When I walked the dogs Wednesday morning it was possible to believe that it was not going to stay hot and humid forever. Although we have had a few relatively cool nights this summer, this felt like the first real hint of fall.

We’re used to July and August being hotter than June on average, but it does seem odd when you think about the fact that the days have been getting shorter since June 21.

I made a plot of average monthly high (in red) and low (in blue) temperatures for Rome. I made it for two years so you can see how the ups and downs cycle through the year. The green line is an arbitrary number that shows how the incoming sunlight varies through the year, normalized so that the values are similar to the temperature values. What this plot shows is that temperature lags the change in heating caused by the change in incoming sunlight, both in summer and in winter.

So, the warmest days are not the longest days and the coldest days are not the shortest days. That’s because the Earth acts like a pot of water being heated on the stove; it takes a while to bring it to a boil. But in July, even with days that are shorter than in June, we’re still getting so much sunlight that the Earth wants to be warmer than it already is. We’re lucky the seasons are as short as they are. If they were longer, it would be so hot that we’d probably all have to move further north. But we’d still have to keep a winter home somewhere even further south.

In the meantime, we have opened all the windows in the house, because it’s finally cooler outside than inside.