Satellites rule in deniersville, except when sea levels are rising

Science deniers at WUWT are a funny lot. Their sole purpose in visiting denier blogs seems to be to sing the refrain "it's not happening", with the occasional faint chorus of "if it is it's not bad". WUWT deniers in the main haven't got quite as far as "if it is bad, there's nothing we can do about it".

Some of Anthony Watts' guest articles are good illustrations of that. There was a "guest essay" by David Middleton  yesterday (archived here) about a press release on the NASA website about how quickly sea levels may rise.  The press release was consistent with other recent estimates that seas will probably have risen by a metre or more by the end of this century or early the next, particularly if we stay on our current emissions trajectory (and maybe even if we don't).

David Middleton, who you might recall thinks all lizards are the same, wanted to reject the NASA article outright, claiming that "The only way sea level rise could approach the high end of the IPCC range is if it exponentially accelerates…". And he drew a chart with an exponential curve. Having made that wrong statement and putting up his exponential chart, he then drew a wrong conclusion, writing: "The rate from 2081-2100 would have to average 20 mm per year, twice that of the Holocene Transgression. This is only possible in bad science fiction movies."

One major flaw in David's argument was that he assumed that seas would rise according to some smooth chart, either linearly or exponentially. What he failed to factor in was that the main contribution to sea level over coming decades will be from melting ice. Another major flaw was that he himself used data and referenced a paper that showed that seas have risen at more than double his "impossible" rate in the relatively recent past.

How Greenland is melting

Before getting into the details of where David went wrong, have a look at what's been happening in Greenland, from NASA:

Three feet of metre sea level rise is "locked in"

According to Dr Steve Nerem from U Colorado, we're "locked in" to at least three feet (~ one metre) of sea level rise. He is quoted in the NASA press release:

“Given what we know now about how the ocean expands as it warms and how ice sheets and glaciers are adding water to the seas, it’s pretty certain we are locked into at least 3 feet of sea level rise, and probably more,” said Steve Nerem of the University of Colorado, Boulder, and lead of the Sea Level Change Team. “But we don't know whether it will happen within a century or somewhat longer.”

Tom Wagner says that seas have risen by 3 metres or more in a century in the past, so a metre this century is not at all beyond the bounds of possibility.:

“We’ve seen from the paleoclimate record that sea level rise of as much as 10 feet in a century or two is possible, if the ice sheets fall apart rapidly,” said Tom Wagner, the cryosphere program scientist at NASA Headquarters in Washington. “We’re seeing evidence that the ice sheets are waking up, but we need to understand them better before we can say we’re in a new era of rapid ice loss.”

In fact, a one metre rise by the end of this century is within the "likely" estimate of the IPCC report if we follow RCP8.5, and that's considered by many experts as being conservative.

Where David Middleton went astray

David Middleton assumed that seas will rise in a steady linear fashion. He briefly considered that sea level rise would follow an exponential curve, but rejected that on flawed grounds as you'll see. It's probable that seas won't follow either a linear curve or an exponential curve. The rise will be more like a series of sharp jumps, with steadier rises in between.

When ice melts from glaciers and ice sheets, it doesn't melt in a nice even fashion. And it certainly doesn't send the water into the sea in nice even drips. What happens is what happened last week, when a massive chunk of ice broke off the Jakobshavn glacier in Greenland and floated off into the sea.

That means that a sea level chart is more likely to look like a set of rising stairs than a straight line or an exponential curve.

What David Middleton said was impossible has happened in the past. Lauren J. Gregoire, Antony J. Payne & Paul J. Valdes  had a paper published in Nature in 2012. In the abstract they wrote about a sea level rise of 14 to 18 meters over 350 years (my emphasis).

The last deglaciation (21 to 7 thousand years ago) was punctuated by several abrupt meltwater pulses, which sometimes caused noticeable climate change1, 2. Around 14 thousand years ago, meltwater pulse 1A (MWP-1A), the largest of these events, produced a sea level rise of 14–18 metres over 350 years3. 

That averages at 40 to 50 mm a year - sustained for 350 years! Though I doubt it happened smoothly. There would have been some years when there was a lot greater rise and some years less.

So David's impossible is not impossible at all, is it.

The possibility of David Middleton's impossible

Let's look at David's charts. First of all, his chart of what he labels as the Holocene Transgression is based solely on a 1996 paper by Edouard Bard et al. He didn't give a reference or link to the paper, but I'd say it was this one, published in Nature (pdf here).  If David had read the paper (or even looked at his own chart), he'd have come across the discussion of meltwater pulses, MWP1a and MWP1b, for example, which were said to raise sea level at the rate of "~50-40 mm y^-1".  Coincidentally, the same rate that I calculated from Gregoire12.

Here is David's chart. I've circled and annotated the regions where there was a very rapid rise in sea level. Click to enlarge it as always:

Source: WUWT with my annotations

David argued that it's not possible for seas to rise quickly this century because the rise over the period in the early Holocene averaged 11 mm a year (from his calculation). There's a logical fallacy in that (Telltale Technique No. 2) as well as a mathematical flaw. What he didn't seem to realise was that his own chart shows times when seas rose much more quickly than the average. In other words, using David's own chart, seas can rise very quickly. And using his own reference, it's not at all impossible for sea level to rise at more than double 20 mm a year, which he claimed was "impossible".

It does take a massive amount of meltwater to rise that quickly. According to David Middleton's reference, Bard96, a sea level rise of 40-50 mm a year requires an injection of around 16,000 km³y^-1 of meltwater. That would be a volume of ice, say, 200 km long and 40 km wide and 2 km deep, each year.

This rapid melting is well within the realms of probability at some stage in the foreseeable future, possibly this century or the next. You might recall the flurry of papers about Western Antarctica last year. Here's an excerpt from one of them, authored by Eric Rignot and colleagues:

We measure the grounding line retreat of glaciers draining the Amundsen Sea Embayment of West Antarctica using Earth Remote Sensing (ERS-1/2) satellite radar interferometry from 1992 to 2011.

• Pine Island Glacier retreated 31 km at its center, with most retreat in 2005–2009 when the glacier un-grounded from its ice plain.
• Thwaites Glacier retreated 14 km along its fast-flow core and 1 to 9 km along the sides.
• Haynes Glacier retreated 10 km along its flanks.
• Smith/Kohler glaciers retreated the most, 35 km along its ice plain, and its ice shelf pinning points are vanishing.

These rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique (MC) that removes residual ambiguities from prior mappings. Upstream of the 2011 grounding line positions, we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin.

Those retreats were over a period of just a decade. Speed it up some more, and then a bit more, and then get massive amounts of water melting into the ocean and you'll get a massive rise in sea level.

Scientists' projections of sea level rise

Generally, deniers don't believe that sea level can rise by a metre this century (~3 feet). (Anthony Watts is a frequent denier of ice melting as it gets hotter. I think rising sea level is one thing that scares him a lot.) Following the release of the IPCC AR5 scientific report, there was quite a bit of discussion among scientists (and in the blogosphere) about the sea level rise projections.

There was a paper published in Quaternary Science Reviews. It was the result of "a broad survey of 90 experts who were amongst the most active scientific publishers on the topic of sea level in recent years".  The authors reported that seas are likely to rise from 0.7 m to more than a metre by the end of this century if we allow warming to progress along the lines of RCP8.5. and maybe an additional two metres by 2300:

• The sea-level rise ranges provided by the experts are on average higher than those of the IPCC 5th assessment.
• For the strong mitigation scenario (RCP 2.6), the likely range is 0.4–0.6 m by AD 2100 and 0.6–1.0 m by AD 2300.
• For the unmitigated warming scenario (RCP 8.5), the likely ranges are 0.7–1.2 m by AD 2100 and 2–3 m by AD 2300.

That's three metres or close to ten feet in three hundred years. Over that time, most of the people living in towns and cities on the coast would have to be relocated. Imagine the storm surges!

There was also a letter published in Science, by fourteen sea level experts led by John Church. This was in response to a News and Analysis piece in Science by R. A. Kerr. As authors of the sea level section of the IPCC AR5 WG1 report, Church et al pointed out that the projections in the IPCC report were not indicative of the maximum possible sea level rise. (The IPCC report gave a likely range of 0.53–0.97 m for RCP8.5). They wrote:

In the calibrated uncertainty language of the IPCC, this assessed likelihood means that there is roughly a one-third probability that sea-level rise by 2100 may lie outside the “likely” range. That is, the AR5 did not exclude the possibility of higher sea levels. However, we concluded that sea levels substantially higher than the “likely” range would only occur in the 21st century if the sections of the Antarctic ice sheet that have bases below sea level were to collapse. We determined with medium confidence that “this additional contribution would not exceed several 10ths of a meter of sea-level rise during the 21st century.” We could not define this possible contribution more precisely because “there is currently insufficient evidence to evaluate the probability of specific levels above the assessed ‘likely’ range.”

Importantly, the authors wrote that:

The upper boundary of the AR5 “likely” range should not be misconstrued as a worst-case upper limit, as was done in Kerr's story as well as elsewhere in the media and blogosphere. For policy and planning purposes, it may be necessary to adopt particular numbers as an upper limit, but according to our assessment, the current state of scientific knowledge cannot give a precise guide.

The bottom line is - how much seas will rise and when depends on how quickly the ice sheets in Greenland and Antarctica disintegrate and melt.

And that brings us back to the NASA press release, to which David Middleton objected (effectively claiming, in true Dunning-Kruger fashion, that he knew more about sea and ice than the world's top experts). It also raises the spectre of East Antarctica:

Although Antarctica’s contribution to sea level rise currently is much smaller than that of Greenland, recent research indicates this could change in the upcoming century. In 2014, two West Antarctica studies focused on the acceleration of the glaciers in the Amundsen Sea sector showed its collapse is underway.

East Antarctica’s massive ice sheet remains the primary unknown in sea level rise projections. Though it appears to be stable, a recent study found under a major glacier two deep troughs that could draw warm ocean water to the base of the glacier, causing it to melt.

“The prevailing view among specialists has been that East Antarctica is stable, but we don’t really know,” said glaciologist Eric Rignot of the University of California Irvine and JPL. “Some of the signs we see in the satellite data right now are red flags that these glaciers might not be as stable as we once thought. There’s always a lot of attention on the changes we see now, but as scientists our priority needs to be on what the changes could be tomorrow.”

Rejecting satellites for a change, despite it being the same as tide gauges

You know how when it comes to surface temperature, deniers reject direct measures on the ground, favouring satellite-derived estimates of columns of air in the troposphere. Yes, many of them seem to think that satellite instruments measure surface temperatures. They don't. Deniers like the satellites because the current reports suggest that it's not warming all that much. (I suggest there may be something awry with the satellite records, because the lower troposphere temperature should by now be shooting up with El Nino.)

However, when it comes to sea level, deniers take it upon themselves to claim that the satellite measurements aren't any good and that tide records are the only reliable measures.  I'm not talking about David Middleton, the guest author. He is fine with the satellite data. No, it's the deniers in the comments that don't like it. Never mind that tide records only show the sea level on the coast. And never mind that tide records produce a similar result to the satellites. Here are some reports of sea level trends from different teams, as I collated in an article last year, from tide gauges and satellites:

• Church and White (2011) - tide gauges and satellite altimetry: For 1993–2009 and after correcting for glacial isostatic adjustment, the estimated rate of rise is 3.2 ± 0.4 mm year−1 from the satellite data and 2.8 ± 0.8 mm year−1 from the in situ data.
• Jevrejeva et al (2013) - tide gauges compared with satellite: There is a good agreement between the rate of sea level rise (3.2 ± 0.4 mm·yr−1) calculated from satellite altimetry and the rate of 3.1 ± 0.6 mm·yr−1 from tide gauge based reconstruction for the overlapping time period (1993–2009).
• Cazenave et al (2014) - satellite altimetry: We find that when correcting for interannual variability, the past decade’s slowdown of the global mean sea level disappears, leading to a similar rate of sea-level rise (of 3.3 ± 0.4 mm yr−1) during the first and second decade of the altimetry era. 
• U Colorado - satellite altimetry: 3.2 +/- 0.4 mm / year since 1993

If all the ice melted

Below are some numbers I put together in a previous article - the sea level rise associated with the complete melting of ice sheets in different regions.

• All Antarctica: 58 metres (190 feet)
• West Antarctic Ice Sheet: 3.3 metres (11 feet)
• Antarctic Peninsula Ice Sheet: 0.24 metres (9 inches)
• Amundsen Sea Embayment glaciers in Western Antarctica: 1.2 meters (four feet)
• East Antarctic Ice Sheet: 53 metres (174 feet)
• All of Greenland: 7.4 metres (24 feet)
• All ice sheet ice (not including glaciers elsewhere): 65 metres (213 feet)

That's just to show there is plenty of potential for a sea level rise of a metre or more in just a few decades.

From the WUWT comments

markstoval starts the ball rolling with an "I don't understand a word, but it's brilliant" comment:

August 28, 2015 at 3:00 pm
Fabulous essay. Thanks to David Middleton.
Climate “science” is just full of such bad science. I don’t know if I will live to see it cleaned up.

Neville plays the concern troll, without citing any evidence for his "concern". Nor any links to his "heap of PR tide gauge studies" on some denier blog:

August 28, 2015 at 3:14 pm
Forgive me if I’m wrong but didn’t the raw satellite data show a lower rate of SLR before the more recent adjustments?
And you can go to Co2 Science and find heaps of recent PR tide gauge studies that show just 1.5mm to 2 mm SLR. So who is correct?

JimS isn't worried by 150 nickels. He might be more worried when he finds that it's more likely going to be 667 or more nickels in 100 years. Then he might think about what a storm surge will do.

August 28, 2015 at 4:09 pm
An American nickel coin is just under 2 mm in thickness. So at an average of 3 mm per year increase of sea level, what does that mean? – in two years, the sea level rises by the thickness of three American nickel coins. Lord help us, we are all going to drown! 

Curious George isn't so curious that he'd investigate how satellites are used to monitor sea level. Hint: it's not done by taking snapshots of waves.

August 28, 2015 at 5:28 pm
Satellite measurements of the sea level change strike me as an extremely difficult undertaking. The sea surface is far from smooth, waves can be many meters high, how do you measure an average rise of 1-3 mm per year? The NASA website explains how it is done, but it looks like – we are measuring this, and it must be an average sea level, because we say so. Magic. I applaud them for trying but I would highly appreciate an analysis of underlying uncertainties.

Ric Werme is an unabashed conspiracy theorist (Telltale Technique No. 5 of a climate science denier):

August 28, 2015 at 5:50 pm (excerpt)
One of the problems of linking to an offsite image is that you never know what might happen to it. It might disappear. It might be replaced by an uncomplimentary photo when the host finds out his site is swamped by WUWT world. For graphs with an x-axis in years, it might confirm your claim – or it might not.

References and further reading

NASA Science Zeros in on Ocean Rise: How Much? How Soon? - NASA press release

Bard, Edouard, Bruno Hamelin, Maurice Arnold, Lucien Montaggioni, Guy Cabioch, Gerard Faure, and Francis Rougerie. "Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge." Nature 382, no. 6588 (1996): 241-244. doi:10.1038/382241a0 (pdf here)

Gregoire, Lauren J., Antony J. Payne, and Paul J. Valdes. "Deglacial rapid sea level rises caused by ice-sheet saddle collapses." Nature 487, no. 7406 (2012): 219-222. doi:10.1038/nature11257 (pdf here)

Horton, Benjamin P., Stefan Rahmstorf, Simon E. Engelhart, and Andrew C. Kemp. "Expert assessment of sea-level rise by AD 2100 and AD 2300." Quaternary Science Reviews 84 (2014): 1-6. doi:10.1016/j.quascirev.2013.11.002 (open access)

Church, John A., Peter U. Clark, Anny Cazenave, Jonathan M. Gregory, Svetlana Jevrejeva, Anders Levermann, Mark A. Merrifield, Glenn A. Milne, R. Steven Nerem, Patrick D. Nunn, Antony J. Payne, W. Tad Pfeffer, Detlef Stammer, Alakkat S. Unnikrishnan. "Sea-level rise by 2100." Science 342, no. 6165 (2013): 1445-1445. DOI: 10.1126/science.342.6165.1445-a (pdf here)

Church, John A., and Neil J. White. "Sea-level rise from the late 19th to the early 21st century." Surveys in Geophysics 32, no. 4-5 (2011): 585-602. doi: 10.1007/s10712-011-9119-1

Jevrejeva, S., J. C. Moore, A. Grinsted, A. P. Matthews, and G. Spada. "Trends and acceleration in global and regional sea levels since 1807." Global and Planetary Change 113 (2014): 11-22. (pdf here)

Cazenave, Anny, Habib-Boubacar Dieng, Benoit Meyssignac, Karina von Schuckmann, Bertrand Decharme, and Etienne Berthier. "The rate of sea-level rise." Nature Climate Change 4, no. 5 (2014): 358-361. doi:10.1038/nclimate2159 (pdf here)

Greenland's Jakobshavn Glacier sheds big ice chunk - report from the BBC, 24 August 2015

Sea level in the 5th IPCC report - by Stefan Rahmstorf at RealClimate.org, with references