Is there anything we can do, apart from the obvious (roll out renewables even faster), to prevent that?
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| Mt Pinatubo eruption, 1991 |
The most "popular" potential solution is to mimic the effect of volcanoes. Take the eruption of Mt Pinatubo in 1991:
The 1991 eruption of Pinatubo produced about 5 cubic kilometers of dacitic magma and may be the second largest volcanic eruption of the century. Eruption columns reached 40 kilometers in altitude and emplaced a giant umbrella cloud in the middle to lower stratosphere that injected about 17 megatons of SO2, slightly more than twice the amount yielded by the 1982 eruption of El Chichón, Mexico. The SO2 formed sulfate aerosols that produced the largest perturbation to the stratospheric aerosol layer since the eruption of Krakatau in 1883. The aerosol cloud spread rapidly around the Earth in about 3 weeks and attained global coverage by about 1 year after the eruption. Peak local midvisible optical depths of up to 0.4 were measured in late 1992, and globally averaged values were about 0.1 to 0.15 for 2 years. The large aerosol cloud caused dramatic decreases in the amount of net radiation reaching the Earth's surface, producing a climate forcing that was two times stronger than the aerosols of El Chichón. Effects on climate were an observed surface cooling in the Northern Hemisphere of up to 0.5 to 0.6°C, equivalent to a hemispheric-wide reduction in net radiation of 4 watts per square meter and a cooling of perhaps as large as -0.4°C over large parts of the Earth in 1992-93. Climate models appear to have predicted the cooling with a reasonable degree of accuracy. The Pinatubo climate forcing was stronger than the opposite, warming effects of either the El Niño event or anthropogenic greenhouse gases in the period 1991-93. As a result of the presence of the aerosol particles, midlatitude ozone concentrations reached their lowest levels on record during 1992-93, the Southern Hemisphere "ozone hole" increased in 1992 to an unprecedented size, and ozone depletion rates were observed to be faster than ever before recorded. The atmospheric impact of the Pinatubo eruption has been profound, and it has sparked a lively interest in the role that volcanic aerosols play in climate change. This event has shown that a powerful eruption providing a 15 to 20 megaton release of SO2 into the stratosphere can produce sufficient aerosols to offset the present global warming trends and severely impact the ozone budget.
If we could (somehow) pump sulphur dioxide into the stratosphere every year, mimicking a volcanic eruption, we would be able to reduce global temperatures by 0.5 degrees--at the cost of expanding the hole in the ozone layer (not good). Who would pay for this? The same people who now reject the switch to renewables "because it's too costly"? And the solution is temporary: within a couple of years the SO2 aerosols will have fallen to earth as acid rain (also not good).
Another kind of geo-engineering (though it's not often thought of that way) is to turn carbon dioxide to rock. This is a permanent solution but will take massive effort and plenty of cash to make it happen. The pilot plant in Iceland turned 220 tonnes of CO2 into rock. But this equals the annual emissions of just 12 people in the US or Australia. We would need 27 million similarly sized plants to turn the emissions of the USA to rock.
The best preventive to runaway global warming remains to replace fossil fuels in power generation and transport, to find different ways of making cement and steel, and to stop clearing and burning forests. As fast as possible.
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