The agricultural gains from the fertilization effect of increasing carbon dioxide levels are greater than climate models account for, and as a result, higher carbon dioxide levels may produce benefits greater than any harms generated by climate change, a new study shows.
The study, published in the January edition of the peer-reviewed journal Environmental Economics and Policy Studies, tracked total world production of corn, rice, soybeans, and wheat per year from 1980 to 2017. Over this interval, the global average land surface was estimated to have warmed by 1.0 degree, carbon dioxide concentrations rose by 68 parts per million, and crop output doubled.
“It has been known for decades that increasing the atmospheric concentrations of carbon dioxide enhances plant growth both by raising the rate of net photosynthesis and increasing water use efficiency with the plant,” study authors Kevin D. Dayaratna, Ph.D., Ross McKitrick, Ph.D., and Patrick J. Michaels, Ph.D., write.
More Carbon Dioxide, Larger Yields
“For numerous crop types around the world, carbon dioxide fertilization more than offsets the negative effects of climate change on crop water productivity, with the largest gains likely in arid and tropical regions,” the study states. “An additional benefit of climate warming arises from lengthening the growing season—the time between the last killing frost in the spring and the first in the fall.”
The researchers note studies of U.S. maize (corn), wheat, and other crops find they experienced significant net yield gains under changing climate conditions, as a result of carbon dioxide fertilization. Although early studies found no carbon-dioxide-induced yield gains for rice, a staple crop in China and other Asian countries, more recent studies demonstrate hybrid rice varieties respond favorably to warming and elevated levels of carbon dioxide.
Satellite-based studies have demonstrated strong general growth effects and general greening of the Earth, much larger effects than modelers have estimated when building their assumptions into climate models, the study found.
“The ratio of land areas that became greener, as opposed to browner, was approximately 9 to 1,” the study states. “The increase in atmospheric carbon dioxide was just under 15 percent over the interval but was found to be responsible for 70 percent of the observed greening, followed by the deposition of airborne nitrogen compounds (9 percent) from the combustion of coal and deflation of nitrate-containing agricultural fertilizers, lengthening of the growing seasons (8 percent), and land cover changes (4 percent), mainly reforestation of regions such as southeastern North America.”
‘Positive Net Growth’
“[T]he record since 1980 provides prima facie evidence that the combined effects of warming, carbon dioxide fertilization, and adaptation can have positive net growth results at the global level, and the meta-analysis results indicate the direction of this balance is likely to persist,” the study states.
Most integrated assessment models have assumed carbon dioxide fertilization has no beneficial effect on crop yields, and some models assume climate change will have a net negative effect on plant growth. As a result, the models have underestimated the positive benefits when calculating the marginal social cost of carbon dioxide emissions (SCC), the authors state.
“[T]here is overwhelming evidence that carbon dioxide increases do have a beneficial effect on plant growth, so models that fail to take these benefits into account overstate the SCC,” the authors write.
Once the beneficial effect on crops is properly accounted for, under the worst-case scenarios the SCC is much smaller than previously estimated, and under a range of scenarios the social cost of carbon is negative, depending on the discount rate used. That means increased carbon dioxide produces net social benefits, the researchers found.
‘The Poor Benefit Most’
Carbon dioxide fertilization of crops results in more-abundant, lower-cost food, especially benefiting the poor, says E. Calvin Beisner, Ph.D., founder of the Cornwall Alliance for the Stewardship of Creation.
“For every doubling of carbon dioxide concentrations, you get an average 35 percent increase in plant growth efficiency, with plants growing better in warmer and cooler temperatures alike and in wetter and dryer soils,” Beisner said. “They [plants] make better use of soil nutrients and resist disease and pests better, consequently increasing their ranges and lessening their chances of extinction.
“Crops also improve their fruit-to-fiber ratio under higher carbon dioxide conditions,” said Beisner. “The result of all these things is more food for everything that eats plants—and everything that eats anything that eats plants. The poor benefit most, as food prices are kept lower than they’d otherwise be.”
Increased carbon dioxide concentrations in the atmosphere have no negative effects, says Jay Lehr, Ph.D., a senior policy analyst with the International Climate Science Coalition.
“While putting numbers to the excellent benefits of increasing carbon dioxide in the Earth’s atmosphere is a great contribution to the public’s knowledge, it is unfortunate it is weighed against potential negative outcomes from that same increase, because there are no negative outcomes, as there is absolutely no observational data linking carbon dioxide to the Earth’s ‘thermostat,'” Lehr said.
“While we need to promote its benefits, we need to stifle the idea carbon dioxide has any impact on the Earth’s climate other than making the planet greener,” said Lehr.
Bonner R. Cohen, Ph.D. ([email protected]) is a senior fellow at the National Center for Public Policy Research and a senior policy analyst with the Committee for a Constructive Tomorrow.
Kevin Dayaratna et al., “Climate Sensitivity, Agricultural Productivity, and the Social Cost of Carbon in FUND,” Environmental Economics and Policy Studies, January 6, 2020, https://heartland.org/publications-resources/publications/climate-sensitivity-agricultural-productivity-and-the-social-cost-of-carbon-in-fund