Geo-engineering is considered by scientists to be our last and most risky option to control the climate change arising from the warming effect of rising levels of atmospheric carbon dioxide. But some scientists are reluctant to publicize the geo engineering option because any consideration of benefits could distract us from the critically important task of reducing emissions.
Almost science fiction in imagination and ambition, geo-engineering would attempt to combat rising temperatures by reducing the amount of sunlight reaching the Earth's surface. This could be done in a number of ways.
One plan is to launch hundreds of huge mirrors into space. When they reach an appropriate orbit, they could be unfolded, adjusted, and used to reflect sunlight away from the planet ‹ think of them as giant sun umbrellas.
Another plan is to send hundreds of millions of micro-thin silicone wafers into the gravitationally neutral place between the Earth and Sun. If these wafers were thin enough, a stack of a million could be positioned by each of the thousands of launches. Each wafer would be adjustable by radio frequency so it could be angled to either allow light to pass to Earth or be reflected away – think of them as venetian blinds.
Either of these solutions could cost trillions of dollars. But a less expensive and complicated option involves blasting huge quantities of shiny micro-particles into the upper atmosphere where they would disperse sunlight and reduce the amount striking the Earth. Since they could not be retrieved, however, the quantity and location would have to be correct for the desired effect.
Perhaps the most economical option is to add sulphate aerosols to the upper atmosphere. We already know a great deal about them by studying the effects of volcanic eruptions, and have fairly precise information about the amounts emitted, their cooling effects, and their 2-5 year stay in the atmosphere. About 1 kg would offset the global warming impact of 100,000 kg of carbon dioxide. These sulphate aerosols could be shot into the air by cannons, launched by magnetic guns and even delivered by high-altitude balloons.
Unfortunately, the sulphate aerosols option has shortcomings. Remediation would have to be continual if CO2 levels remained high. And they are the source of acid rain, the airborne sulphurous chemicals that leach soils, kill forests, poison lakes and cause general environmental havoc ‹ it's the principal industrial pollutant we've been trying for decades to eliminate. They also deplete the ozone layer that protects us from excessive solar radiation. Additionally, they interrupt the amount of direct sunlight reaching plants, interfering with growth and fertility. "And by cooling large land masses like Asia and Africa," writes Sharon Begley (Newsweek Dec. 3/07), "the heat reflecting particles reduce the temperature difference between them and the already cooler oceans, which could stifle the monsoons that millions of people depend on for agriculture."
Geo-engineering thus becomes political. Whose weather would be changed? What countries and food sources would be influenced by what forms of geo engineering? Who decides what measures are undertaken? As Begley asks, "What would Russia, which might profit from global warming, do if India, which would suffer, decided to cool things down through geo-engineering?" Do those who decide then become responsible for the consequences and thereby assume the obligation to compensate and provide food for those stricken with droughts or floods because of altered weather patterns? Who would decide if particular weather events were caused by particular engineering? "Whose hands are on the climate thermostat?" asks climatologist Dr. David Keith (Quirks and Quarks, CBC Radio, Mar. 29/08). The moral and political implications become staggeringly complex.
But geo-engineering's ambitious plans to cool the Earth by reducing the amount of arriving sunlight have the fundamental flaw of not addressing the major environmental damage caused by CO2 itself ‹ levels that have been rising by 1% during the 1990s and have increased to 3% since 2000.
Plants inhale CO2. But rising CO2 levels alter the way they grow and reproduce. While some increases in atmospheric carbon dioxide can encourage growth, higher levels can also impair germination and seed production ‹ not what we want for food crops. Elevated CO2 levels also tend to benefit weeds more than domesticated species, again impairing food production.
Perhaps the greatest danger from rising levels of CO2, however, is its effect on the oceans. About 25% of the 28 billion tonnes of carbon dioxide we emit annually dissolves into the seas to form carbonic acid. If this acidifying process continues, it could corrode the calcium carbonate of corals and eventually impair the ability of keystone micro-fauna to form their shells, thereby threatening the entire marine ecology. If we collapse this food chain, we lose a major source of our nutrition and would set in motion consequences we don't even want to imagine.
Geo-engineering that hopes to cool the planet by regulating arriving sunlight is really our option of last resort. As Begley notes, the fact that we are even considering it is "a sign of how dangerous global warming is starting to look and...how pitiful [are] the world's efforts to control greenhouse gases...."
This is an admonition we might remember when complaining about the cost and inconvenience of reducing our carbon dioxide emissions.