the government signed off on the most robust, comprehensive report of its kind—one that upholds the conclusion of mainstream scientists—will make it nearly impossible to unravel the government's position, despite the rhetoric from the administration.

"For one thing, this summarizes new and stronger evidence for human causation of climate change, and discusses dangerous impacts," said Philip Duffy, executive director of the Woods Hole Research Center, who was a member of the committee that reviewed the report.

"We've learned a lot about this since the original endangerment finding, nearly 10 years ago," he said. "Beyond this, the report was reviewed by the National Academy of Sciences and approved by 13 federal agencies, so it has a strong pedigree and a lot of credibility."