April has been a crazy month in recent years in our great state. It’s likely a reflection of the fact that this is one of the most volatile times of year but also some links to unintended consequences of climate change.
Last April, which was a very cold one, I discussed the link that’s being investigated to polar vortex disruptions. That’s one of the ‘unintended consequences’ potentially, of a rapidly warming arctic. Literally, the warming of our planet is so altering weather patterns that we’re occasionally getting air that has no business being here, or at least on the frequency we’re now seeing.
The logical test as to whether this represents any pause or refute to man-made climate change is the fact that are winters are so undeniably warmer compared to 50 or 100 years ago that it’s clearly a VERY temporary change in weather patterns (i.e. 4-6 week patterns occasionally) occurring namely in February (late winter) or April (early spring). Without diving into a whole different article, these are times of year where the polar vortex is more vulnerable to being disrupted. Since 2010, this period is the fifth coldest for April averages, which might make you think, except that it also came after the decade with the warmest April averages.
To be sure, if we plot April average temperatures in the Twin Cities over the whole period of record since 1873, it would look almost like a flat temperature trend. In truth, it’s a subtle increase, but one of the lowest rates of temperature increase of any of our months for all of the above reasons.
Still, even in a month where the big trends are more subtle, the heat is notably increasing. I discussed in a recent weather video how the ‘firsts of the season’ are coming earlier. Even with temperature trends that are subtle in April, the first 70 and 80 (which have always come, on average, in April or early May) are coming 8 days earlier than they used to.
While 80 degree temperatures in April are no new thing, there is an increase in them. We now see about one and a half times to twice as many 80s in the month of April has earlier in our temperature records.
If we dive further however, and look at 80s that come earlier in April, we see a more pronounced trend and signal. We can look at this current ‘heat wave’ and distinguish between years where the first 80 comes BEFORE April 13, such as this week.
Just as we saw in the charter from earlier that heat is coming earlier, so too do we see this more pronounced trend in Aprils that come earlier in the month. The instances of 80s that come within the first half of April has nearly tripled compared to the historical averages.
The forecast high temperature for Wednesday, April 12th is about 84 degrees. This would break the record of 83 set in 1931 and is an important ‘heat threshold’ in itself. We can calculate, that even with the more subtle warming of Aprils over time, we’ve increased the odds of hitting such a milestone this early in the month by a factor of three.
Yet another way to look at this, is looking at the trends in April extreme highs. While the average April temperature has only increased about 1.2 degrees over the historical record:
Look at how the warmest high temperature of April has changed over time:
The hottest temperature of April is increasing 4.6 degrees compared to the 1.2 degree increase in the average.
It’s one of the lessons of climate change: the extremes are increasing more quickly. Subtle shifts on the ‘dial’ of our climate can have big impacts. So, even in a month where on the big picture it looks almost unchanged, there are big changes if you know where to look.
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