AMAZON
Tropical forests not only act as vital carbon sinks but also regulate interactions between the earth and the atmosphere, thus playing a crucial role in regional and global climate.REUTERS

Clearing of trees in tropical rainforests not only increases carbon dioxide in the air but also affects rainfall patterns and raises temperatures across the globe, says a study showing that forests have many impacts on climate.

This in turn could adversely affect agricultural productivity.

A complete tropical deforestation could lead to a rise in global temperature of 0.7 degrees Celsius (on top of the impact from greenhouse gases).

The study from the University of Virginia in collaboration with Climate Focus provides evidence that tropical deforestation is already affecting local and regional climates.

Thailand, for instance, is experiencing less rainfall due to deforestation and in parts of the Amazon, the rainfall pattern has shifted.

Deforestation would lead to a reduction in rainfall between 10-15% in the region surrounding the area where the deforestation took place.

Much like the 'butterfly effect' in chaos theory which predicts the sensitivity of a dynamical system wherein the flutter of the insect's wings in Brazil can set off a storm in Texas, the present study says that deforestation in South America, Southeast Asia and Africa may alter agriculture as far away as the US Midwest, Europe and China, besides the tropics.

"Tropical deforestation delivers a double whammy to the climate—and to farmers," said Deborah Lawrence, Professor of Environmental Sciences at the University of Virginia, the study's lead author.

The report, 'Effects of Tropical Deforestation on Climate Change and Agriculture,' is published in Nature Climate Change.

Role of forests

Tropical forests not only act as vital carbon sinks (or lungs) that take in carbon dioxide but also regulate interactions between the earth and the atmosphere. They move more water than any other ecosystem on land.

Because forests turn water from soil into moisture in the air, they cool the atmosphere above them when the water evaporates. They are central to the process of generating and regenerating moisture, so clearing these forests leads to a drying and warming effect.

"Tropical forests are often talked about as the 'lungs of the earth,' but they're more like the sweat glands," said Lawrence. "They give off a lot of moisture, which helps keep the planet cool. That crucial function is lost – and even reversed – when forests are destroyed."

An increase in temperature in the tropics due to deforestation generates large upward-moving air masses. When these hit the upper atmosphere they cause ripples, or teleconnections, that flow outward in various directions and impact climate globally.

Models studied in the report show that in the Amazon and, possibly, in the Congo Basin, 30-50% may be the deforestation tipping point that affects rainfall dramatically.

Studies indicate 29% deforestation rates in the Amazon in the period between 2012-2013.

Regional scale models project that in the Amazon Basin, clearing 40% of the forest would decrease wet-season rainfall by 12% and dry-season rainfall by 21%. It would also reduce by 4% rainfall in the Rio de la Plata Basin, miles south of the Amazon where soy, corn and wheat are grown.