February 17, 2004
Plants Will Grow More Rapidly With Higher Carbon Dioxide

Soy will grow more rapidly in higher CO2.

Although ozone slows plant growth, the beneficial effect of the carbon dioxide more than compensates for this effect, Leakey found. His unpublished results predict an increase in soy yields of 13% by 2050. US farmers currently plant about 150 million acres of soybean a year.

The following press release emphasies that the increased plant growth in the presence of higher CO2 is not enough to take all the CO2 out of the atmosphere. But the fact that the trees and plants grow more rapidly is economically valuable.

OAK RIDGE, Tenn., Feb. 16, 2004 -- Trees absorb more carbon dioxide when the amount in the atmosphere is higher, but the increase is unlikely to offset the higher levels of CO2, according to results from large-scale experiments conducted at Oak Ridge National Laboratory and elsewhere.

"Some people have used carbon dioxide fertilization to argue that this is a boon of the fossil fuel era and that it will lead to greater agricultural yields and carbon sinks," said Richard Norby of the Department of Energy's ORNL. "Some recent experiments, however, have suggested that there will be no lasting effect of carbon dioxide fertilization. As is often the case, the truth may lie in between."

Norby is among several scientists participating in a panel discussion titled "CO2 Fertilization: Boon or Bust?" Feb. 16 at the American Association for the Advancement of Science annual meeting in Seattle.

For the last six years, Norby and colleagues at ORNL have examined the responses to elevated carbon dioxide levels in a stand of sweetgum trees a few miles from ORNL. The experiment consisted of pumping tons of carbon dioxide into the plots, raising the concentration of carbon dioxide in the tree stand from the ambient level of about 370 parts per million to 550 ppm, and studying the effects.


In every year since the FACE project began, net primary productivity, which is the total amount of carbon dioxide fixed into organic matter such as leaves, stems and roots, has been higher in plots given extra carbon dioxide. The average increase has been 24 percent, and there is no indication that the increase will not continue. But, Norby notes, while his colleagues have observed a sustained increase in leaf photosynthesis, the response to carbon dioxide fertilization would not be apparent if only above-ground growth were measured. Wood production increased significantly during only the first year of treatment.

While Norby and colleagues have learned a great deal about above-ground allocation of carbon dioxide, in recent years they have focused their efforts on impacts on fine roots and soil sequestration of carbon dioxide. Fine root production has increased substantially in response to elevated carbon dioxide.

Fine roots are important for water and nutrient uptake, but they have a short life and their carbon returns to the soil within a year. Initial results suggest that the increase in carbon supply to fine roots has increased the carbon content of the soil. Norby cautions, however, that the positive effect of carbon dioxide fertilization is insufficient to halt the rising level of atmospheric carbon dioxide.

If some types of forest trees will grow more rapidly then higher atmospheric CO2 holds the prospect of lowering timber costs and hence of lowering housing and furniture costs.

Another forest experiment shows CO2 raises tree growth rates.

SEATTLE -- A futuristic Duke University simulation of forest growth under the carbon dioxide-enriched atmosphere expected by 2050 does not reinforce the optimism of those who believe trees can absorb that extra CO2 by growing faster, said a spokesman for the experiment.

During seven years of exposure to carbon dioxide concentrations 1 times higher than today's, test plots of loblolly pines have indeed boosted their annual growth rates by between 10 and 25 percent, found the researchers. But "the highest responses have been in the driest years, and the effect of CO2 has been much less in normal and wet years," said William Schlesinger, a professor of biogeochemistry and dean of Duke's Nicholas School of the Environment and Earth Sciences.

These counterintuitive findings suggest that nitrogen deficiencies common to forest soils in the Southeastern United States may limit the abilities of loblolly pine forests to use the extra CO2 to produce more tissues as they take in more of the gas, he said.

"In a dry year trees naturally grow less so the amount of nitrogen doesn't make any difference," he said. "In a wet year, when there's plenty of water, the amount of nitrogen does make a difference." Tree growth depends on the availability of nitrogen, which foresters routinely add to Southeastern soils in the form of fertilizer when they plant trees, he added.

One advantage the plants may have in dry years is that with more CO2 in the atmosphere the leaves do not have to open their pores as much to let in the CO2. This reduces water loss from evaporation and allows plants to grow in dry environments. This explanation has been put forward to explain plant growth into the Negev desert in Israel.

The really bad news? More poison ivy:

Meanwhile, some other species in Duke's CO2-bathed forest plots have grown at faster rates than the loblolly pines, scientists report. Still-unpublished data shows 70 percent growth increases for poison ivy, according to Schlesinger.

It seems likely that the growth increase caused by higher CO2 will differ by tree species. Some will experience larger increases in growth rates and others will benefit from higher CO2 to a lesser extent. Also, since water is more of a rate-limiting factor in some areas and less in other areas the extent of the benefit of higher CO2 in terms of faster growth in lower water conditions will be greater in some geographic regions and less in other regions. Higher CO2 probably will increase total tree cover in drier areas and may even make it possible to grow trees into deserts as appears to be happening with the Negev.

Another factor to consider: It should be possible to select for or genetically engineer crop plants that will grow even faster in higher CO2 conditions. So the extent of the benefit of high CO2 seen with existing crop plants understates the size of the benefit likely to be achievable in the longer run.

Of course, higher atmospheric CO2 levels will cause many other effects. If higher CO2 raises global temperatures it could change precipitation patterns, total global precipitation, length of growing seasons (generally longer), wind patterns, and other many other factors. How will all this work out in terms of benefits and costs? It seems impossible at this point to hazard a guess that will have any degree of accuracy. But it seems clear that rising atmospheric CO2 will generate not just costs but benefits as well.

Share |      Randall Parker, 2004 February 17 03:22 PM  Climate Trends

back40 said at February 17, 2004 5:23 PM:

Good post Randall.

anonymous said at February 17, 2004 11:57 PM:

Marijuana growers have been using CO2 atmospheres to increase production for a long time. No big surprise that the same principle works on a global scale.

Engineer-Poet said at February 18, 2004 5:12 AM:

All kinds of greenhouse operators have been adding CO2 to pump up growth rates, but you'll notice that they also exercise lots of control over nitrogen, phosphorus, potash and any other nutrients that might otherwise limit growth.  You cannot generalize from hothouses to nature.

S. Basu said at December 8, 2005 1:10 AM:

I am interested to know the effect of enhanced atmospheric Co2 or soil CO2 content on the "short term crops, like paddy, wheat, various cereals, vegetables etc"

Les Wiegers said at June 4, 2008 5:38 AM:

People bleat about global warming, yet we have seen NO increase in sea levels in 100 years.
What we have seen is higher crop yields, faster timber growth, and reforestation in many areas in North America.
So, since 1900, increased co2 in the atmosphere from carbon fuels has been a NET POSITIVE.
When will the media concede this fact?

Doug Danhoff said at March 4, 2009 9:56 AM:

I am a paleo-geologist with a strong interest in paleo-climatology. In my opinion the concern about the level of CO2 in our atmoshpere is a straw-dog. There are ulterior motives that I will not approach in this post.
NOt only are the effects of more CO2 on greenhouse warming nearly complete (in that the present levels absorb nearly all the radiated energy available in the bands of CO2 absorbtion) but my studies have indicated that the Earth is actually in a CO2 starved era. We are nearly at our all time low in atmpspheric CO2 streaching back hundreds of millions of years. Levels have been more than a thousand times higher in the past, as in the Jurassic when much of our carbon base fuels were layed down, and we have had higher CO2 levels even during past ice ages.
Co2 is not a detriment to man kind in any way, and is totally benificial. Not only does it increase overall plant growth, we can not forget that enhanced plant growth will also increase our Oxygen level which has gradually reduced during the Holocene period.
It is my belief that even if we were to somehow create large dinosaurs from their DNA they would not survive in our (to them) oxygen poor atmoshpere.

Hyman Gesser said at April 21, 2009 1:36 PM:

It would be nice to take advantage of the high CO2 levels by greenhouse grow systems. I am presently developing a water on demand irrigation system that delivers water and/or nutrients to plants. With elevated CO2 levels the enhanced growth would easly pay for the greenhouse costs. Any ideas on this topic would be welcomed.

Kevin said at June 25, 2009 11:21 AM:

Love the discussion. The "Climate Change Crisis" is the biggest bunch of fecal matter ever. Let's assume for a second that the earth is heating up or CO2 Levels are rising. As Doug says above it is FACT that our climate (CO2 levels, average global temp) has been much different than it is today. Both higher and lower. This was long before Exon-mobile ever sunk a drill bit into the ground ie.. man had neither caused it or changed it in any way. So can we agree that it is probably going to continue to change in some kind of cycle regardless of man? If that is the case and this is somehow going to wipe out mankind shouldn't we figure out how to live WITH climate change instead of trying to prevent the unpreventable? Trying to prevent the earth's climate from changing is like a flea trying to derail a freight train. The climate is going to change. Species are going to evolve or become extinct. These are the facts.

rakesh said at October 25, 2009 7:49 PM:

can we havw a way by which we can rapidly grow forests in large areas just by throwing some highly powerful seedlings which would directly try to atach them selfs with soil and will grow with a much faster rates with ussage of some sort of chemical catalyst. by this way will be able to cover larger area in less time. more green is the earth more secure we are

biometria said at February 24, 2012 8:23 AM:

It's like talking to the plant - it's grows faster because of ours CO2.

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