Rockets, ozone and warming

Something to worry about, or much ado about nothing?

I know it’s fashionable to decry the billionaires who can afford to take joy-rides into space. I agree. The stupendous amounts of money needed to satisfy their egos could be much better spent. But how important are they from an environmental perspective?

In that regard, the rapidly-increasing number of rocket launches of unmanned satellites is also important. We can’t blame those on millionaire egos. A recent paper claimed that the warming effect of these rocket launches can’t be ignored. It also claimed that they would reduce ozone, counter the good work achieved by the Montreal Protocol. But to me at least that part of the paper is a bit of a beat-up. Although it appears to come from reputable institutions, it hasn’t yet passed the peer-review. So perhaps it should be taken with a grain of salt.

Note added 9 Dec 2022. A colleague has just informed me that the final version of paper was published here in June.

My interest was piqued when I saw that launches from little old New Zealand - but nowhere else in the southern hemisphere - make a surprisingly large contribution to the problem, as shown in the picture below from the paper.

Locations and fuel types of rocket launches in 2019. Marker size in the map indicates the number of launches at each location. Pie charts indicate the proportion of the four main fuel types at each launch location. Numbers above each pie chart are total propellant mass used in each country.

The heating effect calculated is due mainly to absorptions by the black carbon deposited during combustion. For the future scenario assumed, the authors calculate a warming effect of 0.008 W per square metre after three years. That’s tiny compared with the warming effects from increasing greenhouse gases, which collectively contribute about 3 Wm-2 (nearly 400 times as much). But its perhaps not negligible in the long term if the number of rocket launches to continues to increase.

The paper’s title appears to support the premise that changes in ozone will also be important, but when you read the fine print, it’s obviously a non-issue for the scenario they tested. Projected changes in ozone due to rocket launches reaching a few percent near 35 km. However, most ozone is at much lower altitudes where changes are smaller, so the projected launches only a tiny reduction in total column ozone (much less than 1 percent).

But I don’t think we’ve heard the last of this. Perhaps the world would be better served if future multi-millionaires took a one-way ticket.