At least that's my conclusion from the comments by ten leading scientists interviewed by Kate Ravilious in the 14 April Guardian (see here). [Good to see that Air Marshal Lord Garden thinks the risks of cataclysmic global nuclear war is less than it used to be - but is that 'science'?]
A weakness of the Guardian piece is that it does not assign a numerical value to risk of each the various scenarios (although it does give them a danger score of 1 through 10, with 10 meaning total destruction of the planet)
One can make a rough guess as to what each of the five risk categories could mean. Here is mine: exceedingly low is less than 2%; low is 2% to 30%; medium is 31% to 60%; high is 61% to 85%; very high is 86% to 100%.
According to the article, Nick Brooks of the Tyndall Centre gives climate change a danger score of 6 and risk category high. A simple computation using my perhaps dodgey estimate of what the risk categories mean puts this close to the top of the ten, surpassed only by a robot takeover (high, 8: Hans Moravec) and a supervolcano (7, very high: Bill McGuire).
Three comments on this. One, would super intelligent robots really be such a danger to humanity? If they were wiser and more sensitive wouldnât that be progress? Two, if, as Prof McGuire says, the chance of a supervolcano going off in the lifetime of someone today (80 years or more life expectancy for an infant in the rich West) is 0.15%, why is it rated by the Guardian in the 86% to 100% category? Three, climate change is one of the few mega challenges on the list that can probably be mitigated by political and economic actions easily within the human grasp (by contrast, not much one can do about a cosmic ray blast from an exploding star).
To this one could add that the IPCC and others predict a band of temperature rise on doubling of atmospheric CO2 this century at 1.5 to 4.5 degrees centigrade. The probabilities of reaching the higher end of that band, and meriting a danger score of more than 6, may be greater than low.
That being said, the excercise at the Dana Centre looks worthwhile. Bringing some greater awareness of real but seemingly remote risks into public consciousness is always going to be an uphill battle, fraught with reverses, but no less trying for that.
Recently, Clifford Geertz reviewed two important books on the topic Collapse: How Societies Choose to Fail or Succeed by Jared Diamond and Catastrophe: Risk and Response by Richard Posner. Geertz observes:
The main problem, over and above their mind-bending dimensions, is that [megacatastrophes] seem to most people either so far off, so unlikely, or so thoroughly beyond what they have even vicariously experienced, psychologically off-scale, conceptually out-of-sight as to be beyond the range of rational estimation or practical response. We are both emotionally disinclined and intellectually ill-equipped to think systematically about extreme events. Absorbed as we are in the dailiness of ordinary life, and enfolded by its brevity, the calculation of remote possibilities and the comparison of transcendent cataclysms look pointless; comic, even.
(See here for the full article)