A greener Arctic may be a warmer one

Increased plant growth is trapping more heat, changing local heat budgets and melting Arctic ice.

Scientists have had trouble explaining why the Arctic is warming faster than the rest of the planet, but new research says it may be the plants’ fault: vegetation attracts sunlight, traps heat, and even interacts with the atmosphere to influence sea ice.

Greenpeace may have to go with a new colour following mounting evidence that greenery accelerates the warming of the Arctic. A new study has found that when fast-growing plants interact with the atmosphere and the polar sea ice, the effect is a complex and dangerous feedback loop. 
That system could add 1-2 degrees of warming to high latitudes, explaining for the first time why the Arctic is warming so much faster than the rest of the planet.

“I think this is one of the most important contributions to existing models,” explains author Deliang Chen of the University of Gothenburg. “IPCC models do not incorporate dynamic vegetation.”

Since plants require CO2 to produce energy, a higher-carbon atmosphere stimulates plants to grow more quickly; they also grow more easily in a warmer atmosphere. Plants absorb heat from the sun, and trap warmed air amongst their leaves. On snowy tundra, this effect is amplified as the vegetation, darker than the surrounding snow, reflect less heat, and melt the snow, revealing more dark ground in the area and adding to the effect. 

“The question is, how can this influence the sea ice?” asks Chen. 
Plants’ warming of the tundra has been well established; however, the new study published in Environmental Research Letters shows that the warmed air from the vegetation will also contribute to sea ice melt through atmospheric interactions. 
“That [interaction] has to be carried out by some mechanism,” says Chen. “We believe that is the atmospheric heat transport.”
When the heat is transported to a frozen sea, the melted ice has the same effect as the plants, causing the ocean’s surface to absorb more heat and melting more ice. 
To figure out just how this complex interaction takes place, the researchers simulated a double-CO2 atmosphere, a common technique for investigating future climate conditions. They found that when the sea ice melts faster due to plant growth, it contributes to more vegetation growth the following spring, starting the feedback loop over again. 

Sea ice is melting faster, in part because of atmospheric interactions over the land.
This isn’t the first study to point the finger at plants for contributing to Arctic climate change. Also in a simulated high-CO2 atmosphere, plants were shown to release less water to the surrounding air, reducing their usual cooling effect. In this case, a quarter of North American and Asian warming was due to plants. 
The new study did have its limitations. 
“The results cannot be considered quantitatively realistic,” write the authors, because the models they used did not incorporate the Arctic carbon cycle, most significantly the huge amount of carbon stored in the permafrost and in marine sources like methane hydrates. These are expected to account for 500 Gt and at least 1800 Gt of carbon, respectively. Dr. Chen expects that incorporating the carbon cycle into the models would also introduce some carbon-reducing effects, however.
“Generally speaking, nature has more negative feedbacks,” he says. The nature of those feedbacks, positive and negative, won’t be known until follow-up experiments are conducted, however.
Furthermore, the researchers used a simplified “slab” model of the ocean, which does not realistically model how the ocean would react to complex changes. 
“Sea ice is coupled with ocean dynamics,” admits Chen.  
So while the limited scope prevents the findings from being specifically applicable without a more complete model, Chen and his colleagues have made a significant breakthrough by including dynamic vegetation in climate models for the first time. The mystery of the melting Arctic may have just been solved.