America, Agency. When people talk about ways to mitigate climate change, they often refer to trees, and for good reason they bring up the topic of trees and greenery. Burning fossil fuels releases large amounts of the planet-warming gas carbon dioxide into the atmosphere that forests absorb. When global temperatures rise, will trees be able to keep up with that pace? As companies invest in forests as a form of carbon offset, claiming it cancels out their greenhouse gas emissions is a multi-billion dollar question.

The results of two studies, published on May 12, 2022, in the journal Science and Ecology Letters – one focused on development, the other on death – raise the question of whether the world’s growing global vermin can store the increasing amount of carbon. How much can you rely on forests for? Both studies were carried out by ecologist William Andregh, who explains why.

What does new research tell us about trees and their ability to store carbon? The future of forests is at a knife’s edge with a tug-of-war between two very important forces: trees benefit from rising levels of carbon dioxide and stress from climate, such as heat, drought, fire, pests and pathogens.

Those climate stresses are increasing much faster because the planet is warming up than scientists expected. We are seeing wildfire and drought-induced forest death much sooner than one might have guessed. When those trees die, that carbon goes back into the atmosphere. We are also seeing evidence that the benefits to trees from high levels of carbon dioxide in a warming world may be more limited than people understand.

This tells us that it is probably not a good idea to rely on forests for a comprehensive carbon sink during the 21st century, especially if societies do not reduce their emissions. Trees and forests do all kinds of other wonderful things – they clean the air and water, and they provide economic value in terms of timber and tourism and pollination. Therefore, understanding how they will develop is important for several reasons.

There is an argument that, with more carbon dioxide in the atmosphere, trees will simply grow more and lock in that carbon. What did your study find?

Two major things affect tree growth: photosynthesis, which is how trees convert sunlight and carbon dioxide into food, and the process of cell division and expansion.

There has been a long-standing debate about who is the biggest driver of tree growth. A good metaphor here is a two-horse cart. The tree of the cart going down the road is growing, and two horses are engaged in it, but we do not know who is actually pulling the cart. A horse is photosynthesizing. This makes a lot of sense – it’s where all the carbon comes from to build cells. But we know there’s another horse—to grow more wood, trees have to grow layers of cells, and cells have to expand and divide. That cell growth process is very sensitive to climate change and stops when it becomes dry.

People assume that photosynthesis is the dominant process almost everywhere. But we found strong evidence that these drought-sensitive cellular processes actually do more to speed up or limit growth.

We used tree ring data from thousands of trees in the Americas and Europe and measurements of photosynthesis from towers in surrounding forests to examine whether tree growth and photosynthesis were correlated over time. If they follow the same pattern, increasing or decreasing over the same years, this suggests that the photosynthesis was the horse pulling the cart. Instead, we found no correlation.

This suggests that drought, rather than the amount of carbon dioxide in the air, may have the biggest impact on how fast trees grow in the future. We are already seeing more frequent and severe droughts in many areas.

What did you learn about the risk of tree death in the future?

In the second study, we found that reducing global greenhouse gas emissions can have a major impact on avoiding damage from wildfires, droughts and insects.

We used years of satellite observations, climate data and a network of approximately 450,000 tree plots across the US. Where each tree is monitored for climate stress and survival. With that historical data, we built statistical models of the risk of US trees primarily from drought-related wildfires, insects, and climate stress. Then we looked at what could happen in future climate scenarios with high carbon emissions, moderate emissions and low emissions.

Big picture: As the planet warms, wildfire risk increases significantly in the current century, especially in a moderate emissions scenario in the western US, with wildfire risk projected to increase by a factor of four. Drought and pest risks increase by about 50% to 80%.

What does this mean for the use of carbon offsets?

Taken together these studies suggest that the benefits of carbon dioxide for development may not be nearly as large as people thought, and that climate stress, especially the risk of wildfires, drought and insects, can affect people’s health. may be much larger than expected. What will happen.

This has huge implications for using forests as a carbon offset.

So far, carbon offset protocols and markets have not really been able to cope with this updated scientific understanding of the risks facing forests from climate change. This tells us that climate policy makers and offset developers need to be very careful about how they rely on forest offsets to deliver benefits.

The more optimistic message is that our actions will mean a lot over the next decade. If we can stop the pace of climate change and go down the path of lower emissions, that’s a huge amount to reduce risk and increase profits. This is not a ‘raise your hand and panic’ situation – it is our chance to take steps that ensure that resilient and sustainable forests remain in place for the foreseeable future.

What we do with our own emissions and efforts to reduce climate change matters a lot to the future of forests.

Edited By: Babli Kumari