Climate change Finland
Present climate of Finland
The mean annual temperature is about 5.5°C in southwestern Finland, decreasing towards the northeast. The 0°C mean limit runs slightly to the south of the Arctic Circle. Temperature differences between regions are the greatest in January, when the difference between southern and northern Finland is on average about 12°C. In June and July it is only about 5°C (21).
The mean precipitation in southern and central Finland is between 600 and 750 mm, except on the coast where it is slightly lower. In northern Finland the annual precipitation is 550–650 mm. The seasonal variation in precipitation is similar throughout the country, the driest month being March. From then on, precipitation gradually
increases until July and August, or until September and October on the coast, after which it decreases towards the winter and spring. The lowest annual precipitation recorded is less than 300 mm in northern Finland (21).
Even in southern Finland, some 30% of the annual precipitation is in the form of snow, which remains on the ground for about four months. In Lapland 50–70% of the annual precipitation is snow and remains 6–7 months on the ground (21).
Air temperature changes until now
According to linear trend tests, the mean temperature in Finland increased by 0.76°C in the 20th century. The warming took place during the first two and last three decades of the century, while a slight but statistically insignificant cooling occurred in the time period between them. There was also some evidence of warming in the late 19th century, but the number of observation stations was too small for a reliable analysis (1).
An analysis of the observations indicates that in spring and summer temperature rise was 1,4 and 0,7⁰C/100 year (95% significant), respectively. No trend was found for autumn and winter. It cannot be excluded that these trends are due to the large natural climate variability at regional scales (2). A more recent study shows that mean temperature in Finland significantly (p<0.05) increased during the period 1961–2011, by an estimated 0.4 ± 0.2∘C per decade for the whole year, by 0.4 ± 0.2∘C per decade for the spring and by 0.3 ± 0.2 ∘C per decade for the summer (28).
The mean temperature in March-May over the whole country was 1.8°C higher in 1963–2002 than in 1847–1876. The diurnal temperature variation had become smaller, again mainly in spring. A similar trend has been observed widely on the land areas of the Northern Hemisphere, together with an increase of cloudiness (1).
The warmest year on record was 1938, when the average over the whole country was 2.4°C higher than the mean for the reference period of 1961–1990. The second warmest year was 1989 and the third warmest 2000 (until 2006). By far the coldest was 1867, the year of the great famine, with the nationwide average 3.4°C below the reference period (1).
Since winter 1989, nearly all winters have been warmer than the 20th century average. The culmination occurred in winter 2007, which was the warmest measured since the beginning of the 20th century. Temperature records were also broken in 2008, which was the warmest year ever measured in southern part of Finland. For the country as a whole it was the sixth warmest year (21).
The major climate changes observed in the Baltic Sea region during the late 20th century can be related to changes in atmospheric circulation (1). It is suggested that the increased frequency of anti-cyclonic circulation and westerly wind types have resulted in a slightly warmer climate with reduced seasonal amplitude and reduced ice cover (3). Recent research using tree-ring based chronologies indicates that the variability of recent decades may lie within the natural range (4).
Precipitation changes until now
The mean precipitation in southern and central Finland is between 600 and 750 mm, except on the coast where the rainfall is slightly lower, particularly in Ostrobothnia. In northern Finland, the annual amount is 550–650 mm. The seasonal variation in precipitation is similar throughout the country, the driest month being March. From then on, precipitation gradually increases until July and August, or until September and October on the coast, after which it decreases towards winter and spring. The lowest annual precipitation may be less than 300 mm in northern Finland, while the maximum annual value elsewhere sometimes exceeds 900 mm. The highest daily rainfall recorded is almost 200 mm, but values in excess of 50 mm are rare. Except in coastal regions, over half of the days have some rain in an average year (1).
Even in southern Finland, some 30% of the annual precipitation is in the form of snow, which remains on the ground for about four months. In Lapland, the corresponding figures are 50–70% and 6–7 months. The lakes freeze over in October in Lapland and early December in southern Finland. In severe winters, the Baltic Sea may ice over nearly completely, but in mild winters it remains open except for the Gulf of Bothnia and the eastern part of the Gulf of Finland (1).
From an analysis of a dataset for 165 stations, it was concluded that annual precipitation in Finland has increased by 0.92 ± 0.50 mm/year during the period 1911–2011. According to this analysis, precipitation has increased in this period in winter by 0.46 ± 0.19 mm/year and in summer by 0.32 ± 0.29 mm/year, while no clear trend was found for spring and autumn precipitation (25). It is reported, however, that precipitation has been increasing in southern and central Finland, and also in the north in winter, during the period 1911-2000 (5). Increasing annual precipitation trends were observed for regions in Norway (6), for Sweden (7) and for an average of all land areas between latitudes of 55 ⁰N and 85 ⁰N (8).
The wettest year in Finland was 1974, with a nation-wide mean of 740 mm, while the driest was 1941, with only 394 mm. In addition to significant year-to-year variation, the precipitation climate of Finland is also characterised by notable interdecadal variability, which partly offsets the statistical detection of trends (1).
As to snow conditions, however, there is fairly strong evidence that the maximum snow storage has increased in eastern and northern Finland since the late 1980s, while in southern and western parts of the country the snow accumulation has decreased (1).
A recent decrease in the duration of snow cover and its water equivalent has been observed in the southern parts of all Fennoscandian countries, while the opposite trend prevails in the north. In the Scandic mountains, the increase in precipitation has overshadowed increases in temperature in the past two decades, and the snow cover has become thicker. In Finland, increasing temperatures have intensified the wintertime snow melt in the western and southern parts of the country towards the end of the period 1946–2001, in contrast to eastern and northern Finland, where the maximum snow storage has increased. A similar distribution is evident in Sweden, where there is more snow in the north and the snow cover has become thinner in the southern part of the country (9).
It is widely thought that the impacts of climate change would be more severe in the Arctic than elsewhere in the world. In Finnish Lapland, the observed climatic changes have been relatively small thus far, unlike in many regions in Canada and Siberia. Exceptional snow conditions have, however, occurred; record late arrival of snow in some years, but record high accumulations in late winter in others.
Ice cover changes rivers and lakes until now
The mean duration of ice cover in the south is normally about 140 days, in central Finland mainly 150 to 180 days, in the southern part of northern Finland 180 to 200 days and in Lapland 200 to 220 days (10).
Changes in the duration of ice cover have been reported (10). The longest ice breakup series in Finland started in spring 1693 (river Tornionjoki) and freezing and breakup records are available at least since the mid 19th century from three lakes Kallavesi, Näsijärvi and Oulujärvi. The number of time series starting in the late 19th century amounts to at least twenty. Ice break-up in Finland has also become significantly earlier from the late 19th century to the present time, except in the very north (18).
The analysis of these ice observations clearly showed that there is a statistically significant change towards earlier ice breakup in Finland, from the late 19th century to the present time. There is also a significant trend towards later freezing in the longest series and thus also towards a shorter ice cover duration. The correlations for breakup dates were better than for freezing dates, because the depth of a lake affects the freezing date but not the breakup date.In the series that started in the late 19th century, the ice breakup has moved generally 6 to 9 days earlier over one hundred years. The freezing has been delayed since the late 19th century, in most cases by 5 to 8 days per hundred years (10).
The duration of ice cover has decreased from the late 19th century to the 1920s. Of course, there is considerable variation from year to year. From the 1930s to the early 1950s ice cover periods were generally shorter than in the 1920s or late 1950s, especially in southern and central Finland. From the late 1950s to the present time ice cover period have decreased slowly. The decreasing trend has been stronger in the south (10).
The series of maximum thickness of ice showed both decreasing and increasing trends. These trends were statistically significant for approximately half of the observation sites. Decreasing maximum ice thickness trends were found in the southern part of the country and increasing trends in central and northern regions (10).
Results from an analysis of the inter-annual variability of ice conditions at a coastal site in the Gulf of Finland (Baltic Sea) during the period 1927–2012 showed a significant decrease of the ice season length, by almost 30 days (26). The maximum annual ice thickness decreased by 8 cm in the last 40 years. Surface water temperature increased by almost 1°C. Related studies from the Finnish coast have shown similar decrease, with higher rate after the 1980s (27).
Wind climate changes until now
Wind climate of Finland shows statistically significant (p < 0.05) negative trends over the past decades. The mean linear trend of the annual mean and maximum wind speed of 33 weather stations for the period of 1959-2015 were estimated to be -0.09 and -0.32 m/s/decade, respectively (30).
Air temperature changes in the 21st century
By the 2020s, according to four scenarios, the annual mean temperature is projected to rise by 1–3°C relative to the baseline period of 1961–1990, and by 2–5°C and 2–7°C by the 2050s and 2080s, respectively. The projected temperature trends are markedly stronger than those observed during the 20th century (1,2). More recently (2010), a projection of annual mean temperature increase for 2070–2099, compared with 1971–2000, has been reported of +3°C to +6°C (21) .
Summertime mean temperature is projected to increase by 1 to 5°C by the end of the century compared to the period 1971 to 2000 (24). It seems very likely that changes in mean climate are associated with changes in climate extremes as well (1). Changes in summertime extreme temperatures were assessed based on simulations from 17 global climate models (31). According to this study more than 45% of summer days will be ‘hot days’ (warmer than 20°C) in southern Finland in the future, compared with 24% under current conditions. The study further suggests that by the middle of the 21st century, on the average 1 day per summer will be extremely hot in southern Finland with daily mean temperature exceeding 28°C. This 28°C threshold was never exceeded in Finland in the reference period for this study 1979-2014.
If the projected alterations in the climate by the 2080s for the various emission scenarios are expressed simply by linear trends, the calculated mean change in temperature corresponds to a trend of 0.3-0.6°C per decade. This rate exceeds the observed trend during the past century by a factor of between four and nine (2).
Days with temperatures below 0ºC (frost days) will become less common. At the end of the century, Finland may have 40 to 80 frost days less than at present (11).
According to calculations based on a regional climate model and two different emission scenarios, wintertime average daily temperatures in the period 2071–2100 are simulated to increase with respect to the period 1961–1990 from 3° to more than 7ºC in east Europe and Russia depending on which emission scenario and which driving global model is used (19). The warming in the cold end of the temperature distribution is even larger. The strongest warming occurs on cold days.
The strong increase in wintertime temperature in east Europe and Russia is probably connected to the reduction of the snow cover in the scenario runs. The mechanisms involved are feedback processes involving temperature, snow cover and albedo. With decreasing snow cover the albedo becomes lower. The lower albedo implies that more shortwave radiation is absorbed in the ground which in turn leads to higher surface temperatures. The largest reduction of the length of the snow season is calculated to be in a zone reaching from central Scandinavia through southern Finland and the Baltic countries and further towards the southeast into Russia (20).
Precipitation changes in the 21st century
By the 2020s, according to four scenarios, the annual mean precipitation is projected to rise by 0–15% relative to the baseline period of 1961–1990, and by 0–30% and 5–40% by the 2050s and 2080s, respectively. Seasonally, the projected precipitation changes and their statistical significance are the largest in winter and the smallest in summer. It seems very likely that changes in mean climate are associated with changes in climate extremes as well (1,2). More recently (2010), a projection of annual precipitation increase for 2070–2099, compared with 1971–2000, has been reported of 10 to 25% (21) .
If the projected alterations in the climate by the 2080s for the various emission scenarios are expressed simply by linear trends, the calculated mean change in precipitation corresponds to a trend of 1-2% per decade (2).
The warmer atmosphere of the future may contain more humidity than at present, which will allow for increased heavy rain. According to climate models, the intensity of rain will increase in extensive areas, and torrential rain will become more common (11,21). The intensity of rain will increase also in the summer season. For example, the greatest daily accumulation of rain at the end of the century will increase by 10–20%, in some experiments by more than 30% (11).
The number of days with annual snow cover will decrease by 20–40% in the second half of the century when examining Finland as a whole (11). The period of snow cover in Northern Finland will shorten by more than one month due to warmer autumns and springs (12). Changes will be greater in Southern Finland, because a substantial amount of precipitation will be in the form of water also during winter months; the period of snow cover will be shortened by some two months, and snow depth in midwinter will reduce to about one-third of that at present (11).
As the winters become shorter, snowfall in autumn and spring months is reduced. In the middle of the winter, snowfall may increase in the coldest regions. Even in the areas where snowfall is projected to increase in the middle of the winter, the total annual snow- fall is generally projected to decrease, although the change is small in the coldest regions of northern Europe (29).
Wind climate changes in the 21st century
Model studies in the past gave no clear indication of changes in mean windiness (21). Recently, a study has been carried out where mean and extreme geostrophic wind speeds in Northern Europe were projected for the future periods 2046–2065 and 2081–2100, and compared with the baseline 1971–2000 (based on nine global climate models and the SRES A1B, A2 and B1 scenarios) (22). The geostrophic wind speed is a theoretical, calculated wind speed indicative of true surface wind speed. The results show:
- Mean wind geostrophic speeds: During the windiest time of the year, the monthly mean wind speeds will start to increase in the Baltic Sea already in 2046–2065. In Finland, increases are largest (5–7%) in November and January by 2081–2100. In November–February 2081–2100, a positive shift of 5–10% is projected to materialize in the Baltic Sea.
- Extreme geostrophic wind speeds: The extreme wind speeds (10-year return level estimates) will increase on average by 2–4% in the southern and eastern parts of Northern Europe, whereas a decrease of 2–6% dominates over the Norwegian Sea. These results agree with results on the future projections of 20-year return level estimates of gust winds that showed that the increase in winds is dominant in a zone stretching from northern parts of France over the Baltic Sea towards northeast (23).
Sea water temperature changes in the 21st century
The duration of ice cover in lakes will become shorter. It has already decreased by around ten days in Finnish lakes during the 20th century, like elsewhere in the Northern Hemisphere (13). In the latter half of next century, the middle parts of the largest lakes in southern Finland may even stay ice-free throughout the winter (1).
The maximum ice cover of the Baltic Sea in winter will decrease to 54–80% of the present, depending on the model and scenario (12). On the basis of climate simulations describing the end of the century, it is estimated (14) that the time of freezing will be postponed by less than one month in the northern part of the Gulf of Bothnia, and by approximately one month in the southern parts of the Finnish coast. The time of melting will be almost one month earlier than at present in the southwest, and several weeks earlier than at present in the northern part of the Gulf of Bothnia. Towards the end of the century, the duration of the ice-winter will have shortened to one-half of the present on the southwestern and southern coasts of Finland, and to 70–80% of the present in the Gulf of Bothnia.
Uncertainties in climate projections
The largest uncertainties in predicting the climate change in Finland during the first decades of the 21st century are related to the natural variations in temperature and precipitation, and to the limited ability of the global models to describe correctly the regional distribution of climate change. Further into the future, the projected changes increase and become statistically more significant (2).
Natural climatic variation and differences between the models cause an uncertainty range of slightly less than two degrees in the annual mean temperature change predictions for the period 2010–2039 (11).
Uncertainties in model results
The sources of uncertainty involved in climate change projection are: (1) uncertainties in future emissions of greenhouse gasses and aerosols, (2) inaccuracies in model formulation, (3) noise due to natural climate variability.
No single coupled model van be considered to be the best and, accordingly, the use of a range of coupled models is recommended (16).
In contrast to the annual temperature cycle, the models are unable to reproduce even qualitatively the annual cycle of precipitation. Models have problems in reproducing the observed atmospheric circulation. In addition, the coarse model resolution does not allow a detailed description of the Scandinavian mountains and the Baltic Sea, both factors probably contributing to errors in precipitation (2). … model shortcomings may have a more detrimental effect on the extremes than on the mean values (17).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Finland.
- Ministry of the Environment of Finland (2006)
- Jylhä et al. (2004)
- Omstedt et al. (2004)
- Esper et al. (2002), in: Omstedt et al. (2004)
- Hyvärinen (2003)
- Hanssen-Bauer and Førland (1998), in: Jylhä et al. (2004)
- Räisänen and Alexandersson (2003), in: Jylhä et al. (2004)
- Folland et al. (2001), in: Jylhä et al. (2004)
- HELCOM (2007)
- Korhonen (2006)
- Marttila et al.(2005)
- Räisänen et al. (2003), in: Marttila et al.(2005)
- Magnusson et al. (2000), in: Ministry of the Environment of Finland (2006)
- Räisänen et al. (2003), in: Marttila et al.(2005)
- Tuomenvirta et al. (2000b), in: Marttila et al.(2005)
- McAveney et al. (2001), in: Jylhä et al. (2004)
- Cubash et al. (2001), in: Jylhä et al. (2004)
- Korhonen (2006), in: EEA, JRC and WHO (2008)
- Räisänen et al. (2003), in: Kjellström (2004)
- Kjellström (2004)
- Ministry of the Environment and Statistics Finland (2009)
- Gregow et al. (2011)
- Nikulin et al. (2011), in: Gregow et al. (2011)
- Jylhä et al. (2009), in: Mäkelä et al. (2014)
- Irannezhad et al. (2014)
- Merkouriadi and Leppäranta (2014)
- Alenius et al. (2003); Leppäranta and Seinä (1985); Jevrejeva and Leppäranta (2002); Jevrejeva et al. (2004), all in: Merkouriadi and Leppäranta (2014)
- Irannezhad et al. (2015)
- Räisänen (2016)
- Laapas and Venäläinen (2017)
- Kim et al. (2018)