Trump and Republican Party literally threaten the existence of our species. While this statement may sound alarming, it’s not in the least alarmist. Alarmism is what results when one’s degree of fear goes beyond the best available evidence. It’s not alarmist, for example, to shout “Bear!” when one sees a grizzly charging in one’s direction, just as it’s not alarmist to scream, “Civilization could collapse as a result of environmental degradation!” when one sincerely examines the evidence.

Consider the following two phenomena: biodiversity loss and climate change. The first receives hardly any attention from the popular media, yet it constitutes an immense danger to humanity. For example, according to a 2015 study published in Science Advances, humanity has escorted the biosphere into a new phase of devastation: the sixth mass extinction, also called the Holocene extinction.

To put this in perspective, the first living organisms emerged on Earth some 3.8 billion years ago. Since then, there have been five mass extinctions — dubbed the “Big Five” — the last of which killed off the dinosaurs some 66 million years ago. Today, as a result of ecosystem fragmentation, overfishing, pollution, habitat destruction and global warming, we’re in the early stages of the sixth extinction.

Not only are species disappearing, wildlife populations around the world are dwindling at a shocking rate. For example, the 2014 Living Planet Report notes that the population of wild vertebrates — that is, a wide category of mammals, birds, reptiles, amphibians and fish — declined between 1970 and 2010 by a staggering 52 percent. Yet another paper published in Science shows that if current trends continue, there will be virtually no more wild seafood in the world’s oceans by 2048.

In fact, the oceans are increasingly cluttered with vast graveyards called “dead zones.” This refers to regions in which oxygen levels are too low for most marine organisms to survive. A recent count found more than 500 dead zones worldwide, one of which is the size of Connecticut. And let’s not forget the “Great Pacific Garbage Patch,” an “island” of swirling plastic south of Hawaii that’s estimated to be up to “twice the size of the continental United States.”

Now, let’s turn to climate change. The overwhelming majority of climate scientists agree that humans are causing the Earth’s warming. Temperature increases will almost certainly bring about extreme weather events, hotter surface temperatures, melting glaciers, rising sea levels, mega-droughts, deforestation, desertification, the spread of infectious disease, mass migrations, social upheaval, political instability and food supply disruptions. Even the frequency of lightning strikes will increase by 50 percent, allergies will get worse and the planet will spin faster than it currently does (due to changes in the density and circulation patterns of the ocean).

Of more immediate concern, both scholars and high-level government officials have linked climate change, with its attendant societal stresses, to the rise of global terrorism. For example, a 2015 study implies a causal connection between climate change and the rise of ISIS (also known as Daesh) during the Syrian civil war, which was fueled by record-breaking droughts exacerbated by climate change. And both the former Secretary of Defense Chuck Hagel and the current CIA Director John Brennan — as well as the Department of Defense — have affirmed that the Earth’s warming will nontrivially exacerbate terrorist threats facing the West.

But the consequences of climate change will also be “irreversible.” This was recently confirmed by a 2016 article published in Nature and authored by more than 20 scientists from around the globe. As the authors write:

The next few decades offer a brief window of opportunity to minimize large-scale and potentially catastrophic climate change that will extend longer than the entire history of human civilization… Policy decisions made during this window are likely to result in changes to Earth’s climate system measured in millennia rather than human lifespans, with associated socioeconomic and ecological impacts that will exacerbate the risks and damages to society and ecosystems that are projected for the twenty-first century and propagate into the future for many thousands of years.

Enter Donald J. Trump and the Republicans.

Many leading Republicans refuse to even acknowledge that climate change is happening, much less that it’s the result of carbon emissions. Presidential candidate Ben Carson claimed that, “There is no overwhelming science that the things that are going on are man-caused and not naturally caused. Gimme a break.” Another presidential candidate, Mike Huckabee, incorrectly believes that the “science is not settled.”

This denialist attitude is due partly to the religious convictions of such individuals; as the Christian congressman John Shimkus declared back in 2009, climate change isn’t a concern because God assured Noah after the great deluge that “never again shall there be a flood to destroy the earth” (Genesis 9:11). In other words, if anthropogenic global warming isn’t compatible with the promises of Holy Scripture, then humanity shouldn’t worry about it.

Yet another Republican presidential candidate, Ted Cruz, calls climate change a “pseudo-scientific theory,” and has frequently distorted historical climate data to justify his denialism. During an agriculture summit last year, Cruz said, “The radical left loves attacking people as anti-science when anyone dares question their computer models on global warming. They scream, ‘you’re anti-science,’ when someone points out, for example, that in the last 17 years, satellite data shows there’s been no warming whatsoever.”

This, however, is simply false. As the National Centers for Environmental Information affirms, the hottest 16 years on record — with only a single exception — have all occurred since the beginning of this century. Starting with the hottest, the list goes: 2015, 2014, 2010, 2013, 2005, 1998, 2009, 2012, 2003, 2006, 2007, 2002, 2004, 2011, 2001, 2008. And current data suggests that 2016 will beat the temperature record set by 2015.

Even more alarming, the Republican presidential nominee, Donald Trump, has repeatedly labeled climate change a “hoax” perpetrated “for the benefit of China, because China does not do anything to help climate change.” In an interview with the conservative radio host Hugh Hewitt, Trump claimed he’s “not a believer, and I will, unless somebody can prove something to me, I believe there’s weather. I believe there’s change, and I believe it goes up and it goes down, and it goes up again. And it changes depending on years and centuries, but I am not a believer, and we have much bigger problems.”

Consistent with this position, Trump has vowed to dismantle the Environmental Protection Agency (EPA), which he erroneously calls the Department of Environmental (or, perplexingly, the “DEP”), and renounce the Paris climate accord — an agreement between nearly 200 countries that the venerable Bulletin of the Atomic Scientists describes as a “small bright [spot] in a darker world situation full of potential for catastrophe.”

In fact, the Bulletin’s 2016 Doomsday Clock announcement actually called out the Republicans by name for their dogmatic rejection of established science. “The elections of more climate-friendly governments in Canada and Australia are also encouraging,” the authors wrote, “but must be seen against… the Republican Party in the United States, which stands alone in the world in failing to acknowledge even that human-caused climate change is a problem” (italics added).

As the cosmologist and chair of the Bulletin’s Board of Sponsors, Lawrence Krauss, confirms in an interview with Free Inquiry, the Republican Party is the only major political entity in the world that denies the existence of climate change.

In contrast, not only are liberals more likely to believe in climate change and far more likely to trust experts than conservatives, but all of the Democratic candidates this year acknowledged that climate change is real, anthropogenic and requires immediate action. Bernie Sanders even described it as “absolutely” the United States’ greatest national security threat.

Along these lines, Martin O’Malley claimed that “the cascading effects” of climate change helped fuel the Syrian civil war and the rise of ISIS. This comports with the 2015 study mentioned above, and indeed, PolitiFact rated O’Malley’s statement “Mostly True.” While Clinton, the Democratic nominee for president, has been more reluctant to identify climate change as the country’s greatest threat to national security, her platform nonetheless describes it as “a defining challenge of our time.” The difference between the political Right and Left on the issue of climate change could hardly be more significant.

Given the unique global risks that haunt our species this century, it’s not alarmist to claim that the stakes have never been higher. A failure to heed the advice and warnings of scientific experts could result in catastrophes that affect not only the current human population, but future generations for literally 10,000 years. Yet the Republican Party continues to dismiss the extensive body of scientific evidence about how human activity is shaping — and destroying — the biosphere upon which our collective survival depends.

This should be profoundly alarming to anyone who cares about the future of humanity. It’s also what makes the 2016 presidential election the most important political event in the history of human civilization. When voters enter the booths in November, they’ll be deciding not only what kind of country we’ll have for the next four to eight years, but also how livable our planet will be for millennia hence.

The first step toward ensuring that the public makes a wise decision is to educate people about the immense threat posed by the most powerful, anti-science political movement in the world: the Republican Party.