New Simulation Shows Consequences of a World Without Earth's Natural Sunscreen
Simulations of global ozone concentration show the real-world ozone layer (left)
versus a "world avoided," in which CFCs had never been banned. Reds depict high
concentration; dark blues show low concentrations. Note the seasonal pulse of
ozone over the poles, how it declines to holes (blue), then becomes global
depletion by the 2050s. 2009 shown here. Credit: NASA Goddard's Scientific
March 18, 2009 NASA's Goddard Space Flight Center-The year is 2065. Nearly
two-thirds of Earth's ozone is gone -- not just over the poles, but everywhere.
The infamous ozone hole over Antarctica, first discovered in the 1980s, is a
year-round fixture, with a twin over the North Pole. The ultraviolet (UV)
radiation falling on mid-latitude cities like Washington, D.C., is strong enough
to cause sunburn in just five minutes. DNA-mutating UV radiation is up 650
percent, with likely harmful effects on plants, animals and human skin cancer
This time series from the
ozone "World Avoided" model shows the concentration of ozone over the South Pole
at four key times. Reds represent normal to high concentrations; blues show
The discovery that CFCs
deplete ozone was first announced in 1974, when the ozone layer was still
relatively robust. By 1989, an "ozone hole" had opened over Antarctica, peaking
in size in 2006. By year 2054 in the model, the ozone hole is permanent, and
global ozone has dropped by 67 percent.Annual average concentrations of global
ozone are shown for the "World Avoided" (solid black), a modeled future with
ozone regulation (red), atmospheric chlorine at a fixed amount (green), and a
simulation of past observations (blue). The inset shows how ozone concentrations
decrease as the amount of chlorine in the atmosphere -- effective equivalent
stratospheric chlorine (EESC) -- grows over time. Credit: NASA/Paul Newman, et.
al.; published in Atmospheric Chemistry and Physic
The ozone layer over the far northern hemisphere -- once relatively robust
compared to the Antarctic concentrations -- would have developed a similar ozone
hole by the 2020s if the Montreal Protocol had not limited ozone-depleting
substances. Credit: NASA Goddard's Scientific Visualization Studio
Annual average concentrations of global ozone are shown for the "World Avoided"
(solid black), a modeled future with ozone regulation (red), atmospheric
chlorine at a fixed amount (green), and a simulation of past observations
(blue). The inset shows how ozone concentrations decrease as the amount of
chlorine in the atmosphere -- effective equivalent stratospheric chlorine (EESC)
-- grows over time. Credit: NASA/Paul Newman, et. al.; published in Atmospheric
Chemistry and Physics
The summer ultraviolet (UV) index -- used to alert people to the intensity of
sun-burning radiation at the peak of the day -- triples as ozone is depleted in
the "world avoided" scenario. Credit: NASA/Paul Newman, et. al.; published in
Atmospheric Chemistry and Physics
Such is the world we would have inherited if 193 nations had not agreed to ban
ozone-depleting substances, according to atmospheric chemists at NASA's Goddard
Space Flight Center, Greenbelt, Md., Johns Hopkins University, Baltimore, and
the Netherlands Environmental Assessment Agency, Bilthoven.
Led by Goddard scientist Paul Newman, the team simulated "what might have been"
if chlorofluorocarbons (CFCs) and similar chemicals were not banned through the
treaty known as the Montreal Protocol. The simulation used a comprehensive model
that included atmospheric chemical effects, wind changes, and radiation changes.
The analysis has been published online in the journal Atmospheric Chemistry and
"Ozone science and monitoring has improved over the past two decades, and we
have moved to a phase where we need to be accountable," said Newman, who is
co-chair of the United Nations Environment Programme's Scientific Assessment
Panel to review the state of the ozone layer and the environmental impact of
ozone regulation. "We are at the point where we have to ask: Were we right about
ozone? Did the Montreal Protocol work? What kind of world was avoided by phasing
out ozone-depleting substances?"
Ozone is Earth's natural sunscreen, absorbing and blocking most of the incoming
UV radiation from the sun and protecting life from DNA-damaging radiation. The
gas is naturally created and replenished by a photochemical reaction in the
upper atmosphere where UV rays break oxygen molecules (O2) into individual atoms
that then recombine into three-part molecules (O3). As it is moved around the
globe by upper level winds, ozone is slowly depleted by naturally occurring
atmospheric gases. It is a system in natural balance.
But chlorofluorocarbons -- invented in 1928 as refrigerants and as inert
carriers for chemical sprays -- upset that balance. Researchers discovered in
the 1970s and 1980s that while CFCs are inert at Earth's surface, they are quite
reactive in the stratosphere (10 to 50 kilometers altitude, or 6 to 31 miles),
where roughly 90 percent of the planet's ozone accumulates. UV radiation causes
CFCs and similar bromine compounds in the stratosphere to break up into
elemental chlorine and bromine that readily destroy ozone molecules. Worst of
all, such ozone depleting substances can reside for several decades in the
stratosphere before breaking down.
In the 1980s, ozone-depleting substances opened a wintertime "hole" over
Antarctica and opened the eyes of the world to the effects of human activity on
the atmosphere. By 1987, the World Meteorological Organization and United
Nations Environment Program had brought together scientists, diplomats,
environmental advocates, governments, industry representatives, and
non-governmental organizations to forge an agreement to phase out the chemicals.
In January 1989, the Montreal Protocol went into force, the first-ever
international agreement on regulation of chemical pollutants.
Total ozone in (a) April for the Arctic and (b) October for the Antarctic for
the WORLD AVOIDED (black), reference future (red), fixed chlorine (green), and
reference past (blue) simulations. The curves are smoothed with a Gaussian
filter with a half-amplitude response of 20 years, except for the WORLD AVOIDED,
which is unsmoothed. The inset false-color images show (a) April and (b) October
averages for 1980, 2020, and 2060 with 20-DU color increments (see inset scale).
“The regulation of ozone depleting substances was based upon the evidence
gathered by the science community and the consent of industry and government
leaders," Newman noted. "The regulation pre-supposed that a lack of action would
lead to severe ozone depletion, with consequent severe increases of solar UV
radiation levels at the Earth’s surface."
In the new analysis, Newman and colleagues "set out to predict ozone losses as
if nothing had been done to stop them." Their "world avoided" simulation took
months of computer time to process.
The team started with the Goddard Earth Observing System Chemistry-Climate Model
(GEOS-CCM), an earth system model of atmospheric circulation that accounts for
variations in solar energy, atmospheric chemical reactions, temperature
variations and winds, and other elements of global climate change. For instance,
the new model accounts for how changes in the stratosphere influence changes in
the troposphere (the air masses near Earth's surface). Ozone losses change the
temperature in different parts of the atmosphere, and those changes promote or
suppress chemical reactions.
The researchers then increased the emission of CFCs and similar compounds by 3
percent per year, a rate about half the growth rate for the early 1970s. Then
they let the simulated world evolve from 1975 to 2065.
By the simulated year 2020, 17 percent of all ozone is depleted globally, as
assessed by a drop in Dobson Units (DU), the unit of measurement used to
quantify a given concentration of ozone. An ozone hole starts to form each year
over the Arctic, which was once a place of prodigious ozone levels.
By 2040, global ozone concentrations fall below 220 DU, the same levels that
currently comprise the "hole" over Antarctica. (In 1974, globally averaged ozone
was 315 DU.) The UV index in mid-latitude cities reaches 15 around noon on a
clear summer day (a UV index of 10 is considered extreme today.), giving a
perceptible sunburn in about 10 minutes. Over Antarctica, the ozone hole becomes
a year-round fixture.
In the 2050s, something strange happens in the modeled world: Ozone levels in
the stratosphere over the tropics collapse to near zero in a process similar to
the one that creates the Antarctic ozone hole.
By the end of the model run in 2065, global ozone drops to 110 DU, a 67 percent
drop from the 1970s. Year-round polar values hover between 50 and 100 DU (down
from 300-500 in 1960). The intensity of UV radiation at Earth's surface doubles;
at certain shorter wavelengths, intensity rises by as much as 10,000 times. Skin
cancer-causing radiation soars.
"Our world avoided calculation goes a little beyond what I thought would
happen," said Goddard scientist and study co-author Richard Stolarski, who was
among the pioneers of atmospheric ozone chemistry in the 1970s. "The quantities
may not be absolutely correct, but the basic results clearly indicate what could
have happened to the atmosphere. And models sometimes show you something you
weren't expecting, like the precipitous drop in the tropics."
"We simulated a world avoided," said Newman, "and it's a world we should be glad
The real world of CFC regulation has been somewhat kinder. Production of
ozone-depleting substances was mostly halted about 15 years ago, though their
abundance is only beginning to decline because the chemicals can reside in the
atmosphere for 50 to 100 years. The peak abundance of CFCs in the atmosphere
occurred around 2000, and has decreased by roughly 4 percent to date.
Stratospheric ozone has been depleted by 5 to 6 percent at middle latitudes, but
has somewhat rebounded in recent years. The largest recorded Antarctic ozone
hole was recorded in 2006.
"I didn't think that the Montreal Protocol would work as well as it has, but I
was pretty naive about the politics," Stolarski added. "The Montreal Protocol is
a remarkable international agreement that should be studied by those involved
with global warming and the attempts to reach international agreement on that
NASA's Goddard Space Flight Center