"Your choices will determine whether the United States helps to solve this problem, or whether we remain a major part of the problem itself."

Scientific currency is not about money or power. It's about understanding. If you're a scientist, you are ultimately judged on whether you got the science right. The few scientific voices claiming that our planet is not warming did not get the science right. The same applies to the small number of voices claiming that human actions cannot and do not affect climate. Don't listen to such ignorant voices. As our country's recent history clearly illustrates, we can ill afford to take important decisions based on misinformation or poor intelligence. We all lose if that happens.

Mr. President-elect, you have claimed publicly that "Nobody really knows" about the causes of climate change. That is incorrect. We know, beyond any reasonable doubt, that burning fossil fuels increases levels of heat-trapping greenhouse gases. We've measured these increases. We know that increasing greenhouse gases in Earth's atmosphere causes warming. We've measured warming of Earth's land surface, oceans, and atmosphere. Like it or not, our fingerprints are now on the climate system. We see these human fingerprints everywhere we look – in temperature, rain, snow and ice, sea level, and dozens of other climate records. If we ignore this reality, the climate forecast is not good for us, and is particularly bad for future generations.

Your choices will determine whether the United States helps to solve this problem, or whether we remain a major part of the problem itself. If you choose to remove the United States from the Paris Climate Agreement, our country will be an international pariah. We will be publicly shamed and vilified. The rest of the civilized world will move on without us. The United States will not be the world's leader in solving climate change. We'll be a follower of other, smarter countries. We'll lose relevance, stature, and influence.

Mr. President-elect, you promised throughout your campaign to "Make America great again." You cannot accomplish this goal if your administration embraces ignorance. You won't get to a "Great America" if you and your Cabinet appointees deny the hard scientific reality of human-caused planetary warming. You won't get there if you decide to remove us from the Paris Climate Agreement. America won't be great if you take us out of the international community of nations working to diminish climate risk.

Millions of your fellow Americans are deeply concerned about climate change, and are looking to you for leadership. Your choice on Day 1 is clear. Leadership or denial. If it's the former, you'll have plenty of Americans willing to help you. If it's the latter, you'll have millions of powerful voices allied against you. Please choose wisely.

Commentary by Ben Santer, who studies the nature and causes of climate change. His research has contributed to findings of a discernible human influence on global climate. He is a member of the U.S. National Academy of Sciences and a John D. and Catherine T. MacArthur Fellow. He was one of the four organizers of a letter signed by 376 National Academy members. The letter points out the negative consequences of a U.S. withdrawal from the Paris Climate Agreement.



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