expansion (estimated to be 0.2 to 0.6 m per degree C of global warming in IPCC, 2007a), which would amount to 0.6 to 1.8 m for a long-term warming of 3ºC or 1.2 to 3.6 m for a long-term warming of 6ºC.
Over the coming millennia, some impacts of climate change may settle into new patterns of climate variability with the successful implementation of stabilization policies that cap cumulative emissions and therefore limit increases in global mean temperature. Climate variability could then be distributed around different means (with perhaps different higher moments), but it is possible that societies could become accustomed to these new environments. That world would be different than today, but new conditions could become routine to people living on Earth one or two thousand years from now. Other impacts, however, could continue for many centuries past the date of temperature stabilization.
Rising seas and melting glaciers and/or ice sheets easily fit into this second category of persistent and growing very long-term significance. Figure 6.3 displays, for example, contours of 1 m of sea level rise for Florida, which could occur by 2100 based on Section 4.8. In the longer term, much larger sea level rise is possible over millennia (see Section 6.1). 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.
To get a better understanding of what associated vulnerabilities might look like as the long-term future unfolds, one might contemplate tracking widespread migration over recent time away from areas of exacerbated climate risk, but attribution would be extremely difficult. As noted in Wilbanks et al. (2007: Box 7.2), observed environmental migration is often a temporary reaction to the calamitous ramifications of one extreme event or another. WDR (2010) reports that displaced people (the estimated 26 million people who have moved permanently during recent years) constitute less than 10% of the world’s international migrants and that most of these people relocate still live within the same country or, at worst, somewhere in the same region of the world.
IPCC (2007e) reported, in words that were unanimously approved in the plenary as part of the Summary for Policymakers, that