You Can't Do It All With Mirrors

A costing for a giant sunshade in space shows that there are probably better ways to spend the money.

The leading economist Nicholas Stern has just handed us, in advance, the bill for the impacts of climate change: close to $4 trillion by the end of this century.

And with perfect timing, astronomer Roger Angel of the University of Arizona has delivered the equivalent of a builder's estimate for patching up the problem using a cosmic sunshade. It will set us back by... well, let's make it a nice round figure of $4 trillion by the end of the century.

Both figures are rough estimates — when costs add up to a significant fraction of global GDP no one can expect them to be very accurate. But this happy conflux of figures puts some perspective on the hope that global warming can be addressed with high-tech mega-engineering projects.

In this context, the sunshade solution looks like a bad bargain. If a builder told you that the cost of fixing a problem with your roof was likely to be about the same as the cost of not fixing it, except that the fix was untested and might not work at all, and in any event you know the work is likely to run over budget and probably over schedule — well, what would you do?