What is the human climate niche - and what does it mean for weather monitoring?

Is there a particular climate that most human societies have formed in? A recent investigation suggests that we’re not so adaptable after all.

Sometimes you read something that boils it all down to a clear and unmistakable number. It can make you feel oddly resilient in the face of a horrible situation.

If you know roughly how many days you’ve got left, for instance, you can stop worrying and start making the most of today.

Here’s the number that made me feel like that, recently: 13°C.

That’s the mean average temperature (MAT) of the places that most humans have lived in for millennia.

It was calculated by a team of well-respected climate scientists (including Professor Timothy M. Lenton) and published in a peer-reviewed paper back in 2020.¹

What’s the horrible situation, you ask?

Billions of people will have to move – and fast.

Calculating the human climate niche

In order to avoid making hard-to-defend claims about what human societies can survive in or what they need to survive, the authors make a simple yet completely novel move.

They trawled through mountains of demographic, environmental and geographic data to answer one question: what sort of climates have humans lived in since the last ice age?

What they found was that the location of human cultures doesn’t correlate with soil fertility, nor net primary productivity (NPP) of ecosystems, and these locations represents only a very small section of the planet’s different climates.

Instead, our societies - including the farms and pastures that feed us as well as the business centres where we make all of our money – take root in places that lie within a pretty tight range where certain average annual temperatures (∼11°C to 15°C) meet a certain amount of average annual rainfall (∼500-1250mm).

Having been told so frequently of humanity’s adaptability and survival genius, this finding is quite shocking, even unbelievable – until you look at a map.

Vast sections of Australia, Africa and Asia that are both green and wet remain pretty much uninhabited today, despite all of our technological and economic development.

But when you overlay the map of the human climate niche featured in the paper, you can see that these regions just don’t have the right annual temperatures – well, at time of writing…

What are the short-term effects of climate change?

The most chilling and stark finding of the paper is that ‘over the coming 50 y [i.e., up to 2070], 1 to 3 billion people are projected to be left outside the climate conditions that have served humanity well over the past 6,000 y.’¹

It’s based on another simple but relatively novel concept: ‘human-experienced temperature rise’.

When climatologists talk about average temperatures, they’re talking about an average surface temperature across the whole planet, of which nearly two-thirds is water – a substance that warms only slowly.

A good rule of thumb is that the centre of a continent is twice as warm as the coast. So, with average temperatures up by (nearly) 1.5°C, inland temperatures will have gone up by around 3°C.

In fact, this paper estimates that in 2070, human-experienced temperatures will be higher than pre-industrial by 7.5°C, which is ‘2.3 times the mean global temperature rise [roughly, 3.3°C]’. The authors say that this is ‘amplified somewhat by the fact that population growth is projected to be predominantly in hotter places.’¹    

In any case, this means the sort of temperatures that can be found in just 0.8% of ‘global land surface, mostly concentrated in the Sahara’ will increase by 2,400% to cover 19% in 2070 – a type of global desertification.¹

What’s important to understand, of course, is that without co-ordinated international efforts, such unprecedented migration and re-location of production is unlikely to be peaceful or safe.

In the absence of extensive (and expensive) unilateral preparation, millions of people being displaced in a short period of time are extremely difficult to manage for the simple fact that huge numbers of people need to be humanely transported – being fed and kept healthy along what may be considerable distances – to currently-non-existent cities.

Consider one of the most recent mass displacements: of nearly 13 million Syrians during the Civil War of the 2010s.

The chaotic response of the international community produced extreme social conditions, prompting desperate crossing and fostering malnutrition, disease, violence, and theft. The dangerous poverty of displaced Syrian people has absorbed much of the resources of the United Nations’ Refugee Agency in recent years.

But this isn’t, sadly, new or surprising; the history of the last century alone was characterised by the chaos of mass displacement, both external and internal.

Despite this, we are not prepared for what will be unprecedented numbers of refugees, beginning in the next decade.

What does this mean for weather monitoring?

As a means of galvanising and co-ordinating our response, we’ll need to be keeping taps on changing regional conditions in relation to what we now know about the human climate niche.

Extensive networks of weather monitors will need to be installed in those places that are scheduled to become uninhabitable, as a sort of early warning system that can kick preparations into a higher gear when necessary.

Of course, this will require the drawing up of new international treaties that formally recognise responsibilities and contributions to protecting those that are likely to be displaced.

As part of this preparation, we need to be monitoring those places that are becoming more suitable, in order to ascertain when and how many people can move at various times.

Working in tandem, these monitoring programmes can help to facilitate the most complicated repatriation scheme in human history.

If, as a global community, we can get this right, it will be a moral victory of historic magnitude and a true testament to our common institutions.

But as things stand, that’s a very, very big if.

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1 Future of the human climate niche. Xu et al. PNAS. 2020.