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Earth climate in geological past was changing due to natural processes: planet orbital changes, changes in atmospheric gas composition, tectonic movement of continents, changes in sun and volcanic activity. Variations observed during last 200 years are specific, because they have been caused by human activities. After the industrial revolution, humankind started to influence gas composition of the atmosphere and enhanced the greenhouse effect. Anthropogenic gas, which accumulates in atmosphere is transparent for incoming solar radiation, but is impenetrable for long-wave radiation coming from Earths surface. In unaltered natural system additional heat would be radiated to the space, but now it is trapped in the atmosphere. Main human activities which cause anthropogenic gas emissions are: deforestation, urbanization, extensive and intensive agriculture, transport. Deforestation and land cover changes have impact not only on the gas composition, but also on planet's albedo. Due to permanent growth of industry, agriculture and transport, more and more greenhouse gases are emitted every year.
Impact of climate change: sea level rise, changes in vegetation, changes in precipitation patterns, increasing aridness in some areas and more frequent floods in other. More severe meteorological phenomena are observed around the globe: more frequent and more intense tropical cyclones, tornadoes, thunderstorms, cold and heat waves, etc.
Air temperature observations in Lithuania started in 1770 in Vilnius University. More than 240 years of observations gives a good insight into natural and anthropogenic causes of climate variability. Rapid increase in average annual temperature in Vilnius is observed in last 30 years (Fig. 1).
Fig 1. Average annual temperature in Vilnius, 1778-2010
Average annual temperature, compared with the beginning of 20th century, has increased 0.7-0.9 °C. Which leads to more frequent droughts (for example 1992, 1994, 2002, 2006 summer seasons). Changes in precipitation patterns are not homogenous – in some parts of Lithuania it is increasing, in other – decreasing. However, these changes are not very significant. There is an observed tendency of precipitation increase during cold season and decrease during warm season. Liquid precipitation is becoming more frequent in cold season.
Climate predictions for 21st century are based on outputs from numerical climate models. Having in mind that recent climate change is caused by human activities, future climate projections are made according to the scenarios of social-economical development. They reflect the human population, economical growth and the greenhouse gas emissions caused by this development.
In Lithuania (Vilnius University) climate predictions are made by downscaling COSMO-CLM, HadCM3, ECHAM5 models output data. According to the modelling results, average maximum and minimal temperature in 21st century in Lithuania should increase. Highest changes are predicted during cold season. In Vilnius, average maximum and minimum temperature could increase by 4 °C in year 2100 (Fig. 2). During different months, however, this increase could be up to 7 °C.
Fig. 2. Prediction of average annual maximum temperature (°C) in Vilnius and Klaipėda in 21st century. Projections are made by different emission scenarios.
In 21st century heat waves (days when maximum temperature ≥ 30 °C) will become more frequent. In 2061-2100 there could be 7 heat wave days per year more compared to 1971-2000. On the Baltic Sea coast severe heat waves will not be so frequent (increase could be only 1-2 days). Highest increase is expected in July. Cold spells, on the contrary, will become less frequent with most significant changes in January. Modelling experiments suggest that at the end of 21st century cold spells (days when minimal temperature ≤ -15 °C) will occur only during January-February. In 2061-2100 these events will not last longer when 2 days in Vilnius, and 1 day in Klaipėda.
In 21st century sunshine hours will increase during August – October, and will decrease during rest of the year. This will be caused by the higher cyclonic activity during cold season.
Fig. 3. Projections of precipitation amount and rainy days in 21st century in Klaipėda, from CCLM model output data (A1B and B1 emission scenarios).
Studies made in Lithuania suggest that biggest changes in precipitation patterns will be during winter season and will not be so explicit in summer. Precipitation can double in Klaipėda – by the end of century precipitation amount can increase 16-22% compared to the end of 20th century. In Vilnius changes will be not so significant – projected increase is about 9-10 %. Severe thundershowers will be more frequent on the coast (> 30 %) and in Žemaitija uphills.
Changes in temperature and precipitation patterns will affect different economical activities and natural ecosystems. Coastal region is one of the most vulnerable regions in Lithuania. Lithuanian coast is in the south-eastern region of Baltic Sea which will undergo biggest changes in 21st century, due to the sink of terrain and sea level rise. Pessimistic scenario suggests that water level in this region can rise by 0,5-1,0 m. In that case, there would be high risk of flooding urban areas in Klaipėda and Palanga. Also wind surge could disturb the port activities in Klaipėda more frequently. To avoid negative impacts on social-economical activities, the existing infrastructure should be improved to adapt to the sea level rise.
Fig 4. Average annual sea water level in Klaipėda, 1898-2010.
To reduce the impacts of climate extremes it is important to issue timely warnings for the public. Daily meteorological and hydrological observations and forecasts become more and more valuable. With technical improvements should come social and behavioural changes, that society would be capable to adapt and take responsibility for the climate actions.
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