Air temperature changes until now

Mean air temperature

During the last century, the mean annual temperature has increased by about 0,8-1,4°C (1).

Maximum and minimum temperature

Statistically significant increasing trends in maximum and minimum temperatures were detected for March, April, July, August and annual values over the period 1951–2010 in Lithuania, Latvia and Estonia. At the majority of stations in these countries, the increase was detected also in February and May in case of maximum temperature and in January and May in case of minimum temperature (10). In Rīga, the mean minimum temperature has increased by 0.20°C/decade during 1913–2006, while the mean maximum temperature has increased by 0.18°C/decade (11).

Changes in atmospheric circulation

Part of the major climate changes observed in the Baltic Sea region during the late 20th century can be related to changes in atmospheric circulation (2). It has been  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 (2). Recent research using tree-ring based chronologies indicates that the variability of recent decades may lie within the natural range (3).

Precipitation changes until now

Prevailing west flow provides the whole territory of Latvia with a sufficient amount of precipitation – on average 703 mm annually. The minimum amount of precipitation is in the period of February and March, when the mean monthly amount of precipitation is 26–39 mm (4).

Analyses of long-term precipitation series testify that in general the sums of precipitation in Latvia for the period of the past 50 years tend to increase. Months during which the amount of precipitation had maximum increase since 1950 are January, March and February. Whereas, trend of significant decrease in the precipitation amount in the annual period is identified only in September (4). Winter precipitation significantly increased by approximately 10 mm per decade at the large majority of precipitation stations in Lithuania, Latvia and Estonia during 1966 – 2015. In this period annual precipitation has generally increased, but the trend is mostly insignificant (12). 

In general, the length of snow cover period in Latvia during the past 50 years (period 1951 – 2000) has decreased (4,5).

Sea water temperature changes until now

For the winter period 1928/1929 to the winter period 1999/2000, dates of initial ice appearance on the coast of the Baltic Sea (Liepaja) tend to become earlier but in the Gulf of Riga (Salacgriva) – later. The dates of the start of ice moving in rivers tend to become earlier, therefore the start of high-water is earlier as well, which explains the increase of winter runoff in the rivers of Latvia (4).

Air temperature changes in the 21st century

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 (6). 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 (7).

Precipitation changes in the 21st century

Projections of climate change show a future decrease in mean annual maximum snow depth everywhere over Northern Europe. This decrease is smaller in the northern parts of the Baltic Sea basin than in the southern areas. The simulations also show a decrease in the duration of the snow season. In areas such as Denmark, Germany, Poland, and most parts of the Baltic countries, where the present-climate snow depth is small, the scenario simulations show a complete lack of snow cover (5).

Wind climate changes in the 21st century

Mean and extreme geostrophic wind speeds in Northern Europe have been 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) (8). 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 (9).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Latvia.

1. Lizuma (2000), in: Klavins et al. (2002)
2. According to Omstedt et al. (2004)
3. Esper et al. (2002), in: Omstedt et al. (2004)
4. Ministry of the Environment of the Republic of Latvia (2006)
5. HELCOM (2007)
6. Räisänen et al. (2003), in: Kjellström (2004)
7. Kjellström (2004)
8. Gregow et al. (2011)
9. Nikulin et al. (2011), in: Gregow et al. (2011)
10. Jaagus et al. (2014)
11. Lizuma et al. (2007), in: Jaagus et al. (2014)
12. Jaagus et al. (2018)