Saturday, October 30, 2021

COP26 Too Many Numbers

What is 3?

Mathematician: The third positive integer.
Physicist: A value between 2.5 and 3.5.
Engineer: Three’s three but let’s call it ten to be on the safe side.

Charles Darwin included no numbers whatsoever in his The Origin of Species. Good science does not have to include numbers. Today one would have difficulty finding a piece of writing about climate science that is not peppered with numbers. If it is a scientific paper the numbers will usually be accompanied by measures of error and probability ranges, but these are usually ignored by journalists reporting for a lay audience, often leaving values with too many significant figures, giving a spurious degree of precision.

Forecasting, especially the future, is always difficult and models are always wrong, though some can be useful. The ‘Butterfly Effect’, whereby small changes in initial conditions can produce large changes in outcomes, is well known. Less well known, but more dangerous, is the ‘Hawkmoth Effect’, caused by unknown errors in the model that result in unknowable errors in model output. Wisdom must be applied when dealing with any numbers derived from modelling, as Erica Thompson explained in her Escape from Model-Land.

Unfortunately, in climate science errors are not evenly distributed between good news and bad. If tomorrow’s weather forecast is for 1mm of rain, there is little scope for error on the sunny side, just 1mm. But on the wet side the possibility range of error is boundless.

The most frequently mentioned number is 2.0 (1.5 is already for the birds), the number of degrees centigrade of global heating that the Paris Agreement said we should not exceed. It is an arbitrary number, no more special than 1.9 or 2.1, plucked from the air as thought, by some, at the time, to be a danger threshold. It is a rise since an arbitrary date, and one over which there is disagreement, some favouring the beginning of the industrial age and others favouring 1880, which hides the earliest anthropogenic heating. The global temperature is not a number that can be read from any thermometer. Rather it is an average of thousands of measurements from instruments distributed across the planet, calculated after weighting for local factors and known errors. It does not well reflect actual temperature change experienced by people. Land temperatures have risen faster than over the oceans, the Arctic heats faster than the tropics. Changes in the frequency of extreme weather events are not reflected in this average, yet it is extremes that kill. There is no way to relate that 2.0 figure to actual detriments. We don’t have any direct quantitative link between the average global heating number and storms, floods, droughts, plagues and wars. We just have a qualitative idea that the hotter it gets the worse it will be.

COP26 is very much a numbers based exercise, with countries declaring what steps they intend to take and when they might take them. We know it will all be too little and too late to avert disaster for many, yet it will be built on a great edifice of meticulously calculated ‘carbon budgets’ that imply perfect knowledge of the link between emissions, temperature rise and harm. We do not possess that knowledge.

We have only a very hazy appreciation of the effects of the many potentially big feedbacks in the climate system and some have not been factored into the COP26 discourse at all. Take, for example, greenhouse gas emissions from thawing of Arctic permafrost. It is happening today, with a mere 1.2 degrees of global heating and will continue for centuries. The rate of thawing and consequent emissions will increase as global heating proceeds. If all the nations achieve what they promise and more, and the temperature rise is constrained, the permafrost will still keep thawing, adding more greenhouse gases, undermining the best laid plans and making nonsense of all those calculations that contributed to the Nationally Determined Contributions. The scale of this problem may be equivalent to the emissions of a major economy, USA, China or the EU, and continuing far into the future. Big numbers but not counted.

So what to do? Put the numbers aside. Tell our governments to stop negotiating on the basis of numbers but instead put all their efforts into avoiding burning any more fossil carbon. Each has to do everything they can without looking over their shoulders to check they are not doing more than others. Lead, don’t follow.

If there’s one thing to read next it’s the State of Cryosphere 2021 report, particularly chapter 4, Permafrost. There are some numbers, but not so many that it becomes unreadable.


Blogger Les W Kuzyk said...

As an analyst, on the climate file for 15 years, I totally agree. The challenge I would suggest is to find an easy to understand number, a simple number for the masses, and get that into everyday talk. Political talk and economic talk, such as at COP26. As an analyst, I see around me data, and in the blah blah blah of everyday people, I hear highly incorrect information when quantified. Good article Bill.

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