More about the forecast for flooded cities in the late 21st century

Summary: Much of the efforts to fan climate hysteria rely on false descriptions of current climate science, most especially on the assertion of a consensus that does not exist. The articles on the FM website puncture this simply and surely by showing a diversity of opinion expressed in presigious peer-reviewed journals about the history, causes, magnitude, and forecasts about global warming. Much of this is hidden from the general public by the news media. This post is another in that long series. For a partial list of the these studies see the FM reference page Science & climate – studies & reports.

Rising sea levels are one of the most graphic and easily understood consequences of global warming. Cities, even entire islands, submerged later in this century (per earlier warnings, even by 2010). As shown in the posts below, the climate science literature offer little support for such extreme forecasts. Coming out of the little ice age, sea levels have risen at a steady (if difficult to measure before satellites) rate for over a century. Scientists debate if the melt rate is increasing (other than 10-20 year variations). It’s cutting-edge science, far from consensus — and hence no basis for massive public policy changes. This post describes the latest volley.

As usual, we’ll start with summary intended for a general audience before looking at the underlying study.

(1) The simplest version

“Climate Change: Are the Polar Ice Caps Melting Slower Than We Thought?“, Time, 9 September 2010 — Money quote:

“The Nature Geoscience study also doesn’t change the essential fact that we are losing ice on a daily basis from Greenland and West Antarctica—104 billion metric tons is still a lot of water to be adding to the global seas each year.”

It’s the “big number” tactic of doomster pseudoscience.

A gigaton (metric) of ice forms a cube with sides of aprox one kilometer.
The oceans have an area of aprox 360 million square kilometers and a volume of 335 million cu km.
Melting one gigaton of glacier ice raises the sea level less than 3 microns.
Current rates, still debated, of glacial melt raise ocean levels aprox 3 mm (i.e., one foot) per century.
Melting of floating ice (e.g., at the north pole) does not raise sea levels.
Greenland’s ice cap is roughly 2.5 million cu km; Antarctica’s is 25 cu km.

(2) A better summary

“Sea-level rise: Ice-sheet uncertainty”, David H. Bromwich and Julien P. Nicolas, Nature Geoscience, September 2010 — Abstract here. Free copy here.

“Satellite gravimetry has been playing an increasingly important role in monitoring the state of the polar ice sheets since 2002. A suite of mass-balance studies based on the Gravity Recovery and Climate Experiment (GRACE) mission has revealed substantial losses of ice-sheet mass in Greenland and West Antarctica. What’s more, the contribution of the ice sheets to global mean sea-level rise has accelerated over the past few years. Writing in Nature Geoscience, Wu and colleagues describe an innovative approach employed to derive ice-mass changes from GRACE data and suggest significantly smaller ice-mass loss overall than earlier GRACE-based estimates.

“… The significant scatter among the GRACE-based estimates published thus far results not only from the differing processing methods, but also from the shortness of the GRACE time series, the differing length of the series used in various publications, and the recent acceleration in ice-mass loss.”

Figure 1, above:

“The estimate by Wu and colleagues of Greenland ice-mass loss since 2003 (red) is considerably lower than an earlier predicted value (blue), owing in part to larger than previously estimated subsidence rates of the underlying bedrock. Only the blue curve was corrected for changes in atmospheric mass, but these corrections are small over Greenland, and the curves and their differences can thus be interpreted in terms of contribution to global mean sea level (right-hand scale). The shaded areas reflect stated uncertainties.”

The article

“Simultaneous estimation of global present-day water transport and glacial isostatic adjustment“, Xiaoping Wu et al, Nature Geoscience, September 2010 — Abstract

Global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous. The viscoelastic solid Earth has been responding to this unloading of large ice masses with a rise of the land masses, in a process termed glacial isostatic adjustment. In addition, significant changes in the land/ocean water distribution occur at present. As both present-day changes in the ice/water thickness and glacial isostatic adjustment affect space geodetic measurements, it is difficult to untangle the relative contributions of these two processes.

Here we combine gravity measurements and geodetic data of surface movement with a data-assimilating model of ocean bottom pressure to simultaneously estimate present-day water transport and glacial isostatic adjustment. We determine their separate contributions to movements in the geocentre, which occur in response to changes in the Earth’s mass distribution, with uncertainties below 0.1 mm yr⁻¹. According to our estimates, mass losses between 2002 and 2008 in Greenland, Alaska/Yukon and West Antarctica are 104±23, 101±23 and 64±32 Gt yr⁻¹, respectively. Our estimates of glacial isostatic adjustment indicate a large geocentre velocity of −0.72±0.06 mm yr⁻¹ in the polar direction. We conclude that a significant revision of the present estimates of glacial isostatic adjustments and land–ocean water exchange is required.

For more information about rising sea levels

Two interesting articles:

Climate doomster Joe Romm: “On ‘scientific reticence’ and sea-level rise“, Grist, 25 May 2007: “Sea level rise of 5 meters in one century? Even if most scientists will not say so publicly, that catastrophe is a real possibility, according to the director of NASA’s Goddard Institute Of Space Studies”.
Evidence that such a rise is unlikely, with little or no supporting evidence at this time: “Romm Proves That Hansen’s Sea Level Forecasts Are Way Out Of Line“, Steve Goddard, 10 October 2010

Posts about rising sea levels: