Cliff Mass, in his blog post about recent temperatures, asks the question “Why is the Northwest so warm?” He then proceeds to answer the question “Why is the Northwest warm?” What he doesn’t address is the question he himself asked: why SO warm? Perhaps we should say “so hot.”
We can see that it really was SO hot by comparing the monthly average temperature in the northwest this June, to that of previous Junes:
We can also see it in a histogram of June temperatures:
The lone value on the far right is for June 2015. Not only was this June 7.9 deg.F hotter than the long-term average, it was a full 2.6 deg.F hotter than the second-hottest June on record. It wasn’t just hot, it was SO hot.
To get more context on how exceptional it was, let’s plot data for all months, not just Junes. Of course we should remove the annual cycle and compute anomaly values, to compare each month to what is typical for that month. That gives this:
It makes this June (the final value) seem not exceptional at all. But this is a mistaken impression due to the fact that some months show a large anomaly simply because there’s more natural variability in winter months than summer months. We can see this in a boxplot of temperature anomaly by month:
Note how winter’s values cover such a large range compared to summer’s, so for them to show larger anomalies isn’t at all exceptional. Let’s correct for that by dividing each anomaly value by the standard deviation for that month, producing what I’ll call “scaled anomaly.” That gives this:
So June wasn’t just the most exceptionally hot June for the northwest, it was the most exceptionally hot of all 1,446 months on record.
How unlikely was it? Let’s ignore global warming for the moment, just pretend it hadn’t happened, and estimate the likelihood of such an extreme based on the data observed prior to June 2015. Fitting an extreme-value distribution suggests that this June was a once-in-1200-years event. That’s quite exceptional, certainly justifying the moniker “SO hot.”
But global warming did happen, it even affected the northwest. We can estimate its effect by fitting a smooth (modified lowess) to the anomaly data:
It’s hard to see on this scale, but northwest temperature has increased by about 2.5 deg.F since 1895.
Let’s replace anomaly values with detrended anomalies by subtracting the estimated long-term trend. Then, to see how exceptional June was, we still have to allow for the fact that winter months show so much more variation naturally than summer months. We’ll re-compute the standard deviation for each month and divide the detrended anomalies by their month’s standard deviation to compute “detrended scaled” anomalies. Now we have this:
Having removed the estimated effect of global warming, June’s scaled anomaly is no longer the most extreme on record. By the narrowest of margins it’s now the 2nd-most extreme.
Again fitting an extreme-value distribution suggests that this June was only about a once-in-90-years event. It’s hardly exceptional to find that in slightly more than 120 years of data. Essentially, when we remove the effect of global warming we see that this June in the northwest was hot, one might even say quite hot — about once-in-a-century hot — but not so extreme as to qualify for “SO hot” with a capital “SO.”
That’s what global warming has done to the Pacific northwest in the USA: made what would have been a once-in-1200-years event into a once-in-90-years event. The extremity of June’s temperatures have been made more than 10 times as likely. The reason is: us.
But Cliff Mass seems insistent on dismissing the effect of man-made climate change on this, as well as other, extreme events at every turn. He even insists that “the more extreme the weather anomaly, the less likely it is to be caused by human-induced (anthropogenic) global warming.” He just can’t seem to wrap his mind around the fact that without global warming, it would indeed have been hot in the northwest this June but it wouldn’t have been SO hot.
He even trivialized the effect of global warming with this bit of misinformation:
While the Northwest has been hot and dry, much of the eastern U.S. has been much cooler and wetter than normal. Even the Rockies have been wetter than normal. Global warming would warm them as well. This week I was at a weather conference in Chicago….it was quite chilly there at times.
Was much of the eastern U.S. really “much cooler … than normal” this June? Not according to the national climate data center:
Only three New England states were notably cooler than normal, and not one of them was anywhere near as much cooler than normal as the northwest was hotter than normal. It’s the kind of offhand remark that’s easy to spout to give the impression you want to give, but falls flat on its face when we look at the actual data.
As for Chicago being “quite chilly at times,” that’s about as “scientific” an argument as Oklahoma’s Senator Inhofe showing up on the senate floor with a snowball during winter.