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Destroying tropical forests alters Earth’s energy balance

An emerging body of research on the non-carbon impacts of deforestation reveals that destroying tropical forests significantly alters the Earth’s delicate energy balance, rainfall, and wind systems, leading to warmer and drier conditions near cleared forests and out-of-whack weather patterns across the globe, according to a new report by leading forest experts released at a major global forest gathering on Wednesday, June 27, 2018.

The Amazon rainforest

The research suggests these “new” impacts of deforestation, rooted in the flow of solar energy through forests across the upper atmosphere, disruptions to the atmosphere’s chemical cocktail, and dramatic declines in water cycling are just as damaging to the climate as the carbon released into the atmosphere when trees are cut down.

“We’ve known for a long time that chopping down tropical forests spews dangerous amounts of carbon into the atmosphere,” said Nancy Harris, Research Manager of the Forests programme at the World Resources Institute and working paper co-author. “Now we are learning that removing trees from the earth’s surface also throws off the energy, water and chemical balances that make it possible for us to grow food and live our lives in predictable and productive ways. If we continue to cut down trees, we’ll have to rewrite what we know about the weather – and we can forget about global goals to keep temperature rise below 1.5 degrees Celsius.”

The working paper, “Tropical Forests and Climate Change: The Latest Science,” is one of nine studies released on Wednesday at the opening of the two-day Oslo Tropical Forest Forum, an event hosted by the Norwegian government to celebrate results and identify remaining challenges 10 years after reducing emissions from deforestation and forest degradation (REDD+) was included in the climate change negotiations, and to advance strategies for mobilising forests to help achieve the ambitions of the Paris Agreement and the Sustainable Development Goals (SDGs).

The working paper synthesises findings from a slew of recent studies that, when they come together, conclude that large-scale forest loss in any of the three major tropical forest zones – Latin America, Southeast Asia and Central Africa – would lead to a rise in local temperatures, and disruptions to the water cycle locally and half a world away. These studies use sophisticated modelling to determine the physical, chemical and reflective impacts of removing forests from the surface of the earth enmasse, and satellites to measure the changes that have already happened. “When you add up these impacts of forest loss, one thing is clear: people living closest to deforested areas face a hotter, drier reality,” said Harris. “These changes won’t hit Brazilians, Indonesians, or Congolese sometime in the future – they are hitting them now, and they’ll only get worse as more forests disappear.”

Areas in the tropics that experienced deforestation in the last decade have seen significant and long-lasting increases in local air surface temperatures. “Observed local temperature impacts of deforestation are in one direction: hotter,” said Michael Wolosin, Forest Climate Analytics’ President and working paper co-author. “Daily average temperatures went up by a degree and maximum temperatures by 2 degrees C, in just a decade. Over the same period, the global carbon and GHG impact was less than one fifth as much – 0.2 degrees C. Deforestation is wreaking havoc on local climates across the tropics.”

The Amazon region of South America, home of the world’s largest rainforest, would feel the most heat and drought from forest loss. Complete deforestation would lead to regional warming of about two degrees Celsius and a roughly 15 percent drop in annual rainfall. Researchers have already linked the 2015 drought that hit Brazil, impacting people, crops and industry, to forest loss in the Amazon.

“In its focus on ending greenhouse gas emissions, the Paris Agreement only takes the first step in addressing the drastic consequences of deforestation on the climate,” said Wolosin. “If global and national policymakers fail to come up with an action plan for staving off the immediate and debilitating impact of deforestation on local and global weather patterns, they could put the lives of millions in peril. The question is, what’s more important – the short-term income generated from fields after fields of soy or palm oil, or a stable, predictable weather patterns for generations to come?”

Tropical forests drive the global movement of air, water, and heat in diverse ways, leading to profound impacts on the climate. Through the process of evapotranspiration, trees pump water from their roots through their leaves as water vapour, humidifying the air and causing surface cooling. Because forests have more leaf surface area and deeper roots than grasslands or croplands, they cycle more water. The water pumped through a single tree can cause local surface cooling equivalent to 70 kWh for every 100 litres, enough energy to power two household central air-conditioners per day. Removing these trees can lead to local flooding, soil erosion and droughts.

Impacts from these tropical forest cover changes on water and heat cycling extend well beyond the tropical regions themselves through “teleconnections”, associated with the mass movement of air and conditions in the upper atmosphere. 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, similar to the way an underwater earthquake can create a tsunami.

According to one landmark study about this phenomenon, complete deforestation could put the climate in some of the world’s most important agriculture regions off kilter. These variations in rainfall and spikes in temperature could occur across the world. For example, complete deforestation of the Amazon Basin would likely reduce rainfall in the US Midwest, Northwest and parts of the south during the agricultural season. The complete deforestation of Central Africa would likely cause declines in rainfall in the Gulf of Mexico and parts of the US Midwest and Northwest and increase it on the Arabian Peninsula. There could also be precipitation declines in Ukraine and Southern Europe.

“Halting deforestation, allowing damaged forests to grow back, and keeping undisturbed forests intact, are necessary to ensure the stability of the climate,” said Frances Seymour, Program Chair of the Oslo Tropical Forests Forum and lead author of “Why Forests? Why Now?” “Fortunately, we know a lot about ways to stop deforestation, but developing countries can’t do this alone. Donor countries should ramp up funding of efforts by tropical forest nations to halt deforestation, and address the global consumption, trade and investment patterns that drive forest loss.”

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