Wednesday, February 23, 2005

Oxygen

In the debate over global warming, little has been said about its affect on oxygen balance. Atmospheric oxygen serves two crucial purposes for sustaining life on earth. In the upper atmosphere it takes the form of ozone and blocks ultraviolet radiation. Without this layer, no life on the surface of the earth could exist. The second purpose is as an oxidant for respiring life forms. Most of the oxygen on earth is sequestered in rocks like silicon dioxide. Atmospheric oxygen comes exclusively as a waste product of photosynthesis of plants and prokaryotic organisms. The bulk of atmospheric oxygen comes from photosynthesizing bacteria near the surface of the oceans.

The air is comprised of 78% nitrogen, 21% O2 and the rest as trace gases such as argon and carbon dioxide. The oceans also contain a large supply of dissolved carbon dioxide and oxygen. As water warms, it can hold a smaller amount of oxygen. Thus, as the oceans warm due to global warming, they are actually outgassing some oxygen (Keeling and Garcia, PNAS 99:7848-7853, 2002) . At the same time, oxygen in the atmosphere is also slightly decreasing due to combustion of fossil fuels.

Right now the decrease of oxygen in the ocean is 0.7 ┬Ámol per kg per decade. For comparison , the concentration of oxygen in the ocean is on the order of a few hundred ┬Ámol per kg. So the decrease is small but not insignificant. Given that one hypothesis for the extinction event 250 million years ago known as the Great Dying (see my previous entry) was due to a lack of oxygen in the oceans, I think that this is of some concern. We simply don't know enough to predict the consequences of global warming. However, I really think we need to take it seriously. Affecting the carbon balance could have implications beyond the melting of glaciers and the increase of hurricanes. It could affect the oxygen that we breathe.

11 comments:

steve said...

CC,

What's the status of the "hockey stick" graph? Last I heard it was hardly trustworthy and there was a warmer period not so long ago (middle ages).

Am I really supposed to believe the evidence for humans causing global warming? How many smart people are working on this who aren't ideologically driven?

Are you ready to say, as an unbiased physicist who has looked into the problem, that humans are responsible at the 95 or 99 percent confidence level?

Do these amazing, CPU-hogging, climate models capture basic physics issues like clouds, deep ocean convection, etc.?

PS I actually read the report of the UN panel and even they didn't seem likley to assign a high certainty to their conclusions.

Carson Chow said...

The hockey stick graph was challenged recently but I think the challenge was successfully refuted. You can check out www.realclimate.org for details. The original group used two principle components from their data and zeroed the means differently for different eras. The challenge claimed that if you zero-meaned the entire record and you used two components then the hockey stick disappears. However, the original investigators now show that if you use more components or all of the data then the stick returns.

I believe the evidence clearly shows that CO2 in the air is increasing and temperatures are rising. Now, can I unambiguously tell you that they are causally connected? No. But, I think the evidence is pretty good (and I'm somewhat of a skeptic).

The models do try to incorporate coulds and convection, etc. However, I believe the models are still inadequate to really tell us what will happen. My take is that we are definitely affecting the carbon cycle. It may or may not matter but are you willing to take the chance? I'm not sure we need to be completely alarmist about it but I think we should take it seriously. There are measures we could take now that would not be overly costly and still slow down the release of CO2 and methane.

Anonymous said...

There simply is much to be gained by acting as though we are adversely effecting the climate. However skeptical we may be about the evidence, there is every reason to increasingly emphasize conservative and energy efficiency. What birds, closely watch birds, as I do, and you will know the New England climate is changing. Why I can not say, but changing it is.

Anne

Anonymous said...

Steve

Why do you question the general ability and sincerity of researchers in the field of climate change? There is always poor and distorted research done in any applied field, but there are all sorts of clever and honest scholars. To slant an entire field is possible, but not simply to be expected.

Anne

steve said...

It is hard for researchers to keep a balanced view, even when dealing with very abstract topics like elementary particles or DNA or cell biology. People become wedded to their models or beliefs and fight for them irrationally.(Or even rationally, but out of self-interest rather than the interests of science.) It is only when the data gets to be of high quality that the irrationality can be defeated. In some subjects, where data (or rigorous mathematical proof) plays no role, idiosyncratic but incorrect beliefs are *never* defeated and simply go in an out of fashion. (Perhaps it is more polite to say that in those fields there is no such thing as an incorrect hypothesis :-)

Now, climate change research *is* very ideologically driven. I know it from talking to the practitioners. And, it is a very difficult, complex problem. In the absence of very good models and very good data the intermediate-term "conclusions" of researchers could be primarily determined by ideology and not by dispassionate scientific analysis.

I'm not saying I know the answer, just that I wouldn't be surprised if the current prevailing wisdom turns out to be wrong.

Carson Chow said...

It is possible that inherent fluctuations could swamp out any anthropogenic effects but the data is increasingly showing otherwise. The problem is that if we wait until the evidence is unambiguous, it could be too late. I'm not saying that we should act rashly but policy decisions must be made. If you were told that we found some possible correlations between nutrasweet and cancer would you stop drinking diet soda or would you wait until more data was in? That may be a personal decision but what would you do if you were the principal of a school? Would you get rid of vending machines?

I agree that there could be some economic hardship for reducing the use of fossil fuels. However, there are also benefits of such a policy that are independent of any putative effect on global warming. I think a reduction could be made without severe economic consequences and possibly beneficial ones in the long run. If this is the case, why should we not pursue it?

steve said...

CC,

I agree - I am not all for certain policy remedies. I would be for increasing CAFE mileage requirements substantially, and building more public transportation in the US - I myself ride my bike to school most days :-)

However, you have to agree that, scientifically, strong claims by these climate modelers are probably not justified. If you say "30% chance they're wrong, but we can't really take the risk," I can accept that.

steve said...

Oops, I meant "all for" certain policy remedies (as in, I support them :-)

Anonymous said...

Thanks, Steve and Carson :)

Anne

Carson Chow said...

I think we're in agreement. Unfortunately, loud screaming is sometimes the only way to get policy changes.

Anonymous said...

Scream we must :)

Anne