Agreement polar ice sheets are melting

Many climate scientists felt the conclusions on effects of global warming in the 2007 IPCC review were too conservative. One reason was the estimation of likely melting of ice sheets and its effects.

Problem was that there was insufficient knowledge to draw definite conclusions. And the measurements of changes in ice sheets just wasn’t accurate enough.

That’s now changed and a large number of experts agree global warming has caused loss of ice from these ice sheets. And this has contributed to measured increases in sea level.

Richard A. Kerr reports in Science (see Experts Agree Global Warming Is Melting the World Rapidly):

“Forty-seven glaciologists have arrived at a community consensus over all the data on what the past century’s warming has done to the great ice sheets: a current annual loss of 344 billion tons of glacial ice, accounting for 20% of current sea level rise. Greenland’s share—about 263 billion tons—is roughly what most researchers expected, but Antarctica’s represents the first agreement on a rate that had ranged from a far larger loss to an actual gain. The new analysis, published on page 1183 of this week’s issue of Science, also makes it clear that losses from Greenland and West Antarctica have been accelerating, showing that some ice sheets are disconcertingly sensitive to warming.”

He’s referring to the major paper by Andrew Shepperd and others, A Reconciled Estimate of Ice-Sheet Mass Balance.

Over recent years climate change deniers/contrarians/sceptics have cherry picked data to counter any suggestion that the earth’s large ice sheets are melting. They have pointed to increased amounts of ice in Eastern Antarctica to balance reports of massive losses of ice in the Arctic. (Have a look at this animation to see how such data can be cherry picked). Similarly they have tried to hide concern of the loss of land ice by stressing reports of local increases in sea ice.

But the paper by Shepperd et al. combined data from satellite altimetry, interferometry, and gravimetry measurements. This provides more reliable estimates of changes in the ice sheets, and gives some detail of these changes. This figure from the paper gives an idea of the detail of their findings. It shows that all the major regions of the polar ice sheets except one (East Antarctica) have lost mass since 1992. The authors also estimate that mass loss from the polar ice sheets has contributed roughly 20 percent of the total global sea level rise during that period (at a rate of 0.59 ± 0.20 millimeter year⁻¹ ).

Figure S1 from Shepperd et al.: Cumulative ice mass change of West Antarctica ((WAIS) East Antarctica (EAIS), Greenland (GrIS), and the Antarctic Peninsula (APIS).

And to underline the fact that denier claims of amounts of ice increasing in Antarctica are false, NASA recently displayed this figure showing data from Antarctica from their satellite measurements

Monthly changes in Antarctic ice mass, in gigatones, as measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 to 2011. Image credit: NASA-JPL/Caltech; NASA GSFC; CU-Boulder; Technical University of Munich; Technical University of Denmark; Delft University of Technology, Aerospace Engineering, Netherlands; Durham University, UK; Leeds University, UK

Could those climate change deniers/contrarians/sceptics please stop hiding behind claims that gains by Antarctic ice sheets balance losses from ice sheets in Greenland and the Arctic.

They don’t.

See also:
Science: Major Regions of Polar Ice Have Been Shrinking Since 1992
Polar Ice Sheets Losing Mass, Several Methods Show
New Study Shows Global Warming Is Rapidly Melting Ice at Both Poles
Human-Caused Climate Change Signal Emerges from the Noise
Study: Polar ice sheets in Antarctica, Greenland melting 3 times faster than in ’90s
Ice Sheet Loss at Both Poles Increasing, Study Finds
Projections of sea level rise are vast underestimates
“Hard” “Authoritative” Evidence Of Climate Change Begins To Overwhelm Even Fox

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“Other ways of knowing” – some sense at last

There’s been a lot of rubbish written about “other ways of knowing”. So it’s quite refreshing to read Richard Carrier’s classification of methods of knowing. This is from his book Sense and Goodness Without God: A Defense of Metaphysical Naturalism. Well worthy reading by the way.

He starts by pointing out that no method of obtaining knowledge can produce absolute certainty. We can always be wrong, make mistakes. But we can list possible methods in order of reliability:

“What is rational is to assign degrees of conviction to degrees of certainty established by a tried-and-tested method. What is rational is reasonable certainty, not absolute certainty.”

“The methods of logic and mathematics are well-developed and provide the greatest certainty we have yet been able to find regarding anything, other than a present, uninterpreted experience. The next greatest certainty has been found in the application of scientific methods to empirical problems. In third place is our own daily experience, when interpreted with a logical or scientific mindset. Fourth is the application of critical-historical methods to claims about past events. Fifth is the application of the criteria of trust to the claims of experts. Sixth is the untested but logical application of inferential generalizations from incomplete facts—that is, plausible deductions. Such is the scale of methods that we have historically been able to discover and confirm as effective.”

“Experience shows that our degree of certainty will generally be weaker with regard to facts at each stage down this six-rung ladder, though within each category lies its own continuum of certainty and uncertainty, and the ladder itself is a continuum of precision and access to information: the more data we have to ground our conclusions, the farther up the ladder we find ourselves. Thus, mathematics is just perfected science; science, perfected experience; experience, perfected history; and history, perfected attention to experts; while plausible inference is what we are left with when we have none of those things.”

“Lacking any of the above approaches to the truth, we are faced with untrustworthy hearsay and pure speculation, where only the feeblest of certainty can ever be justified, if at all.”

Carrier writes that accurate methods of knowing have the properties of predictive success and convergent accumulation of consistent results.  However, these should be evaluated intelligently. Even the best method may produce faulty knowledge if used incorrectly.

So how do the different methods rate?: