As this is written, all four remaining candidates in the race for the Republican presidential nomination vehemently reject the fundamental findings of modern climate science. These findings are simple to state:

The Earth's climate is now unequivocally warming. Many chains of evidence demonstrate the warming, including increasing atmospheric and ocean temperatures, rising sea levels, shrinking glaciers and ice sheets, and changing precipitation patterns. The main cause of the warming is human activities, especially burning fossil fuels, which increases the amount of heat-trapping gases in the atmosphere. The effects of man-made climate change are already being felt, and they are mainly harmful. The consequences of climate change will become much more severe in the future, unless global actions are taken soon to drastically reduce the amount of heat-trapping gases emitted into the atmosphere.

These conclusions are the results of decades of research by the international scientific community. They have been endorsed by the Intergovernmental Panel on Climate Change, and by the National Academy of Sciences and leading scientific professional societies in the US and other countries. The great majority of mainstream climate scientists such as ourselves find these results persuasive.

Nevertheless, Ted Cruz heaps scorn on what he has called "a pseudo-scientific theory." He has dismissed it as, "not science, it's a religion." John Kasich says, “I don't believe that humans are the primary cause of climate change." Marco Rubio agrees, stating, "I do not believe that human activity is causing these dramatic changes to our climate the way these scientists are portraying it." Donald Trump speaks of a "global warming hoax," calling it, "created by and for the Chinese."

These public figures reject mainstream climate science because they view it through a lens that incorporates their firmly held values and convictions. They have a high regard for American capitalism and private industry, or the free enterprise system, and a low regard for taxes and regulation, which they regard as government interference. In rejecting mainstream science, they are expressing their opposition to policies that governments might implement, if the science were accepted.

In the United States, aspiring Republican politicians may also feel the pressure to conform to a litmus test. In order to obtain political and financial support, especially from sources allied with the fossil fuel industry, they may conclude that they must attack mainstream climate science and insist that man-made climate change is not a problem.

However, Mother Nature, or the physical climate system, is not concerned with anybody's values or convictions or political litmus tests. Mother Nature is concerned with natural laws. Heat-trapping gases in the atmosphere do trap heat. That leads to warming. After every politician has expressed an opinion, Mother Nature bats last. Daniel Patrick Moynihan, a politician and sociologist, famously said, "Everyone is entitled to his own opinion, but not to his own facts."

Yet the Republican Presidential candidates have gone to a great deal of trouble to avoid confronting the facts about climate change. They tirelessly repeat climate myths, the refutations of which are easily found on websites such as www.skepticalscience.com. These politicians like to say, "I am not a scientist," a truth sadly obvious to any scientist. Yet they have refused to learn what science has discovered about climate change. When Republicans in Congress have held hearings on climate change, they produce tired re-runs of political theater. The scientists invited to testify often include the same handful of outlier witnesses whose opinions are known to be compatible with Republican political positions.

Science is the best process that humanity has developed to learn about natural laws. It is self-correcting, based on facts and evidence, not on belief. Marcia McNutt, the distinguished geophysicist who is the incoming president of the US National Academy of Sciences, has said, “Science is a method for deciding whether what we choose to believe has a basis in the laws of nature or not.”

Most of the world now accepts that climate science can provide useful input to policymaking. Some 196 countries recently produced the Paris agreement. Stabilizing the climate and preventing dangerous levels of climate disruption, the goal of this agreement, will require vigorous international efforts and strong American leadership. Only one major country today has an important political party that overwhelmingly rejects climate science. That country is the United States; the party is Republican.

Science shows that the climate system responds to the cumulative emissions of heat-trapping gases. Today's generation thus has its hands on the thermostat controlling future climate. Failure to sharply reduce emissions can lead to sea level rise that will literally change the map of the world. Electing a president who, head in the sand, rejects modern climate science would be risky and potentially disastrous. It would needlessly increase the likelihood that future generations will be condemned to cope with a severely disrupted climate.