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How Plants Could Impact Global Warming

Biodiversity influences climate at local, regional and global levels, yet most climate models do not take biodiversity into consideration because its variables and effects are too diverse and complex to compute. Two recent studies, however, demonstrate the importance of being able to consider the response of vegetation to elevated levels of carbon dioxide in climate models as we try to predict our climate future.

Photo credit: David Darricau

Scientists at the Carnegie Institution for Science found that carbon dioxide’s direct effects on vegetation contribute to global warming. Through the pores called stomata in their leaves, plants take in carbon dioxide from the atmosphere that they use for photosynthesis. They then give off water through the stomata in a process called evapotranspiration which cools the plant just as perspiration cools human beings. Evapotranspiration also cools the surrounding air—a tree can transpire up to ten gallons of water on a hot day. But when carbon dioxide levels increase, plants’ stomata shrink, releasing less water into the air and reducing the cooling effect.

Stomata: open and closed

Carnegie scientists Long Cao and Ken Caldeira doubled the level of carbon dioxide in their model and found that globally the reduced evapotranspiration was responsible for 16 percent of the land warming; the rest was due to CO2’s heat-trapping effects. In North America and Asia, more than 25 percent of the warming was due to the impact of increased CO2 on vegetation. “There is no longer any doubt that carbon dioxide decreases evaporative cooling by plants and that this decreased cooling adds to global warming,” said Cao. “This effect would cause significant warming even if carbon dioxide were not a greenhouse gas.”

Another effect of the doubled CO2 is increased runoff from the land as more precipitation bypasses the plant’s evapotranspiration system and makes its way directly into streams and rivers.

The Carnegie study did not take into consideration other effects of increased carbon dioxide such as an increase in leaf area, variations in vegetative distribution and resulting changes in albedo (the reflectivity of Earth’s surfaces which affects how much solar radiation is absorbed).  These aspects were fixed in their model. But they cited earlier research on increased CO2 that showed that cooling due to increased leaf area produced an overall cooling effect over land, and that a decrease in albedo due to the expansion of coniferous forests resulted in land warming.

“These results really show that how plants respond to carbon dioxide is very important for making good climate predictions,” said Caldeira. “So if we want to improve climate predictions, we need to improve the representation of land plants in the climate models.

A new NASA study that did take plant growth into consideration found that doubling the level of CO2 resulted in a cooling effect. The model used by Lahouari Bounoua of the Goddard Space Flight Center in Greenbelt, Md., was innovative in its consideration of a reaction that plants have to increased CO2 called “down-regulation.” Down-regulation is the process that enables plants to use water and nutrients more efficiently when there is increased CO2, so that they are able to maintain previous levels of photosynthesis, which can ultimately boost leaf growth.

Photo credit: Sten

The increased leaf area resulted in more evapotranspiration globally, and thus created a cooling effect.  The amount of cooling in the study measured -0.6 degrees C (-1.1 F) over land, compared to models that didn’t include down-regulation.

Bounoua stressed, however, that the cooling was not enough to offset the warming trends that are predicted.

Climate models usually factor in a doubling of CO2 to simulate global warming, and scientists generally agree that under this scenario, temperatures would increase from 2 to 4.5 degrees C (3.5 to 8.0 F). Bounoua’s model found a warming of 1.94 degrees C globally without the inclusion of down-regulation. The range in temperature results from unknowns about various “feedbacks,” i.e. how the various systems on Earth such as clouds, plant growth, methane release, the water cycle, albedo, etc. might respond to warming and interact with each other.

Bounoua and her colleagues also looked at how plant growth is stimulated by warmer temperatures, increased precipitation in some areas, and the plants’ more efficient use of water and nutrients when CO2 is doubled. The results suggest that in the long term, increases in vegetation due to elevated CO2 might reduce temperatures after CO2 levels stabilize.

“As we learn more about how these systems react, we can learn more about how the climate will change,” said the study’s co-author Forrest Hall. “Each year we get better and better.”

New climate models are being designed to consider dynamic global vegetation that allows plant types to shift interactively with climate, and ecosystem demography that accounts for how communities of diverse plants might respond to climate change over time.

Science for the Planet: In these short video explainers, discover how scientists and scholars across the Columbia Climate School are working to understand the effects of climate change and help solve the crisis.
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John Baezb
12 years ago

“A new NASA study that did take plant growth into consideration found that doubling the level of CO2 resulted in an overall cooling effect.”

That’s a misleading sentence. If you say “an overall cooling effect”, it sounds like you mean that when all known processes are taken into account, the overall effect of doubling CO2 is to cool the planet!

But that’s not what you mean. Indeed later you write “Bounoua stressed, however, that the cooling was not enough to offset the warming trends that are predicted.”

Otherwise, a great article! I don’t mean to nitpick, but some so-called “climate skeptics” will take any misleading sentence, remove it from its context, and make it say what they want.

Mike Purpura
Mike Purpura
Reply to  Renee Cho
2 years ago

Yes, God forbid that anyone would let a healthy dose of skepticism into a scientific discussion of climate change. Despite the use of your super computers you still cannot enter all the variables that determine climatic out comes. Mankind hs reduced vegetative cover by 50%. In our race to do something about the climate, let’s turn off the Crays, stop mining for crypto and start planting trees.

Sami
12 years ago

Ever thought someone could invent us posts or like that of lamp posts that can spray water/mist on the streets to give us some coolness in the air?

And other than that some of us [url=http://thinkrant.wordpress.com/2011/05/07/global-warming]always wear sunblock[/url], we could just wear coats that give us some cooling effect from underneath those cloth like that of plants? Because wearing sunblock also can destroy our skin.

Just having some wild ideas after reading this. It’s the first time I heard about plants having the ability of “evapotranspiration”. It wasn’t taught to us when we were in primary school.

samira
samira
11 years ago

There is no longer any doubt that carbon dioxide decreases evaporative cooling by plants and that this decreased cooling adds to global warming,” said Cao. “This effect would cause significant warming even if carbon dioxide were not a greenhouse gas

Dave
Dave
9 years ago

I’m confused. I thought that with increased temperatures, stomata will be closed to prevent water loss, therefore reducing the evapotranspiration effect. So how can there be a cooling affect in a tropical rainforest? Whereas a boreal forest has a warming affects?

Sue
Sue
7 years ago

Hi, I Wld like to understand why would the plants’ stomata shrink with increase level of CO2?

“But when carbon dioxide levels increase, plants’ stomata shrink, releasing less water into the air and reducing the cooling effect.”

Thank you.

Karthik
Karthik
7 years ago

In another website, it had said that when there is a lot of CO2 the plants defense systems against insects are less and some plants lose their ability to photosynthesize. Does this do with the shrinking of stomata?

Gregory Michael Howard
6 years ago

water vapor is the largest greenhouse gas responsible for much, much more than CO2

Roberto
Roberto
6 years ago

You lie by omission.

Higher CO2 levels are increasing plant density and range. You can see it now by comparing satellite images of the African deserts over recent years. Plants THRIVE at these higher levels.

Have you not considered that the shrinking stomata and reduction in evapotranspiration represent increased efficiency of the photosynthetic process?

This increased plant coverage certainly will result in lower albedo, but the energy is not released as heat in the troposphere. It is converted into energy (biomass).

You do a great disservice to your field of study by ignoring and even vilifying those who question your dogma. Your models are a mess, and your career depends upon propping up a lie.

Please retire.

Luis fonsi
Luis fonsi
4 years ago

thanks for providing information about climate change

we are conducting conference on plant science and molecular biology on may 18-19,2020

we will provide more information about plant disease and natural culture and plant tissue culture etc…………… on our conference subject expertise will come and join our conference
for details feel free to contact us we will provide you more information on our conference

conference email id :plantscience@expert-meeting.com

best regards
Luis Fonsi

Robert Webman
Robert Webman
4 years ago

As a potential solution, has any engineering been attempted to manipulate plants to take in more CO2 and produce more oxygen by genetic engineering?

luis fonsi
luis fonsi
3 years ago

nice information
we are conducting a conference on plant science and molecular biology conference on May 18-19,2020 in New Zealand
https://world.plantscienceconferences.com/

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