Protagoras,

John Church has a very good paper in the Journal Science this week. However, other research by Nicholls and Cazenavel in the same issue (18 June 2010: Vol. 328. no. 5985, pp. 1517 – 1520 DOI: 10.1126/science.1185782) summarises the SLR issue quite well. Here is an extract if you can’t access the whole paper:

>> Although mean sea level remained nearly stable since the end of the last deglaciation (~3000 years ago) tide gauge measurements available since the late 19th century indicate that sea level has risen by an average of 1.7 ± 0.3 mm/year since 1950. Since the early 1990s, SLR has been routinely measured by high-precision altimeter satellites. From 1993 to 2009, the mean rate of SLR amounts to 3.3 ± 0.4 mm/year, suggesting that SLR is accelerating.

Two main factors contribute to SLR: (i) thermal expansion of sea water due to ocean warming and (ii) water mass input from land ice melt and land water reservoirs. Ocean temperature data collected during the past few decades indicate that ocean thermal expansion has significantly increased during the second half of the 20th century. Thermal expansion accounts for about 25% of the observed SLR since 1960 and about 50% from 1993 to 2003. Since then, upper-ocean warming has been smaller and on average over the satellite altimetry era (1993 to 2009), the contribution of ocean temperature change to the global mean sea level may be ~30%.

Numerous observations have reported worldwide retreat of glaciers and small ice caps during recent decades, with an appreciable acceleration of this retreat during the 1990s. The glacier contribution to SLR from 1993 to 2009 may be ~30%. Change in land water storage, due to natural climate variability and human activities (e.g., underground water mining, irrigation, urbanization, and deforestation), contributes little (<10%) to current sea-level change. By contrast, intensive dam building along rivers during the second half of the 20th century lowered sea level by ~ –0.5 mm/year.

Cont’d

Since the early 1990s, different remote-sensing tools (airborne and satellite radar and laser altimetry; synthetic aperture radar interferometry [InSAR]; and, since 2002, space gravimetry from the Gravity Recovery and Climate Experiment [GRACE] mission) have provided good data on the mass balance of the polar ice sheets. These data indicate that Greenland and West Antarctica mass loss is accelerating. Between 1993 and 2003, <15% of the global SLR was due to the ice sheets. However, since about 2003, their contribution has nearly doubled; increasing glacier and ice sheet mass loss has compensated for reduced ocean thermal expansion, such that SLR continues at almost the same rate. Although not monotonic through time, we estimate that on average over the altimetry era (1993 to 2009), total land ice mass loss explains ~60% of the rate of SLR.

The rapid changes observed in Polar Regions suggest that the ice sheets respond to current warming on much shorter time scales than previously anticipated. However, it is unknown whether these processes will continue into the future, resulting in a partial collapse of the ice sheets after a few centuries, or whether a new equilibrium will be reached. For the near term (next decades), the largest unknown in future SLR is the behaviour of the ice sheets. Although IPCC AR4 projections did not account for dynamical changes of large ice sheets, simple kinematics and observations of current velocities of marine-terminated glaciers in Greenland and West Antarctica suggest that future ice-dynamics discharge could lead to SLR of about 80 cm by 2100. <<

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Loudmouth

2 degrees (global average) by 2100 doesn’t seem much, but regional averages will be much greater (happening already here in Australia and other parts of the globe) AR5 will be more regionally specific due to more data and access to faster computers.

qanda,

Thank you (I'll bet you don't see that too often): 2 inches' sea-level rise in fifty years. In the next century, perhaps 8 inches ? So if nobody does anything, the parts of Sydney less than 20 metres above sea-level will be under-water in about 10,000 years.

Now to prise temperature change out of somebody ..... any takers ?

Rip van Winkle

Thanks for the update Qanda and it’s not cheery news and it appears that Perth is particularly vulnerable. Significant areas of Perth are situated along the banks of the flood prone Swan River and close to Australia's most active earthquake zone. There are several limestone belts to the north and south of Perth where karst systems have been discovered and the city's coastline already suffers significantly from coastal creep and erosion.

Winthrop Professor Chari Pattiaratchi from The University of Western Australia also said sea levels around Perth and the South West were now estimated to become up to one metre higher by the end of this century, affecting foreshore developments, beaches and housing.

http://www.news.uwa.edu.au/200911121880/media-statements/perth-water-levels-a-metre-higher-end-century

I will be interested to read of the outcome of the following conference on SLR, hosted by the ATSE which is to be held next month in Perth

http://www.gsa.org.au/pdfdocuments/Divs_SGs_Newsletters/city%20to%20cape_Prog%20and%20link%20to%20registration.pdf

However, I don’t think any of this will be of interest to the aburrido, do you?

Loudmouth, you say:

>> 2 inches' sea-level rise in fifty years. In the next century, perhaps 8 inches ? So if nobody does anything, the parts of Sydney less than 20 metres above sea-level will be under-water in about 10,000 years. <<

You seem to be having difficulty understanding, I'll try again.

The rate of sea level rise is accelerating and the observations (since AR4) taking place at glaciers meeting the ocean in both Greenland and West Antarctica suggest a sea level rise of 8o centimetres by 2100.

Now, 8o centimetres might not seem very much to some people (you think it equates to 8 inches for Pete's sake!) but if you add a 'king' tide and an extreme weather storm surge, that 80 cm can turn into 1.2 metres (some places more, some less).

I agree, all this talk of 20 metres SLR happening anytime soon is just silly, but one metre SLR is bad enough - maybe not for you, Loudmouth, but for the millions of others that will be affected.

Anyway, the planet does not stop in 2100 - sea levels will continue to rise, and by all accounts, at an an ever-increasing rate, Loudmouth.

As to temperatures and takers. We've been through this on OLO before. In this thread, you have been given the links, why can't you look at the research papers yourself?

Let me guess:

. You don't remember, you don't know how to, or are too busy or lazy, or

. You don't know where to look other than 'denialist' blog sites or,

. You clasp your ears with your hands, close your eyes and drone on about la-la-de-da, or something similar.

A combination of all 3, probably.

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Protagoras: probably not. Sad really, being a real sceptic I would be the first to gather as much information as possible, especially the bits that run counter to the scientific consensus.

Did I miss something qanda? Did you post a link to some scientific proof of contribution of human emissions to global warming.

There is no such link, qanda, which is why you talk about all sorts of other issues, which are irrelevant, unless human emissions have any contribution to global warming, and of course, you know that there is no scientific basis for any assertion that human activity contributes in any measureable way to global warming.

There is the pretend science of the disingenuous IPCC, which pretended that there is scientific agreement by scientists that it is “very likely”.

As a scientific basis this is meaningless, and the support for it is a mere 5 scientists, if you do not count the 55 conflicted scientists, who should not, in their circumstances, have offered an opinion

As against that there are over 31,000 scientist who signed a petition to have it noted that there is no science to support the assertion of AGW.

Why do you continue to try to support this scam, qanda, do you wish to become as disreputable as Naomi Oreskes?