Sunday, October 08, 2006

The build-up of CO2 in our atmosphere will be good!

A common argument you hear goes like this:
because increased CO2 will lead to increased plant growth, the build-up of CO2 must therefore be a net benefit rather than a net harm to our society
Does this type of argument make sense? To understand why it doesn't, realize that in any environmental disaster, some groups always benefit. Consider the destruction of New Orleans by Katrina. Few people consider this event to be a net benefit to our society. However, it is easy to pick out small groups that greatly benefitted from it. The owners of demolition companies, construction companies, construction material companies, etc., are all making money hand over fist.

Thus, one could make the argument:
Katrina's destruction of New Orleans was a highly beneficial event because it greatly stimulated the construction industry on the Gulf Coast.
This is, of course, extremely misleading and most people would agree is wrong. While some benefitted from the destruction of New Orleans, the net result, considering all harms and benefits, was clearly negative.

So when people argue that climate change must be good because plants grow better at higher CO2, think about the Katrina example. Plants might indeed do better(*), but that tells us nothing about all of the other harms and benefits. As I discussed in a previous post:
Clearly, some people will benefit from warming, while others will suffer. There are a lot of dimensions to this (economic, moral, etc.), but I'll just give the broadest answer. For small warming (e.g., 1 deg C over the next 100 years), current thinking is that harms and benefits are largely comparable, although it is estimated that harms still outweigh the benefits. As the warming increases, the harms get much bigger, and begin dominating over benefits somewhere around 2-3 deg C of warming. That's why 2-3 deg C is often referred to as a tipping point or threshold for dangerous anthropogenic interference. Warmings much greater, say 5 deg C, would be a calamity of Biblical proportions ... real Wrath of God stuff.
Make no mistake. Estimates of harms and benefits are highly uncertain. However, there is clearly a significant risk of serious net harms over the next century as the climate warms. People arguing that there is no risk of serious harms are either dishonest or disconnected from reality.

* For the record: While most plants do grow better as atmospheric CO2 increases, there's dispute about whether this means that plants will grow better under global warming scenarios. While CO2 is definitely going up, which will help plant productivity, there are other changes that might not benefit plants, like changes in precipitation patterns, soil moisture, migration of invasive species, etc. Overall, it's unclear how much plant productivity will actually increase.


EliRabett said...

The probability is that increased growth of C3 plants will saturate a bit over 600 ppm (~2X).

I do not think you should automatically accept the argument that crop yields will increase indefinitely with increased CO2 mixing ratios and temperatures. At best, this remains open. Moreover, many other factors are limiting for plant growth.

Finally, by looking at CO2 mixing ratios measured at various locations, I have constructed an argument about the NET effect of increasing temperature and CO2 on CO2 concentrations which, at least at first order, indicates that there is a relatively small effect that will not be very useful

Nexus 6 said...

Results from the recently conducted FACE experiments probably represent the best current estimates as to how crops will perform under increased CO2 concentrations ( Significantly higher yield increases were demonstrated in earlier CO2 enrichment greenhouse experiments. FACE represented the first large-scale "real world" field-based experiments. Unfortunately, some crops showed lower than expected yield increases and some showed none at all. Add in elevated ozone and yield then became significantly negative. In a presentation I saw by Steve Long last week, another unexpected finding was that bugs preferred the plants grown in the CO2-enriched environment for some reason (Greenhouse experiments had not shown this at all).

Still lots to be learned, but it does appear that any crop yield benefits from the build up of CO2 will be minimal.

(A good roundup of the FACE experiments here:
Science 30 June 2006: Vol. 312. no. 5782, pp. 1918 - 1921)

Mark UK said...

Of course there is issue that as I understand it the most severe results of global warming will be in those areas that are already struggling with agriculture such as Africa and Asia. I can already hear the skeptics say as we watch tv footage of people dying in Africa that hunger has always been there, so nothing new...

Dano said...

And in case anyone wants to tout certain phrases in Nexus 6's excellent comment without providing context, increased CO2 in graminaceous plants reduces the amount of N apportionment going to seeds (the part we eat), meaning less nutrition in the yield.



Anonymous said...

Well you have to go with the obvious.

Any best estimate has to leave one thinking that extra CO2 will lead to massive net benefits because of the extra productivity of agriculture and the natural world.

Plus extra precipitation mean MORE AND NOT LESS RAINFALL. So when you say CHANGES IN PRECIPITATION what are you talking about?

We will get more rainfall and greater productivity through extra CO2.

That seems clear enough.

The Katrina analogy is not a very good one.

In the experiment that Nexus mentions they used OZONE which reduces the plant growth. That being so however the experiment reaffirmed the extra productive power of CO2.

There are thousands of experiments using CO2 and Nexus has unscientifically chosed to predjudice one of them. Yet that very study that Nexus has singled out reaffirms the power of CO2 to improve plant growth. Even when the plant growth is being hampered by Ozone.


Andrew Dessler said...


You seem to ignore the main point here. If we assume that CO2 will indeed increase productivity, that ignores all of the other harms of climate change. Do you think they don't exist?

As far as what I meant about changes in precip, I mean changes in intensity, location, timing, phase, and amount.


EliRabett said...

Well, it appears Anon needs to read Science on a recent metasudy of FACE experiments

The bottom line is that

* There is no CO2 fertilization effect for C4 crops although increased drought resistance may be significant.

* FACE studies show that current ag models significantly overestimate CO2 fertilization for crops

* C3 crop CO2 fertilization saturates somewhere between 600 and 800 ppm CO2. This means no benefit above 2xCO2

* Crop breeders should work on developing strains that can benefit from higher CO2

Anonymous said...

"You seem to ignore the main point here. If we assume that CO2 will indeed increase productivity, that ignores all of the other harms of climate change. Do you think they don't exist?"

It doesn't DO any net harm.

On the contrary since we are on a planet that is hard-wired for catastrophic COOLING and not catastrophic WARMING then the CO2 is presumably doing A GREAT DEAL OF GOOD.

Dessler you aren't going to vouch for anything Rabbet here is saying are you?

Because pretty much everything he says here is in error.

Will you step outside your expertise and make the case for FACE technology? And for the idea that FACE technology DOES NOT show that CO2 increases yields?

It DOES still show that yields are increased but thats not the point. It is not to be thought that FACE represents the most indicative type of study in the first place.

And notice how Rabett all of a sudden is only concerned with one group of plants and only with one study to do with this one group.

Some people just make you laugh with their mindless prevarications.

Peter Keen said...

It should be remembered that the “greenhouse effect” is a theory; not a proven fact. It should be remembered that there have been warm periods in history long before the motor car – what caused it then? Factors controlling conditions on earth are not well understood and to claim that warming is due to burning fuel is simplistic. In Britain the warm dry summer of 1976 was heralded as proof of the “greenhouse effect” – this was the shape of our future summers – there hasn’t been another like it since. In Britain in 1981 we had the coldest winter temperatures recorded. This was also claimed to be due to the “greenhouse effect” – Britain was going to get colder while other countries warmed up. In short, every freak weather situation is held to be the “greenhouse effect” whether it be cold or heat or wet or dry or calm or windy.

The bandwagon has been seized by the politicians who use it for an excuse to raise “green” taxation while doing little to alter the increasing use of fuel or to provide viable alternatives.

The world depends on oil for transport and many other industries, for example, plastics. Of far more fundamental importance is the fact that at current escalating use of oil it will probably have run out within a few years. The “spent oil effect” will have a far more dramatic and devastating consequence than the “greenhouse effect” in the short term.

Combined with other existing and pending problems is summed up in the Biblical summation of these times as “distress of nations with perplexity”. The knowledge that things are in the control of God rather than us is reassuring. While waiting for His intervention, if the British weather does warm up I shall enjoy switching my heating off and hanging my fleece lining up.