Wednesday, March 20, 2019

A Sea Level Rise Conundrum – Greenland’s Cycles

After France fell to the Nazis, Britain desperately prepared for an invasion. The United States shuttled hundreds of planes to England via the Snowball Route, a series of secret bases on Newfoundland, Greenland and Iceland. But in 1942 one squadron never completed the journey. A sudden July storm forced 8 planes to land on a slushy glacier surface in southeast Greenland. Although the crews were rescued, later attempts failed to locate the Lost Squadron. The glaciers had ferried the planes miles downstream as they were increasingly buried in ice. One plane was finally recovered in 1992 and the second, recovered in 2018, was under more than 300 feet of ice. Southeastern Greenland had been gaining ice at a rate of 4 feet per year. 

In contrast, climate scientists project Greenland will increasingly lose ice as CO2concentrations increase. Indeed, its melting ice has been the biggest contributor to accelerating sea level rise for 2 decades.  But that is rapidly reversing. City planners along California’s coast are struggling with competing theories. How much sea level rise should we plan for?  Fearing an accelerating rise, some argue we abandon the coast. Others argue, and I agree, we should protect our homes with seawalls. But how high must we build? Understanding Greenland’s contribution is critical.

If we removed all ice from Greenland, the land would reveal a bowl-shape. A ring of mountains paralleling the coastline prevents the ice cap from sliding into the sea, no matter what scary climate stories suggest. Several gaps in those mountains allow glaciers to transport ice from inside “the bowl” to the oceans. Given enough time the Lost Squadron may well have been shuttled out to sea. Whenever more ice accumulates inside the “bowl” than leaks out via glaciers, Greenland gains ice and sea levels fall.  If more ice reaches the ocean than accumulates inland, sea level rises. But predicting any imbalance is difficult.

During the last 100 years, Greenland oscillated between gaining and losing ice. Its greatest loss raised sea level by 0.07 inches in 2012, about half the total sea level rise of 0.12 inches a year. That accelerated loss was trumpeted as just what climate models predict. However, Greenland’s melt rates then declined and by 2017 it was gaining enough ice to slightly reduce sea level rise.

Furthermore, the cause of rapidly melting ice since the 1990s was fewer clouds. Fewer summer clouds allow more solar heating and cycles of atmospheric circulation naturally alter cloud cover. In addition, researchers reported Greenland’s ice-free regions experienced various warming and cooling trends over the past 15 years, but concluded if there was any general trend, “it is mostly a cooling”. They also admitted they “cannot differentiate between anthropogenic forcing [in other words: warming from human added CO2] and natural fluctuations.”

A similar warming and melting episode occurred decades earlier. Climate scientists determined Greenland had warmed most rapidly between 1920 and 1940. As reported by the IPCC, “temperature has risen significantly since the early 1990s, reaching values similar to those in the 1930s.”Regards accelerated rates of sea level rise from melting ice, the IPCC reported “It is likely that similarly high rates occurred between 1920 and 1950.”  Intriguingly, much lower CO2concentrations still resulted in similar warming, melting and rates of sea level rise.

Until Greenland’s temperatures and ice-melt exceed the 1930s episode, scientists cannot distinguish between natural variability and human-caused warming. The current trend is too short to be certain, but the past 2 years suggest Greenland is now entering a cooling cycle. In fact, based on my analyses of published scientific reports regards decades-long cycles of migrating fish into and out of the Arctic, and circulation effects of Atlantic oscillations, I boldly blogged in 2014, we would soon see Greenland begin to gain ice, as it is now doing.

Of course, that prediction was attacked by the ill-informed. They claimed my analyses of published scientific observations was cherry-picking, pseudo-science and I ignored the (mythical) 97% consensus.  My response is always, there is absolutely no consensus regards climate’s sensitivity to a doubling of CO2. Some IPCC experts predict 1 degree warming, others predict as much as 5 degrees. Nonetheless the scientific method demands, to prove rising CO2is causing an effect like melting Greenland ice, we must show current changes exceed past natural variability. But most people are unaware that has yet to happen. 

We are an adaptable people. Seawalls we build to protect our coastal homes for the next hundred years, likely need to plan for just 8 inches of sea level rise, but certainly not 5 or 10 feet. Yet to be confident, we need another 20 years to determine the contribution of natural cycles.

Jim Steele is retired director of the Sierra Nevada Field Campus, SFSU


  1. Hi there. Not sure how you can assert that Greenland is gaining ice—where’s the data on that coming from? In fact, it appears to be melting faster than predicted:

    1. Hi Jules,

      Your confusion arises from the paper cited in your NatGeo link is out of date. Typically claims that Greenland is now losing ice at an accelerating pace is based on 2 faulty assumptions. 1) They don’t show year to year trends but use an average of the most rapidly melting decade, and 2) the do not report the most recent data.

      Go to the Polar Portal which summarizes the Danish Meteorological Institute’s research. for 2017 they write:

      “Autumn 2017 and winter 2017/2018 were snow-rich. They were followed by a cool summer with a weak melting season. As a consequence, the inland ice experienced a tiny increase. While the ice cap lost 268 gigatons (268 milliard tons) on average over the period 2000-2016, there was a small surplus of 44 Gt in 2017.”

      You can also do a back of the envelope calculation based on DMI estimates of Greenland’s surface mass balance at the end of the melt season (first of September). Surface Mass Balance (SMB) minus ice lost from glacier calving and melting determines gain or loss. When glaciers are more rapidly retreating subtract 500 Gt from SMB. The last two years SMB has exceeded 500 Gt and thus Greenland gained a small amount of ice

      When glaciers loss slows subtract 400 Gt. And indeed the glaciers have slowed their loss or even gained ice recently . Read just published research “Interruption of two decades of Jakobshavn Isbrae acceleration and thinning as regional ocean cools” in which they conclude

      “Here we use airborne altimetry and satellite imagery to show that since 2016 Jakobshavn has been re-advancing, slowing and thickening. We link these changes to concurrent cooling of ocean waters in Disko Bay that spill over into Ilulissat Icefjord.”