While the focus is often on eustatic (global) sea-level rise, regional variations can be substantial and can magnify coastal vulnerability. For example, a 2009 review by James Syvitski and colleagues notes that many of the world's deltas (which are densely populated regions) are sinking much faster than global sea level is rising. Relative sea- level rise is four times larger on average than that for nearby bedrock shorelines. The reasons include human activities such as mining of water and petroleum, and the construction of dams that reduce the delivery of sediment to river mouths. A short summary of this issue can be found in Syvitski's article in this special issue of the Past Global Changes (PAGES) newsletter: http://www.pages-igbp.org/products/2011-03-28-16-23-06/522-pages-news-vol-20-no1.
I am no expert in the technical aspects of geoengineering, but it would appear that at least the regional magnification of sea-level rise would be amenable to engineering (if not sensu stricto geoengineering) solutions. For example, enhancing sediment delivery to deltas by appropriate infrastructural solutions (or by not building giant dams in places where this is still possible). For the Mississippi River, Blum and Roberts (2009) point out that "...significant drowning is inevitable, even if sediment loads are restored, because sea level is now rising at least three times faster than during delta-plain construction." Nevertheless, they do find some value in upstream diversions, which they suggest will help in building more land-surface area in relatively upstream regions of the delta. I am not aware of a comprehensive assessment for other deltaic systems, but would be worth looking into. Ninad References: Syvitski JPM et al. (2009) Sinking Deltas, Nature Geoscience 2: 681-689, doi:10.1038/ngeo629. Blum MD and Roberts HH (2009) Drowning of the Mississippi Delta due to Insufficient sediment supply and global sea-level rise, Nature Geoscience 2: 488-491, doi:10.1038/ngeo553. On May 26, 8:19 pm, Mike MacCracken <[email protected]> wrote: > One of the major reasons for the large range in the projections of sea level > rise (i.e., about 9 to 89 cm by 2100) that was included in IPCC’s Third > Assessment Report was due to the uncertainty in the term related to > terrestrial water storage, so just the subject of this letter. It was > because this range was so large and got up near 1 m/century that the chapter > went forward as there was significant criticism by US reviewers about the > importance of having left out the potential contribution from the dynamic > movement of ice sheets. > > In the Fourth Assessment Report, I don’t think they included this term due > to its significant uncertainty—and again they were not able to specifically > include the effects of the dynamic movement of the ice sheets, and so they > came out with a narrower and smaller numerical projection for sea level > rise. So, interesting letter and estimate—I wonder how long it could > continue (that is, how much water could be depleted from groundwater, etc.)? > > Mike > > On 5/26/12 4:20 AM, "Andrew Lockley" <[email protected]> wrote: > > > > > > > > > This interesting letter from nature geoscience shows that control of a > > substantial fraction of sea level rise is beyond the control of > > geoengineering, as it's anthropogenic in origin. > > > We may therefore have to hit the SRM brakes harder and earlier than > > expected, > > if we want to save the coastal cities > > > I find SLR interesting, as we will have to wind back the climate clock to > > control it. Stopping temperatures increasing won't stop glaciers melting. I > > fear that's often overlooked by current estimates of the scale of > > intervention > > needed. > > > A > > > Nature Geoscience | Letter > > Model estimates of sea-level change due to anthropogenic impacts on > > terrestrial water storage > > Yadu N. Pokhrel, Naota Hanasaki, Pat J-F. Yeh, Tomohito J. Yamada, Shinjiro > > Kanae & Taikan Oki > > Affiliations > > Contributions > > Corresponding author > > Nature Geoscience (2012) doi:10.1038/ngeo1476 > > Received 25 October 2011 Accepted 17 April 2012 Published online 20 May 2012 > > Article tools > > Print > > Email > > Download citation > > Order reprints > > Rights and permissions > > Share/bookmark > > > Global sea level has been rising over the past half century, according to > > tide-gauge data1, 2. Thermal expansion of oceans, melting of glaciers and > > loss > > of the ice masses in Greenland and Antarctica are commonly considered as the > > largest contributors, but these contributions do not entirely explain the > > observed sea-level rise1. Changes in terrestrial water storage are also > > likely > > to affect sea level3, 4, 5, 6, but comprehensive and reliable estimates of > > this contribution, particularly through human water use, are scarce1. Here, > > we > > estimate sea-level change in response to human impacts on terrestrial water > > storage by using an integrated model that simulates global terrestrial water > > stocks and flows (exclusive to Greenland and Antarctica) and especially > > accounts for human activities such as reservoir operation and irrigation. We > > find that, together, unsustainable groundwater use, artificial reservoir > > water > > impoundment, climate-driven changes in terrestrial water storage and the > > loss > > of water from closed basins have contributed a sea-level rise of about > > 0.77 mm yr−1 between 1961 and 2003, about 42% of the observed sea-level > > rise. > > We note that, of these components, the unsustainable use of groundwater > > represents the largest contribution. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. 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