Volcano eruption seen from space and how a volcano works

Here's an interesting concept: Fight climate change by inoculating the atmosphere with millions of tonnes of air pollutants.

Simulate the natural effects of a volcano and fire sulphur into the stratosphere using balloons and heavy artillery guns, scientists say, and deflect sunlight away from Earth.

It's an idea that stems from the "Year without Summer," after Indonesia's Mount Tambora erupted into an explosive, fiery blast in 1815. The following year, heavy ash-filled skies blocked sunlight from reaching Earth, resulting in frost and rain-soaked summers around the world.

Cold temperatures dumped a foot of snow on Quebec in June, devastated crops worldwide and plunged countries into famine.

Similarly, the eruption of the Philippines' Mount Pinatubo in 1991 is widely cited as an example of how to cool the Earth with stratospheric aerosols.

The volcanic event spewed enough sulphate particles into the air to cool the Earth's surface on average 0.5C over the following year.

Like other geoengineering schemes -- the large-scale manipulation of Earth systems -- reproducing an artificial volcano comes with a host of caveats and warnings from wary scientists. But as noted by Nobel Prize-winning scientist Paul J. Crutzen, "Given the grossly disappointing international political response to the required greenhouse gas emission," more research on a possible "escape route" like this one shouldn't be tabooed.

In an editorial essay published in the journal Climate Change in 2006, Crutzen says the climate would respond quickly to the injection of sulphates into the atmosphere -- within half a year -- and could be effective on "short notice" if needed.

Blue skies, however, would be a thing of the past as this kind of climatic engineering would whiten the skies and produce fiery, colourful sunrises and sunsets.

The scheme would cost about $50 billion US, or about $50 per capita in the Western world.

In response to Crutzen's article, meteorologist Lennart Bengtsson of the Max Planck Institute for Meteorology in Germany, pointed out in the same journal that such a scheme would have to be carried out for hundreds of years as conditions would return quickly to the same levels if the process were stopped.

But that poses an ethical question, critics say: Is it fair to leave this kind of burden and commitment to the next generations? Is it fair to risk environmental uncertainties to placate immediate concerns?

Tom Wigley of the National Center for Atmospheric Research in the U.S. writes that the scheme could provide a "grace period" of up to 20 years before major cutbacks in greenhouse gases would be required.

And like all geoengineering schemes, therein lies the problem. The danger, Wigley, Bengtsson and Crutzen agree, is that policymakers will use climate engineering as an excuse not to cut emissions.

But a two-pronged approach to mitigating the effects of climate change --cutting emissions and engineering the climate -- could help stabilize global temperatures for the next 40 years, Wigley says.

Nor do stratospheric aerosols sequester carbon, a major drawback considering how present levels of carbon are already undoing Earth systems.

Crutzen also points out that replicating a large-scale volcanic eruption would mimic the same negative consequences. When Mexico's El Chichon erupted in 1982, it destroyed 16% of the local ozone, while Mount Pinatubo caused a global column ozone loss of 2.5%.

"The very best would be if emissions of the greenhouse gases could be reduced so much that the stratospheric sulphur release experiment would not need to take place," Crutzen concludes in his essay.

"Currently, this looks like a pious wish."

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HUMAN CAUSES

Human activities currently account for about 10% of the total amount of aerosols in our atmosphere. Most of that 10% is concentrated in the Northern Hemisphere.

AEROSOLES & CLIMATE CHANGE

STRATOSPHERE

- Aerosols are tiny particles suspended in air. Some occur naturally -- from volcanoes, dust, storms, forest fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels and the alteration of natural surface cover, also generate aerosols.

- A severe volcanic eruption can also put aerosols in the stratosphere (above the troposphere). Since it doesn't rain in the stratosphere, these aerosols remain for months.

- Tiny water droplets which form around aerosol particles reflect the sun's energy back to space, preventing some heating of Earth's surface.

TROPOSPHERE

- Under normal circumstances, the majority of aerosols form a thin haze in the lower atmosphere (troposphere) and get washed away by rain.