Sea level rise discussion thread

curryja

12 years ago

by Judith Curry

Recently, there have been a number of interesting papers on sea level rise. Let’s take a look.

World ocean heat content and thermosteric sea level change (0-2000) 1955-2010

Levitus et al.

Abstract. We provide updated estimates of the change of heat content and the thermosteric component of sea level change of the 0-700 and 0-2000 m layers of the world ocean for 1955-2010. Our estimates are based on historical data not previously available, additional modern data, correcting for instrumental biases of bathythermograph data, and correcting or excluding some Argo float data. The heat content of the world ocean for the 0-2000 m layer increased by 24.0×1022 J corresponding to a rate of 0.39 Wm-2 (per unit area of the world ocean) and a volume mean warming of 0.09ºC. This warming rate corresponds to a rate of 0.27 Wm-2 per unit area of earth’s surface. The heat content of the world ocean for the 0-700 m layer increased by 16.7×1022 J corresponding to a rate of 0.27 Wm-2 (per unit area of the world ocean) and a volume mean warming of 0.18ºC. The world ocean accounts for approximately 90% of the warming of the earth system that has occurred since 1955. The thermosteric component of sea level trend is 0.54 mm yr-1 for the 0-2000 m layer and 0.41 mm yr-1 for the 0-700 m layer of the world ocean for 1955-2010.

Key Points

A strong positive linear trend in exists in world ocean heat contentsince 1955
One third of the observed warming occurs in the 700-2000 m layer of the ocean
The warming can only be explained by the increase in atmospheric GHGs

Citation: Levitus, S., et al. (2012), World ocean heat content and thermosteric sea level change (0-2000), 1955-2010, Geophys. Res. Lett., doi:10.1029/2012GL051106 [link] to abstract.

Pielke Sr. has a comment on the paper [here]. Punchline:

Thus either using the 1955 to 2010 time period, or the shorter time period from 1990 to 2010 in the Levitus et al 2012 paper, the diagnosed magnitudes of ocean warming and global warming are significantly less than claimed by Jim Hansen in 2005. This discrepancy is even larger if we use the NOAA’s Pacific Marine Environmental Laboratory data.

Niche Modelling also discusses the paper [here]. Punchline:

If one accepts the IPCC radiative forcing values of anthropogenic radiative forcings of +1.6 (+0.6 to +2.4) Watts per meter squared and/or the solar radiative forcing of +0.12 (+0.06 to +0.30) Watts per meter squared as correct, what the Levitus et al data shows is that the global radiative feedback is negative(and this necessarily would include the water vapor, sea ice etc radiative feedbacks). That is global radiative feedback < global radiative forcing. Alternatively, the IPCC anthropogenic radiative forcings and/or the solar radiative forcing could be in error.

Either way, the 2007 IPCC WG1 report has a serious error in it.

Model estimates of sea-level change due to anthropogenic impacts on terrestrial water storage

Yadu Pokhrel, Naota Hanasaki, Pat Yeh, Tomohito Yamada, Shinjiro Kanae, Taikan Oki

Abstract. Global sea level has been rising over the past half century, according to tide-gauge data^1, 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 level^{3, 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.

As explained by Zorita at Die Klimazweibel:

As usual, I would interpret that these estimations may be better than previous ones, but I would put more confidence on these figures once they have been confirmed by other groups in the next years. This paper will be likely discussed in the next IPCC report, but any follow-up studies, confirming or rebutting these numbers, will not, as the dead line to submit articles to be considered by the IPCC is due in 2 months.

The new estimations of GWD may have, however, consequences for the so called ‘semi-empirical’ estimations of future sea-level rise. These methods are based on statistical relationships between global mean temperature and the rate of sea-level rise. If a larger part than previously thought of the observed sea-level rise is not climate-related, these statistical estimation may be then biased high.

Stefan Rahmstorf at Realclimate is shocked:

Last week the science community was shocked by the claim that 42% of the sea-level rise of the past decades is due to groundwater pumping for irrigation purposes. What could this mean for the future – and is it true?

An aerial view of 80 years of climate-related glacier fluctuations in southeast Greenland

Anders Bjork, Kurt Kjaer, Niels Korsgaard, Shfaqat Khan, Kristian Kjeldsen, Camilla Andresen, Jason Box, Nicolaj Larsen, Svend Funder

Abstract. Widespread retreat of glaciers has been observed along the southeastern margin of Greenland. This retreat has been associated with increased air and ocean temperatures. However, most observations are from the satellite era; presatellite observations of Greenlandic glaciers are rare. Here we present a unique record that documents the frontal positions for 132 southeast Greenlandic glaciers from rediscovered historical aerial imagery beginning in the early 1930s. We combine the historical aerial images with both early and modern satellite imagery to extract frontal variations of marine- and land-terminating outlet glaciers, as well as local glaciers and ice caps, over the past 80 years. The images reveal a regional response to external forcing regardless of glacier type, terminal environment and size. Furthermore, the recent retreat was matched in its vigour during a period of warming in the 1930s with comparable increases in air temperature. We show that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s, whereas marine-terminating glaciers retreated more rapidly during the recent warming.

Nature Geoscience (2012) doi:10.1038/ngeo1481. Full paper available online [here].

Pat Michaels sums it up: Such results throw a bit of cold water on alarmist ideas that rising temperatures will lead to ever-accelerating ice loss from Greenland and accelerating sea level rise.

21st Century Evolution of Greenland Outlet Glacier Velocities

T. Moon, I Joughin, B. Smith, I Howat

Abstract. Earlier observations on several of Greenland’s outlet glaciers, starting near the turn of the 21st century, indicated rapid (annual-scale) and large (>100%) increases in glacier velocity. Combining data from several satellites, we produce a decade-long (2000 to 2010) record documenting the ongoing velocity evolution of nearly all (200+) of Greenland’s major outlet glaciers, revealing complex spatial and temporal patterns. Changes on fast-flow marine-terminating glaciers contrast with steady velocities on ice-shelf–terminating glaciers and slow speeds on land-terminating glaciers. Regionally, glaciers in the northwest accelerated steadily, with more variability in the southeast and relatively steady flow elsewhere. Intraregional variability shows a complex response to regional and local forcing. Observed acceleration indicates that sea level rise from Greenland may fall well below proposed upper bounds.

Science 4 May 2012: Vol. 336 no. 6081 pp. 576-578
DOI: 10.1126/science.1219985 [link] to abstract

Rahmstorf comments at Realclimate:

The bottom line is that Greenland’s glaciers are still speeding up. But the results put speculation of monotonic or exponential increases in Greenland’s ice discharge to rest, an idea that some had raised after a doubling over a few years was reported in 2004 for Jakobshavn Isbræ (Greenland’s largest outlet glacier). Let it not be said that journals such as Science and Nature are only willing to publish papers that find that thing are “worse than we thought”!

JC comments: When I raise the issue of emphasizing adaptation over mitigation, the response I often get is that the sea level rise issue is so global and overwhelming that mitigation is the only sensible way to deal with the global sea level rise. It is good to see these new data-driven analyses of relevance to sea level rise that highlight the uncertainties in our understanding of past sea level rise (and by inference, future sea level rise).

It will be interesting to see how all this plays out in the AR5. I found the “science community was shocked” comment by Rahmstorf to be very illuminating; that is what happens when you do “consensus” science rather than focusing on the uncertainties and challenging your science.

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