Claim: CO2 is good for plants, and more CO2 is good for the Earth.

Note the changes in hardiness zones in just 20 years

Why this Claim is Wrong: While CO2 is used by plants to make their own biomass, it is deliberately misleading to sell the notion that human-caused rapid injection of CO2 into the atmosphere will be good for plant life. It is not true that 21st century

Higher CO2 levels degrade the nutritional value of key foods. Note the the zinc, iron, and protein content of the key staples drops by roughly 6%. These provide most of the calories that feed most of the people on Earth.


rising CO2 levels will be helping plants in general. Quite the contrary. CO2-induced climate change is stressing plants more than CO2 is helping them, and agricultural scientists are pointing out that rising night-time temperatures, a signature of greenhouse gas-induced warming, are reducing crop yields in the major

breadbaskets of the world, as well as putting stresses on animals grown for agriculture -see the testimony of Dr. J. Hatfield in front of Congress. Natural plants are nearly always nitrogen-limited in their growth, not CO2-limited. The drop in crop yields which experiments show we can expect are devastating and alarming... "Holding Current Growing Regions Fixed, Area-Weighted Average Yields Are Predicted to Decrease by 30–46% Before the End of the Century Under the Slowest Hadley III Warming Scenario (B1), and Decline by 63–82% Under the Most Rapid Warming Scenario (A1FI)" from Schlenker and Roberts 2008. Since the early IPCC projections were made, we have so far been following the most pessimistic of the emission scenarios. A new study, published in Nature - Climate Change and announced by the National Science Foundation, shows that after a short, initial growth spurt when CO2 levels rise, plants then become stunted.

Perhaps even more alarming is the global decline in the plants of the ocean - the base of the world's food chain. Global phytoplankton has declined measurably in over 60% of the world's oceans in the past century (Boyce et al. 2014). When greenhouse warmed air is in contact with the ocean, the surface ocean warms and the warmer water is less dense and inhibits mixing with nutrient-rich lower layers. Ocean phytoplankton, which produces half of the living biomass of our planet, and roughly half of our oxygen - is declining at a very rapid 1% every year (Nature 2010).

A slight improvement in crop yields at slightly elevated CO2 and temperatures, turns to a steep fall off in yields as CO2 levels and temperatures continue to rise. From Schlenker and Roberts 2008 "Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change" in Proceedings of the National Academy of Sciences


Update 2013: Here's a new summary of the published literature on how rising CO2 will devastate existing agriculture. This NASA study shows vast regions of the Eastern U.S. where the forest canopy is declining due to global warming's add-on effects. Nevertheless, in mid '13 this false claim is still getting press (May 12, 2013 Wall Street Journal link to article and what the science actually says).

Update 2014: Climate change is also damaging to the nutritional content of food. The protein and mineral content of staple crops such as corn, wheat, rice, and soybeans, is being significantly reduced under a higher CO2 atmosphere (Meyers et al. 2014, and summary for the layman here, and see graph above right).

Update 2015: Mora et al. (2015) studied the effects of rising temperatures on global plant growth,

People in tropical regions will struggle the most with future changes in plant growth. Areas in dark green are least vulnerable. Light green regions are somewhat vulnerable, yellows are very vulnerable and reds are highly vulnerable.

and find it will be very damaging to crops and other plants especially in the Asia and Africa and other lower latitudes, where most of the Earth's population lives. The thaw in the polar areas is much less helpful in their study than the harm to the tropical and mid latitudes. In the Arctic, warmer temperatures will not make up for the lack of sunlight. But the increasing drought and high temperatures will cripple plants in the lower latitudes.



In Short: SOME CO2 in our atmosphere, held constant, is clearly good and necessary for plants, but those repeating this "good for plants" meme hope you will stop there and not notice that (a) the nutritional value of staple food crops drops under higher CO2 atmospheric concentrations, (b) most plants are nitrogen-limited, not CO2 limited, (c) that rapidly rising CO2 makes for climate change far faster than ecosystems can accommodate to, and (d) an initial growth spurt is followed by stunted growth in actual observations. Rapidly rising CO2 is destructive to most plant species (one strong exception is poison oak and poison ivy, which thrive in higher atmospheric CO2 concentrations). Finally, drought and heat stress cripple plants in the areas where population actually lives.



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