Carbon offsets are always a compromise, not a substitute for avoiding emissions. However, if you have to fly, there are better options than the airlines’ voluntary offset programs.
by Stephen Warren, Emeritus Professor of Atmospheric Sciences, University of Washington, Seattle, USA
Airplanes are responsible for less than three percent of global CO2 emissions1, but aviation fuel cannot easily be replaced by non-fossil fuels, so “offsetting” one’s flight emissions has become popular. Extracting CO2 from the atmosphere (“direct air capture”, DAC) and sequestering it deep underground now costs in the range $200 to $800 per ton of carbon dioxide.2 But DAC is not yet operating at a large scale, so for now I will do my offsetting by paying to mitigate others’ emissions rather than paying to capture my own emissions. I’ll use a middle rate of $500 per ton as a guideline for what I should pay.
The CO2-offset strategies currently on offer are questionable. For example, some land claimed to be “reforested” land had never been cleared, and some “protected” rainforest areas used as offsets were then logged anyway.3,4 So I’m looking into an alternative approach. Here’s my thinking:
(1) CO2 is emitted by human activities, so reducing the number of humans being born will reduce the total emissions, as well as reducing other environmental impacts. Indeed, since children can beget grandchildren, and so on, having fewer children is by far the most effective way to reduce CO2 emissions.5,6 The highest per-capita CO2 emissions are in the rich countries, so for this particular environmental problem, population-reduction is most urgent in the rich countries. Babies in the U.S., even those born to poor immigrant parents, often grow up to become affluent citizens, emitting large amounts of CO2. The U.S. population has been growing by about 2 million per year.
(2) In the United States, about 45% of pregnancies are unintended.7,8 The Planned Parenthood organization provides services to American women for contraception and abortion, thus reducing the number of unplanned births and preventing the CO2-emissions that would have occurred, had those additional humans been born.
(3) The CO2 emitted by commercial flights averages to 90 grams per passenger-kilometer.9,10 Last December I compiled my year’s travel. In 2023 I flew 28,000 km (twice to California, once to Indiana, and once to Europe), so my CO2 emissions from flying were about 2.5 tons. But I’ve just started on this offset-policy, so I added in my flights from 2022, which was a heavy travel year for me, emitting 8.7 tons, making a total of 11.2 tons for the two years. Doing the multiplication, $500×11.2= $5600, which I have donated to Planned Parenthood of the Pacific Northwest as my CO2-offset, in addition to my routine annual contribution.
(4) A convenient number to remember is that at $500 per ton, each kilometer you fly requires an offset of about 5 cents. The price will drop in the future, as engineering advances are made. Some DAC innovators expect that extraction and sequestration will soon cost less than $100 per ton.11,12
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