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Business News/ Opinion / Online-views/  Rain and radiation
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Rain and radiation

Rain and radiation

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As if it weren’t enough that sleeping on foam mattresses or dry-cleaning clothes harms the ozone layer. They do, you know, by releasing chlorofluorocarbons (CFCs), the chemicals responsible for 80% of the damage to the protective atmospheric layer that allows life on Earth by absorbing all, but 3% of the Sun’s lethal ultraviolet rays.

The Harvard scientists found that summer storms flung water vapour into the lower levels of the stratosphere, creating the right conditions to strip it of ozone. The stratosphere, home to ozone, is the second layer of the atmosphere, starting about 10km above the earth at mid latitudes, the area of study. The stratosphere is a relatively calm, dry area. It is where jets fly to avoid the turbulence of the troposphere, which is the atmosphere’s lowest layer, the realm of clouds, humans and other life.

This ozone is at risk when otherwise harmless water vapour enters the stratosphere, which appears to bring out the devil in many substances. Consider CFCs and other ozone-depleting chemicals: They are stable, capable of surviving for centuries, non-toxic and do not damage the environment—at lower altitudes. That stability allows them to slowly float to the stratosphere (chemicals released 80 years ago are still winding their way up), where ultraviolet light breaks them apart, releasing chlorine and bromine, These molecules devastate ozone, which is three oxygen atoms stuck together (instead of two, as in the oxygen gas we breathe). A single chlorine molecule can tear apart thousands of ozone molecules.

Conventional wisdom is that chlorine and bromine were produced during chemical reactions in very cold temperatures, one reason why a hole in the ozone layer opened up over the world’s coldest area, Antarctica. The stratosphere behaves differently from the troposphere, becoming warmer as you go higher. But if the concentration of water vapour increases, then chlorine free radicals, as the separated molecules are called, can form at higher temperatures. Using data from a National Aeronautics and Space Administration aircraft flying over the US, the Harvard scientists found unexpected quantities of water being injected into the lower stratosphere during summer storms, disrupting the delicate chlorine-bromine chemistry. The result: ozone loss.

This is not good news at a time when the damage to the earth’s ozone is being repaired. In 1987, in a rare show of global unity, the world’s leaders signed the Montreal Protocol, an agreement to ban CFCs, used in that era primarily in refrigerators and aerosols. The ozone hole over Antarctica has stabilized, and global ozone concentrations started to rise by 1993.

The Harvard scientists hypothesize that as summer storms become stronger and more frequent over the mid-latitudes, in line with climate-change predictions, the previously unrecognized process of ozone damage by water vapour will accelerate.

To be sure, any mention of climate change spurs ifs and buts. After decades of observation, scientists do not yet know the tipping points. What concentrations of greenhouse gases are dangerous to life on earth? How far can temperatures rise? How sensitive is the planet to rising atmospheric carbon dioxide levels?

What we do know is that greenhouse gases add roughly three watts—a measure of energy, in the form of heat in this case—per square metre. Over the last century, the Earth has warmed up by about 0.75 degrees Celsius, and though limiting warming to a 2-degree-Celsius rise is the target of climate-change negotiations, no one can say with certainty.

What isn’t in the realm of speculation is the danger to life on Earth if the ozone layer is further damaged. UV radiation causes sunburn, cancer and cataracts, now the major cause of blindness. Most of the world’s crops are vulnerable to UV radiation, specifically their growth, flowering and photosynthetic ability. Increased UV radiation could disrupt aquatic life; in the oceans specifically by killing plankton, the base of the food chain.

Even as Antarctic-ozone stabilizes, the Earth must grapple with growing ozone loss over the Arctic, damage so severe that 20km above the ground, 80% of the ozone was lost, damaging enough to be called a new hole, a seminal paper in the journal Nature revealed last year. The Arctic ice may be melting as the earth warms, but over the last few decades, say scientists, the winters that are cold have been getting colder.

Although ozone depletion over the poles follows a different process than over mid-latitudes, resulting from cold instead of water vapour and warmth, the underlying cause is increasingly the same—industrial activity. The good news: Our understanding of climate change, a discipline of contradiction and confusion, is growing. The bad news: So, too, are its deleterious effects.

Samar Halarnkar is a Bangalore-based journalist. This is a fortnightly column that explores the cutting edge of science and technology. Comments are welcome at frontiermail@livemint.com

Also Read |Samar Halarnkar’s earlier columns

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Published: 26 Jul 2012, 09:43 PM IST
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