Man-made climate change (now dubbed “climate crisis” by The Guardian’s editors) poses potentially serious risks for humanity in this century. But acknowledging the hazard is not enough for a growing claque of meteorological apocalypse porn peddlers who insist that if their prescriptions for solving the problem are not followed then civilization will momentarily come to an end.
Recent hawkers of fast approaching climate doom include David Wallace-Wells in his book The Uninhabitable Earth: Life After Warming, Cumbria University professor Jem Bendell’s “Deep Adaptation” paper, and environmental activist Bill McKibben’s Falter: Has the Human Game Begun to Play Itself Out? (my review is forthcoming).
Now comes a policy paper, Existential climate-related security risk: A scenario approach, from an Australian climate action advocacy group the Breakthrough National Centre for Climate Restoration. The headline over at Vice says it all: “New Report Suggests ‘High Likelihood of Human Civilization Coming to an End’ in 2050.”
In his foreword to the 8-page sketch of purported climate calamity, retired Australian admiral Chris Barrie asserts that it lays “bare the unvarnished truth about the desperate situation humans, and our planet, are in, painting a disturbing picture of the real possibility that human life on earth may be on the way to extinction, in the most horrible way.”
To justify their alarm, the authors of the paper, David Spratt and Ian Dunlop, are basically channeling Harvard economist Martin Weitzman’s dismal theorem. In deriving his dismal theorem, Weitzman probed what it would mean if equilibrium climate sensitivity (ECS)—conventionally defined as global average surface warming following a doubling of carbon dioxide concentrations—exceeded the likely range of 1.5–4.5°C.
Weitzman outlined a low probability-high consequence scenario in which ECS could be as high as 10°C. Such a case would indeed be catastrophic considering that the temperature difference between now and the last ice age is about 5°C and it took several thousand years for that increase to occur.
So just how likely is such an extremely high ECS? In its Fifth Assessment Report, the United Nations Intergovernmental Panel on Climate Change (IPCC) noted that the “equilibrium climate sensitivity (ECS) is likely in the range 1.5°C to 4.5°C, extremely unlikely less than 1°C, and very unlikely greater than 6°C.” More reassuringly, a 2018 article in Climate Dynamics calculated a relatively low climate sensitivity range of between 1.1°C and 4.05°C (median 1.87°C).
The Breakthrough Centre paper rejects conventional cost-benefit analysis in favor of sketching out a “hothouse earth” scenario that relies on projections in a 2017 Proceedings of the National Academy of Sciences article that average global temperature will exceed 3°C by 2050. They devise their scenario with the aim of alerting policymakers to the idea that climate change could turn out to be worse than current climate model projections suggest.
In their scenario, sea level rises by about 20 inches by 2050 and by 6 to 10 feet by 2100. Fifty-five percent of the world’s population is subjected annually to more than 20 days of heat “beyond the threshold of human survivability.” Wildfire, heatwaves, drought, and inundating storms proliferate. Ecosystems collapse including the Amazon rainforest, coral reefs, and the Arctic. Global crop production falls by at least 20 percent. Unbearable heat, along with food and water shortages would force billions of people to migrate. The result of this “hothouse earth” scenario would be “a high likelihood of human civilization coming to an end.”
On the basis of their scenario, the authors assert that only thing that can protect human civilization is “a massive global mobilization of resources is needed in the coming decade to build a zero-emissions industrial system and set in train the restoration of a safe climate. This would be akin in scale to the World War II emergency mobilization.”
Before racing to embrace their scenario, let’s consider what is known about the current rate of climate change. According to relatively uncontroversial data, average global surface temperatures have increased by 0.9°C since 1880. Getting to an increase of 3°C above the pre-industrial level by 2050 would mean that temperatures would have to increase at the rate of about 0.7°C per decade from now on.