From the Cliff High Volume Weather Blog
There’s been a lot of talk about the short-term heatwave in Europe with some suggesting that the record warmth is a result of climate change/global warming.
Several media and climate advocates have been at the forefront of their statements (see below), stating that the event is the result of human-caused global warming.
The situation is very similar to the Northwest heat wave of last summer; with many of the same elements.
A short but dramatic heat event
As noted in the media, some locations have broken all-time temperature records, with some locations in the UK reaching 40°C (104°F). The map below shows the record-breaking locations on July 18, with x’s showing position surpassing the all-time record high.
In some locations, previous all-time highs were broken by a few degrees, as illustrated by this graph of central England temperatures (shown below). The blue line is this year’s temperature, the black line is the average, and the pink line shows previous daily records.
This week’s high for central England is absolutely unparalleled, especially in terms of its deviation from the previous record high. It is also important to note that the heat wave is very short-lived.
In many ways, the event resembles last year’s heatwave in the Northwest, with previous records completely broken.
Ironically, such an extremely unusual event is an indication that global warming played a very small role in the event. This reflects
The golden rule of extreme climates:
The more extreme a climate or weather record is, the greater the contribution of natural variability and the smaller the contribution of anthropogenic global warming.
Let me demonstrate how to apply the “Golden Rule” in this event.
Background heating
Europe and the UK have warmed over the past decades, and part of that can be attributed to an increase in greenhouse gases like CO2. To illustrate, below are the long-term changes in maximum summer temperatures in the UK from the UK Met Office.
Average maximum temperatures tended to generally be very little from 1890 to about 1970 and then warmed by about 1 C (about 2 F) over the past 50 years.
I can show you similar charts of other locations in Europe, all showing a warming of about 1-1.5C.
Let’s assume ALL this warming is due to an increase in CO2 and other greenhouse gases. Let’s further assume that none of this is due to urbanization or changes in instrumentation (which can also produce warmer temperatures).
The background temperature of about 1°C is totally short equal to the magnitude of the heat wave, where the maximum temperature is 20C higher than normal (as shown in the figure above).
So why are the temperatures so extreme this week?
It is caused by the development of a large peak of high pressure, the so-called ridge, which produces warming by sinking and moving air northward on its western slope.
This is the upper (pressure level 500 hPa, about 18,000 ft) at 5 p.m. PDT on July 17. The ridge (high altitude or pressure) is indicated in red-orange. Note that there is a depression (in blue) to the southwest of it. This feature increases southward flow bringing in warmer air.
Now a shock. Below is the same chart for the major heatwave in the Northwest.
OH MY GOD! Very similar, including low to southwest!
Such a low center, by increasing southward flow moving into the high pressure area, acts as a booster for warmth.
High amplitude, wave patterns are probably produced by natural variability and there is no evidence that the mountains in question are the result of global warming.
Ironically, such a pattern also produces enhanced cooling in the east and west, something represented by temperature anomalies (differences from normal) six hours later. (red/brown above normal, blue below normal).
It should be noted that major heat waves frequently hit Europe, such as in 2003 and 1976.
The bottom line is that the recent European heatwave was caused by an amplification of the northern hemisphere wave pattern, with global warming perhaps contributing 5-10% of the warmth. The natural variability of the atmosphere is the closest cause of warming and not an existential threat to the population of Europe.
Related
