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).


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