Garth Paltridge: Climate’s Uncertainty Principle

  • Date: 07/04/19
  • Garth Paltridge, Quadrant

The bottom line of politically correct thought on climate alarm is so full of holes that it brings the overall sanity of mankind into question.

That is, we need to put a dollar number to the cost of doing something now, a dollar number to the benefit thus obtained by the future generations, and a number to a thing called “discount for the future”—this last being the rate at which our concern for the welfare of future generations falls away as we look further and further ahead. Only the first of these numbers can be estimated with any degree of reliability. Suffice it to say, if the climate-change establishment were to have its way with its proposed conversion of the global usage of energy to a usage based solely on renewable energy, the costs of the conversion would be horrifically large. It is extraordinary that such costs can even be contemplated when the numbers for both the future benefit and the discount for the future are little more than abstract guesses.

Assessment of the future benefit is largely based on two types of numerical modelling. First, there are the vast computer models that attempt to forecast the future change in Earth’s climate when atmospheric carbon dioxide has increased as a consequence of the human activity of burning fossil fuel. Second, there are the computer-based economic models which attempt to calculate the economic and social impact of the forecasted change of climate. Reduction of that impact (by reducing the human input of carbon dioxide to the atmosphere) is the “benefit” in the cost-benefit calculations.

Taking the climate change calculations first, it should be emphasised that in order to be really useful, the forecast must necessarily be of the future distribution of climate about the world—on the scale of areas as small as individual nations and regions. Calculating only the global average of such things as the future temperature and rainfall is not useful. The economic models need input data relevant to individual nations, not just the world as a whole.

Which is a bit of a problem. The uncertainty associated with climate prediction derives basically from the turbulent nature of the processes going on within the atmosphere and oceans. Such predictability as there is in turbulent fluids is governed by the size (the “scale”) of the boundaries that contain and limit the size to which random turbulent eddies can grow. Thus reasonably correct forecasts of the average climate of the world might be possible in principle. On the scale of regions (anything much smaller than the scale of the major ocean basins for example) it has yet to be shown that useful long-term climate forecasting is possible even in principle.

To expand on that a little, the forecasts of the global average rise in temperature by the various theoretical models around the world range from about 1 degree to 6 degrees Celsius by the end of this century—which does little more than support the purely qualitative conclusion from simple physical reasoning that more carbon dioxide in the atmosphere will increase the global average temperature above what it would have been otherwise. It does little to resolve the fundamental question as to what fraction of the observed rise in global surface temperature over the last thirty or so years (equivalent to a rise of about 1 degree Celsius per century if one is inclined to believe observations rather than the theory) is attributable to the human-induced increase in atmospheric carbon dioxide. There is still a distinct possibility that much of the observed rise in global temperature may be the result of natural (and maybe random) variability of the system.

While the forecasts of future global average climate are not really trustworthy and would probably not be very useful even if they were, the potentially much more useful forecasts of regional climates are perhaps just nonsense. A good example supporting this rather negative view of the matter is the variability of the set of hundred-year forecasts of the average rainfall over Australia. Each forecast was produced by one of the many climate models from around the world. The present-day measured average is about 450 millimetres per year. The forecasts for the next century range from less than 200 mm to more than 1000 mm per year. That sort of thing makes finding a model to support a particular narrative just too easy.

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