气候变化领域集成服务门户(CCPortal): Yes, the climate crisis may wipe out six billion people

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Yes, the climate crisis may wipe out six billion people 科技资讯

时间：2019-04-30 来源：[美国] Daily Climate

We needn’t bother Roger Hallam with this question. He can scarcely be held up as a “messiah of hope.” Quite the contrary. Hallam, a co-founder of Extinction Rebellion, has been desperately warning of societal collapse for years.

But on Aug. 15, in a memorable session of the BBC’s HardTalk, Hallam irritated multiple cultural nerves by claiming, on the basis of “hard science,” that six billion people will die as a result of climate change in coming decades.

More specifically, our ruling elites’ inaction and lies on climate change will lead to climate turmoil, mass starvation and general societal collapse in this century. Normally unflappable HardTalk host, Stephen Sackur, just couldn’t wrap his mind around Hallam’s unyielding assertions.

Sackur is no solitary skeptic. UC Davis research scientist Amber Kerr dismisses Hallam outright. The idea that six billion people are doomed to die by 2100 “is simply not correct. No mainstream prediction indicates anywhere near this level of climate-change-induced human mortality, for any reason.”

Similarly, Ken Caldeira, senior scientist, Carnegie Institution, points out, “There is no analysis of likely climate damage that has been published in the quality peer-reviewed literature that would indicate that there is any substantial likelihood that climate change could cause the starvation of six billion people by the end of this century.”

One key to understanding these scientists’ rejections is their language. They assert that there is “no mainstream prediction” nor analysis in the “peer reviewed literature” that climate change will precipitate such catastrophic human mortality.

But keep in mind that scientists are reluctant, for professional reasons, to go far beyond the immediate data in formal publication. Moreover, organizations like the United Nations, including even its Intergovernmental Panel on Climate Change, are so dominated by economists’ concerns and bent by political considerations that extraneous noise obscures the scientific signal.

Prominent climate scientist Hans Joachim Schellnhuber, director emeritus of Germany’s Potsdam Institute for Climate Impact Research, argues that, in these circumstances “a trend towards ‘erring on the side of least drama’ has emerged” and “when the issue is the survival of civilization is at stake, conventional means of analysis may become useless.”

Exploring this argument, policy analysts David Spratt and Ian Dunlop conclude, “Climate policymaking for years has been cognitively dissonant, ‘a flagrant violation of reality.’ So it is unsurprising that there is a lack of understanding amongst the public and elites of the full measure of the climate challenge.”

It seems that in mainstream scientific publications and official reports, the truth about climate change and the fate of civilization may be buried deeply between the lines.

Fortunately, there are other contexts in which experts are not quite so reticent and whose assertions echo Roger Hallam’s. As much as a decade ago a climate symposium organized to discuss the implications of a 4 C warmer world concluded, “Less than a billion people will survive.” Here Schellnhuber is quoted as saying: “At 4 C Earth’s... carrying capacity estimates are below 1 billion people.” His words were echoed by professor Kevin Anderson of the U.K.’s Tyndall Centre for Climate Change: “Only about 10 per cent of the planet’s population would survive at 4 C.”

Similarly, in May of this year, Johan Rockström, current director of the Potsdam Institute opined 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.” Meanwhile, greenhouse gas concentrations are still increasing.

Keep in mind that a global temperature increase averaging 4 C means land temperatures would be 5.5 to 6 C warmer away from the coasts. Much of the tropics would be too hot for humans and many densely populated parts of the temperate zone would be desertified. A 4 C warmer world map suggests that as much as half the planet would become uninhabitable. (A ‘4 C world’ assumes business-as-usual or no new climate policies in coming decades. Note, however, that known and unknown ‘feedback’ mechanisms could make 4 C possible, even with new politically acceptable policies in place.)

In a recent review of this debate and related evidence, David Spratt asks (and answers): “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.”

Making forbidden calculations

Which begs the question of whether “all those” would countenance any uncomfortable conversation. Population has long been a forbidden topic despite being at the root of the ecological crisis. Where might a discussion of population ecology lead and would its conclusions be any more politically acceptable?

1. We can begin by gaining some insight into the startling implications of exponential growth. When something is growing exponentially, it has a constant doubling time. For example, a population growing at two per cent a year will double every 35 years. Interestingly, the increase that occurs during any doubling period will be greater than the sum of the increases experienced in all previous doublings.

As the figure below shows, it took 200,000 years for the human population to reach its first billion in the early 1800s. In other words, population growth was essentially negligible for 99.95 of human history. But when sustained exponential growth kicked in, it took just 200 years — 1/1000th as much time — for the population to top 7.5 billion early in this century!

原文来源：https://thetyee.ca/Analysis/2019/09/18/Climate-Crisis-Wipe-Out/