Forests, like other ecosystems, provide ‘ecosystem services’. These are services people need (such as pollination and flood control) and use, but often don’t realise we depend on. They provide us with essential services like the uptake and storage of carbon - reducing human’s impact on the climate. Now, new science is emerging on another ecosystem service provided by forests: Their influence on global weather patterns.
Forests are a vital part of the water cycle as they transfer water from the ground into the atmosphere (evapotranspiration), which eventually falls back to earth as rain. It’s been known for some time that deforestation weakens this cycle locally. However, it now appears that the influence of forests over rainfall and weather patterns is not just local, but extends to whole regions, and even globally. A new report by Greenpeace reviews studies on these indirect impacts of deforestation and their potential impact on agriculture.
Computer modelling studies indicate changes to weather patterns in places far away from the site of deforestation. For example,
- loss of forests in areas such as the Amazon and Central Africa is predicted to reduce rainfall in the US Midwest at times when water is crucial for agricultural productivity in these regions;
- predicted temperature increases in South America, Canada and Africa as a result of Asian deforestation could impact crop harvests and
- deforestation in Asia could lead to changes in the route storms take over Europe, whilst Amazon deforestation could increase annual rainfall in northern Europe.
This regulation of climate and rainfall might exhibit non-linear behaviour. That is, instead of a steady decline of forest influence on weather patterns with deforestation, there may be little or no noticeable effect for a period but then a sudden change when a “tipping point” is reached. This would be evident in abrupt changes in weather patterns.
We already know that deforestation destroys natural habitats and homes for biodiversity while emitting carbon dioxide into the atmosphere. It’s now evident that deforestation can also indirectly lead to impacts on global weather patterns. Although our understanding of the magnitude and extent to which deforestation affects regional and global weather patterns is incomplete, it is clear that deforestation is capable of altering weather patterns far from where the deforestation occurs.
Using the precautionary principle and conserving existing forest ecosystems under a “Zero Deforestation” footprint is the only way to ensure that forests continue to regulate our weather and climate, minimise the indirect effects of deforestation and conserve biodiversity.
Dr. Janet Cotter is a Senior Scientist at the Greenpeace International Science Unit.