A few quotes:
(d ) Planet Earth today: imminent peril
The imminent peril is initiation of dynamical and thermodynamical processes
on the West Antarctic and Greenland ice sheets that produce a situation out of
humanity’s control, such that devastating sea-level rise will inevitably occur.
Climate forcing of this century under BAU would dwarf natural forcings of the
past million years, indeed it would probably exceed climate forcing of the middle
Pliocene, when the planet was not more than 2–38C warmer and sea level 25G
10 m higher (Dowsett et al. 1994). The climate sensitivities we have inferred from
palaeoclimate data ensure that a BAU GHG emission scenario would produce
global warming of several degrees Celsius this century, with amplification at
It is difficult to predict time of collapse in such a
nonlinear problem, but we find no evidence of millennial lags between forcing and
ice sheet response in palaeoclimate data. An ice sheet response time of centuries
seems probable, and we cannot rule out large changes on decadal time-scales
once wide-scale surface melt is underway. With GHGs continuing to increase, the
planetary energy imbalance provides ample energy to melt ice corresponding to
several metres of sea level per century
Present knowledge does not permit accurate specification of the dangerous
level of human-made GHGs. However, it is much lower than has commonly
been assumed. If we have not already passed the dangerous level, the energy
infrastructure in place ensures that we will pass it within several decades.
We conclude that a feasible strategy for planetary rescue almost surely requires a
means of extracting GHGs from the air. Development of CO2 capture at power
plants, with below-ground CO2 sequestration,may be a critical element. Injection of
the CO2 well beneath the ocean floor assures its stability (House et al. 2006). If the
power plant fuel is derived from biomass, such as cellulosic fibres5 grown without
excessive fertilization that produces N2O or other offsetting GHG emissions, it will
provide continuing drawdown of atmospheric CO2.
TokyoTom and I disagree somewhat about the last paragraph. He thinks it lends support for open-air carbon capture, the approach favored by Roger Pielke Jr. and the only semi-mainstream idea more speculative than geoengineering. I think Hansen's referring to carbon sequestration from biomass power generation, which is a means of extracting GHGs from the air.
I don't know what this "Injection of the CO2 well beneath the ocean floor assures its stability" is about though. I know of below-ground carbon sequestration, and deep-ocean sequestration, but not of an approach that combines the two. I guess I should read the reference.