Clark College geographer believes that extra bushes do not all the time create a cooler planet – Watts Up With That?

Clark researchers discover that some US forests are contributing to global warming


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WORCESTER, Mass. – New research by Christopher A. Williams, environmental scientist and professor at Clark University’s Graduate School of Geography, shows that deforestation in the US does not always warm the planet as is commonly believed. instead, it actually cools the planet in some places. A peer-reviewed study by Williams and his team on “Climate Impacts of US Margin of Forest Loss from Net Warming to Net Cooling,” published today (February 12) in Science Advances. The team’s discovery has important implications for policy and management turning to forests to help curb climate change.

It is known that forests take up carbon dioxide from the air and store it in wood and soil, which slows down the accumulation of greenhouse gases in the atmosphere. However, this is not their only impact on the climate. Forests also tend to be darker than other surfaces, Professor Williams said, which causes them to absorb more sunlight and retain heat, a process known as the “albedo effect”.

“We found that in some parts of the country like Intermountain West, more forest actually makes a hotter planet when we consider the full climatic impact of both carbon and albedo effects,” said Professor Williams. It is important to consider the albedo effect of forests along with their known carbon storage in order to cool the planet, he adds.

The research was funded by two grants from NASA’s Carbon Monitoring System. Williams and his research team – consisting of data scientist Huan Gu, Ph.D. by The Climate Corporation and Tong Jiao, Ph.D. – found that for about a quarter of the country, forest loss causes persistent net cooling, as the albedo effect outweighs the carbon effect. They also discovered that the loss of forests east of the Mississippi and Pacific Coast states caused the planet to warm, while the loss of forests in the Intermountain and Rocky Mountain West tended to result in net cooling.

According to Professor Williams, scientists have known for some time that increasing forest cover cannot be expected to cool the planet or mitigate global warming. However, this has not always been widely recognized.

“If we ignore both carbon and albedo effects, large-scale tree-planting initiatives like Canada’s 2 Billion Trees Initiative and The Nature Conservancy’s Plant’s One Billion Trees campaign could result in trees being placed in locations that are counterproductive for cooling the air conditioning system, ”said Professor Williams.

“It’s about putting the right trees in the right place,” said Williams, “and studies like ours can help identify where the potential for cooling is greatest.”

Each year, approximately one million acres of forest are converted to non-forest in the lower 48 states of the United States. This is mainly due to the expansion and development in suburbs and suburbs. Professor Williams’ team found that the net climate impact of 15 years of forest loss is approximately 17% of a single year of US fossil fuel emissions.

Williams’ research team used state-of-the-art satellite remote sensing to obtain a detailed observational perspective to investigate this problem that had previously been assessed primarily using computer modeling. The three researchers located the places of forest loss and identified what those places became – city, agriculture, grassland, scrubland, pasture, or something else. It then quantified how much carbon from forest biomass was released into the atmosphere and how much additional sunlight was reflected into space. By comparing these two effects, they measured the net impact of deforestation on the climate system.

The new data sets and methods used in Professor Williams’ study show that the tools are available to account for the albedo effect. The Clark team hopes to generate actionable datasets over the next year or two that can be shared with land managers and policymakers around the world to ensure their tree planting efforts are focused on the right places and have the intended impact.


Founded in 1887, Clark University is a liberal arts based research university preparing its students to face tomorrow’s greatest challenges and seize their greatest opportunities. Through 33 undergraduate programs, more than 30 advanced degrees, and nationally recognized community partnerships, Clark combines rigorous scholarship with authentic world and workplace experiences that enable our learning community to pursue lives and careers with meaning and consequence. Clark’s academic departments and institutes develop solutions to complex global problems in all disciplines.

For more information, including a copy of the paper, see the Science Advances press kit online at

For more information on Professor Williams’ research, publications, and appointments, please visit the following links:

Nature Turns to Professor Williams for Expertise on Forests and Climate Change (2019).

Natural climate solutions reduce global warming (2018)

Geography Professor selected for the Scientific Leadership Group of the Carbon Research Program (2017)

Study: Ecosystems Slow Down the Rise in CO2 Concentration (2016)

Researcher: Global warming leads to drier air, stressed plants (2016)

Clark Geographer in Australia to study climate change, drought and tree death (2016)

Clark geographer awarded NASA grants to study carbon release and uptake in US forests (2014)

New Clark study on Clearcuts shows surprising trends in carbon, water (2013)

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