Deforestation Has Driven Up Hottest Day Temperatures, Study Says

The average hottest day of the year in Europe, North America and Asia has been made significantly more intense as a result of deforestation since the start of the industrial revolution, a study finds.

Photo-illustration: Pixabay

The research considers the dual impact that deforestation has on the climate: first, that clearing forests releases CO2 into the atmosphere where it contributes to rising global temperatures; and second, the large impact it can have on physical processes in the local climate—which can have a net warming or cooling effect more widely.

The combined impact of deforestation has been so large in some areas that, until around 1980, it played a greater role in hottest day temperature rise than greenhouse gas emissions, the lead author told Carbon Brief.

The findings suggest that replanting trees—via afforestation or reforestation—could be a way of shielding against further increases in hottest day temperatures, the author added.

The new study, published in Nature Climate Change, estimates how deforestation from the start of the industrial era to recent times has affected temperatures on the hottest day of the year for a range of countries.

Deforestation is a key contributor to human-caused climate change. When forests are cleared or burnt, they release the carbon they store. Removing trees also diminishes an important carbon “sink” that takes up CO2 from the atmosphere.

Since 1990, around 129m hectares of forest—an area roughly the size of South Africa—have been chopped down by humans. Deforestation, along with other types of land use change, accounts for close to 11 percent of annual global CO2 emissions. From 1861-2000, deforestation accounted for 30 percent of CO2 emissions, according to the new research.

Deforestation can also affect temperatures through its effect on a range of different physical processes. These effects occur at local and regional scales, but can have global repercussions.

One such process is evapotranspiration, a term describing the exchange of water between the land and the atmosphere.

As part of this process, forests absorb water from the soil through their roots and later release it into the air as moisture, which has a cooling effect on the air above. When trees are cut down, this cooling effect disappears.

When these physical processes are considered alongside the impacts of carbon release, it is possible to deduce that deforestation has played a “significant” role in driving up hottest day temperatures, says lead author Dr. Quentin Lejeune. Lejeune is currently a research associate at Climate Analytics, a not-for-profit climate science and policy institute based in Berlin. He told Carbon Brief:

“During the industrial period, many areas over the mid-latitudes—especially in North America, the current Eastern Europe and Russia—experienced high rates of deforestation. We found that this led to significant local increases in daytime temperature during hot days.”

Source: Eco Watch