The Fool on the Hill: The 'everyone dies' event comes home

[This essay is not complete; a draft of it has been sent to the Meteorological Office for their comment. It will be updated when they respond]

On 23^rd June, the Meteorological Office published a blog post in which they claimed that 'UK could see 45°C by 2056'. As you'll know, I've blogged before of the issue of excessive heat events in our changing climate. So the fact that they projected temperatures above 35° Celsius without commenting on humidity triggered my attention.

The projected weather map (data from Meteorological Office)

I'm preferring links to the Meteorological Office's published information over links to other authorities in this post for reasons which will become apparent later...

Why Britain is wet

Britain sits to the east of a large ocean. Because of the Coriolis effect, average wind flow has a westerly bias irrespective of climate, and, additionally, for at least the period during which people have been navigating the seas and leaving records, the prevailing winds at our latitude in the north Atlantic have been westerly.

Throughout recorded history, there have been substantial areas of the tropics where prevailing winds have been easterly, overcoming the Coriolis effect, because of patterns of climatic circulation. I don't have the theoretical knowledge to say confidently that the prevailing wind over Britain could not change as a result of the warming global climate. But I've seen no projection, either scientific or otherwise, to suggest that it will.

Additionally, wind circulates clockwise around a high pressure area in the northern hemisphere, so if the centre of the area is to the south of us (high pressure often in summer ridges up to us from the Azores, and thus the centre is to the south of us) the airflow will be westerly. So wind in summer heatwaves will tend to be off the sea. Only if the centre is north of us will it be easterly, for example when the high is centred over Scandinavia (which does happen but is rarer).

What is certain is that prevailing wind off the sea has meant that Britain's air is relatively humid. Of course, it is particularly humid because the Atlantic Meridional Overturning Circulation means that the surface temperature in the temperate north Atlantic is warmer than one would otherwise predict for our latitude. There is evidence that this circulation is slowing and may stop altogether, in which case it might be reasonable to project that Britain would become somewhat less humid. I don't know, I haven't studied this. The Meteorological Office at least ought to have done so.

Of course, if the circulation does stop, that will cause other changes to the weather which will call into question the viability of a dense human population in Britain, but that is not the subject of this essay.

The upper climatic limits to human survival

People maintain a homeostatic temperature by sweating. If our body temperature rises only a few degrees above normal, proteins in our tissues start to denature, leading quite rapidly to death.

Sweat cools the body by evaporating. It can evaporate only if the air around the body can absorb moisture; if the air is already saturated, nothing (more) can evaporate. The humidity at which air becomes saturated varies with temperature. I covered this in more detail in my essay 'The Everyone Dies Event Class'.

Maximum survivable temperature, by humidity

Data from Bioarxiv.

The typical daily high humidity in England in July is around 90% (data from Current Results). Figures for Scotland are similar.

The average humidity levels in July for cities and towns in England

An Everyone Dies event?

So: given the data above, and the projected map above, the 'everyone dies' event projected by the Meteorological Office covers the triangle bounded by Plymouth-Norwich-Glasgow — and yes, that includes us here in Auchencairn.

Let me repeat that carefully, for those at the back: if I understand this correctly, the Meteorological Office, a scientific agency of the UK government established to forecast the weather, appear to be projecting that by 2057 the overwhelming majority of the population of England and Wales, and a majority of the population of Scotland, will either have emigrated somewhere cooler, or else will have been killed — killed as in dead — by the weather.

Even widespread installation of air conditioners¹ does not greatly alter that projection, because

1. All those air conditioners, pumping heat out of the buildings, would raise the ambient temperature still further; and
2. We don't have grid capacity to power them.

However, of course, in extreme heat people will tend to gather (and will probably be advised to gather) in buildings where there's good air conditioning (e.g. hospitals, chilled warehouses, some office buildings) and in places which are protected from extreme heat (e.g. railway tunnels, crypts, cellars).

But if there's a prolonged heatwave — the Meteorological Office blog is talking about one lasting a fortnight, which is more or less what we have as I write this — then the logistics of feeding and sanitation for large number of people crowded into spaces many of which were not designed to house large numbers of people become problematic; and any grid failure, when large numbers of people are crowded into air conditioned buildings, would leave those people unprotected. Grid failures are common in heatwaves.

There's also the point that modern cities, because of their structure and design, tend to be significantly warmer than their surrounding environment, and are also where the population is most dense; so providing shelter for city populations will be especially difficult.

So while shelters may help protect many people, it seems to me unlikely that they could protect a significant proportion of the population.

Checking my understanding

But do I understand this correctly? The only circumstance which would alter my conclusion would be if the Meteorological Office has evidence to suggest that Britain's summer humidity levels will fall by more than one third by that time. It's possible that that's true; I certainly don't have the theoretical knowledge to say that it's false. So, I asked them.

Dear Met Office

I've read your blog UK could see 45°C by 2056, scientists reflect on 1976 heatwave anniversary, published this week, and note that it does not give figures for projected humidity.

As you will know, human beings die in an environment with a wet bulb temperature above 35° C. At 45° C, that implies a maximum survivable humidity of about 55%; at 41° C, a maximum survivable humidity of about 68%. The humidity here in southern Scotland yesterday, in summer heatwave conditions, had a low of 77%, and a high above 90%.

Looking at your projected map, with my current understanding of probable UK summer humidity, it would seem that you are forecasting that in such an event, everyone in the triangle bounded by Exeter, London and Sheffield will die; and if that is what you are forecasting, then I think you have some public responsibility to say so.

You may, of course, have some reason to believe that, while temperatures will rise in future summers, humidity will decrease. But if so I would really appreciate a reference to a document in which the reasons for this belief are laid out.

Yours sincerely

Simon Brooke

The Meteorological Office reply

And their reply?

Dear Simon,

Thank you for your email.

The temperatures featured in the blog are taken from a plausible future climate scenario designed to help illustrate how heat extremes in the UK could change in a warming climate. The scenario is based on temperature projections and was not intended to represent a comprehensive assessment of all meteorological variables or associated health impacts.

Humidity levels during future extreme heat events cannot be assumed to remain the same as those experienced during present-day weather events, and the scenario should not be interpreted as a forecast of unsurvivable conditions. Rather, it is intended to highlight the increasing likelihood and severity of extreme heat events and the importance of preparing for their impacts.

For further information on how climate change may affect temperature, humidity and heat stress in the UK, you may find the UK Climate Projections (UKCP)https://www.metoffice.gov.uk/research/approach/collaboration/ukcp resources helpful.

Kind regards,

This strikes me as a non answer. 'Humidity levels during future extreme heat events cannot be assumed to remain the same as those experienced during present-day weather events', they write. No, indeed they can't; that's why I wrote to the Meteorological Office to ask the question. But unless they change dramatically, that is a 'forecast of unsurvivable conditions.' Are humidity conditions expected to change dramatically? They don't say, except to refer me to their UK Climate Projections resource.

The key document, as far as I can see, in that collection is this one. It projects, for the UK, temperatures (page 96); precipitation rate (pages 97-98); wet day frequency (pages 99-100); average temperature and precipitation by month (page 101); winter and summer temperature extremes (page 103); precipitation extremes (page 104); precipitation intensity (page 105); changes in air temperature by season (pages 108-109); precipitation by season (pages 110-111); and so on.

Many of these projections clearly have a relationship to humidity. It is possible that an experienced meteorologist may be able to derive conclusions about humidity from this data. But I as a lay person cannot, and the document contains no explicit projections of UK summer time humidity.

As far as I can find, the nearest thing to an answer to my question is this paragraph, from page 111, discussing changes in summer precipitation:

Changes in summer precipitation (Fig. 4.8d) reveal a consistent drying response in RCM-PPE in most regions. The only exceptions are some coastal areas of Northern Scotland, where the high responses shows the potential for some small increases. The UK average reductions are 41% (low), 26% (central) and 18% (high). Rajczak and Schär (2017) find a smaller level of drying in the EuroCordex ensemble mentioned above. In this, spatial average changes for the British Isles revealed that three simulations gave a small increase (maximum value 10%), and twelve of the fifteen simulations simulated a drying. However, the largest reduction was only 28%

There's further discussion of summer drying on pages 117-118, on page 124, on page 133 and (further into the future) on page 137; I don't think these add significant new information that I can interpret.

In each case 'drying' is commented on in relation to precipitation, not humidity, and while the two must be linked, it is not obvious to me that the link must be either direct or linear. I'm certainly familiar with days of very high humidity when it does not rain.

However, if one interprets 'drying', here, as meaning lower humidity, then yes, there may be a reason to believe that summer humidity will drop. But, crucially, if that last sentence should be interpreted as saying the maximum probable reduction in humidity is 28%, then 28%, given the projected temperature map with which we started, is not enough to prevent an 'everyone dies' event (although it would be limited to an area covering Bristol-London-Birmingham).

On page 151 of the document we find

The ensemble-average drying for England reaches 50% by the end of the 21st century, compared with a median reduction of about 40% in Strand 1

which, again, if we interpret 'drying' to mean reduction in humidity, would make 45° Celsius (just) survivable — but that's by 2099, by which time those who died in the summer of 2056 are already long dead, if (probably) not buried. Because who will be left to bury them?

Why might the Meteorological Office not want to answer?

If you tell people that they're going to die, they're inclined to panic. That's not a good thing. You can see why a responsible government agency would not wish to induce panic.

But, the information that they referred me to in answer, while it is not written for a lay audience and I am not qualified to fully understand it, does seem to me to confirm that they are predicting a mass death event; in which case, they must know it.

At its simplest, if they are not, they could have replied, 'no, you are wrong, and here is why'. They did not do that.

But this raises another issue. The situation is as bad as it is because our politicians are taking grossly insignificant action. If the voters knew how bad the situation is, our politicians would be forced to take stronger action. But to significantly change the climate trajectory at this very late stage, only an absolutely dramatic reversal in many areas of policy would be sufficient.

So the question facing the Meteorological Office (and all of the rest of us) now, is, is it better to bimble quietly on in the fairly confident knowledge that advanced civilisation will end within the lifetimes of people now living, or risk very radical social and political change now in the very uncertain hope that possibly something might be salvageable from the wreck?

It's a hard question.