Climate Change – What you can argue about

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Weather and climate are subjects for discussion at all levels. Some discussions are well informed. Others less so. On this page, following discussions and arguments on web forums, sometimes vitriolic, I try to suggest what can be discussed sensibly.

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Statistics

Statistics can prove negatives but not positives. If there is no correlation between two events, then a physical cause and effect is unlikely. However, a positive correlation can indicate that there may be a physical cause and effect but does not prove that one exists.

A simple example is the strong relationship between persistent condensations trails from aircraft and the likelihood of rain in the next 24 hours. Fairly obviously, that does not indicate a cause and effect. From this example, I suggest that arguing about statistical evidence for or against anthropgenic effects on climate simply generates much heat and liitle light.

Statisticians at the World Meteorological Organisation, NOAA or the UK Hadley centre can produce convincing eveidence to all but the sceptics. The sceptics can trot out counter statistics that the scientist can refute. There will be no meeting of minds.

”Rational” argument

Climate change sceptics often produce arguments along the lines of "It stands to reason that ....." Unless quantifiable, these carry little weight. For example, we know that industrial activity increases the amount of greenhouse gases in the atmosphere. We know that deforestation decreases the capacity of vegetation to absorb CO2. Therefore, man’s activities lead to the increased ability of the atmosphere to absorb more long wave radiation from the earth.

At the same time, both industrial processes and deforestation lead to more dust and other aerosols. These have a cooling effect. Further, it might be suggested that warmer air will lead to more evaporation from the sea and, consequently, more cloud. If so, that could well mean that more radiation from the sun is reflected back out to space. While all these sound and are plauible, our brains cannot quantify the resultant effects.

Melting of ice-caps could lead to less solar radiation being reflected out to space and more warming of the earth’s surface. On the other hand, melt water will change the salinity in waters near the polar regions. That would affect ocean currents. In turn that would affect the atmosphere. But the atmosphere drives the oceans. Again, we cannot quantify the effects.

My conclusion from the above is that any argument about how and why climate is changing cannot be based on any such subjective ideas.

Climate models

If we want answers to one of the, if not the most, important question facing mankind today then a cold blooded scientific approach is the only way. That is what climate modelling is all about whether at NCAR, NOAA, The Hadley Centre, ECMWF, or any other major meteorological organisation.

Climate models have to take into account and use input from oceanographers and many other earth scientists. I cannot conceive of any other way of making progress – other than simple minded guesswork.

Modelling for day to day forecasting has been in development since the late 1940s. Some examples of NWP output, chosen fairly randomly, show that models can now give pretty good, never precise, forecasts up to about 5 days ahead. This is far better than in 1980 and models have reached a standard unimaginable in 1949 – the date of the first crude attempt at NWP.

Climate modelling has been in development effectively since the 1980s. However, the most powerful computers are still miniscule compared to the atmosphere. Progress is incremental depending on continual increases in computer power and continual increases in understanding about all the factors that determine climate and how they interact. It is a long haul. The best that can be said is that the models give the best answer possible but not the best possible answer.

Where do we go from here?

The whole question of whether or not man is having a deleterious effect on the climate is complicated by the question of sources of energy; how much fossil fuel is available for exploitation; to what extent those sources are secure in terms of geo-po;itics; what other sources of energy are affordable and acceptable.

I am not competent to discuss these issues which are beyond the scope of this page. My only suggestion is that when considering the whole enrgy question, this should be done in the light of the best climate science available. Such considerations have to take into account the error bars in the model outputs. Further, policies and plans should e kept under review as the science improves, as it will.

And, finally

Forget the statistical arguments about climate change. Ignore unquantified statements about effects on climate. By all means, question the climate modellers on their assumptions, how well they can model atmospheric physics on the gloal scale and what they regard as the major uncertainties.


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