Spurred by the continued failure of too many political leaders and "great concern" over Donald Trump's specific threat to cancel U.S. participation in the Paris climate agreement if elected president, 375 top American scientists published an open letter on Tuesday castigating climate denialism and urging bold action to address a threat that is "real, serious, and immediate."

All established members of the National Academy of Scientists, the signers of the letter argue there is no equivocation within the scientific community and that the United States has a special responsibility to show immediate leadership to forge solutions to the crisis.

"For those who vote in anti-science politicians who attack the scientific experts rather than our pollution problem, your legacy will be the climate change that you could have helped prevent. Those voters will own climate change."

—Dr. John Abraham, thermal scientist"Human-caused climate change is not a belief, a hoax, or a conspiracy. It is a physical reality," the letter begins. "Fossil fuels powered the Industrial Revolution. But the burning of oil, coal, and gas also caused most of the historical increase in atmospheric levels of heat-trapping greenhouse gases. This increase in greenhouse gases is changing Earth's climate."

It continues: "Our fingerprints on the climate system are visible everywhere. They are seen in warming of the oceans, the land surface, and the lower atmosphere. They are identifiable in sea level rise, altered rainfall patterns, retreat of Arctic sea ice, ocean acidification, and many other aspects of the climate system. Human-caused climate change is not something far removed from our day-to-day experience, affecting only the remote Arctic. It is present here and now, in our own country, in our own states, and in our own communities."

Citing the enormous body of evidence, research, and data—including this year's record-breaking global temperature averages and new worrying studies about rapidly warming oceans—the scientists say the possibility of planetary tipping points—described as "climatic points of no return." Such phenomenon, which can set in motion "large-scale ocean circulation changes, the loss of major ice sheets, and species extinctions," can no longer be ignored by policy makers and politicians running for office. And because humanity's "proximity to these tipping points is uncertain," the scientists warn, the potential "consequences of exceeding such thresholds are not confined to the next one or two electoral cycles. They have lifetimes of many thousands of years."

According to the letter, "During the Presidential primary campaign, claims were made that the Earth is not warming, or that warming is due to purely natural causes outside of human control. Such claims are inconsistent with reality."

Like the planetary climate system itself, the scientists argue, the nation's political system also has "tipping points" and they warn that the consequences of Republicans pulling out of climate agreements "would be severe and long-lasting."

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Writing in the Guardian, Dr. John Abraham, a thermal scientist who was not part of the letter, says his colleagues that did sign should be applauded for "venturing deeper into politics than scientists are generally willing to tread." Abraham cites the "inane Republican platform and the foolish position of the Republican nominee Donald Trump" as the primary reason for that. He continues:

We scientists have warned the country and the world about the dangers of climate change for decades. We are now seeing our predictions come true. There are no longer any reputable scientists who disagree that humans are the major factor changing the climate. We have also seen that real action can be taken to reduce pollution. That action will not hurt our economy, rather it has built the new energy economy of the future. Despite this progress, some people want to take us backwards in time – they want to undo our progress. For those who vote in anti-science politicians who attack the scientific experts rather than our pollution problem, your legacy will be the climate change that you could have helped prevent. Those voters will own climate change. What will that conversation be like with your kids?

Read the scientists' letter in full below (a full list of signatories can be found here):

Human-caused climate change is not a belief, a hoax, or a conspiracy. It is a physical reality. Fossil fuels powered the Industrial Revolution. But the burning of oil, coal, and gas also caused most of the historical increase in atmospheric levels of heat-trapping greenhouse gases. This increase in greenhouse gases is changing Earth’s climate.



Our fingerprints on the climate system are visible everywhere. They are seen in warming of the oceans, the land surface, and the lower atmosphere. They are identifiable in sea level rise, altered rainfall patterns, retreat of Arctic sea ice, ocean acidification, and many other aspects of the climate system. Human-caused climate change is not something far removed from our day-to-day experience, affecting only the remote Arctic. It is present here and now, in our own country, in our own states, and in our own communities.



During the Presidential primary campaign, claims were made that the Earth is not warming, or that warming is due to purely natural causes outside of human control. Such claims are inconsistent with reality.



Others argued that no action is warranted until we have absolute certainty about human impacts on climate. Absolute certainty is unattainable. We are certain beyond a reasonable doubt, however, that the problem of human-caused climate change is real, serious, and immediate, and that this problem poses significant risks: to our ability to thrive and build a better future, to national security, to human health and food production, and to the interconnected web of living systems.



The basic science of how greenhouse gases trap heat is clear, and has been for over a century. Ultimately, the strength of that basic science brought the governments of the world to Paris in December 2015. They went to Paris despite pronounced differences in systems of government, in national self-interest, in culpability for past emissions of greenhouse gases, and in vulnerability to future climate change. The leaders of over 190 countries recognized that the problem of human-caused climate change is a danger to present and future citizens of our planet. They made national commitments to address this problem. It was a small but historic and vital first step towards more enlightened stewardship of Earth’s climate system.



From studies of changes in temperature and sea level over the last million years, we know that the climate system has tipping points. Our proximity to these tipping points is uncertain. We know, however, that rapid warming of the planet increases the risk of crossing climatic points of no return, possibly setting in motion large-scale ocean circulation changes, the loss of major ice sheets, and species extinctions. The climatic consequences of exceeding such thresholds are not confined to the next one or two electoral cycles. They have lifetimes of many thousands of years.



The political system also has tipping points. Thus it is of great concern that the Republican nominee for President has advocated U.S. withdrawal from the Paris Accord. A “Parexit” would send a clear signal to the rest of the world: "The United States does not care about the global problem of human-caused climate change. You are on your own." Such a decision would make it far more difficult to develop effective global strategies for mitigating and adapting to climate change. The consequences of opting out of the global community would be severe and long-lasting – for our planet’s climate and for the international credibility of the United States.



The United States can and must be a major player in developing innovative solutions to the problem of reducing emissions of greenhouse gases. Nations that find innovative ways of decarbonizing energy systems and sequestering CO2 will be the economic leaders of the 21st century. Walking away from Paris makes it less likely that the U.S. will have a global leadership role, politically, economically, or morally. We cannot afford to cross that tipping point.

The following signers of this letter do so as individual NAS members and not on behalf of the NAS itself or their Institutions.