Bill Nye, the revered Science Guy of the mid-1990s and author of "Unstoppable," says the planet is reaching a fateful moment.
"My claim is that 2016 is a huge turning point," Nye told Tech Insider.
"If this presidential election, in the United States, here on Earth, goes to a president who denies climate change, then the world is in for a lot of trouble."
Nye pointed out that 13 of the last 16 years have been the warmest on record, which go back 134 years. The mean global temperature has also risen 1.4 degrees Fahrenheit since 1980.
You can see that upward trend in this chart:
Less than 2 degrees might not seem like a lot, but data taken from ancient tree rings and ice cores show the Earth's average temperature is stable on short time scales — so an abrupt shift during our lifetimes is cause for alarm.
In fact, global warming has already melted 13.4 percent of the planet's sea ice, and the West Antarctic Ice Sheet is dangerously close to collapse. That could cause up to 20 feet of sea level rise in the long term, even if we manage to limit warming to the 3.6-degree-Fahrenheit target the world agreed on in Paris last December.
So if you live on a coastline, you should be very concerned.
But somehow during this US presidential election, only 45 percent of Americans believe that climate change "is a very serious problem."
Yet Nye's message isn't all doom-and-gloom.
If the US elects a president "who's concerned about climate change and gets to work on it, applies resources to it, then we could improve the quality of life for a great many people."
Check out Nye's entire interview with Tech Insider below: