Warmer Where It’s Colder – Watts Up With That?


Guest Post by Willis Eschenbach

For some years now I’ve been saying that the largest warming is occurring in the northern extratropics, at night, in the winter … and today I realized that I’d always just taken that on faith because I read it somewhere.

Now, folks who know me are aware that I don’t like to trust any claim until I’ve run the numbers myself. So I set out to do that.

I figured I’d look at fairly recent land data since we have much more of that than older data or ocean data. Overall, here are the decadal trends in the maximum temperatures. I’ve used Berkeley Earth data, although I strongly suspect it exaggerates the warming, for a couple of reasons. First, all the records seem to exaggerate the warming, and second, I’m interested in relative trends, not absolute trends.

Figure 1. Maximum monthly average temperature trends, 1950-2020

We can see that the greatest change in maximum temperature is in the northern hemisphere (0.23°C/decade), with the arctic warming the fastest.

Next, here are the trends in the monthly average minimum temperatures. These, of course, are night-time temperatures.

Figure 2. Minimum temperature trends, 1950-2020

Again, the minimum temperatures in the northern hemisphere are indeed warming fastest. They are also warming faster than the maximum temperatures (0.25°C/decade vs. 0.23°C/decade). It’s also worth noting that there are actually a few areas where nighttime temperatures have cooled …

Finally, I took a look at the summer and winter trends by latitude. Figure 3 below shows that result.

Figure 3. Maximum and minimum surface temperature trends by latitude, northern hemisphere (NH) winter and summer.

Turns out that my claim was right. The largest warming is indeed in the northern extratropics, in the winter, at night (dark blue line). Second largest warming is same location, same season, during the day. As you can see, the winter warming is increasing as you go north of about 45°N latitude.

And what are the average daytime and nighttime NH winter temperatures? Figure 4 shows that result.

Figure 4. Northern hemisphere winter daytime (red) and nighttime average temperatures, by latitude

Note that at about 45°N latitude (thin blue vertical line), approximately where the increased warming starts, the daytime temperature averages just below freezing, and the nighttime temperature average is -13°C (9°F) … cold.

This is good news, because I doubt if the people in Vladivostok are going to be unhappy with slightly warmer winter nights … or days, for that matter

And having slept a few times in my youth on a piece of cardboard on the streets of Manhattan in wintertime, with newspapers wrapped around my legs and arms inside my clothing to help keep out the cold, I can personally guarantee that the homeless in New York City won’t object if the winter nights are a bit warmer.

Makes me glad I’m in my nice warm fossil-fuel-heated house tonight …

Best of the late autumn to all,

w.



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