Antarctic ozone
hole on the mend
Researchers detect healing
sooner than they expected
By Alexandra Witze
Scientists may have spotted Antarctica’s
ozone hole on the road to recovery, at
least a decade sooner than they thought
healing would be noticeable.
In 1989, an international agreement
called the Montreal Protocol began
phasing out chemicals that have gnawed
away at Earth’s protective ozone layer.
Most researchers thought it would
take until at least 2023 to detect the
hole’s slow recovery, but researchers in
Australia now claim to have seen ozone
ticking upward since the late 1990s.
“The key is to account for large year-to-year fluctuations that have obscured
a gradual increase in the long-term
evolution of ozone,” says atmospheric
scientist Murry Salby of Macquarie University in Sydney. His team published
its findings online May 6 in Geophysical
Research Letters.
First spotted in 1985, the Antarctic
ozone hole was quickly linked to chemicals called chlorofluorocarbons, emitted
mainly in the Northern Hemisphere but
concentrated over the South Pole by
atmospheric circulation. Chlorine atoms
from these CFCs react with ozone molecules, seasonally destroying the layer that
shields the Earth from cancer-causing
and crop-damaging ultraviolet radiation.
Scientists had predicted that ozone loss
would bottom out and start recovering by
now. They just didn’t think they would be
able detect that change yet, since complex
atmospheric processes cause ozone levels to vary dramatically from year to year,
sometimes by as much as the magnitude
of the ozone hole itself.
To better understand these year-to-year ozone fluctuations, Salby’s team
looked at “dynamical” influences such as
607
million
Average annual global
corn production in metric
tons, 1998–2002
waves that ripple through the
planet’s atmosphere much
like the ocean’s swells.
The researchers found
that winter dynamical
factors closely tracked
how much ozone was
depleted the following
spring. In essence, these
processes control how much
chlorine breaks away from CFCs
each winter, which determines how much
ozone will later break down.
Knowing what caused these year-to-year changes, the scientists could then
subtract out these effects, unmasking the
long-term signal of ozone. After plummeting since the analysis began in 1979,
that signal leveled off and began creeping
586
million
Average annual global
wheat production in metric
tons, 1998–2002
Scientists report signs that
the annual Antarctic
ozone hole, shown here
in September 2006, is
healing thanks to an
international treaty.
up after 1996, Salby says.
Not all experts are convinced by the new work.
The link between year-to-year
dynamics and ozone levels seems strong
now but could change on further analysis, says Darryn Waugh, an atmospheric
scientist at Johns Hopkins University.
“I expect Antarctic ozone to be slowly
recovering,” he says, “but would have
thought that we need several more years
of data to statistically show this.”
Warming hits corn and wheat yields
Rising temperatures have decreased global grain production
By Daniel Strain
Farms worldwide produced 3. 8 percent
less corn and 5. 5 percent less wheat than
they could have from 1980 to 2008 thanks
to rising temperatures, a new analysis
estimates. These wilting yields may have
contributed to recent increases in food
prices, a team of U.S. researchers reports
online May 5 in Science . Climate-induced
losses could have driven up prices of corn
by 6. 4 percent and wheat by 18. 9 percent
since 1980.
The researchers tracked country-by-
From 1980 to 2008, hotter weather
reduced wheat yields in some nations
(red), while in a few countries warming
increased production (blue).
country yields of these common foodstuffs over nearly three decades. Harvests
of corn and wheat have climbed steadily
since 1980 due in part to technological
advancements, says David Lobell, a land-use scientist at Stanford University. But
based on the team’s statistical analysis,
farmers could have produced a lot more
food if the weather had been cooler. For
corn, annual global losses amount to
millions of tons — about equal to Mexico’s yearly production of the crop.
This analysis of the last three decades
largely falls in line with what other studies have projected, says Andy Challinor
of the University of Leeds in England,
who studies the impacts of climate
on agriculture.
While it’s far from a prediction,
Lobell says his study identifies a
number of problem areas that do need
attention—not later but now. “If we
really invest a lot in the development
of crops that can withstand really high
temperatures,” he says, “that would
potentially change things a lot.”
