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How climate change has warmed Finland's winters since the 1960s

A comparison of two 30-year periods shows that winter temperatures have clearly risen all over Finland.

Clearing a track for distance skating on Jyväskylä's Lake Jyväsjärvi in January 2019. Image: Jarkko Riikonen / Yle

Last December was colder than usual. According to the Finnish Meteorological Institute (FMI), the month was unusually cold at a few coastal stations. December is only this cold about once every decade or so in Finland.

In the second week of January, mild föhn winds from the west brought a thaw. And last June was exceptionally hot, with the highest average temperatures ever recorded in parts of northern Finland.

Climate change is not measured by individual days, months or even years, though. According to the guidelines of the World Meteorological Organisation (WMO), climate statistics must be calculated from weather statistics stretching across at least 30 years.

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Finland's average annual temperature has risen by about two degrees since the 1880s. Image: Kalevi Rytkölä / Yle

The FMI also considers a three-decade period to be long enough to detect fundamental variations. With 2021 data still being analysed, its most recent reference period is 1991-2020. Each 30-year set of data includes about 2,700 days.

Statistics indicate that Finland's average annual temperature has risen by about two degrees from the 1880s to the present day.

1991-2020 significantly warmer than 1961-90

Yle meteorologist Anne Borgström has collected comparative data on Finnish winter temperatures over the past two 30-year periods – and the results are clear. The last period, 1991–2020, was significantly warmer than the 1961–1990 era.

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Pictures of Helsinki's Railway Square January 2013 and January 2020. Image: Sakari Kiuru, Anne Pietarinen

In Helsinki, for example, a study of the lowest temperatures between 1961 and 1990 shows that in those 30 years there were a total of 192 days with a low of between -12 and -14 degrees Celsius. During following period (1991-2020), the number of such days dropped to 103.

Meanwhile the number of days with a low around the freezing point was previously just over 300, but in the later 30-year period grew to well over 400. In other words, the number of mild days was much higher.

Jyväskylä, in central Finland, shows a similar trend as Helsinki. The number of days remaining above zero has increased dramatically. The number of days between zero and two degrees of temperature has increased by more than 100. While there were only 77 such days suitable for making snowballs in 1961-90, there were 182 in the next 30-year period.

Record-cold days in Finnish Lapland

In Oulu, northern Finland, there were plenty of cold days in the 1961–90 period. On 136 days, the low was between -24 and -26. In the most recent reference period, there were only 68 such days.

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A former FMI weather station in Vuotso village, Sodankylä, in March 2018. Image: huutokaupat.com

In Sodankylä, Finnish Lapland, winter temperatures between -6 and -8 are considered quite mild. The number of such days has risen from 134 to 227.

On the other hand, reference data from the past three decades in Sodankylä shows one bitterly cold day between -46 and -48 degrees and two days between -48 and -50 degrees. The material from 1961-90 does not include any such severe frosts.

As Borgström points out, climate change does not only bring milder weather, but also more extremes.