High levels of carbon dioxide in the air from fossil fuel burning will thicken plant leaves, making plants less effective at holding carbon and worsening climate change, according to University of Washington researchers.

And as the planet warms, sea level rise intensifies, causing more frequent flooding in places like the Jersey Shore.

Climate models have not taken leaf thickening into account, according to a paper published Oct. 1 in the journal Global Biogeochemical Cycles.

When the researchers added the information into global climate models, under high carbon levels expected later this century, plants' global "carbon sink" was less productive. It left about 6.39 billion more tons of carbon in the atmosphere per year, they reported.

The added levels are similar to the amount of carbon released annually by fossil fuel emissions -- about 8.8 billion tons.

Global temperatures could rise an extra 0.3 to 1.4 degrees Celsius beyond what has already been projected, according to simulations run by Abigail Swann, a UW assistant professor of atmospheric sciences and biology, and Marlies Kovenock, a UW doctoral student in biology. 

"If this single trait -- leaf thickness -- in high carbon dioxide levels has such a significant impact on the course of future climate change, we believe that global climate models should take other aspects of plant physiology and plant behavior into account when trying to forecast what the climate will look like later this century," said Kovenock, who is lead author on the paper.

Scientists don't know why plants thicken their leaves when carbon dioxide levels rise. But the response has been documented in different types of plants, from woody trees to staple crops like wheat, rice and potatoes.

Plants undergo C3 carbon fixation, the form of photosynthesis that accounts for about 95 percent of photosynthetic activity on Earth, the researchers said.

Leaves can thicken by as much as a third, which changes the ratio of surface area to mass in the leaf and alters plant activities like photosynthesis, gas exchange, evaporative cooling and sugar storage. 

The concentration of carbon dioxide in the atmosphere today is about 410 parts per million and is projected to hit as much as 900 ppm by the end of the century.

The carbon level that Kovenock and Swann simulated with thickened leaves was 710 ppm. 

There are many other changes in plant physiology and behavior under climate change that researchers could model next, such as how thicker leaves may hamper evaporative cooling by plants or cloud formation, said Kovenock.

"We now know that even seemingly small alterations in plants such as this can have a global impact on climate, but we need more data on plant responses to simulate how plants will change with high accuracy," said Swann. "People are not the only organisms that can influence climate."

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Staff Writer

In my first job after college got paid to read the New York Times and summarize articles for an early online data base. First reporting job was with The Daily Record in Parsippany. I have also worked in nonprofits, and have been with The Press since 1990.

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