The Economist - USA (2020-03-28)

(Antfer) #1

68 TheEconomistMarch 28th 2020


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I


n venice, waterin the canals is running
clear, offering glimpses of fish swim-
ming against the current. As human activi-
ty grinds to a halt, natural rhythms resume.
A similar, less visible story is being played
out in the skies. Around the world, levels of
toxic air pollutants are dropping as places
go into lockdown in an attempt to curb the
spread of sars-cov- 2 , the virus causing a
pandemic of a new disease called covid-19.
Emissions of greenhouse gases are follow-
ing a similar pattern.
One example of pollution falling is that
satellites looking down on China’s large
cities have witnessed a dramatic drop since
January in levels of nitrogen dioxide, a gas
generated by machinery such as internal-
combustion engines. This fall coincides
with the imposition of a countrywide quar-
antine, travel restrictions, and the shutting
down of power stations and factories. Ni-
trogen dioxide causes respiratory pro-
blems. A drop in its levels therefore brings

benefits. The concentration of another pul-
monary irritant—fine soot particles—was
also lower in those cities, by 20-30%, in
February of this year compared with levels
in the previous three years.

Clearing the air
Similar patterns have shown up elsewhere,
as the virus spreads and lockdowns follow.
Satellite data from Italy reveal a marked de-
cline in nitrogen-dioxide concentrations,
particularly in the Po valley, the original fo-
cus (see box on next page) of the country’s
epidemic, and where Italy’s shelter-at-
home rules were first imposed. South Ko-
rea also saw a drop, starting in mid-Febru-
ary. And in New York City, data collected by

TomTom, a gps-navigation firm, show
peak-hour traffic down between 13.5% and
26%. Not surprisingly, carbon-monoxide
levels in the city are half those during the
corresponding period last year, according
to researchers at Columbia University.
Drops like these, in pollutants that are
directly harmful to human health, would
be expected to be matched by falling emis-
sions of those more-subtly harmful pollut-
ants, the greenhouse gases produced by
human activity. And the team at Columbia
did indeed find that carbon-dioxide con-
centrations over New York have fallen.
They dropped by 8-10% this month com-
pared with March 2019. In China, mean-
while, industrial shutdowns are estimated
to have caused a 25% drop in emissions of
CO 2 in February, compared with the same
month in 2019.
An optimist might see these changes as
a silver lining to what is an extremely dark
cloud. But that would depend on their be-
ing sustained when things return to nor-
mal. As François Gemenne of the Universi-
ty of Liège, in Belgium, puts it, “the climate
needs a sustained drop in greenhouse-gas
emissions, not a year off”. Unfortunately,
not only is that unlikely to happen, but the
response to the crisis could easily make
things worse.
The short-term amelioration of CO 2
emission is likely to be real. On March 16th

Covid-19 and climate change

Clear thinking required


The coronavirus pandemic is causing a short-term improvement in air quality,
but the long-term outlook is grim

Science & technology


69 Covid-19andpollution
70 Detecting elevated body heat

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