These are facts: Global warming is real, and almost entirely caused by human activities. Natural variability in temperature is minor compared with what we're doing. This increase in temperature is causing the climate to change, in many ways that are not only predictable but actually observed. This in turn is causing other effects, like Arctic and Antarctic ice loss, sea level rise, coral bleaching, more extreme weather, and much, much more.

Again: Those are facts. The vast majority of scientists who have dedicated their lives to studying the climate agree on this.

And yet a small but vocal minority of people won't accept that. Why? Some are sponsored by fossil fuel companies, the same ones who for decades have pumped money into disinformation campaigns, as well as politicians' pockets. And of course some are ideologically inclined to dismiss science, or progressive politics (which has nothing to do with the science).

Still, some people honestly question the existence of global warming and its effects on the climate. Given all these facts, why do they do so?

Part of the problem -- outside the general atmosphere of denial the media helps promote -- is the scope and scale of climate change itself coupled with our puny brains trying to deal with it.

We humans have a miserable sense of scale. We see what's immediately around us, and have difficulty extrapolating to the greater world. Even those of us who travel around the country and the world can still easily fail to grasp the scale of humanity's presence. There are more than 7 billion of us! And billions of cars, millions of buildings, billions of houses, all of which use up energy and contribute to the emission of carbon dioxide.

But we can't hold those numbers in our hands (why do you think we use the phrase "grasping a situation"?) and so our impact seems like it must be small.

But then look at the other side of the equation. The Earth is huge! So huge, again we can't grasp it. Five hundred million square kilometers of surface area! Five quadrillion tons of air in the atmosphere! A hurricane is an unbelievable event, releasing as much energy as tens of thousands of nuclear bombs going off over a few days!

How could we possibly have an affect on a planet with scales like that?

And the answer is that we do have an affect, and it is small. But it never stops.

That can be hard to swallow, because time is long and our perception narrow. We have firm memories of recent experiences, fuzzier ones going further into the past, and dim ones going back decades.

And that is the true evil of climate change. It's slow and patient. It's everywhere but takes its time. It operates every day, but its effects don't manifest for decades. Weather changes every day, every hour, and that noise washes out the signal of climate change.

Unless, that is, we too are patient and keep our eyes on the long view. When we do, we see the trend, not the bumps and wiggles.

If we watch the trend, and not the wiggles, we see the impact of humanity on our planet. The temperature trend is actually quite clear now. And that trend is up.

As it will continue to be, unless we act. We put 40 billion tons of carbon dioxide into the air every year, and this is the root cause of all this. We can cut that back significantly if we decide to. It's not easy, and it won't be without cost, but it can be done. The alternative is to have the effects of climate change get more and more obvious, on shorter and shorter timescales.

What can we do? We can charge companies that put carbon into the air. We can rely on more renewable energies (solar and wind, of course, but we can also reopen the books on nuclear).

And the most important thing? We can vote.

The Republican Party has made it clear how they feel about climate change. Their official platform only mentions it a few times, and that's to dismiss it, and their presidential candidate, Donald Trump, calls it a "hoax" and chose a denier as his energy consultant and another as his vice presidential pick. The Democratic Party platform talks about it much more realistically, categorizing it as a threat to our nation and our world. I have issues with Hillary Clinton's climate change strategy, but those are minor to the point of nonexistent compared with the flat-out denial and active promotion of fossil fuels from the GOP. Accepting there's a problem is step one, and even a slow approach is better than fueling the fire. Literally.

Look up your senators, your representative. Find out where they stand on this issue. Contact them, write a letter (that's the most effective means of getting your voice heard), supporting them if they understand the reality of climate change, or briefly and politely letting them know how you feel if they don't.

And if you hear someone denying climate change, may I suggest giving them facts and links to more information? Good sources include my blog on Slate called Bad Astronomy, NASA's climate site, the National Oceanic and Atmospheric Administration's climate site, Skeptical Science, DesmogBlog, RealClimate and Climate Central.

It's not too late. If we choose wisely, that is.

Phil Plait writes Slate's Bad Astronomy blog and is an astronomer, public speaker, science evangelizer and author. Twitter: @BadAstronomer