18 August 2019

At 4°C of warming, would a billion people survive? What scientists say.

Courtesy: The Guardian
by David Spratt

In a way it’s an obscene question: if the planet warms by 4 degrees Celsius (°C), would only a billion
people survive and many billions perish?  Obscene in the sense of the obscenity of arguing about the exact body count from a genocide. In the end it’s about the immorality, the crime, the responsibility, not the precise numbers.

But it’s a relevant question, in that Earth is heading towards 4°C  of warming, based on emission reduction commitments so far. The Paris commitments are a path of warming of around 3.3°C, but that does not include some carbon cycle feedbacks that have already become active (e.g. permafrost, Amazon, other declines in carbon store efficiency) which would push that warming towards 5°C. So saying we are presently on a 4°C path is about right.

It’s also a relevant question because there has been some controversy about comments made by Extinction Rebellion co-founder Roger Hallam to the BBC HARDtalk programme three days ago: “Teenagers are shitting themselves about what’s happening for the future, they’ve got another 50, 60, 70 years to live on this planet, by that time there could only be a billion people left. I mean that’s six billion people that have died from starvation or slaughtered in war.” The BBC accused Hallam of “going too far” and there was some social media flutter about it.

There’s no science to support such statements was a frequent refrain.  But there is. In May this year, Johan Rockström, director of the Potsdam Institute for Climate Impact Research, told The Guardian that in a 4°C-warmer world: “It’s difficult to see how we could accommodate a billion people or even half of that… There will be a rich minority of people who survive with modern lifestyles, no doubt, but it will be a turbulent, conflict-ridden world.” Rockström is one of the world’s leading researchers on climate “tipping points” and “safe boundaries” for humanity.

And there are other scientists with similar views. But before I get to them, let’s take a moment to understand what a 4°C-warmer world would look like. That same Guardian article, by Vince Gaia, sketches a dramatic picture. And eight years ago I wrote a primer, “4 degrees hotter”, available here.

And just two months before the fifteenth meeting of the Coalition of the Parties (COP15) in Copenhagen, “4 degrees and beyond” was the focus of a September 2009 International Climate Conference at Oxford.  The proceedings were published by the Royal Society. 4 degrees was also the focus of a conference in Melbourne in 2011, with the proceedings published as a book.

The 4°C story goes like this:
  • On the present path, we may well exceed 4°C this century. At the moment Earth appears to be heading towards 1.5°C by 2030 and 2°C before 2050, and if the feedbacks kick in, 4°C some 30-50 years after that.

  • Whilst it would take several centuries to a millenia or so to melt all the ice, sea levels could be up by 2–3 metres by 2100, and in the end a 4°C-warmer world would have no large ice sheets at either of the poles, or on the Himalayas; sea-levels would eventually rise by 70 metres.  This we learn from the planet’s climate history. Almost two billion people in Asia rely to some extent on rivers which are fed in part by Himalayan snow melt.

  • Ocean acidification renders many calcium-shelled organisms at the base of the ocean food chain artefacts of history. There would be no coral reefs of note. Ocean ecosystems and food chains collapse. The world is full flight into the sixth mass extinction in history. If the rate of warming consistently exceeds 0.4°C per decade, all ecosystems are likely to be quickly destroyed, opportunistic species dominate, and break-down of biological material will lead to even greater emissions of carbon dioxide.

  • Warmer ocean waters decrease the photosynthetic productivity of phytoplankton, and a warm ocean surface layer stays unmixed with the cooler, nutrient-rich waters below, severely reducing the algae population. Algae, which comprise most of the ocean’s plant life, are the world’s greatest carbon dioxide sink, pumping down the gas, as well as contributing to cloud cover by releasing dimethyl sulphide (DMS) into the atmosphere, a gas connected with the formation of clouds, so that warmer seas and less algae will likely reduce cloud formation and further enhance positive feedback. Severe disruption of the algae/DMS relation would signal spiralling and irreversible climate change.

  • Hundreds of billions of tonnes of carbon locked up in Arctic permafrost – particularly in Siberia – enter the melt zone, releasing globally warming methane and carbon dioxide in immense quantities.  The Amazon would no longer be a rainforest, but savannah. 

  • Aridification emerges over more than 30 percent of the world’s land surface. Desertification is severe in southern Africa, the southern Mediterranean, west Asia, the Middle East, inland Australia and across the south-western United States. Agriculture becomes nonviable in the dry subtropics.

  • Vince Gaia in his Guardian article reports: “A wide equatorial belt of high humidity will cause intolerable heat stress across most of tropical Asia, Africa, Australia and the Americas, rendering them uninhabitable for much of the year…  To the south and north of this humid zone, bands of expansive desert will also rule out agriculture and human habitation. Some models predict that desert conditions will stretch from the Sahara right up through south and central Europe, drying rivers including the Danube and the Rhine… by 2100, most of the low and mid latitudes will be uninhabitable because of heat stress or drought; despite stronger precipitation, the hotter soils will lead to faster evaporation and most populations will struggle for fresh water.”

  • Food production tumbles as a consequence of a greater than one-fifth decline in crop yields, a decline in the nutritional content of food crops, a catastrophic decline in insect populations, desertification, monsoon failure and chronic water shortages, and conditions too hot for human habitation in significant food-growing regions.

  • The destabilisation of the Jet Stream very significantly affects the intensity and geographical distribution of the Asian and West African monsoons and, together with the further slowing of the Gulf Stream, impinges on life support systems in Europe, where new deserts spreading in Italy, Spain, Greece and Turkey: the Sahara has effectively leapt the Straits of Gibraltar. In Switzerland, summer temperatures hit 48°C, more reminiscent of Baghdad than Basel.. The sort of climate experienced today in Marrakech will be experienced in southern England, with summer temperatures in the home counties reaching a searing 45°C. Europe’s population may be forced into a “great trek” north.

“Most of Australia” can expect extreme temperatures of more than 50 degrees by end of century
 Johan Rockström’s view that a 4°C world might only support one billion people is not a figure plucked out of the air.  A decade ago, considerable research was done on the food production and carrying capacity of a hotter planet. As a result of this work, in March 2009, at the Copenhagen science conference, Professor Hans Joachim Schellnhuber, then director of the Potsdam Institute, and one of Europe’s most eminent climate scientists, told his audience: “In a very cynical way, it’s a triumph for science because at last we have stabilized something –- namely the estimates for the carrying capacity of the planet [at 4°C], namely below one billion people”, as reported by the New York Times.

Schellnhuber was viciously attacked for the comment, accused of advocating genocide and expressing support for reducing the world's population to one billion. When he spoke at the 4°C conference in Melbourne in 2011, an audience member held up a noose. It was very ugly.

Speaking in 2015 to ABC Radio National, Schellnhuber said that this was a false interpretation of what he said, spread by enemies of climate action to discredit him. He explained:
In the world of Google you can raise any myth and you can raise any lie… Here is what I really said. It was a scientific conference, preceding the infamous Copenhagen conference in 2009, and actually I talked about the carrying capacity of the Earth, which is an interesting issue. What I said is, if global warming is not in any way mitigated, and we go into a six or eight degrees warmer world, then our planet will probably only be able to support a billion people.
On 29 September 2009, at the conclusion of the “4 degrees and beyond” conference, The Scotsman reported:
Professor Kevin Anderson, director of the Tyndall Centre for Climate Change, believes only around 10 per cent of the planet’s population – around half a billion people – will survive if global temperatures rise by 4°C...
Anderson, who advises the government on climate change, said the consequences were “terrifying”.
“For humanity it’s a matter of life or death,” he said. “We will not make all human beings extinct as a few people with the right sort of resources may put themselves in the
right parts of the world and survive. But I think it’s extremely unlikely that we wouldn’t have mass death at 4°C. If you have got a population of nine billion by 2050 and you hit 4°C, 5°C or 6°C, you might have half a billion people surviving.”
This story is archived here. Anderson may have corrected what was reported, but I have so far not located it. The previous day, the Scotsman reported Anderson as saying:
The other thing to remember is that 4C is a global average. It's probably nearer 5C on land, and would be up to 15C in some areas.
There's no evidence to suggest that humanity can actually survive at this sort of temperature. Small pockets of human beings might continue to exist but I don't consider that to be a success.
Three years earlier, in 2006, James Lovelock — scientist extraordinaire, inventor of the microwave oven and propounder of the Gaia thesis — told an audience that the Earth has a fever that could boost temperatures by up to 8°C, making large parts of the surface uninhabitable and threatening billions of peoples’ lives. He said a traumatised Earth might only be able to support less than a tenth of its six billion people: “We are not all doomed. An awful lot of people will die, but I don’t see the species dying out... A hot Earth couldn’t support much over 500 million.”  This was reported by The Scotsman as “Scientist says global warming will ‘kill billions'” (http://news.scotsman.com/scotland.cfm?id=1768202006) but is no longer available online. Lovelock made similar comments in at one of his books, as I remember, The Revenge of Gaia, published in 2006.

So did Roger Hallam “go too far”?  Not at all, there is serious research and eminent voices in support of his statements. The gross error in all of this are all those who cannot countenance this conversation.