Thinner layer of soil frost

As the climate gets warmer, the soil does not freeze as deep as it does now. In the southwestern archipelago soil frost will disappear almost completely in ordinary winters.

As the climate gets warmer, the soil does not freeze as deep as it does now

The figure shows what the percentage decrease of soil frost will be without snow cover if warming complies with the average estimates given by models. The change is more distinct in the south than in the north. In Lapland, soil frost will be approximately one quarter less by mid-century, and towards the end of the century, as much as 30-40% less. Inland areas in southern Finland will see less than one half of the depth of soil frost we have now. In the southwest archipelago, there would be no soil frost at all at most times.[1][2]

In future, too, the depth of soil frost will vary year on year, depending on the amount of subzero temperatures each winter. The maps on the figure show the situation for a winter with typical temperatures. Coldest winters would see the top soil freeze in future even in the outer archipelago.

Model results differ

The calculation shown is based on the average rise in temperature that models predict, and it is also the mean for three greenhouse gas scenarios. In reality, both different greenhouse gas scenarios and simulations of models differ, which makes the results uncertain.

Depth of soil frost depends on snow cover depth, too

The calculation now given only applies to areas without snow, e.g. airports and main roads. In these areas, the greatest depth of soil frost in winter depends on the soil type and the frost sum.

It is not possible to deduce on the basis of the figure how deep soil frost is for instance in fields and forests. There, snow cover acts as an efficient thermal insulation. Therefore, the soil does not freeze as deep as in areas where the snow is cleared away. 

Predicted thinning of soil frost in snow-free areas

Predicted thinning of soil frost in snow-free areas (per cent) for an ordinary winter. The figure to the left is based on rise in temperatures predicted by models in 2040-2069. The figure to the right shows the situation for 2070-2099. For both, the reference period is 1971-2000.

References

  1. Jylhä, K., Ruosteenoja, K., Räisänen, J., Venäläinen, A., Ruokolainen, L., Saku, S. ja Seitola, T., Arvioita Suomen muuttuvasta ilmastosta sopeutumistutkimuksia varten, ACCLIM-hankkeen raportti 2009. https://helda.helsinki.fi/bitstream/handle/10138/15711/2009nro4.pdf?sequence=1
  2. ACCLIM II-hankkeen lyhyt loppuraportti http://ilmatieteenlaitos.fi/c/document_library/get_file?uuid=f72ce783-0bae-4468-b67e-8e280bec1452&groupId=30106

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