The durations of the thermal seasons and the growing season till the
end of this century are inferred from projected monthly mean
temperatures, separately for the SRES A2 and B1 scenarios. For the
baseline period 1971-2000, we use a high-resolution observational data
set covering Finland, and an average of the temperature responses
simulated by 19 global climate models is added to the observed
temperatures to obtain projections for the future. Daily
climatological temperatures, needed for determination of the onset and
end dates of the seasons and the effective temperature sum, are
derived from the monthly means employing a Fourier algorithm that can
reproduce monthly mean temperatures perfectly.

Under baseline conditions, there are four thermal seasons everywhere
in Finland apart from the elevated area in north-western Lapland.
Under the A2 scenario, thermal winter will disappear in the
southwestern part of the country by the period 2070-2099. Elsewhere
winter shortens by 2-4 months. Summer lengthens by slightly over one
month. Intermediate seasons become longer everywhere except in
northernmost Lapland. The thermal growing season lengthens in inland
areas by 40-50 days, on the southwestern coast even more. The
effective temperature sum doubles in the north and increases 1.5-fold
in the south. Conditions in Lapland would thus resemble those
currently prevailing in southern Finland. Under the B1 scenario the
change is smaller, especially in the second half of the century.

The robustness of the findings was assessed by considering the
differences between the temperature change projections of the various
models. The uncertainty in the onset and termination dates was
typically of the order of $\pm$ two weeks. Regional downscaling
based on RCM data did not alter the main conclusions.

Last Updated: 2011-02-18