Aerosols may solve the climate crisis

An aircraft soars overhead, releasing a strange gas high into the upper atmosphere. This gas isn’t Agent Orange, a pesticide, or any other gas ever released by a plane. Instead, this gas is composed of tiny sulfuric acid drops that will bounce the sun’s rays back into space, preventing them from reaching the Earth’s surface and warming the planet.

Nearly everyone is aware of the looming effects of climate change, such as increased air temperatures, rising sea levels, and the spread of tropical diseases. Even if greenhouse gas emissions are halted today – an unlikely scenario to even the most optimistic observer – studies show that these consequences are inevitable. Now, scientists are getting creative in an attempt to buy more time in the race, or what has seemed more like a crawl, to reduce greenhouse gases. Geo-engineering techniques are in development which could manipulate Earth’s climate on a global scale to stave off climate disaster.

“We are warming and we are trying to engineer our way out of it,” says Dr. Peter Huybers of the Department of Earth and Planetary sciences at Harvard University.

One of the most feasible geo-engineering techniques on the table right now is injection of aerosols into the atmosphere. Aerosols are gases containing tiny droplets of liquid that can reflect sunlight. If aerosols were injected into the atmosphere, the amount of solar energy reaching Earth’s surface would decrease and the surface would cool. The scheme has a natural precedent in volcanoes; aerosols released by volcanic eruptions reduced the earth’s temperature by as much as half a degree a few times in the 20th century.

The injection idea has been analyzed to new depth by a recent article in Geophysical Research Letters. A computer model representing aerosol interaction with the ocean and atmosphere calculated the balance of aerosol quantity and size needed to offset warming expected later this century.

Although the solution may seem like a dream come true, there are problems. Among them is the complexity of the climate. Dr. Huybers explains that scientists’ limited understanding makes it hard to predict where things might go wrong.

“It is difficult to tinker with a system that we only partly understand. The biggest risks are the ones we can’t foresee now,” he said.

In addition to the unknown risks, it’s clear that the scheme would impact vegetation, weather patterns, ozone depletion, and acid rain. There is also a danger that if aerosol injection began, it would need to continue for a very long time to offset the lingering impact of greenhouse gases. If aerosol injection were not regularly maintained, the result would likely be 15 to 20 years of rapid and catastrophic global warming.

A positive aspect of aerosols is that they remain in the upper atmosphere for between only two and three years. So if anything went horribly wrong, the climate would be back to normal within a short time. Dr. Phillip Rasch, of the National Centre for Atmospheric Research, remarks that the short lifetime of aerosols in the atmosphere also makes tests feasible.

“A short-term test would be relatively easy to control, and if we stopped injection the Earth’s climate system would return to a normal state relatively quickly,” he says.

Although the new model is a step in the right direction, the uncertainties surrounding aerosol injection are still significant. Dr. Rasch explains that far more work must be done before an experiment can be carried out.

“The kind of study we just completed is the tip of the iceberg. The IPCC (Intergovernmental Panel on Climate Change) assessments of climate change represent the works of thousands of scientists over several years. Any geoengineering experiment would require the same,” he said.

Deliberate alteration of Earth’s atmosphere should neither be taken lightly nor perceived as a quick fix. However, temperatures are rapidly approaching levels that will have severe consequences for life on earth, and Carbon Dioxide emissions continue to increase yearly. Faced as we are with the problem of how to save the climate, aerosols are an attractive option.

As Dr. Rasch says, “It doesn’t solve all problems, and it may cause a few more, but perhaps it’s better than nothing.”

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