- A new modeling study finds that largely unrestricted “business-as-usual” Brazilian Amazon and Cerrado deforestation could result in the loss of an estimated 606,000 square kilometers of forest by 2050, leading to local temperature increases of up to 1.45 degrees Celsius, in addition to global rises in temperature.
- Under a Brazil Forest Code enforcement model, researchers predict deforestation would be limited to 79,000 square kilometers, with reforestation occurring over 110,000 square kilometers, leading to an average local increase of just 0.02 degrees Celsius.
- Researchers say loss of tree cover must be halted and reforestation program begun to protect people and wildlife, and curb regional warming.
- Reptiles and amphibians would be especially vulnerable to deforestation-triggered temperature rises and loss of humidity.
It is well known that the burning of fossil fuels and deforestation both lead to the emission of carbon dioxide, raising temperatures worldwide. Less well understood is how removing tree cover is contributing to increased temperatures at a local level – until now.
In a new study published in the open-access journal PLOS ONE, scientists from Brazil’s Rio de Janeiro State University and the University of California, Santa Cruz (UCSC), have found that the temperature increase in the immediate vicinity of a deforested area could be as much as 1.45 degrees Celsius (2.6 degrees Fahrenheit) by 2050 in tropical areas such as Brazil’s Amazon basin or in the Cerrado, the nation’s savanna biome.
“Everyone is familiar with how hot it is in cities compared to a forest environment, and this is because the energy is absorbed and then generates infrared radiation that heats up the environment. The same happens if you deforest,” explained study co-author Barry Sinervo of the UCSC Department of Ecology and Evolutionary Biology in a Mongabay interview.
The paper explores how the albedo effect (whereby lighter-colored surfaces reflect heat, while darker ones absorb it), and the loss of evapotranspiration (whereby water goes back into the atmosphere from land, trees and plants) can both lead to warming on a local scale within deforested tropical areas. By contrast, loss of vegetative cover in sub-Arctic boreal forests has little impact on local temperatures.
“We show that the heating in those [tropical] deforested habitats can have an effect at a very local scale,” Sinervo said. “And that means, even if you have an intact forest, it is getting hotter because of the deforestation that’s occurring around it.”
The researchers used newly released datasets on forest cover, evapotranspiration rates, sunlight reflection, and land surface temperatures to develop a model based on their interrelationships. They then determined what might happen heat-wise under predicted scenarios over the next 30 years.
The model showed that deforestation caused consistent local warming in tropical areas of 0.38 degrees Celsius (0.7 degrees Fahrenheit) between 2000 and 2010. Then the scientists looked at what might happen after that under two scenarios: a “business-as-usual” (BAU) scenario, which “assumes no effective control of deforestation in Brazil,” and under a scenario in which Brazil’s Forest Code is properly enforced, curbing native vegetation loss.
Under BAU, it is estimated that 606,000 square kilometers (234,000 square miles) of forest could be lost by 2050, leading to local temperature increases of up to 1.45 degrees Celsius (2.6 degrees Fahrenheit), with an average increase of 0.11 degrees Celsius (0.2 degrees Fahrenheit).
Under the Brazil Forest Code scenario, researchers predict deforestation would be limited to 79,000 square kilometers (31,000 square miles) by 2050, with reforestation occurring over 110,000 square kilometers (42,000 square miles), leading to an average local increase of just 0.02 degrees Celsius (0.036 degrees Fahrenheit).
Sinervo told Mongabay that future temperature rises could be even higher than predicted in their paper. “We only did calculations on the basis of 50 percent deforestation versus the Forest Code,” he said. “If you make it even worse (75 percent deforestation) – though this isn’t in the paper – I did some rough and ready calculations, you get a 2 degree Celsius [3.6 degrees Fahrenheit]” increase locally.
Sinervo pointed out that this is on top of predicted global temperature increases of up to 2 degrees Celsius. “That makes two + two, which is 4 degrees Celsius [7.2 degrees Fahrenheit] warming from [global] climate change and [local] deforestation [together], and that is a horrific set of numbers to take in.”
The paper makes it clear that large local temperature increases could escalate human mortality rates, along with demand for electricity, while reducing agricultural yields and biodiversity.
Guarino Colli, a zoologist at the University of Brasilia studying lizard populations in the Cerrado, told Mongabay that reptiles are especially sensitive to changes in temperature because they do not produce their own heat through metabolism, and also because the sex of the young in some groups – freshwater turtles and crocodiles, most notably – is dependent on incubation temperature.
If local temperatures rise steeply, especially at midday, he explained, many tropical reptiles will have reduced time available when they can forage, mate and reproduce.
“Most people think [animals] will overheat and die, but the impact is more subtle,” he said. “[Rather] it’s a reduced activity period, but that can have profound consequences in terms of reproductive success and recruitment.”
Colli postulated that this heat effect might be replicated in other taxonomic groups, such as insects, which are less well studied. “What we are talking about with lizards is just a snapshot of what might happen to entire communities,” he said.
There is evidence of local lizard populations disappearing as a result of rising temperatures in Mexico. A paper published by Sinervo and his colleagues in Science in 2010 found that 12 percent of 200 local spiny lizard populations had ceased to be, and the researchers were able to demonstrate their loss was due to rising temperatures.
Amphibians are also especially sensitive to temperature increases and other changes to climate such as humidity, according to Denis Otavio Vieira de Andrade, who is collaborating with Sinervo at UCSC. “In the case of amphibians, they are quite constrained by humidity because they have very permeable skins,” de Andrade said. “If you reduce the humidity, they lose more water through their skin, which can cause dehydration and compromise them even more.”
Whether, and how many, species might go extinct due to local temperature rises, and changes in humidity, in the Amazon, the Cerrado and other tropical environments remains to be seen.
Colli pointed out that, Brazil, with its current Forest Code, has a strong environmental law: “In Amazonia, under the code, you can’t [ever] cut more than 80 percent [of native vegetation on private lands, and that permitted percentage is often significantly less], and if that were observed, we would have a much better [environmental] situation,” he said. “The PLOS ONE paper shows a figure for business-as-usual versus the Forest Code, but the Forest Code [model] should be business-as-usual because that’s what the law says.” However, what the new rightest Bolsonaro administration position toward the Forest Code will be remains in question; the government has already announced major environmental deregulation.
Sinervo said that an active reforestation program is crucial to off-setting the impacts of global temperature increases. It’s estimated that there are 20 million square kilometers (7.7 million square miles) of land available for reforesting worldwide, but current global commitments are only to restore 3.5 million square kilometers (1.4 million square miles) by 2030.
Forests once covered an estimated 40 percent of the Earth’s terrestrial surface, and we have lost about a quarter of that cover to date – bringing us down to about 30 percent forest cover today – with much of that loss occurring in the past 300 years. If forests are to be effectively utilized as a means of sequestering carbon and of keeping local temperatures down in the tropics, then the world must reverse its 3-century-long tree cutting trend.
Prevedello JA, Winck GR, Weber MM, Nichols E, Sinervo B (2019) Impacts of forestation and deforestation on local temperature across the globe. PLoS ONE 14(3): e0213368. https://doi.org/10.1371/journal.pone.0213368
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