A couple of weeks ago the Northeast was in the grip of a severe heat wave. As I write this, however, it’s a fairly cool day in New Jersey, considering that it’s late July. Weather is like that; it fluctuates.

And this banal observation may be what dooms us to climate catastrophe, in two ways. On one side, the variability of temperatures from day to day and year to year makes it easy to miss, ignore or obscure the longer-term upward trend. On the other, even a fairly modest rise in average temperatures translates into a much higher frequency of extreme events — like the devastating drought now gripping America’s heartland — that do vast damage.

On the first point: Even with the best will in the world, it would be hard for most people to stay focused on the big picture in the face of short-run fluctuations. When the mercury is high and the crops are withering, everyone talks about it, and some make the connection to global warming. But let the days grow a bit cooler and the rains fall, and inevitably people’s attention turns to other matters.

Making things much worse, of course, is the role of players who don’t have the best will in the world. Climate change denial is a major industry, lavishly financed by Exxon, the Koch brothers and others with a financial stake in the continued burning of fossil fuels. And exploiting variability is one of the key tricks of that industry’s trade. Applications range from the Fox News perennial — “It’s cold outside! Al Gore was wrong!” — to the constant claims that we’re experiencing global cooling, not warming, because it’s not as hot right now as it was a few years back.