Simon Fraser University researchers are zeroing in on how global forestation efforts impact our climate system beyond CO2 removal in a new study.
Forestation, including reforestation and afforestation, is a key tool used globally to tackle rising carbon dioxide (CO2) emissions and help countries close the gap on their climate goals.
While forestation is widely understood to reduce CO2 levels in the atmosphere, this nature-based climate solution is also known to have non-CO2-related impacts that travel well beyond tree planting sites.
Study lead Pierre Etienne Banville, a master's student in SFU Geography and a member of SFU's Climate Research Lab , explains that large-scale forestation alters land surface properties which can lead to temperature changes.
For example, forests absorb more sunlight than grasslands due to their darker surface. Grassy areas, especially when covered in snow, reflect a lot of sunlight which keeps temperatures lower than in forested areas. Foresting grassy areas, especially in regions that receive significant snowfall can "have an additional warming effect," says Banville.
This warming doesn't just stay local to the site where trees are planted. Instead, this warmer air enters the atmosphere's circulation and can cause additional remote climate effects.
"When air warms, it can increase the amount of water vapor — a natural greenhouse gas — in the atmosphere, and water vapor increases temperatures as well," says Banville. "So, you have an important feedback there."
The study, published in Earth System Dynamics , used an Earth system model to better understand these non-CO2 remote effects of large-scale forestation, and homed in on the role oceans play in how and when they are realized.
The study found that when this warmer air travels over oceans, it increases ocean temperatures, causing evaporation, turning liquid water into water vapor and leading to additional temperature increases — further amplifying this feedback loop.
"What happens is, you have even more water vapor in the atmosphere, and that causes a stronger greenhouse gas effect," says Banville.
In addition to oceans amplifying warming temperatures, study authors also shine a light on the impact of the timescale of the oceans' response.
Banville explains that oceans absorb heat very slowly, taking centuries to see the full extent of that remote warming from forestation efforts.
"We can see the benefit of CO2 removal relatively quickly. As trees grow, they're going to take up that CO2. But then these other effects might creep up a little bit slower and offset some of that cooling from CO2 removal," says Banville.
Banville explains that understanding how forestation efforts impact Earth's systems beyond CO2 removal alone is essential for implementing effective climate policy and targets.
"It's important to have an awareness when you develop policies, especially when it comes to nature-based solutions, that there's a lot of other effects that are non-CO2 related; and they may also not have the same timeframes," he says. "If you want to achieve certain climate goals by a certain date, you need to account for all those other effects that will happen."
