A new paper in Nature Climate Change affirms what you may have learned in an early biology class. Since carbon dioxide (CO2) is necessary for plants to engage in photosynthesis, a boost will rev up the engines a little.
If you have looked at the edges of deserts decades ago versus now, you can see what has happened as carbon dioxide concentrations in the atmosphere rose; water-use efficiency in plants went up and things got more green. That is because higher CO2 levels reduce the amount of water crops lose. Leaves contain tiny pores called stomata that open and collect carbon dioxide molecules for photosynthesis, a process known as transpiration. As carbon dioxide concentrations increase, the pores don't open as wide, resulting in lower levels of transpiration by plants and therefore increased water-use efficiency.
Those may be also be one of the reasons why wheat, maize, soybean and rice crops are doing better than ever.
By simulating changes in crop yield and evapotranspiration (the combined transfer of water vapor to the atmosphere due to evaporation and transpiration) the researchers in the new paper were able to calculate the amount of yield produced per unit of water, a common measurement for assessing crop water-use efficiency. With 30 simulations of six global crop models, driven by climate data from five different global climate models where concentrations of carbon dioxide double by the year 2080 compared with 2000, they found that crops responded better with double the CO2 than with year 2000 CO2 levels and higher temperatures.
For wheat and soybean crops, in terms of yield the median estimated negative impacts of yield losses due to more warming were fully compensated, and rice crops recouped up to 90 percent while maize recouped up to 60 percent of their losses.
The study offers some hope for crops grown in arid, often economically challenged areas, said Cynthia Rosenzweig, a climatologist at NASA's Goddard Institute for Space Studies (GISS) in New York City, in the NASA press release. "For example, farmers may switch to crops where their improved photosynthesis and more efficient water use more than offsets losses due to the high temperatures that climate change will bring."
Let's not get crazy, though. It's the dose that makes the poison. It is well-known that something in moderation can be bad in excess. If you want to believe Joe Mercola about acupuncture, for example, that is fine, but if you believe him about everything you will die.
And too much CO2 is bad for us. How much is too much? Well, submarine captains want to keep things at under 5,000 parts per million (ppm). They think about that because they are in a small pressurized tube under the ocean and human breath exhalation is 40,000 ppm.
What is the atmospheric CO2 level right now? 400 ppm. And in a thriving cornfield during the day, it drops to 200 ppm because plants absorb it to generate energy.
So we have some room to breathe as we continue to switch to cleaner energy sources like natural gas and nuclear and, in the future, solar, and perhaps even hydrogen.
Citation: Delphine Deryng, Joshua Elliott, Christian Folberth, Christoph Müller, Thomas A. M. Pugh, Kenneth J. Boote, Declan Conway, Alex C. Ruane, Dieter Gerten, James W. Jones, Nikolay Khabarov, Stefan Olin, Sibyll Schaphoff, Erwin Schmid, Hong Yang & Cynthia Rosenzweig, 'Regional disparities in the beneficial effects of rising CO2 concentrations on crop water productivity', Nature Climate Change April 18 2016 doi:10.1038/nclimate2995
