The National Academies Press

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From page 217... ... Earth System Sensitivity involves a number of processes that are less well understood than those involved in fast-feedback climate sensitivity or transient climate response. The challenges are compounded by the slow nature of these feedbacks, which makes them difficult to study through current observations of the changing climate. Read the entire page →
From page 218... ... Moreover, the length of time over which the climate is substantially warmer than previous interglacials becomes longer, allowing more time for slow components of the climate system to respond. The very long-term human imprint on climate can be assessed by computing the warming remaining after many centuries, taking into account only the climate sensitivity ap plied to the CO2 remaining after allowing for uptake of carbon emissions by land and ocean. Read the entire page →
From page 219... ... . The upper red curve gives the maximum, the heavy black curve the median, and the lower green curve the minimum warming over all combinations of climate sensitivity and carbon-cycle models. Read the entire page →
From page 220... ... To obtain observational constraints on equilibrium climate sensitivity or Earth System Sensitivity, one must look into the more distant past. There are many ways to make use of the past climate record as a guide to the future, and in evaluating the published re sults, one must take care to distinguish the kind of climate sensitivity being estimated, which categories of climate forcings are regarded as feedbacks, and which categories of climate forcings are regarded as known or diag nosed forcings to be used in determining the sensitivity of the rest of the climate system. Read the entire page →
From page 221... ... (2010) estimate that the Pliocene global mean temperature was 3°C warmer than at present. Read the entire page →
From page 222... ... . Methane or other, currently unknown, radiative forcing agents may have affected the Pliocene climate and the PETM warming, but for now the simplest explanation of the PETM would appear to be that climate sensitivity is very high. Read the entire page →
From page 223... ... At present, our assessment is that it is not possible to quantify these risks. A challenge for climate science is not only to evaluate the physics and chemistry of the underlying processes, but also to explain why local observations or evidence from past climates do not necessarily imply that these factors are important for current and future anthropogenic climate changes. Read the entire page →
From page 224... ... As an example, let's suppose that 100 GtC is released suddenly into the atmosphere as methane. This would increase the atmospheric methane concentration by 46 ppm over its present value of 1.8 ppm, leading to a radiative forcing of 6 W/m2, which would cause a transient climate warm ing of 2.1 to 3.6°C, based on the likely range of transient climate sensitivity. Read the entire page →
From page 225... ... . This figure is probably an underestimate of terrestrial organic carbon storage, as it doesn't fully account for carbon storage in peatlands, and there is considerable potential that permafrost systems may store an additional 1,000 GtC or more of organic carbon (Schuur et al., 2008) Read the entire page →
From page 226... ... It should be kept in mind that there are many important physical processes that are not well represented in current ice-sheet models, so that any thresholds based on models should be taken as only a general indication of what ice sheets can do, rather than precise, definitive values. The waxing and waning of large land ice sheets has a profound effect on sea level. Read the entire page →
From page 227... ... Calculated Greenland melt is shown in Figure 6.2. During the Eemian about 130,000 years ago, Arctic temperatures were about 3-5°C warmer than present, and it has been estimated that the loss of ice from Greenland and other Arctic ice fields contributed up to 4 m to sea level rise (Jansen et al., 2007) Read the entire page →
From page 228... ... , the Greenland Ice Sheet is shown to disappear within 3,000 years, raising sea level by about 7.5 m. For lower CO2 concentrations, melting proceeds at a slower rate, but even in a world with twice as much CO2 (550 ppm or a 3.7°C summer warming) Read the entire page →
From page 229... ... , global sea level was at least 3 m, and probably more than 5 m, higher than at present. But some studies suggest that the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet, with model studies attributing only 1-2 m of sea level rise to meltwater from Greenland. Read the entire page →
From page 230... ... If uncompensated by increase in water storage in East Antarctica, the total loss of the Greenland ice sheet would lead to a sea level rise of 7.5 m (Bamber et al., 2001) , while the total loss of the West Antarctic Ice Sheet would lead to an additional rise of 5 m (Bamber et al., 2009) Read the entire page →
From page 231... ... . Clearly, increases in risks from inundation, repeated flooding, and coastal erosion that have already been documented in some places for modest sea level rise could therefore continue as the future unfolds and could well be amplified over the long term depending upon the rate at which they occur as the climate system changes. Read the entire page →
From page 232... ... Source: University of Arizona, see http://www.geo.arizona.edu/dgesl/research/other/ 6.3.eps climate_change_and_sea_level/sea_level_rise/sea_level_rise_technical.htm. bitmap There is high confidence that neither adaptation nor mitigation alone can avoid all climate change impacts; however, they can complement each other and together can significantly reduce the risks of climate change. Read the entire page →
From page 233... ... Since rising seas are the source of one such persistent and growing threat across the world, though, it is entirely plausible that displaced people may be forced to migrate even if temperature increases are capped. They may move within a country or region (like, as reported in Kates et al. Read the entire page →

From page 217...

... Earth System Sensitivity involves a number of processes that are less well understood than those involved in fast-feedback climate sensitivity or transient climate response. The challenges are compounded by the slow nature of these feedbacks, which makes them difficult to study through current observations of the changing climate.