Levels of carbon dioxide
in Earth’s atmosphere
are rising. Rob Banino
investigates how satellites
are being used to monitor
CO
2
levels from space
S
omething big happened in 2020. According
to the Global Carbon Project, carbon dioxide
(CO 2 ) emissions declined by 2.4bn tonnes – the
biggest drop ever recorded. It is a faint silver
lining to a year of COVID-19 lockdowns, and a
distraction from the longer-term trend – in 2019,
CO 2 emissions hit a record high (36.8bn tonnes). Now, as
restrictions ease thanks to vaccination programmes,
CO 2 emissions are returning to pre-pandemic levels.
Nevertheless, 2021 could be a big year for cutting
CO 2 $IWHUWDNLQJRIƅFHLQ-DQXDU\3UHVLGHQW-RH%LGHQ
reinstated America’s commitment to the Paris Agreement,
an international treaty on climate change. In April, Prime
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reduction targets for the UK. In May, Germany brought its
deadline to become carbon neutral forward to 2045. And
further pledges to cut CO 2 may come in November’s
UN Climate Change Conference of the Parties (COP26).
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to keep them. And how will we know if those actions are
having an effect? More to the point, how do we know
how much CO 2 there is in the atmosphere to begin with?
Scientists, such as Dr Annmarie Eldering, can answer those
questions with the help of CO 2 -monitoring satellites.
Rise to the challenge
Eldering has been involved in the task since NASA’s Orbiting
Carbon Observatory-2 (OCO-2) got the go-ahead in
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in the late 1990s to work on measuring air pollution from
space. “It was a pretty small leap to go from air pollution to
measuring CO 2 ,” she says. “CO 2 is the most important of the
gases humans emit for driving climate change. It’s a really
big problem, for us and the globe. It’s something we’ve got
WRXQGHUVWDQGDQGVWDUWDFWLQJRQ%XWPHDVXULQJ&2 2 from
space is challenging.”
Challenging is an understatement. Since 2016, the
concentration of CO 2 in the atmosphere has been over
400 parts per million – a level unseen since the mid-
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DVWDJJHULQJO\GLIƅFXOWDPRXQWWRNHHSWUDFNRI,PDJLQH
trying to account for 400 pennies scattered among one
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August 2021 BBC Sky at Night Magazine 37>ROBERTO
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