Less water loss from plants causes the surrounding air to heat up, and currents can carry that heat toward the poles.
The Arctic is one of the fastest warming places on the planet, and scientists are still not entirely sure why.
Melting snow and ice may be accelerating warming. Changes in atmospheric circulation could be playing a role. Many factors could be influencing temperatures in the region, which are rising at least twice as fast as the rest of the world.
Now scientists think they may have discovered an additional piece of the puzzle. It turns out that plants can have an unexpected influence on global warming.
As carbon dioxide levels increase in the atmosphere, plants become more efficient at carrying out photosynthesis and other basic functions of life. And they can often save more water in the process.
The water that plants exchange with the air helps cool local temperatures. When they lose less water, their surroundings begin to heat up.
A study published last month in Nature Communications suggests that this process is helping to warm the Arctic.
"The influence of plants has been overlooked before," said study co-author Jin-Soo Kim, a scientist at the University of Edinburgh, in an email to E&E News. "This study highlights the impacts of vegetation on warming the Arctic under a world elevated CO 2."
The study used a set of Earth system models to arrive at its findings.
Models suggest that increased CO2The result of human greenhouse gas emissions is causing plants to lose less water throughout the Northern Hemisphere, including heavily vegetated regions in the tropics and mid-latitudes. This process causes temperatures in these places to heat up even more than they would with climate change alone.
At the same time, large-scale atmospheric circulation patterns help transport heat between the tropics and the Arctic. The study suggests that this additional heat is heating up the Arctic at an even faster rate.
In fact, the additional warming may contribute to other processes that also accelerate climate change in the Arctic. For example, scientists believe that melting sea ice plays an important role in warming the Arctic. Sea ice, with its shiny, reflective surface, helps draw sunlight away from the planet. As the ice disappears, more sunlight — and more heat — can pass through the Earth's surface.
The researchers suggest that the additional heat rising from lower latitudes may be helping the sea ice melt faster. And this, in turn, also contributes to faster Arctic warming.
AN IMPORTANT UNKNOWN
Overall, the study estimates that the plant effect can account for nearly 10% of the Arctic warming each year. And it could explain up to 28% of the warming in the lower latitudes of the Northern Hemisphere.
But there is still a lot of uncertainty about those estimates.
The scientists used a set of eight models in their study and considered all the model results together. But from one model to another, there are quite large differences in the size of the plant effect.
This may be due in part to the fact that the sea ice response is still uncertain and tends to vary between different models.
But there has also been some debate among scientists about the exact effect of increased CO2 on plants.
Plants absorb CO 2 and also exchange water with the atmosphere through small pores in their leaves called stomata. More CO 2 means that plants do not have to keep their stomata open as wide. They can still get enough carbon dioxide through smaller openings, and they can save water in the process.