"The threat of a large sea level change is a principal element in our argument (Hansen et al 2006a, 2006b, 2007) that the global community must aim to keep additional global warming less than 1 °C above the 2000 temperature, and even 1 °C may be too great. In turn, this implies a CO2 limit of about 450 ppm, or less" [emphasis added]. Or else, it's "Goodbye Miami", as New Scientist says on a recent cover. Their map of Florida in 2007 and 2107 would come as a shock to the many Canadians who are familiar with South Florida's sunny shores. It gets worse: as Michael Le Page points out,
"Without mega-engineering projects to protect them, a 5-metre rise would inundate large parts of many cities - including New York, London, Sydney, Vancouver, Mumbai and Tokyo - and leave surrounding areas vulnerable to storm surges. In Florida, Louisiana, the Netherlands, Bangladesh and elsewhere, whole regions and cities may vanish. China's economic powerhouse, Shanghai, has an average elevation of just 4 metres" (New Scientist, "If sea level rises by 5 metres..." [near bottom of page; emphasis added]).For the devastating effects on Canada's Maritime Provinces, see my previous blog post.
Hansen and his co-authors write in another recent scientific paper :
"With GHGs continuing to increase, the planetary energy imbalance provides ample energy to melt ice corresponding to several metres of sea level per centuryAmong other things, Hansen and his co-authors have a plan to save the Earth:
"The gravest threat we foresee starts with surface melt on West Antarctica and interaction among positive feedbacks leading to catastrophic ice loss.
Our concern that BAU [Business As Usual] GHG scenarios would cause large sea-level rise this century (Hansen 2005) differs from estimates of IPCC (2001, 2007), which foresees little or no contribution to twenty-first century sea-level rise from Greenland and Antarctica. However, the IPCC analyses and projections do not well account for the nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves, nor are they consistent with the palaeoclimate evidence we have presented for the absence of discernable lag between ice sheet forcing and sea-level rise.
"The best chance for averting ice sheet disintegration seems to be intense simultaneous efforts to reduce both CO2 emissions and non-CO2 climate forcings. As mentioned above, there are multiple benefits from such actions. However, even with such actions, it is probable that the dangerous level of atmospheric GHGs will be passed, at least temporarily. We have presented evidence (Hansen
et al. 2006b) that the dangerous level of CO2 can be no more than approximately 450 ppm. Our present discussion, including the conclusion that slow feedbacks (ice, vegetation and GHG) can come into play on century time-scales or sooner, makes it probable that the dangerous level is even lower.
"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" [bolding added; italics in original].
"...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 fibres... grown without excessive fertilization that produces N2O or other offsetting GHG emissions, it will provide continuing drawdown of atmospheric CO2"  [bolding added].In other words:
- Take more CO2 out of the air than we are putting in.
- Use biomass fuels to remove CO2 from the air.
- Don't let the CO2 from the biomass go back into the air, for a new crop of plants to absorb (the conventional biofuels cycle). We don't want the CO2 to be released at all, as that would provide no net reduction.
- Instead, sequester the CO2 at source, right from the power plant.
- Put it below the ocean floor, where it would be safe forever.
On the other hand, some environmentalists are sceptical about CO2 sequestration and storage, and an international convention may regulate any materials stored in or under the ocean.
But what if there's even a 10% chance that Hansen is right about the potential damage if we do not follow his proposals? Multiply that 10% chance by the forecast amount of damage, and you still get an awesome risk!
Is it time for both politicians and environmentalists to start taking his latest research very seriously?
 James Hansen, 2007. Scientific reticence and sea level rise, Environ. Res. Lett. 2 (April-June 2007) 024002, doi:10.1088/1748-9326/2/2/024002 (via newscientist.com)
 James Hansen et al, 2007. Climate Change and Trace Gases. Philiosophical Transactions of the Royal Society - A. Vol 365, pp 1925-1954. doi: 10.1098/rsta.2007.2052. [PDF] screen pages 25-26 of 30 (via monbiot.com)
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