|William H. Calvin, PhD, Professor at|
University of Washington,
author of: Global Fever: How to
Treat Climate Change
1. Prospects for an Emergency Drawdown of CO2
Suppose we had to quickly put the CO2 genie back in the bottle. After a half-century of “thinking small” about climate action, we would be forced to think big—big enough to quickly pull back from the danger zone for tipping points and other abrupt climate shifts.
By addressing the prospects for an emergency drawdown of excess CO2 now, we can also judge how close we have already come to painting ourselves into a corner where all escape routes are closed off.7
Getting serious about emissions reduction will be the first course of action to come to mind in a climate crisis, as little else has been discussed. But it has become a largely ineffective course of action11 with poor prospects, as the following argument shows.
In half of the climate models14, global average overheating is more than 2°C by 2048. But in the US, we get there by 2028. It is a similar story for other large countries.
Because most of the growth in emissions now comes from the developing countries burning their own fossil fuels to modernize with electricity and personal vehicles, emissions growth is likely out of control, though capable of being countered by removals elsewhere.
But suppose the world somehow succeeds. In the slow growth IPCC scenario, similar to what global emissions reduction might buy us, 2°C arrives by 2079 globally–but in the US, it arrives by 2037.
So drastic emissions reduction worldwide would only buy the US nine extra years.
However useful it would have been in the 20th century, emissions reduction has now become a failed strategy, though still useful as a booster for a more effective intervention.
We must now resort to a form of geoengineering that will not cause more trouble than it cures, one that addresses ocean acidification as well as overheating and its knock-on effects.
Putting current and past CO2 emissions back into secure storage5 would reduce the global overheating, relieve deluge and drought, reverse ocean acidification, reverse the thermal expansion portion of sea level rise, and reduce the chance of more4 abrupt climate shifts.
Existing ideas for removing the excess CO2 from the air appear inadequate: too little, too late. They do not meet the test of being sufficiently big, quick, and secure. There is, however, an idealized approach to ocean fertilization5 that appears to pass this triple test.
It mimics natural up- and down-welling processes using push-pull ocean pumps powered by the wind. One pump pulls sunken nutrients back up to fertilize the ocean surface—but then another pump immediately pushes the new plankton production down to the slow-moving depths before it can revert to CO2.
How Big? How Fast?
The atmospheric CO2 is currently above 390 parts per million and the excess CO2 growth has been exponential. Excess CO2 is that above 280 ppm in the air, the pre-industrial (1750) value and also the old maximum concentration for the last several million years of ice age fluctuations between 200 and 280 ppm.
Is a 350 ppm reduction target12, allowing a 70 ppm anthropogenic excess, low enough? We hit 350 ppm in 1988, well after the sudden circulation shift18 in 1976, the decade-long failure of Greenland Sea flushing24 that began in 1978, and the sustained doubling (compared to the 1950-1981 average) of world drought acreage6 that suddenly began in 1982.
Clearly, 350 ppm is not low enough to avoid sudden climate jumps4, so for simplicity I have used 280 ppm as my target: essentially, cleaning up all excess CO2.
But how quickly must we do it? That depends not on 2 C overheating estimates but on an evaluation of the danger zone2 we are already in.
The Danger Zone
Global average temperature has not been observed to suddenly jump, even in the European heat waves of 2003 and 2010. However, other global aspects of climate have shifted suddenly and maintained the change for many years.
The traditional concern, failure of the northern-most loop of the Atlantic meridional overturning circulation (AMOC), has been sidelined by model results20-22 that show no sudden shutdowns (though they do show a 30% weakening by 2100).
While the standard cautions about negative results apply, there is a more important reason to discount this negative result: there have already been decade-long partial shutdowns not seen in the models.
Not only did the largest sinking site shut down in 1978 for a decade24, but so did the second-largest site23,28 in 1997. Were both the Greenland Sea and the Labrador Sea flushing to fail together2, we could be in for a major rearrangement of winds and moisture delivery as the surface of the Atlantic Ocean cooled above 55 N. From these sudden failures and the aforementioned leaps in drought, one must conclude that big trouble could arrive in the course of only 1-2 years, with no warning.
So the climate is already unstable. (“Stabilizing” emissions4 is not to be confused with climate stability; it still leaves us overheated and in the danger zone for climate jumps. Nor does “stabilized” imply safe.)
While quicker would be better, I will take twenty years as the target for completing the excess CO2 cleanup in order to estimate the drawdown rate needed.