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| Ranesvare nature reserve, Jokkmokk/Gällivare – Photo: Frédéric Forsmark/Länsstyrelsen i Norrbottens län |
Forests influence the climate in a number of ways aside from carbon dioxide flux.
- Albedo (”whiteness”) is the fraction of sunlight that is reflected from the surface of the earth. If it is zero, all sunlight is absorbed, for instance in a dark forest. If the albedo is one, all light is reflected back into space. White surfaces like clouds, ice or snow reflect sunshine and effectively cool the earth (although clouds also contain heat below them).
- Evaporation of water. Forests have a complex impact on weather and climate through evaporation from leaves, contributing to cloud formation. Water vapor is a greenhouse gas, but clouds also have higher albedo.
- Water is buffered in forests and released slowly (if there are no ditches) to the surrounding area, cooling the climate locally.
- Forests release a range of organic compounds and particles that influence climate and cloud formation often times in combination with salt particles.
Forests with broad-leaved trees have higher albedo than pine forests, because the leaves fall in winter and because the leaves are lighter in color than needles. So converting mixed forest to pine forest plantations is bad for the climate.
Some modelling studies predicted a cooling effect from deforestation at northern latitudes because clear-cuts have higher albedo than forest, in particular when there is snow on the ground. Authors do not recommend deforestation however, because functioning ecosystems are a crucial prerequisite for life on earth. An empirical study based on satellite measurements finds that clear-cuts heat the climate in tropical and temperate forests while the net effect is close to zero in boreal forests. Deforestation also contributes to larger local temperature variation between day and night, or summer and winter.
A study of forest bioenergy taking both carbon-flows and albedo into account found that bioenergy warms the climate more than fossil fuels in a time span of at least 50 years. Results depend on latitude, snow cover, which fossil fuel is considered (and to what extent) and what fraction of the trees is harvested.