Tag: sea level rise

Is Greenland Melt “Off the Chart?”

That’s what the second author said about a new paper on Greenland’s ice, which arrived just in time for the annual meeting of the signatories of the UN’s 1992 treaty on climate change, this time in Katowice, Poland. Appearing in Nature, Rowan University Geologist Luke Trusel and several coauthors claimed ice-core data from Central-Western Greenland revealed melting in the recent two decades that has been “exceptional over at least the last 350 years.” The paper appeared in the December 6 issue of Nature.

How exceptional?

“Our results show a pronounced 250% to 575% increase in melt intensity over the last 20 years” as measured in four ice cores in west-central Greenland. Three of the cores were in the Jakobshavn Glacier, the largest-discharging glacier in the entire Northern Hemisphere. The Ilulissat icefjord, created by the glacier, some 25 miles in length, has historically calved nearly 50 cubic kilometers of ice per year into Disko Bay, near the town of Ilulissat. 

They then correlated their ice-core data with a model for ice behavior in all of Greenland. The correlations, while significant, were modest, with the explained variance of the island-wide melting maxing at around 36%. The melt reached its maximum in the very strange summer of 2012, where the amount at the Summit site, near Greenland’s highest elevation, was the largest since the summer of 1889—worth noting because that was well over 100 years ago.

There’s a long-standing quality weather station at Ilulissat, and it certainly shows summer warming of about 2⁰C from its beginning around 1850 to the 1920s.

For a broader comparison, we looked at the summer temperature anomalies for the 5 X 5 degree gridcell that includes Disko Bay and the icefjord. Because it is relatively hospitable and settled, there are a number of stations within the cell so the data is quite reliable. The data we show is from the Climate Research Unit at the University of East Anglia, version HadCRUT4.

There’s very little to see in this temperature record. The authors are well-aware of this and offer a rather unsatisfactory explanation:

The non-linear melt-temperature sensitivity also helps explain why episodes of mid-twentieth-century warmth resulted in less intense and less sustained melting compared to the last two decades, despite being only marginally cooler…Additional factors, such as recent sea-ice losses, as well as regional and teleconnected general circulation changes may also play a part in amplifying the melt response.

You Ought to Have a Look: How-to Guides to Undoing the Climate Action Plan, Fixing the National Flood Insurance Program, and Killing Mosquitoes

You Ought to Have a Look is a regular feature from the Center for the Study of Science.  While this section will feature all of the areas of interest that we are emphasizing, the prominence of the climate issue is driving a tremendous amount of web traffic.  Here we post a few of the best in recent days, along with our color commentary.

With news of the past week or so dominated by announcements and then post-announcement scrutiny of Trump’s cabinet picks, we highlight a few pieces that go into deeper waters on these (and other) topics.

First up is an informative piece by Vox’s Brad Plumer that’s built from an interview he conducted with Jody Freeman, a Harvard law school professor and former climate adviser to President Obama. Over the course of their conversation, Plumer and Freeman pretty much lay out a road map as to how the Trump Administration could go about undoing much of President Obama’s ill-advised (in our opinion) Climate Action Plan. The selection of Scott Pruitt to head the EPA is definitely a big step in that direction.

Sixty-Six Years of Island Shoreline Dynamics on Jaluit Atoll, Marshall Islands

According to a conventional narrative, tropical islands are eroding away due to rising seas and increasingly devastating storms. Not really, according to the recent work of Ford and Kench (2016).

Writing as background for their study, the two researchers state that low-lying reef islands are “considered highly vulnerable to the impacts of climate change,” where an “increased frequency and intensification of cyclones and eustatic sea-level rise [via global warming] are expected to accelerate shoreline erosion and destabilize reef islands.” However, they note that much remains to be learned about the drivers of shoreline dynamics on both short- and long-term time scales in order to properly project future changes in low-lying island development. And seeking to provide some of that knowledge, the pair of New Zealand researchers set out to examine historical changes in 87 islands found within the Jaluit Atoll (~6°N, 169.6°E), Republic of the Marshall Islands, over the period 1945-2010. During this time, the islands were subjected to ongoing sea level rise and the passage of a notable typhoon (Ophelia, in 1958), the latter of which caused severe damage with its >100 knot winds and abnormal wave heights.

So what did their examination reveal?

Analyses of aerial photographs and high-resolution satellite imagery indicated that the passage of Typhoon Ophelia caused a decrease in total island land area of approximately five percent, yet Ford and Kench write that “despite [this] significant typhoon-driven erosion and a relaxation period coincident with local sea-level rise, [the] islands have persisted and grown.” Between 1976 and 2006, for example, 73 out of the 87 islands increased in size, and by 2010, the total landmass of the islands had exceeded the pre-typhoon area by nearly 4 percent.

Such observations, in the words of Ford and Kench, suggest an “alternative trajectory” for future reef island development, and that trajectory is one of “continued island expansion rather than one of island withering.” And such expansion is not just limited to Jaluit Atoll, for according to Ford and Kench, “the observations of reef island growth on Jaluit coincident with sea level rise are broadly consistent with observations of reef islands made elsewhere in the Marshall Islands and Pacific (McLean and Kench, 2015).” Given as much, it would thus appear that low-lying islands are not as vulnerable to climate change as previously thought.

 

Reference

Ford, M.R. and Kench, P.S. 2016. Spatiotemporal variability of typhoon impacts and relaxation intervals on Jaluit Atoll, Marshall Islands. Geology 44: 159-162.

McLean, R.F. and Kench, P.S. 2015. Destruction or persistence of coral atoll islands in the face of 20th and 21st century sea level rise? WIRES Climate Change 6: 445-463.

Taming the Greenland Melting Global Warming Hype

Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

There is a new paper generating some press attention (e.g. Chris Mooney at the Washington Post) that strongly suggests global warming is leading to specific changes in the atmospheric circulation over the Northern Hemisphere that is causing an enhancement of surface melting across Greenland—and of course, that this mechanism will make things even worse than expected into the future.

We are here to strongly suggest this is not the case.

The new paper is by a team of authors led by Marco Tedesco from Columbia University’s Lamont-Doherty Earth Observatory. The main gist of the paper is that Arctic sea ice loss as a result of human-caused global warming is causing the jet stream to slow down and become wigglier—with deeper north-south excursions that hang around longer.  This type of behavior is referred to as atmospheric “blocking.”

If this sounds familiar, it’s the same theoretical argument that is made to try to link wintertime “polar vortex” events (i.e., cold outbreaks) and blizzards to global warming. This argument which has been pretty well debunked, time and time again.

Well, at least it has as it concerns wintertime climate.

The twist of the new Tedesco and colleagues’ paper is that they’ve applied it to the summertime climate over Greenland. They argue that global warming is leading to an increase in blocking events over Greenland in the summer and that is causing warm air to be “locked” in place leading to enhanced surface melting there. Chris Mooney, who likes to promote climate alarm buzzwords, refers to this behavior as “weird.” And he describes the worrysome implications:

The key issue, then, is whether 2015 is a harbinger of a future in which the jet stream keeps sending Greenland atmospheric systems that drive major melt — and in turn, whether the Arctic amplification of climate change is driving this. If so, that could be a factor, not currently included in many climate change simulations, that would worsen the ice sheet’s melt, drive additional sea level rise and perhaps upend ocean currents due to large influxes of fresh water.

As proof that things were weird over Greenland in recent summers, Tedesco’s team offers up this figure in their paper:

<--break->

This chart (part of a multipanel figure) shows the time history of the North Atlantic Oscillation (NAO—a pattern of atmospheric variation over the North Atlantic) as red bars and something called the Greenland Blocking Index (GBI) as the black line, for the month of July during the period 1950-2015. The chart is meant to show that in recent years, the NAO has been very low with 2015 being “a new record low of -1.23 (since 1899),” and the GBI has been very high with the authors noting that “[c]oncurrently, the GBI also set a new record for the month of July [2015].” Clearly the evidence is showing that atmospheric blocking increasing over Greenland which fits nicely into the global warming/sea ice loss/wiggly jet stream theory.

So what’s our beef?

A couple of months ago, some of the same authors of the Tedesco paper (notably Ed Hanna) published a paper showing the history of the monthly GBI going back to 1851 (as opposed to 1950 as depicted in the Tedesco paper).

Here’s their GBI plotted for the month of July from 1851 to 2015:

This picture tells a completely different story. Instead of a long-term trend that could be related to anthropogenic global warming, what we see is large annual and multidecadal variability, with the end of the record not looking much different than say a period around 1880 and with the highest GBI occurring in 1918 (with 1919 coming in 2nd place). While this doesn’t conclusively demonstrate that the current rise in GBI is not related to jet stream changes induced by sea ice loss, it most certainly does demonstrate that global-warming induced sea ice loss is not a requirement for blocking events to occur over Greenland and that recent events are not  at all “weird.”  An equally plausible, if not much more plausible, expectation of future behavior is that this GBI highstand is part of multidecadal natural variability and will soon relax back towards normal values.  But such an explanation isn’t Post-worthy.

Another big problem with all the new hype is that history shows the current goings-on in Greenland to be irrelevant, because humans just can’t make it warm enough up there to melt all that much ice. For example, in 2013, Dorthe Dahl-Jensen and her colleagues published a paper in Nature detailing the history of the ice in Northwest Greenland during the beginning of the last interglacial, which included a 6,000 year period in which her ice core data showed averaged a whopping 6⁰C warmer in summer than the 20th century average. Greenland only lost around 30% of its ice with a heat load of (6 X 6000) 36,000 degree-summers. The best humans could ever hope to do with greenhouse gases is—very liberally—about 5 degrees for 500 summers, or (5 X 500) 2,500 degree-summers. In other words, the best we can do is 500/6000 times 30%, or a 2.5% of the ice, resulting in a grand total of seven inches of sea level rise over 500 years. That’s pretty much the death of the Greenland disaster story, despite every lame press release and hyped “news” article on it.

While you won’t find this kind of analysis elsewhere, we’re happy to do it here at Cato. 

References:

Dahl-Jensen, D., et al., 2013.  Eemian interglacial reconstructed from a Greenland folded ice core.  Nature 489, doi: 10.1038/nature11789.

Hanna, E., et al., 2016. Greenland Blocking Index 1851-2015: a regional climate change signal. International Journal of Climatology, doi: 10.1002/joc.4673.

Tedesco, M., et al., 2016. Arctic cut-off high drives the poleward shift of a new Greenland melting record. Nature Communications, DOI: 10.1038/ncomms11723, http://www.nature.com/ncomms/2016/160609/ncomms11723/full/ncomms11723.html

A Historic Perspective on the Greenland Ice Sheet and its Contribution to Global Sea Level

One of the most feared of all model-based projections of CO2-induced global warming is that temperatures will rise enough to cause a disastrous melting/destabilization of the Greenland Ice Sheet (GrIS), which would raise global sea level by several meters. But how likely is this scenario to occur? And is there any way to prove such melting is caused by human activities?

The answer to this two-part question involves some extremely complex and precise data collection and understanding of the processes involved with glacial growth and decay. Most assuredly, however, it also involves a scientifically accurate assessment of the past history of the GrIS, which is needed to provide a benchmark for evaluating its current and future state. To this end, a recent review paper by Vasskog et al. (2015) provides a fairly good summary of what is (and is not) presently known about the history of the GrIS over the previous glacial-interglacial cycle. And it yields some intriguing findings.

Probably the most relevant information is Vasskog et al.’s investigation of the GrIS during the last interglacial period (130-116 ka BP). During this period, global temperatures were 1.5-2.0°C warmer than the peak warmth of the present interglacial, or Holocene, in which we are now living. As a result of that warmth, significant portions of the GrIS melted away. Quantitatively, Vasskog et al. estimate that during this time (the prior interglacial) the GrIS was “probably between ~7 and 60% smaller than at present,” and that that melting contributed to a rise in global sea level of “between 0.5 and 4.2 m.” Thus, in comparing the present interglacial to the past interglacial, atmospheric CO2 concentrations are currently 30% higher, global temperatures are 1.5-2°C cooler, GrIS volume is from 7-67% larger, and global sea level is at least 0.5-4.2 m lower, none of which signal catastrophe for the present.

Clearly, therefore, there is nothing unusual, unnatural or unprecedented about the current interglacial, including the present state of the GrIS. Its estimated ice volume and contribution to mean global sea level reside well within their ranges of natural variability, and from the current looks of things, they are not likely to depart from those ranges any time soon.

 

References

Reyes, A.V., Carlson, A.E., Beard, B.L., Hatfield, R.G., Stoner, J.S., Winsor, K., Welke, B. and Ullman, D.J. 2014. South Greenland ice-sheet collapse during Marine Isotope Stage 11. Nature 510: 525–528.

Vasskog, K., Langebroek, P.M., Andrews, J.T., Nilsen, J.E.Ø. and Nesje, A. 2015. The Greenland Ice Sheet during the last glacial cycle: Current ice loss and contribution to sea-level rise from a palaeoclimatic perspective. Earth-Science Reviews 150: 45-67.

On the Bright Side: A Deceleration of Sea Level Rise Along the Indian Coastline

Parker and Ollier (2015) set the tone for their new paper on sea level change along the coastline of India in the very first sentence of their abstract: “global mean sea level (GMSL) changes derived from modelling do not match actual measurements of sea level and should not be trusted” (emphasis added). In contrast, it is their position that “much more reliable information” can be obtained from analyses of individual tide gauges of sufficient quality and length. Thus, they set out to obtain such “reliable information” for the coast of India, a neglected region in many sea level studies, due in large measure to its lack of stations with continuous data of sufficient quality.

A total of eleven stations were selected by Parker and Ollier for their analysis, eight of which are archived in the PSMSL database (PSMSL, 2014) and ten in a NOAA sea level database (NOAA, 2012). The average record length of the eight PSMSL stations was 54 years, quite similar to the average record length of 53 years for the eleven NOAA stations.

Results indicated an average relative rate of sea level rise of 1.07 mm/year for all eleven Indian stations, with an average record length of 51 years. However, the two Australian researchers report this value is likely “overrated because of the short record length and the multi-decadal and interannual oscillations” of several of the stations comprising their Indian database. Indeed, as they further report, “the phase of the 60-year oscillation found in the tide gauge records is such that sea level in the North Atlantic, western North Pacific, Indian Ocean and western South Pacific has been increasing since 1985-1990,” which increase most certainly skews the rate trend of the shorter records over the most recent period of record above the actual rate of rise.

The Spin Cycle: Accelerating Sea Level Rise

The Spin Cycle is a reoccurring feature based upon just how much the latest weather or climate story, policy pronouncement, or simply poo-bah blather spins the truth. Statements are given a rating between 1-5 spin cycles, with less cycles meaning less spin. For a more in-depth description, visit the inaugural edition.

A popular media story of the week was that sea level rise was accelerating and that this was worse than we thought. The stories were based on a new paper published in the journal Nature Climate Change by an author team led by the University of Tasmania’s Christopher Watson.

Watson and colleagues re-examined the satellite-based observations of sea level rise (available since the early 1990s) using a new methodology that supposedly better accounts for changes in the orbital altitude of the satellites—obviously a key factor when assessing sea levels by determining the height difference between the ocean’s surface and the satellites, the basic idea behind altimetry-based sea level measurements.

So far so good.

Their research produced two major findings, 1) their new adjusted measurements produced a lower rate of sea level rise than the old measurements (for the period 1993 to mid-2014), but 2) the rate of sea level rise was accelerating.

It was the latter that got all of the press.

But, it turns out, that in neither case, were the findings statistically significant at even the most basic levels used in scientific studies. Generally speaking, scientists report a findings as being “significant” if there is a less than 1-in-20 chance that the same result could have been produced by random (i.e., unexplained) processes. In some fields, the bar is set even higher (like 1 in 3.5 million). We can’t think of any scientific field that accepts a lower than a 1-in-20 threshold (although occasional individual papers do try to get away with applying a slightly lower standard).