A Reply to Dyson

This is a guest blog post by my colleague R. Shankar

Dyson starts of with a critique of climate scientists.

"But I have studied the climate models and I know what they can do. The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world that we live in. The real world is muddy and messy and full of things that we do not yet understand. It is much easier for a scientist to sit in an air-conditioned building and run computer models, than to put on winter clothes and measure what is really happening outside in the swamps and the clouds. That is why the climate model experts end up believing their own models." -Dyson-

Somewhat unkind. All earth scientists I have talked to are acutely aware of the limitations of the models. The discussion in the IPCC report also reflects this. Eg to quote from their latest report (AR4, pp 113)

"A parallel evolution toward increased complexity and resolution has occurred in the domain of numerical weather prediction, and has resulted in a large and verifiable improvement in operational weather forecast quality. This example alone shows that present models are more realistic than were those of a decade ago. There is also, however, a continuing awareness that models do not provide a perfect simulation of reality, because resolving all important spatial or time scales remains far beyond current capabilities, and also because the behaviour of such a complex nonlinear system may in general be chaotic" -IPCC report-

Much of the effort in climate sciences is in observation and data collection. I would put the number who "sit in airconditioned offices and run computer models" as a very small fraction of the total. The IPCC report is based on a huge amount of field observations and data.

Next he makes a statement:

"There is no doubt that parts of the world are getting warmer, but the warming is not global. I am not saying that the warming does not cause problems. Obviously it does. Obviously we should be trying to understand it better." -Dyson-

When people say global warming, what is meant is that the average global temperature has increased by about 1 degree C in the past century. This is based on instrumental observations which have been taken by Met stations all over the world. Nobody says that it is uniform in all parts of the globe.

The reason to worry about this one degree per 100 years is that the "natural" rate of temperature change (due to the glacial cycles which Dyson also discusses) is about 10 degrees in 100,000 years i.e 1 degree in 10,000 years. This is concluded from the ice-core data which goes back to 800,000 years. Even during the sharp rises and falls the rate never exceeded about 1 degree per 1000 years. So the current rate of increase is abnormally high.

Coincident with this rise is the rise of C02 levels. It is 380 ppm today and has never exceeded 300 ppm in the past 800,000 years.

He then says:

" I am saying that the problems are grossly exaggerated. They take away money and attention from other problems that are more urgent and more important, such as poverty and infectious disease and public education and public health, and the preservation of living creatures on land and in the oceans, not to mention easy problems such as the timely construction of adequate dikes around the city of New Orleans."

While development and conservation efforts could definitely be much more, I don't think that the hype about climate change is a significant cause for them being less that what they should be.

He then talks about what are called "geo-engineering solutions" (there are many such in the market) but without mentioning if any serious research has been done to back his statements.

He then says:

"When I listen to the public debates about climate change, I am impressed by the enormous gaps in our knowledge, the sparseness of our observations and the superficiality of our theories. Many of the basic processes of planetary ecology are poorly understood. They must be better understood before we can reach an accurate diagnosis of the present condition of our planet. When we are trying to take care of a planet, just as when we are taking care of a human patient, diseases must be diagnosed before they can be cured. We need to observe and measure what is going on in the biosphere, rather than relying on computer models."

There are of course huge gaps in our knowledge (which is why one should be cautious about implementing geo-engineering solutions) but again he gives the impression that the the entire case of climate change is based on simulations. Even a cursory reading of the IPCC reports should convince anyone that this is not true.

The statements of the recent past (approx 100 years) are based on observation. The climate models do reproduce average quantities like global average temperature of the recent past (100 years) reasonably well. These models are then used to project for the immediate future (next 100) years. They predict temperature rises that are sensitive to the carbon emission levels with a worst case of about 4 degrees rise in the next century.

As Dyson points out, the carbon cycle is indeed not well understood and a lot of fudge factors must be going into the models to make them fit the past data. One has to therefore use one's judgment to decide how reliable they are. But rejecting them completely, in my opinion, is very bad judgment. A doctor has to make a diagnosis based on whatever observations and tests he/she has conducted and however incomplete his/her knowledge of the processes in the human body may be.

In my opinion, the model predictions should be reasonably reliable for the immediate future where the validity of the fudge factors may not breakdown. What will happen over time scales of thousands of years is indeed unpredictable and the IPCC report says nothing about it. The worry is more about the immediate future (2000-2100). So even if the rise in CO2 levels and temperature is a transient phenomenon of a few hundred years, we have to worry about it and think about corrective action. Controlling emissions seems to be the most reliable way.

The details of how the average temperature rise will affect details of climate is still open (again for the immediate future). eg. I feel that the questions most relevent to India are how it will affect (i) Agriculture (ii) Monsoon (iii) Disease. All of them seem to be very open questions.

The next part of his article talks about time scales of thousands of years where it is really anybody's guess.

The final part is philosophical and I do not think classifying all the opinion on this issue into 2 classes is correct (smells of the attitude "you are either with us or against us"). People have all types of permutations and combinations of extreme opinions. Nevertheless, apart from a few fringe elements nobody would deny that ideally we should aim for a pattern of sustainable development. Of course the devil is in the details of what is meant by sustainable development but I do not see any major ethical conflict here.

Even without the climate models, the data (given in the graph)

along with the basic physics of the greenhouse effect is enough to convince me that the problem is genuine. (the url of the ice core data graph is given in the picture, the other 3 graphs are from the IPCC report AR4, comments below the graphs are mine).

Roddam Narasimhan has pointed out recently that Arrhenius had estimated a rise of 5 degrees C if the CO2 levels in the atmosphere doubled (from what it was in his time). All the complicated climate models also predict roughly the same. So as he put it, the number has not changed only our confidence in it. Roddam Narasimhan is working on clouds and he motivated it by saying that this is one of the poorly modelled things.

With this in mind and looking at the graphs, I feel it is really unlikely that the downturn in CO2 levels and temperature will come due to natural processes alone (if emissions are not controlled) within a few hundred years (if at all).