Press release archive: 2010

ACCLIM project: Winters getting warmer clearly faster than summers

19.1.2010 12:00

Photo: Eija Vallinheimo

Global warming will bring about changes in the Finnish climate as well. The ACCLIM project of the Finnish Meteorological Institute and the University of Helsinki assessed how climate change will be reflected in the Finnish climate. This research project provided new information on climate extremes and estimated the pace of climate change.

The findings of the ACCLIM project predict that, owing to the advancing greenhouse effect, the warming in Finland will emerge relatively clearly from the background of natural climate variability within the next few decades.

Winters 3-9° C warmer
According to the results, it is highly likely that the mean temperature of the next full decade (2011-2020) in Finland will be higher than that of the baseline period 1971-2000. The probability of this is greater than 95 per cent. By the end of the century, Finland's mean annual temperature is predicted to rise by 2-6° C. During the last decades of the century, winters will be 3-9° C and summers 1-5° C warmer. Assuming that the actual warming falls close to the midpoint of these projections, by the end of the century the climate in central Lapland will be similar to that in present-day southern Finland.

Even in the short term, winter temperatures are likely to rise more than summer temperatures, although natural temperature variations are also especially marked in winter. Climate change means that cold winters will become increasingly rare. As mean temperatures rise, the number of frost days will decrease and the thermal growing season will become longer. Temperature variations will even out in winter, which means that the warming effect will be greater in the lowest temperatures than in the mean temperature. It seems that thermal winter (when average daily mean temperature remains below 0° C) would disappear completely in southern and southwestern coastal areas by the end of this century. According to model simulations, thermal winter would also shorten by one to two months in Lapland. Winters will become cloudier and less snowy.

Very cold temperatures rarer
Warming has so far been fairly slight when seen against the wide year-to-year variation of temperatures in Finland. However, even a small temperature rise affects the occurrence of record-high temperatures. For instance in 2008, the winter in southernmost Finland was milder than ever before in recorded history. If the observed rise in mean temperatures is ignored, equally mild winters could be expected to recur only once in 200 years. But if the climate change already evident is taken into account, the warmth of winter 2008 is no longer so exceptional: equally high temperatures would recur once every 35 years. With global warming, the probability of high extreme temperatures keeps rising while extreme cold temperatures become rarer.

The impact of the advancing greenhouse effect on precipitation will become more slowly discernible from the background of natural climate variability than changes in temperature. Both temperature and precipitation are projected to increase more in winter than in summer. According to the model results, days with precipitation (TAI: wet days) in winter will become more frequent, precipitation will increase in volume, and the longest periods of consecutive dry days will become shorter. Heavy precipitation will also become more common in summer.

Preparation requires reliable information
The ACCLIM project provided information on the current and future climate for the Climate Change Adaptation Research Programme (ISTO). The project surveyed the needs of climate data users and offered expert guidance on the application of climate data in research concerning the impacts of climate change and adaptation to it. Changes in the climate have many different impacts on the environment, the economy and on human living conditions. It is therefore important for social and political decision-making about the future that information on the past, present and future climate is available and grounded in the latest research. Information is needed on average values as well as on variation and extreme events.

Minimisation of adverse effects resulting from climate change, and utilisation of the opportunities created simultaneously, require controlled adaptation to circumstances that have already undergone changes and will change even more in the future. In the long term, the greatest sources of errors in climate projections stem from uncertainties associated with climate models and with trends in greenhouse gas emissions. The goal is to express the estimates concerning climate change and its impacts as probability distributions; this is also the goal in the continuation project ACCLIM II (Climate Change Survey and Expert Service for Adaptation Assessment), where the Finnish Meteorological Institute and the University of Helsinki are joined by the Finnish Environment Institute.

Additional information:

Finnish Meteorological Institute, Senior Researcher Kirsti Jylhä, tel. +358 9 1929 4125, kirsti.jylha@fmi.fi
University of Helsinki, University Lecturer Jouni Räisänen, tel. +358 9 191 50872, jouni.raisanen@helsinki.fi

The report is available here

ISTO Research Programme