Uncertainty and the Daily Mail

(Note: Daily Mail links now go via the wonderful istyosty service, which means that the Mail does not get the advertising revenue from the hits)

The word “uncertainty” has a special meaning in science, quite different to its normal everyday meaning. If I say that I am uncertain about my future, or what to have for tea tonight,* then it might mean that I am “undecided” or “unsure”. If however I do an experiment and I say that there are uncertainties in my data, that does not mean I am undecided or unsure about the results, or that the whole thing was a waste of time.

Instead, all it means is that I realise that my measurements are not – and can never be – 100% precise and accurate. For example, my kitchen scales weigh things in units of grams, so they could tell me the difference between 99 grams of flour and 100 grams, but aren’t precise enough to tell me the difference between 100.1 grams and 100.2 grams. That’s an example of an uncertainty (±0.5 grams in this case), but it’s not one that means that the scales are completely useless; they might not be perfectly accurate but I can still use them to bake a cake.

I say this because apparently the Daily Mail‘s science editor apparently fails to grasp this fairly simple idea:

Royal Society issues new climate change guide that admits there are "uncertainties" about the science

The UK’s leading scientific body has been forced to rewrite its guide on climate change and admit that it is not known how much warmer the Earth will become.

The Royal Society has updated its guide after 43 of its members complained that the previous version failed to take into account the opinion of climate change sceptics.

Now the new guide, called ‘Climate change: a summary of the science’, admits that there are some ‘uncertainties’ regarding the science behind climate change.

And it says that it impossible to know for sure how the Earth’s climate will change in the future nor what the possible effects may be.

Of course there are uncertainties in climate change predictions, just like there are uncertainties in every field of science, but the fact we can’t know “for sure” doesn’t mean we can’t know at all. Sure enough, the Royal Society’s guide (PDF) does not say that it is uncertain about whether climate change is happening. Instead, the word “uncertainty” is mentioned only in sentences like these:

Measurements show that averaged over the globe, the surface has warmed by about 0.8°C (with an uncertainty of about ±0.2°C) since 1850.

Calculations, which are supported by laboratory and atmospheric measurements, indicate that these additional gases [resulting from human activity] have caused a climate forcing during the industrial era of around 2.9 Wm-2, with an uncertainty of about ±0.2 Wm-2.**

It is not possible to determine exactly how much the Earth will warm or exactly how the climate will change in the future, but careful estimates of potential changes and associated uncertainties have been made. Scientists continue to work to narrow these areas of uncertainty.

(Emphasis mine)

In other words, there are uncertainties in the data, but whether the surface has warmed by 0.6°C or 1.0°C, there is no scientific dispute that the planet has warmed and that the warming has been caused by humans. The Royal Society has not turned denialist, and contrary to what the Daily Mail suggests, according to this guide it remains certain that climate change is happening – it just realises we don’t always know the exact figures. To suggest otherwise, based on quoting out of context a single word with several different meanings, is not just misleading, it borders dangerously close to dishonest.

* Homemade tomato soup ± crusty bread
** Climate forcing, measured in Wm-2 (watts per square metre), is a measurement of how much heat the atmosphere traps versus how much it lets go. A positive climate forcing means that gases are trapping heat faster than it can get released.

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