In terms of climate mitigation, forests are like green gold—working overtime to cool the planet, while also supporting a wealth of biodiversity. But we have not been saving them as one would a precious asset. Despite pledges to end deforestation, old growth forests are being cut down at alarming rates. And planting new trees is widely prioritized and incentivized over protecting existing forests. Across the board, standing forests are vastly undervalued. This has to change if we are to stand a chance of limiting warming to internationally agreed targets.
According to a recent study from scientists at Woodwell and the University of Virginia, tropical forests alone are holding back approximately 1 degree Celsius of warming. About 75% of that cooling effect is due to carbon sequestration. Forests grow, trees lock away carbon in their trunks and roots and shunt it into the soil. The other 25% comes from the innate properties of forests that work to cool vast regions of the globe.
Through photosynthesis, plants release water vapor into the air in a process called evapotranspiration. The vapor contributes to cooling near the ground, as well as cloud formation higher in the atmosphere that reduces incoming solar radiation. The shape of the tree canopy also contributes. So-called canopy “roughness” disrupts air flow above the forest. The more uneven the canopy, the more turbulent the air, which disperses heat away from the surface. In the tropics, evapotranspiration and canopy roughness are high, which means that surface temperatures remain relatively low, with the heat dispersed throughout the deep atmosphere.
Forests also naturally produce molecules called biogenic volatile organic compounds (BVOC), which can either contribute to cooling by encouraging the formation of clouds, or to warming by creating ozone and methane. In the tropics, the net effect of these chemicals is cooling.
The cumulative result of these properties is that when forests are removed, the land around them begins to heat up even faster, which can increase the frequency of extreme heat and drought events. Without forests, some regions will become a lot less resilient to sudden shocks. And the release of carbon contributes to global warming which further exacerbates hot, dry conditions.
“Forests act like air conditioners,” says Woodwell Assistant Scientist, Dr. Ludmila Rattis, who studies the impacts of deforestation on agriculture in Brazil. “Deforesting in the face of climate change is like getting rid of your air conditioners before an upcoming heatwave.”
Protecting forests, and maintaining the cooling services they provide, is vital to limiting warming. But, with forests covering 30% of the Earth’s land, prioritizing protection is a massive task. And when it comes to carbon storage, not all forests are equally valuable. Older, healthier forests tend to have a more secure hold on their carbon.
“Mature forests have higher biodiversity and create their own microclimate,” says Woodwell Associate Scientist, Brendan Rogers. “They’re more resistant to drought and other types of disturbance. And because of that, they tend to be more stable in the face of environmental perturbations over time.”
New research from Woodwell and Griffith University has developed a method of identifying high-value forests using satellite imagery. Estimating the metric of “forest stability” through satellite data on the light reflected by vegetation and a water stress index of the tree canopy, researchers were able to determine gradients of stability within forest patches in the Amazon and boreal forests.
Using a gradient of forest stability allows for a better prioritization of forest protection strategies based on their carbon value.
“The first priority is to protect stable forests from further human disturbance,” says paper co-author Dr. Brendan Mackey. “The second priority is to identify forest areas where restoration efforts will be most cost effective.”
But if the state of existing forests is any indication, forest protection continues to be deprioritized. Many wildfires are left to burn unless they threaten human settlements. Governments continue to incentivize deforestation for development or agricultural expansion. Indigenous and local communities are not compensated for their work stewarding their territories and keeping forests safe. And the warmer the planet gets, the more susceptible even protected forests become to drought, fire, and disease.
Research has shown that stewarding standing primary forests, and reviving degraded ones, represents the greatest opportunity for near-term carbon storage and removal. A study of global land-based carbon storage potential found that improved management of existing forests alone could store approximately 215 billion metric tons more than they currently do.
Protecting forests is cost effective, too. For example, in the United States, investing in fire fighting in Alaska’s boreal forests would require just $13 per ton of CO2 emissions avoided. That’s easily on par with other mitigation strategies like onshore wind or solar energy generation.
Effective strategies for protecting forests already exist, they’ve just been suffering from a lack of force—and often funding—behind their implementation. For example, forest carbon markets—where landowners and forest stewards are paid to protect standing forests that are otherwise vulnerable to deforestation—have the potential to keep forests safe while offsetting emissions from other sectors. But nascent carbon markets are inefficient, with weak standards for verifying the quality of credits being sold, and lacking the transparency needed to ensure credits are actually reducing overall emissions, rather than greenwashing carbon-intensive business practices.
Credits are also priced incorrectly for their relative climate value—the market currently values reforestation credits more highly, reducing incentive for landowners to conserve standing, old-growth forests when there is a better livelihood to be made in legally deforesting land for other uses. A truly effective carbon markets system would require large investments in science that can verify credit standards.
Forests are like our global carbon savings accounts—when we cut them down, we’re drawing out money and limiting our ability to collect interest and keep growing our funds. Successful mitigation can’t be accomplished without taking the full value of forests into account and strengthening policies to reflect that. If they aren’t, the planet will pay a far greater price for it as temperatures rise.
“We can’t afford to keep cutting forests. We need to reduce emissions now, and protecting forests is one of our best available solutions. Despite the obstacles, it’s worth the investment,” says Dr. Rogers.Nature-based climate solutions like reforestation, climate-smart agriculture, and wetland restoration harness natural processes to reduce greenhouse gas concentrations in the atmosphere and slow climate change. These approaches have substantial and growing support from bipartisan lawmakers, the private sector, and conservation-minded NGOs, but scientific tools to guide implementation and to accurately monitor outcomes are not adequately developed.
To confront that uncertainty and put nature-based climate solutions on a sound scientific footing, several dozen scientists and policy experts gathered in Washington D.C. in June of this year for a workshop sponsored by Indiana University, the U.S. Department of Energy, and the U.S. Carbon Cycle Science Program. The resulting white paper report reviews the current state of knowledge in this field, and describes the necessary research and technology investments to support effective mitigation policy.
According to the report’s lead author, Dr. Kim Novick from the Paul H. O’Neill School of Public and Environmental Affairs at Indiana University, “Nature-based climate solutions can play an important role in slowing the pace of climate change, but only if they are pursued alongside economy-wide decarbonization and guided by the best-available science.”
The white paper authors identify critical gaps in the science needed to support large-scale implementation of nature-based climate solutions and lay out a research agenda to fill these gaps. They also outline a set of principles that should guide future assessments of the effectiveness and viability of nature-based climate solutions. The result is a road map for producing information that will foster successful programs and policies—while avoiding energy wasted on those that do not.
Woodwell Senior Scientist, Dr. Jonathan Sanderman attended the gathering in June and contributed to the development of the paper.
“We’re at a unique moment in U.S. climate policy where the hard work of the research science community can be directly and immediately leveraged to help the U.S. fight climate change and become a world leader in implementing nature-based climate solutions.”
The report calls for a ~$1 billion (USD) coordinated investment in a national nature-based climate solution “Information Network” organized around coordinated ground-based experiments and monitoring that can inform rigorously benchmarked maps, model predictions, and protocol evaluations.
According to Dr. Benjamin Runkle, another report co-author and associate professor in the College of Engineering at the University of Arkansas: “Although the investment necessary to generate this information is not small, it is a fraction of the amount already allocated to implementation of nature-based solutions. Investing in sound science to predict, monitor, and verify the benefits of these strategies is fundamental to ensuring their success.”
In addition to their potential to stave off climate change, nature-based solutions also have a range of other benefits, including improving air and water quality, promoting biodiversity, and providing economic opportunities. Many can also help communities adapt to a changing climate and improve resilience of agricultural and food systems.
“There is broad-scale agreement that many nature-based climate solutions benefit people and the environment through co-benefits,” said Dr. Emily Oldfield, a report co-author and agricultural soil carbon scientist with the Environmental Defense Fund. “We should push to incentivize those practices using a wide range of policy tools, while acknowledging there is no one-size-fits-all approach to ecosystem-based climate solutions.”
It’s a hot, humid day in late August and we’re all already sweating as Arman Bajracharya begins to tell us about his project.
Bajracharya is a second year Ph.D. student in the geography department at Clark University in Worcester, MA, where we’re standing now. He pulls out a green and orange map of the city and points to our location on one of the orange blocks that signals industrial land use and impervious land cover.
We’re standing in the sparse shade of some trees ringing the edge of an old millpond, but we had to walk across a hot, cracked parking lot to access it. The neighborhood is called Webster Square. It is located in the southern reaches of Worcester, which was once a vibrant epicenter of the industrial revolution.
That industrial heritage is evident both on the maps Bajracharya shows us as well as in our surroundings. Truck beds and spare pvc piping and gravel piles rest at the edge of the water. It’s also scorching hot.
Temperature varies with land cover. In cities, the presence of impervious surfaces like asphalt, concrete, and metal trap heat, while natural surfaces—water or vegetation—can help buffer it. The distribution of these hotspots and heat buffers in Worcester, as in many cities, is not equal. Some neighborhoods endure much higher temperatures than others during the summer months.
Bajracharya’s research during the Summer of 2021 made possible by the Edna Bailey Sussman Fund employed remote sensing and census data to determine what features make a neighborhood more susceptible to extreme heat. He mapped temperature, land cover, and land use onto areas of greatest social vulnerability in Worcester, as well as two other post-industrial cities in Massachusetts, Haverhill and New Bedford. The results show that as climate change warms cities, the communities that have already experienced environmental inequities are likely to face more.
Worcester, Haverhill, and New Bedford are designated as gateway cities. These places, often important centers of the industrial revolution, have served as “gateways to the American dream,” offering job opportunities and housing for many who immigrated to the region.
Worcester began its industrial life as a mill town but soon grew into a manufacturing center for a variety of goods. It was also a crossroads of canal, and later, rail thoroughfares connecting the rest of Massachusetts with Providence and New York. Today, at the edge of the millpond in Webster Square, the remnants of an old rail bridge are still visible and active trains can be heard traveling the present day rail lines in the distance.
Industrial neighborhoods built to serve mills and factories often filled in with minority populations, and over time, wealthier families moved to quieter and more suburban areas of town. In the case of Haverhill, some communities also suffered the consequences of redlining, a discriminatory Federal Housing policy during the post-Depression era that limited financial services available to people, overwhelmingly African-American and people of color, deemed “hazardous to investment,” limiting social mobility and enforcing racial housing segregation. These factors often intensified the overlap between areas of high social vulnerability and industrial infrastructure.
“In the 1930s, these practices delineated which areas were defined to be good for financial services like loans,” Bajracharya says. “Which is why there is a historical divide between which areas are favorable and which areas are not. That can impact how we see the land being used today, especially where the greenspaces are.”
Bajracharya used available satellite data to show the relationship between land cover and social vulnerability. Examining the imagery, he created an index of relative heat in the city. Areas with high tree cover correlated with lower land surface temperatures. He then overlaid social vulnerability and environmental justice datasets that index communities in Massachusetts based on socioeconomic status, minority status, primary language, and other demographic information.
“Throughout many or most U.S. cities, neighborhoods facing greater environmental risks (such as from heat waves, urban flooding, and hazardous wastes) were historically settled by poorer families or racial and ethnic minorities,” Bajracharya says. “And there really is a lot of evidence for communities of color, or low-income communities, continuing to be disproportionately exposed to risk.”
According to Bajracharya, the analysis showed a startling overlap between the hottest areas of the city and the most vulnerable. Neighborhoods classified as Environmental Justice Communities tended to have a lower percentage of green vegetation (especially tree cover), with higher average temperatures. The most vulnerable areas are clustered in the core of the city.
The satellite maps only tell part of the story, however, which is why Bajracharya and his advisor Dr. Rinku Roy Chowdhury have brought us out onto the streets of Worcester. A few blocks away from the millpond, a grassy field rolls out behind a chain-link fence. In Bajacharya’s maps, this appears as a patch of vegetation interspersed among the developed land uses. The field sits under metal towers belonging to a nearby power station.
Often, Roy Chowdhury reminds us, the “green” and “blue” spaces that do exist in vulnerable areas may be inaccessible to residents, either cordoned off as private property or unsuitable for use due to safety concerns or an absence of trails or paths. The sign on the chain-link fence here warns of danger from high voltage.
This is where the distinction between land cover and land use becomes important. Land cover refers to what is currently on the land— whether that’s forest, grassland, or concrete. Land use data shows how humans are interacting with an area of land. For example, an area of grassy land cover could be used for conservation, residential or commercial purposes.
When natural land covers such as trees and water bodies are present but inaccessible, it limits potential social co-benefits that green and blue spaces can offer. Beyond regulating temperature, these spaces can reduce air pollution and provide recreational opportunities. Bajracharya and Dr. Roy Chowdhury emphasize the importance of field trips like this one, along with more in-depth work to ground truth satellite image analysis in local realities.
“There’s a really interesting mix of industrial and commercial uses interspersed with areas important for conservation and recreation, that could also potentially help in bringing down surface temperatures,” Dr. Roy Chowdhury says. “Tree cover and water are really helpful for buffering against the urban heat island, but so much more needs to be done to understand and steward such ‘ecosystem services,’ especially in underserved areas of cities.”
With climate change accelerating, every patch of green and blue on the map will become indispensable in regulating city temperatures. To prevent a crisis of infrastructure failures and heat-related illnesses and even deaths from unfolding during brutal summers, cities like Worcester are going to have to get greener, faster—and do so in a way that benefits residents equitably.
Dr. Roy Chowdhury and Bajracharya are interested in investigating further to figure out the most promising pathways towards greener, more equitable cities. Questions still remain around finding the best proportion and distribution of land cover and implementation strategies that will improve environmental equity and encourage citizen participation. Woodwell’s Dr. Chris Neill has been collaborating with Dr. Roy Chowdhury and Clark University over the last decade to analyze land cover and ecological structure of urban vegetation in several US cities.
“Every tree makes a difference, but there are scale effects as well. What is the minimum threshold to make a difference? What’s the mix in different cities or neighborhoods? What do local residents value and want? These are really interesting and important questions to ask,” says Dr. Roy Chowdhury.
Research into the interactions between these green spaces and rising temperatures could help city planners make more conscious decisions about climate adaptation. Baracharya’s future projects may also examine flooding risk in cities, which adds another dimension to potential inequities in climate risk. Future research could also incorporate social interviews in different neighborhoods to understand residents’ concerns regarding their environment, climate change, and quality of life.
The last stop on our Worcester tour is Beaver Brook Park— an example of what’s possible when a city decides to reinvest in its natural spaces. The neighborhood surrounding the park was a primary destination for Black Americans moving north after the Civil War and has a history as a vibrant minority community. The titular brook had been paved over years ago, running in darkness under the city until 1990, when it was daylighted again to serve as a central feature of the park.
The area is now a green haven for recreation in the neighborhood and a stop on Worcester’s East-West trail, which Dr. Roy Chowdhury describes as “an emerald necklace” running through Worcester—one of the ways the city and numerous environmental stewardship organizations are working towards broader greenspace protections and access.
The feel of the air here contrasts sharply with where we started the day—a hint of the power urban greenspaces hold. Despite the heat warping off the street pavement, in the shade of old oak trees by the gurgling brook, it’s easy to stop sweating for a moment and just feel the breeze.