The Economist UK - 27.07.2019

The EconomistJuly 27th 2019 67

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xtreme heatis ruinous to productivi-

ty, particularly if you are a criminal.

Several American police forces posted

messages to their social-media accounts

last weekend declaring a moratorium on

crime. “It is just too hot to be outside com-

mitting crimes,” wrote the Park Forest Po-

lice Department in Illinois, on its Facebook

page. In some cases, it seems to have

worked. “We have had zero customers stay

the night at our ‘hotel’, so we appreciate all

of the criminals adhering to the heat advi-

sory,” tweeted the Malden Police in Massa-

chusetts on Sunday.

The messages came as scorching tem-

peratures swept across America, placing

more than 100m people under excessive-

heat warnings. Temperatures hovered ei-

ther side of 40°C on the east coast. On July

18th Mitch Petrus, a well-known retired

player of American football, died of heat-

stroke after working outdoors all day. At

least five other deaths have been reported.

Europeans have also been sweating, for

the second time this summer. A month

ago, warm air from the Sahara contributed

to making it the continent’s hottest June on

record. At the top of Mont Blanc, western

Europe’s highest mountain, instruments

recorded 7°C (the normal June temperature

would be below freezing). At Gallargues-le-

Montueux near Nîmes, in France, tempera-

tures peaked at 45.9°C. The previous record

anywhere in that country was 1.8°C lower.

Linked to these temperatures, in Alaska

(see Lexington) and Portugal (pictured),

forest fires are raging.

If your hunch is that this kind of ex-

treme weather is more common today than

it was once-upon-a-time, you are correct.

When, in 2003, tens of thousands of people

in Europe died prematurely as a result of a

two-week heatwave, it was deemed to be a

once-in-1,000-years event. Twelve years

later, a study led by Nikolaos Christidis of

the Hadley Centre, the climate-research di-

vision of Britain’s Met Office, found that

heatwaves of this severity had become

once-in-100-years events, and would be

commonplace by the 2040s.

The question on many people’s minds is

whether these changes, and specific events

like this week’s temperatures in America

and Europe, are caused by greenhouse gas-

es accumulating in the atmosphere. For

years, the semi-official line was that no

single weather event could be blamed on

climate change, only trends. That began to

change in 2004, with the publication of the

first “attribution” study. This focused on

the European heatwave of 2003, when aver-

age summer temperatures broke through a

threshold until then unbreached in 150

years of records. By comparing simula-

tions of a world with and without green-

house-gas emissions, Peter Stott at the Met

Office and his colleagues found that cli-

mate change had made the record-break-

ing heatwave at least twice as likely as it

would otherwise have been.

Extreme weather

Climate blame game

Greenhouse-gas emissions contribute to the rising frequency of heatwaves

Science & technology

68 Living tree stumps

69 Flat lenses

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