This is written for a less expert audience than seen here at Google Groups
Geoengineering, but bear with me as this is an example of how to frame
policy priorities. wcal...@uw.edu
————
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 shift
18 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.
*The Size of the Cleanup*
It is not enough to target the excess CO2 currently in the air, even though
that is indeed the cause of ocean acidification, overheating, and knock-on
effects. We must also deal with the CO2 that will be released from the
ocean surface as air concentration falls and the bicarbonate buffers
reverse, slowing the drawdown.
Thus, I take as the goal to counter the anthropogenic emissions4,5 since
1750, currently totaling 350 gigatonnes of carbon. (GtC =1015g of
Carbon=PgC.)
During a twenty year project period, another 250 GtC are likely be emitted,
judging from the 3% annual growth in the use of fossil fuels5 despite some
efforts at emissions reduction. Thus we need to take back 600 GtC within 20
yr at an average rate of 30 GtC/yr in order to clean up (for the lesser
goal of countering continuing emissions, it would take 10 to 15 GtC/yr).
Chemically scrubbing the CO2 from the air is expensive and requires new
electrical power from clean sources, not likely to arrive quickly enough.
On this time scale, we cannot merely scale up what suffices on submarines.
Thus we must find ways of capturing 30 GtC/yr with traditional
carbon-cycle8biology, where CO
2 is captured by photosynthesis and the carbon incorporated into an organic
carbon molecule such as sugar. Then, to take this captured carbon out of
circulation, it must be buried to keep decomposition methane and CO2 from
reaching the atmosphere.
*Sequestering CO2 *
One proposal26 is to bundle up crop residue (half of the annual harvest is
inedible leaves, skins, cornstalks, etc.) and sink the weighted bales to
the ocean floor. They will decompose there but it will take a thousand
years before this CO2 can be carried back up to the ocean surface and vent
into the air.
Such a project, even when done on a global scale, will yield only a few
percent of 30 GtC/yr. Burying raw sewage3 is no better.
If crop residue represents half of the yearly agricultural biomass, this
also tells you that additional land-based photosynthesis, competing for
space and water with human uses, cannot do the job in time.5 It would need
to be far more efficient than traditional plant growth. At best, augmented
crops on land would be an order of magnitude short of what we need for
either countering or cleanup.
*Big, Quick, and Secure*
Because of the threat from abrupt climate leaps, the cleanup must be big,
quick, and secure.
Doubling all forests might satisfy the first two requirements but it would
be quite insecure—currently even rain forests4 are burning and rotting,
releasing additional CO2.
*Strike One. * We are already past the point where enhanced land-based
photosynthesis can implement an emergency drawdown. They cannot even
counter current emissions.
Basically, we must look to the oceans for the new photosynthesis and for
the long-term storage of the CO2 thus captured.
*Fertilization per se*
Algal blooms are increases in biological productivity when the ocean
surface is provided with fertilizer containing missing nutrients15 such as
nitrogen, iron, and phosphorus.
A sustained bloom of algae can be fertilized by pumping up seawater5,16,19from
the depths, a more continuous version of what winter winds
9 bring up.
Currently about 11 GtC/yr settles out of the wind-mixed surface layer into
the slowly-moving depths13 as plankton die. To settle out another 30
GtC/yr, we would need about four times the current ocean primary
productivity. Clearly, boosting ocean productivity worldwide is not, by
itself, the quick way to put the CO2 genie back in the bottle.
*Strike Two. *Our 41% CO2 excess is already too large to draw down in 20 yr
via primary productivity increases in the ocean per se.
However, our escape route is not yet closed off. There is at least one
plausible prospect for an emergency draw down for 600 GtC in 20 yr. It
seeks to mimic the natural ocean processes of upwelling and downwelling.
* *
*References (numbers refer to reference list in the following “Push-pull
ocean pipes” Topic*
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