If it is, why are some world leaders under the delusion that it is not?
Well, the overwhelming consensus among scientists is that the climate is indeed changing.
It's absolutely clear that over the last half a century or so, temperatures have been rising pretty steadily.
And we know what's causing this warming.
Since the advent of the Industrial Revolution, we've burned fossil fuels for energy, and that has increased CO2 levels in the atmosphere and warmed the planet.
It looks as though the average world temperature is not far short of one degree centigrade higher than it was in pre-industrial times.
Why are some world leaders deluded about this?
Well, in some sense, they're paid to be.
Some world leaders, most importantly, means Donald Trump.
The US president who, I think, at one point said climate change is a hoax invented by the Chinese.
That's partly because some of the Republicans would say, "Well, yes, the climate is changing, but that's not man-made."
"It's just kind of inevitable."
But there's also a stream of the Republican party today in America that's saying, "Actually, the climate probably is changing, but we don't want to use the word 'climate change' because we want to make sure that the energy sector in America and American energy interests are still protected."
There are very large interests in favor of denying climate change.
Economic interests invested in the fossil fuels industrial system, which is, after all, the basic backbone of our economies.
But also, you have to remember, the doubts of ordinary people who think that what they're being asked to do is to give up their way of life.
The impacts of climate change are very, very complex.
Some areas of the world might even get cooler or rainier at certain times, while other areas of the planet get hotter and drier.
It could bring wildfires to California.
It could also bring the polar vortex to Chicago.
So the complexity of the changes that the planet is undergoing and the way that scientists have spoken about the statistical range of probabilities I think has, in the past, contributed to some doubt.
It's a complicated picture.
But right now, what's clear is that when it comes to things like the Paris climate change accord, it's essentially America against most of the rest of the world.