The Earth’s climate is in “imminent peril” of the initiation of dynamical and thermodynamical processes on the West Antarctic and Greenland ice sheets that will result in a situation out of humanity’s control, such that devastating sea-level rise will inevitably occur, according to a open-access paper by six leading US scientists published in the peer-reviewed journal Philosophical Transactions of the Royal Society A.
Only intense simultaneous efforts to slow CO2 emissions and to reduce non-CO2 greenhouse gas emissions and other forcings can keep climate within or near the range of the past million years, according to authors James Hansen, Makiko Sato, Pushker Kharecha, and Gary Russell of NASA Goddard Institute for Space Studies and Columbia University Earth Institute; David W. Lea from the University of California, Santa Barbara; and Mark Siddall of the Lamont-Doherty Earth Observatory, Columbia University.
Earth’s climate is remarkably sensitive to forcings, i.e. imposed changes of the planet’s energy balance. Both fast and slow feedbacks turn out to be predominately positive. As a result, our climate has the potential for large rapid fluctuations. Indeed, the Earth, and the creatures struggling to exist on the planet, have been repeatedly whipsawed between climate states. No doubt this rough ride has driven progression of life via changing stresses, extinctions and species evolution. But civilization developed, and constructed extensive infrastructure, during a period of unusual climate stability, the Holocene, now almost 12,000 years in duration. That period is about to end.
One critical feedback mechanism is this process has been the “albedo flip” property of ice and water.
Climate forcing of this century under BAU [business as usual] 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 2–3°C warmer and sea level 25 ±10 m higher. 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 high latitudes. Such warming would assuredly activate the albedo-flip trigger mechanism over large portions of these ice sheets. In combination with warming of the nearby ocean and atmosphere, the increased surface melt would bring into play multiple positive feedbacks leading to eventual nonlinear ice sheet disintegration... 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.
The authors explicitly disagree with the conclusions of the IPCC, which forsees little or no contribution to 21st century sea-level rise from Greenland and Antarctica. The paper’s authors argue that the IPCC analysis does not account well for the nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves, and point out that the IPCC conclusions are not consistent with the palaeoclimate evidence.
In the absence of realistic representations of the physics of ice streams and ice quakes in existing ice sheet models, the authors assert, it is better to rely on historical data.
That history reveals large changes of sea level on century and shorter timescales...We infer that it would be not only dangerous, but also foolhardy to follow a BAU path for future GHG emissions.
Although CO2 is the largest human-made forcing, reducing the non-CO2 forcings are also important—especially given the difficulty in slowing the growth rate in CO2 emissions and stabilizing the atmospheric concentration.
The authors argue that it would better not to package all the climate forcings together into an interchangeable bundle for mitigation strategies.
Sources of different gases are usually independent and greater progress is likely from complementary focused programmes. However, in regulations of a specific activity or industry, the rules should be based on information about the effect of the activity on all climate forcings.
Since it seems likely that readily available oil and gas reservoirs will be fully exploited, it will be necessary to phase out coal use—except where carbon capture and sequestration is used—and to put the same constraint on the development of unconventional fossil fuels (oil sands, shale, CTL, etc.), they state.
In practice, achievement of these goals surely requires a price (tax) on CO2 emissions sufficient to discourage extraction of remote oil and gas resources as well as unconventional fossil fuels. Furthermore, the time required to develop fossil-free energy sources implies a need to stretch supplies of conventional oil and gas. In turn, this implies a need for near-term emphasis on energy efficiency.
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. If the power plant fuel is derived from biomass, such as cellulosic fibres grown without excessive fertilization that produces N2O or other offsetting GHG emissions, it will provide continuing drawdown of atmospheric CO2.