Weather | Exceptionally warm autumns will increase – Researcher: “This is exactly what the climate science community has known about for decades”

Last the weekend already had time to resemble slightly more usual September weather. On Tuesday, however, the temperature will rise again, for example in southern Finland, to a summer-like 18 degrees.

A researcher at the Institute of Meteorology Mika Rantanen September of the current year has been exceptional by many measures. Temperature records have been broken in September at almost every weather station.

“I don’t remember the last time there was a month like this, when half a month was so mild compared to normal. We may have to go to January 2020, which was a wildly mild winter.”

According to Rantanen, September last year was already record warm in Finland. However, according to him, it was not expected that the same would happen again this year.

Rantanen according to, exceptional temperatures are always caused by extreme weather conditions.

The warmth of late summer and early autumn can be explained by the fact that there has been a strong high-pressure ridge in northwestern Russia, as a result of which warm air has flowed into Finland from the south.

On the other hand, it is more difficult to assess the factors influencing the formation of the big weather condition itself. After all, the climate is very chaotic, Rantanen reminds.

He has considered that the temperature of the Atlantic Ocean might have something to do with it. The North Atlantic has been about one degree warmer than usual both this year and last year.

“On the scale of the oceans, a deviation of even one degree can have a huge impact.”

It is possible that the warm Atlantic increases the probability that the early autumn will be warm in Northern Europe.

Rantanen also thinks the farmers have noticed the warm weather. In addition to the temperatures, the heat totals during the growing season have been record-breaking in almost the entire country.

The growing season is measured by the so-called heat sum.

The amount increases whenever the average daily temperature is above 5 degrees and there is no snow cover on the ground. The part that exceeds five degrees of the daily average temperature is therefore included in the sum. If the daily average temperature is, for example, 8, the heat total increases by 3 degrees.

According to Rantanen, for example, the heat total in Sodankylä was already 1,300 degree days, which would be the usual amount in the Päijät-Häme area, i.e. about 500 kilometers further south.

“In the south, the growing season can continue until mid-October. In Kumpula, 1,800 degree days were exceeded, which is currently the third largest in the measurement history.”

Warm and a long summer enables a longer growing season, but at the same time increases the number of pests. According to Rantanen, for example, letterpress destructions can be big this year.

The bookworm is a bark beetle that especially destroys spruce trees.

“The beetles are able to raise several generations if it’s a long and warm summer.”

In addition, a warm September can also be seen, for example, in the Baltic Sea.

According to Rantanen, the sea water in the Gulf of Finland is still 17 degrees, which would be normal for early August. At this time of year, the seawater temperature should be around 12 degrees.

“Although the Baltic Sea is shallow, it does get cold quickly.”

Although September has indeed been exceptionally warm, Rantanen is not particularly surprised as a researcher. The development still worries him.

“This is exactly what the entire climate science community has known for decades, that climate change will bring. It’s always surprising.”

According to climate forecasts, winters in Finland will warm faster than summers this century. According to Rantanen, exceptionally warm autumns will therefore increase.

“Summer is getting longer on both ends. For example, in Sodankylä this year, the summer was the second longest in the history of measurements.”