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Won’t extra carbon dioxide help to increase crop growth?

Why has there been no publicity for the findings that the projected increase in carbon dioxide is likely to increase crop growth by 20%? This increase will surely be needed if we continue to ignore population growth in our obsession with climate change.
P Douglass from Angus (Age 55+)


3 Responses

  1. This so-called ‘carbon dioxide fertilisation effect’ was once hoped to be a major negative feedback to human-induced climate change. It is quite right that many plants, including some crops, grow more rapidly when carbon dioxide concentrations are increased. In theory then, this effect would help soak up some of our carbon dioxide emissions and give us more productive fields. In reality, plant growth in most natural ecosystems becomes limited by other factors, such as nitrogen supply, and the big boom in plant growth from extra carbon dioxide fails to materialise. For crops, the extra growth that the carbon dioxide enrichment provides tends to mean that the nutritional quality of the crop falls. Most importantly, any increase in yields because of more carbon dioxide must be offset by decreased yields due to climate change impacts (drought, wind damage, pest attack etc). Globally, the latter are projected to far outweigh the former, with those areas with the highest rates of population growth also being those at greatest risk of big downturns in crop yields.

  2. Yes, additional atmospheric carbon dioxide (CO2) will act to enhance plant growth, and this will extend to crops. Models of plant response to climate change now routinely include the effects of CO2 fertilisation. However, the positive impacts of CO2 fertilisation will be limited where there are other constraints on plant growth, such as lack of water, extreme temperatures, lack of other nutrients etc. So the overall effect of climate change on crops will depend on a number of interacting and competing factors, of which CO2 fertilisation is just one.

    CO2 fertilisation is likely to combine with warmer temperatures associated with longer growing seasons to increase crop productivity in some parts of the world, mostly in middle and high latitudes. However, in low latitudes, particularly the arid and semi-arid subtropics, the impacts of reduced water availability and extreme temperatures are likely to dominate, and crop productivity is expected to decline.

    Overall, it is expected that global food production potential will increase for global temperature increases of up to about 2-3 degrees C, with most of this increase being in mid- to high-latitudes. At lower latitudes net productivity is expected to be adversely affected even at low temperature increases (1-2 degrees C). If global temperatures rise much above 2-3 degrees C, global food production potential is expected to fall.

    Chapter 5 of Working Group II of the IPCC Fourth Assessment Report summarises some of these impacts, and can be downloaded (for free) fromhttp://www.ipcc.ch/ipccreports/ar4-wg2.htm.

  3. These comments seem at odds with the results of the FACE experiments published in the Annual Review of Plant Biology 2004.

    Of course nutritional value will fall if the extra growth is not accompanied by adequate plant nutrition. That applies to any attempt to increase crop growth and yield.

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