Tuesday, February 20, 2007

Asteroids, global warming & planning for catastrophic risk

According to stargazers an asteroid (called 99942 Apophis) with a 1 in 45,000 chance of hitting the earth in 2036 should be targeted for ‘deflection’ by a ‘gravity tractor’ space vehicle mission organised by the UN. The cost of a direct hit by the asteroid on earth is estimated at $400 billion. The expected damage cost today – the expected benefit of avoiding a collision, ignoring discounting - is a shade under $8.9 million. It is $5 million if a discount rate of 2% is used.

Defecting an asteroid would require a substantial space investment program – I doubt investments in the range $5-$8.9 million would pay the cafeteria costs of such an enterprise! The cost of putting a person on the moon today would be $127 billion!

In fact, the costs of dealing with the asteroid depend on the degree of desired deflection. These increase dramatically after 2029 as the cost of deflecting the asteroid rises strongly – certainly faster than the discount rate. Thus if it isn’t worth doing now it probably won’t be in the future - at least if you respect the expected value criterion – and rely on expected value calculations.

Of course if the catastrophic event was the extinction of humankind you would need to rethink your analysis. That’s a harder issue I am not prepared to argue at this time.

The ‘asteroid problem’ sounds analogous to the theoretical paradigm for dealing with global warming by accounting for catastrophic risks that I have commented on before. Indeed, one commenter on my earlier discussion raised the specific issue of a meteorite (rather than an asteroid) strike. In my response to his comment I got it wrong by denying there was much one can do about such a strike (I had not heard of the ‘deflection’ option) so that the prospect of catastrophe inevitably reduced the value of future human existence. It suggested we should ‘have a party’ rather than waste our money trying to prevent the inevitable.

One twist that is different about the ‘asteroid problem’ is that, if tagging of the asteroid can be done quickly enough, the decision to intervene in planning a defection mission can be postponed until the likelihood of a hit is known with certainty. The idea that catastrophic outcomes associated with climate change can be deferred until their likelihood is known with certainty is implausible.

Another interesting reflection on catastrophic events is posed by the analysis of ‘unknown unknowns’ in John Quiggin’s post on dead zones in the ocean, where life is extinguished. The cause of such zones is uncertain - they are proximately linked to changes in ocean currents which are in a complex way linked to climate.

‘The known (but uncertain) possible consequences of doing nothing add a lot more to the expected costs than do the known (but uncertain) possibilities of adaptation and so on producing lower-than-expected costs. Even more important, the ‘unknown unknowns’, that is, the possible consequences of which we are not yet aware, are dominated by nasty surprises that await us if we continue changing the climate rapidly.’

Sounds plausible. Seeking to maintain the climate status quo through adaptation will leave us less exposed to ‘unknown unknowns’ than will the uncertain consequences of doing nothing and allowing the climate to change.

It is only sensible to apply the ‘asteroid problem’ logic if you can delay taking strong and expensive policy actions to deal with the potentially catastrophic effects of climate change until you know for sure that it will occur. As argued this is questionable. Given the pace of climate change and the extent of uncertainties the time for anticipatory action is right know.


James Dudek said...

Interesting stuff Harry.

Begs the question of why exactly NASA exists at all. The only logical reason for its existence at all is a security warning system against Asteroid detection. Everything else that they do is really just interesting without being necessary.

robert merkel said...

James, what NASA does is no more or less necessary than a bunch of other scientific research (there are arguments to suggest that the research payback is poor for the money spent, but that's not the argument you made).

Do you advocate the abolition of, say, Opera Australia and the state orchestras as well?

James Dudek said...


Particularly if the opera subsidies ran into the hundreds of billions and the singers had the ability to prevent a catastrophe, but instead spent their time doing stuff that was interesting rather than necessary.

Kenneth Cooke said...

James, nothing is necessary, not even our own existence. Existence would be even more pointless were it not for the amusement we get from satisfying our curiosity.

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