CO2 and Plants

Back in January, there was a huge debate in the comments here about “flora gains” – the suggestion by one of the regular commenters that we’d benefit from enhanced carbon dioxide because the plants on which we depend for food etc. would do better, with CO2 fertilization more than making up for any negative effects from climate change. It was one of those classic blog comment shouting matches, mostly heat and not much light, and I pretty much stayed out of it.

There are a couple of papers in tomorrow’s Science that add some light, and they suggest that the case for CO2 fertilization benefits has been overstated.

The problem, outlined by Stephen Long of the University of Illinois and colleagues is that the “enclosure studies” supporting flora gains were not terribly realistic. With better technologies that have allowed testing of enhanced CO2 in real-world settings, the benefits are far smaller.

I don’t know enough about the issue to understand where this fits in the broad sweep of research on this question. But I do know that this is a fair piece more interesting and important than hockey sticks, as this is the sort of stuff we actually need to understand in order to figure out what to do.

Food for Thought: Lower-Than-Expected Crop Yield Stimulation with Rising CO2 Concentrations, Long et. al, Science 30 June 2006: Vol. 312. no. 5782, pp. 1918 – 1921, DOI:10.1126/science.1114722

Climate Change and Crop Yields: Beyond Cassandra, Schimel, Science 30 June 2006: Vol. 312. no. 5782, pp. 1889 – 1890, DOI: 10.1126/science.1129913


  1. Hmm, where’s Steve Hemphill? Off somewhere having a crisis of faith?

    I haven’t has a chnace to read the papers yet, but when one conbines their apparent conclusions (of a remaining slight CO2 benefit) with the implications of changed weather patterns, in particular the increases in drought, and the poleward shift of climate zones, it seems highly unlikely that the net effect of global warming on crops over the next century or so will be anything but substantially negative. Potentially that could change over a longer period of time (with, e.g., wheat growing regions shifting onto lands formerly occupied by boreal forests), but the relative short term doesn’t look good.

  2. Interesting that someone would consider CO2 fertilization would more than make up for any negative effects from climate change. It’s certainly a possibility, despite this anecdote. However, we hardly know enough to predict that at this time… (although I see plenty of simplistic analyses predicting the other way).

    I didn’t see anywhere that they considered increased CO2 would increase the potential range for crops. Typical anecdote.

    Steve Bloom’s Chicken Little cries aside, I don’t believe I’ve heard the models consider that increased temp due to decreased transpitation would increase temps (a quarter of a degree F here – in the middle of the pack of apparent physical forcing). This week’s illustration of the models’ incompleteness.

    Funny, Steve B, that you would call my agnostic position “faith.” Your comment “it seems highly unlikely that the net effect of global warming on crops over the next century or so will be anything but substantially negative.” shows what cult you belong to…

    P.S. If the arctic warms more than the tropics, as projected (easy to believe with an increase of clouds as negative feedback), then climate zones will not “shift” so much as widen.

  3. Steve H., most of what I said was based on the Science paper, so I’m not sure what the basis is for your comments about anecdotes. Have you read the paper?

  4. Yes, I did, Have you read them now? You said you hadn’t read them yet, yet you say what you said was based on them. Slight logic problem there Steve B?

  5. I based my comments on the abstract, although now I have read the entire paper (and the commentary). But what I was curious about was your apparent description of peer reviewed work as mere anecdotes. What exactly is anecdotal?

    Also, Steve, FYI the sky is rising (i.e., the height of the tropopause is increasing).

  6. Anecdotal means an account of a single incident (location in this case). It is exactly the same as declaring global warming based on one glacier’s retreat. I should have said “these” anecdotes.

    In this case, these are but a few locations, hardly representative of e.g. lands on the edge of a plant’s range in arid regions, which generally should increase based on the reduced need for water. It’s like looking at the same number of glaciers.

  7. Steve H –

    Thanks very much for sharing your ideas on this subject. As I mentioned in my original post, I don’t know much about this, so it would be useful if you could point me to the relevant literature.

  8. John –

    Although some alarmists will jeer, again, at the source, has some interesting info.

    And, again, with hundreds of thousands of papers out there any position can be defended by quoting papers.

    I don’t know much about it either, except that people who miss concepts I can easily ignore. One concept here is that CO2 is not fertilizer for plants. It’s food. Therefore, someone calling it fertilizer has been mislead or is misleading – whatever – but is not what I consider a reliable source.

  9. Steve H –

    This new gambit of yours – “with hundreds of thousands of papers out there any position can be defended by quoting papers” – is intellectually bankrupt.

    You have a position, which you say is based on “studying this climate stuff for over a decade now.” Yet time and again in these discussions, both here and on the NMSR mailing list, you’ve been unwilling to defend it by pointing to the scientific papers that lead you to your views. Simply waving the question aside with the dismissive argument that one can support any position one wants in the “hundreds of thousands of papers” is of no use – just a trip down the postmodern rabbit hole.

    I’m asking you to make a positive contribution to the discussion. If all you’re willing to do is dismiss the studies you disagree with, without citing alternatives, then there’s really not much point.

  10. John,

    Apparently you’re not getting it. In fact, it’s the same as Al Gore stated here:

    “When Mr. Stephanopoulos confronted Mr. Gore with the fact that the best estimates of rising sea levels are far less dire than he suggests in his movie, Mr. Gore defended his claims by noting that scientists ‘don’t have any models that give them a high level of confidence’ one way or the other and went on to claim–in his defense–that scientists ‘don’t know. . . . They just don’t know.”

    My position is that we need to implement a massive research project of Manhattan Project magnitude.

    When you get right down to it, as Al said: “They just don’t know”.

    To falsely claim we need to institute a carbon trading scheme is ludicrous.

    To claim we *do* know what’s going on with climate is what is intellectually bankrupt. The point is CO2 may be the closest thing we have to manna and it may be relatively benign when it comes to climate change. To embark on a “sequestering” effort may be, in this time of burgeoning population, shooting ourselves in the foot. Do you really think a border fence is going to help in the long run?

    Is that clear enough for you?

  11. Clear? Yes. Helpful? No, frankly, not at all. Seems like a pretty cheap dodge to me to avoid having to defend your views about what we know and don’t know. But it is effective in leaving nothing further to discuss. Thanks for stopping by.

  12. Yes, well, some people don’t want reality interfering with their self perceived wizardry. Such are computer gamers.


  13. There is a video call global warming or global governance, if you fast wind through some of the political rubbish you will find some good science and a section on CO2 fertilisation, this is a real world study and enhanced CO2 production of plants and produce is carried on world wide, a doubling of CO2 gives an increase for :

    Barley 66%, rapeseed 82%, rice 37%, Sunflower 36%, Wheat 48%, Carrots 60%, Onions 28%, Potatoes 35%, and on and on.

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