Glaciers and Sea Level Rise

By Andy May

This is the seventh and last post in my series on the hazards of climate change. In this post we examine the effects of climate change on glaciers and sea level rise. The first six examined the effect of humans on the environment, the effect of the growing human population, climate change and the food supply, the cost of global warming, the effect of man and climate change on extinctions, climate (or weather) related deaths, and extreme weather and climate change.

Source: Mike Lester

The IPCC AR5 report has the following to say about the risks of sea-level rise:

“Risks increase disproportionately as temperature increases between 1°–2°C additional warming and become high above 3°C, due to the potential for a large and irreversible sea level rise from ice sheet loss. For sustained warming greater than some threshold [Current estimates indicate that this threshold is greater than about 1°C (low confidence) but less than about 4°C (medium confidence) sustained global mean warming above preindustrial levels.], near-complete loss of the Greenland ice sheet would occur over a millennium or more, contributing up to 7 m of global mean sea level rise.” AR5, WG2, page 61.

OK, if temperatures increase enough, we could go to a rate of sea level rise of as much as 7 mm/year (possibly less). We have no idea how much of a temperature increase it would take, but with low to medium confidence it is between 1°C and 4°C.

Due to sea level rise projected throughout the 21st century and beyond, coastal systems and low-lying areas will increasingly experience adverse impacts such as submergence, coastal flooding, and coastal erosion (very high confidence). The population and assets projected to be exposed to coastal risks as well as human pressures on coastal ecosystems will increase significantly in the coming decades due to population growth, economic development, and urbanization (high confidence). The relative costs of coastal adaptation vary strongly among and within regions and countries for the 21st century. Some low-lying developing countries and small island states are expected to face very high impacts that, in some cases, could have associated damage and adaptation costs of several percentage points of GDP.” AR5, WG2, page 68.

A very reasonable statement, as more people build and live on the coast, they are more vulnerable to sea level rise. Costs to protect these developments vary a lot, depending upon where they are.

Kip Hansen reports that The New York Times rather breathlessly tells us in 2017:

“A rapid disintegration of Antarctica might, in the worst case, cause the sea to rise so fast that tens of millions of coastal refugees would have to flee inland, potentially straining societies to the breaking point. Climate scientists used to regard that scenario as fit only for Hollywood disaster scripts. But these days, they cannot rule it out with any great confidence.   The risk is clear: Antarctica’s collapse has the potential to inundate coastal cities across the globe. … If that ice sheet were to disintegrate, it could raise the level of the sea by more than 160 feet — a potential apocalypse, depending on exactly how fast it happened.” The NY Times, Looming Floods, Threatened Cities, a three part series by Justin Gillis

So, sustained warming over some unknown threshold, perhaps between 1° to 4°C, will cause the Greenland ice sheet to melt in over 1,000 years. Antarctica has ten times as much ice as Greenland and it will rapidly disintegrate? This paragraph, from the once great New York Times, is laughably speculative and dishonest.

This is particularly true because NASA has recently shown that Antarctica is getting colder and gaining in ice. This is based on studies by Jay Zwally and colleagues in 2015 and 2011. Further, Antarctic sea ice extent set records in 2012 and 2014, as discussed by NASA here. Finally, the record cold temperature in Antarctica of -135.8°F (-93.2°C) was set in 2010 and nearly the same temperature was reached in 2013.

Notice I name my sources and link to peer-reviewed articles, as opposed to the New York Times article which sites anonymous “climate scientists” and “recent computer forecasts.” They do allude to Columbia University’s Dr. Nicholas Frearson in the previous paragraph, but do not attribute the idea to him. They note the computer forecasts are described as “crude” and “rough” by Robert M. DeConte, University of Massachusetts at Amherst.

The one paper they do cite is DeConte and Pollard, 2016, who use a computer model and the RCP8.5 emissions scenario, to attempt to show it is possible for Antarctica to contribute a meter of sea level rise by 2100 (12 mm per year) and 13 meters by 2500. Dr. Roger Pielke Jr. and Ritchie and Dowlatabadi, 2017 have called the RCP8.5 scenario implausible. All-in-all a very shoddy piece of journalism, but the journalist (Justin Gillis) got a free trip to Antarctica out of it.

The current rate of sea level rise

The IPCC reports in AR5 WG1 (page 1139):

Proxy and instrumental sea level data indicate a transition in the late 19th century to the early 20th century from relatively low mean rates of rise over the previous two millennia to higher rates of rise (high confidence). It is likely that the rate of global mean sea level rise has continued to increase since the early 20th century, with estimates that range from 0.000[–0.002 to 0.002] mm yr–2 to 0.013 [0.007 to 0.019] mm yr-2. It is very likely that the global mean rate was 1.7 [1.5 to 1.9] mm yr-1 between 1901 and 2010 for a total sea level rise of 0.19 [0.17 to 0.21] m. Between 1993 and 2010, the rate was very likely higher at 3.2 [2.8 to 3.6] mm yr-1; similarly, high rates likely occurred between 1920 and 1950.

Three credible estimates of sea level change from the IPCC AR5 WG1 (page 1147) are shown in figure 1.

Figure 1: Sea level change by Church and White (2011) in orange, Jevrejeva, et al. (2008) in blue, and Ray and Douglas (2011) in green.

All three estimates of sea level rise from 1880 show a steep rise from about 1930 to 1960, followed by a slowing or decline in sea level rise from 1960 to 1967 and then a steep rise to 1983, another pause for a few years and a rise from 1985 to 2013, followed by another pause until today. Figure 2 shows the components, with the AMO (Atlantic Multidecadal Oscillation) index overlain in green. The AMO is a normalized index of North Atlantic sea-surface temperatures. When it is positive, the North Atlantic is warm and when it is negative the North Atlantic is cool. The longer term Bray cycle is in a warming phase as we come out of the Little Ice Age, this provides a background trend of ocean warming and thus, sea level rise due to thermal expansion of the ocean water. The sea level rise component due to thermal expansion is currently about 1 mm/year (0.8 to 1.4) according to the IPCC WG1 AR5 report, page 1151. The slopes of the equations shown in figure 2 are the rate of increase in sea level for that segment in mm/year. The slope is the coefficient of “x.”

Figure 2, data sources CSIRO and NOAA

In figure 2 the AMO index is shown as is, but perhaps should be lagged a few years. The periods of more rapid sea level rise occur when the index is increasing (more thermal energy being taken up by the ocean) or very high. Periods of less rapid sea level increase are associated with a low or decreasing AMO index (thermal energy being expelled by the ocean).

In the CSIRO record, there is an overall increase in the rate of sea level rise, from about 2 mm/year (1930-1960) to 3 mm/year (1985-2013). This is a small change and well within the margin of error, the standard deviation of the estimated error (global mean sea level uncertainty) in the Church and White sea level data from 1930 to 2013 is 1.9 mm. The acceleration, if real, could be an increasing rate of recovery from the Bray cycle low in the Little Ice Age or due to human greenhouse emissions, or some other ocean process, I don’t know of any data that can tell us which it is. The possible acceleration is modest, and we only have decent data for two AMO lows and recoveries, it is very hard to draw any conclusions with only two values. In another 20 years we will have completed a second AMO high and will know more. The AMO is important, but it is only one of many long-term ocean climate cycles, to read more I recommend Marcia Wyatt’s web site here.

Table 1 shows the components of recent sea level rise. The values are from the IPCC WG1 AR5 report, NSIDC and NASA.

Table 1, sources: NSIDC, NASA, and the IPCC WG1 AR5 Chapter 13 (Table 13.1 and summary)

We only have a short record of ocean temperature and it is only to a depth of 2,000 meters. The average depth of the oceans is 3,688 meters. However, making a few reasonable assumptions, we can produce figure 3 from the JAMSTEC ocean temperature grid, it shows the oceans warming at a rate of 0.003°C per year.

Figure 3, Data source JAMSTEC MOAA GPV grid.

The graph shows the ocean temperature change from the surface to 3,688 meters. Zero to 2,000 meters are measured with Argo floats and gridded by JAMSTEC. The ocean temperature at 3,688 meters is assumed to be zero and an interpolation from 2,000 meters (where the temperature is very close to 2.4°C all the time) is made. Due to the nearly constant temperature at 2,000 meters, the interpolation should not affect the trend. The AMO index is overlain on the plot in orange. It explains some of the variability in the whole ocean temperature as we would expect.

Church and White (2011) write:

“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. The global average sea-level rise from 1880 to 2009 is about 210 mm. The linear trend from 1900 to 2009 is 1.7 ± 0.2 mm year-1 and since 1961 is 1.9 ± 0.4 mm year-1.”

For the most part, all the better-known estimates of recent sea level rise fall in the range of 3 mm/year +-1 mm/year or so. However, this is a very small number and the error is large. Nils-Axel Mörner has pointed out that that there is a considerable amount of evidence that the rate of sea level rise is much smaller than reported by the IPCC. He finds evidence from tidal gauges, vegetation and satellite data, that sea level has barely risen at all in the last 25 years. In his publication Sea Level is not Rising, he lays out some convincing evidence. Since the satellite altimeter data do not agree with the worldwide tidal gauges, our measurements of millimeters of change in sea-level rate are buried in uncertainty.

Kip Hansen, in a series of very well documented and well written posts, has explained the complexities involved in measuring sea level and its rise and fall. In his recent post (part 3 of 3) he summaries his conclusions as follows (I have paraphrased them):

  1. Sea level rise is a threat to coastal cities and very low elevation populated areas (part 1).
  2. Sea level is not a threat to anything else (part 1).
  3. Because land also rises and falls depending upon where you are, local tidal gauges are the most important source of information for communities on the coast (part 2).
  4. Local changes in sea level, due to tectonics and tides are much larger than changes in global sea level change and much faster occurring. Eustatic sea level change is not irrelevant, but it is small and very slow moving (part 2).
  5. The tools we use to measure changes in global sea level (satellites and “corrected” tidal gauge records) are only accurate to several centimeters, in practice, and we are trying to use them to measure the change in a dynamic ocean surface. The surface change over an entire year is less than 3 mm, about a tenth of the accuracy of the instruments (part 3). As Hansen points out, we cannot even be sure sea level is rising at all.

Land-based sea level measurements are accurate to +-20 mm and affected by land subsidence or uplift as well. The very best and most modern satellites have a measurement accuracy of +-3 mm, under perfect conditions. They can be affected by weather patterns and problems with orbital decay. Further sea-level change around the world is not uniform, the global distribution of changes are affected by the ocean cycles mentioned earlier. Beyond these comments, I will encourage the interested reader to read Kip Hansen’s posts on how sea-level change is measured and the accuracy of the measurements.

Due to the variation in sea level rise from place to place, which is mostly due to variations in land movement and tidal ranges over time, local communities should evaluate their own risks, based on local measurements. They need to prepare their community’s infrastructure for the specific threats they face. Global sea level changes at a small rate that is swamped by error, the focus should not be on it, but the local threat to your community.

Glaciers are retreating

Glaciers have been advancing for most of the past 6,000 years according to Mayewski, et al. 2004 as the world has cooled from the Holocene Thermal Optimum. Figure 4, from Mayewski’s paper, shows some of the evidence. The global cooling from 6,000 years ago is apparent from the worldwide glacial advances plotted in figure 4c, present day is to the left in this plot. In Switzerland (figure 4d), except for a brief glacial retreat during the Medieval Warm Period 1,000 years ago, glaciers were generally smaller than today before 2,200 years ago.

Figure 4, from Mayewski, et al. 2004

The dates along the top of figure 4 are B2K (years before 2000). The green vertical bars in figure 4 are periods of rapid climate change (RCC). We are currently coming out of the latest RCC, the sixth major rapid climate change in the Holocene. Figure 4a is a proxy for Icelandic low-pressure events, these events correlate well with northern hemisphere ice sheet growth (Mayewski, et al., 1997). Figure 4b is a proxy for the Siberian high-pressure event, which also correlates with ice-sheet growth in the northern hemisphere (Mayewski, et al., 1997). Figure 4f shows the winter insolation values for the northern hemisphere (black) and the southern hemisphere (blue). Figure 4g shows the summer insolation for both hemispheres, the summer insolation has decreased in the Holocene in the Northern Hemisphere and increased in the Southern Hemisphere.

Javier created a figure (figure 5) with some of the same data.

Figure 5, source Javier, here.

Figure 5 shows the Marcott, et al., 2013 global temperature reconstruction modified to reflect the known temperature difference between the Little Ice Age and the Holocene Thermal Optimum of 1.2°C. See the appendix (here) for more on Javier’s adjustment to the curve. For an alternative global temperature reconstruction, with some problematic proxies removed that shows a 1.2°C difference between the Little Ice Age and the Holocene Thermal Optimum, without adjustment, see here. The key point is that the Little Ice Age was the coldest period in the Holocene and this is largely due to changes in the Earth’s orbital tilt, or obliquity, which is plotted in figure 5 with a purple line.

Lomborg reports in Cool It:

“… most glaciers in the Northern Hemisphere were small or absent from nine thousand to six thousand years ago. While glaciers since the last ice age have waxed and waned, they overall seem to have been growing bigger and bigger each time until reaching their absolute maximum at the end of the Little Ice Age. It is estimated that glaciers around 1750 were more widespread on Earth than at any time since the ice ages twelve thousand years ago. So, it is not surprising that as we’re leaving the Little Ice Age we are seeing glaciers dwindling. We are comparing them with their absolute maximum over the past ten millennia.”

“… with glacial melting, rivers actually increase their water content, especially in the summer, providing more water to many of the poorest people in the world. Glaciers in the Himalayas have been declining significantly since the end of the Little Ice Age and have caused increasing water availability throughout the last centuries, possibly contributing to higher agricultural productivity. But with continuous melting, the glaciers will run dry toward the end of the century. Thus, global warming of glaciers means that a large part of the world can use more water for more than fifty years before they have to invest in extra water storage. These fifty-plus years can give the societies breathing space to tackle many of their more immediate concerns and grow their economies so that they will be better able to afford to build water-storage facilities.” Lomborg, Bjorn. Cool It (Kindle Locations 884-930).

Global warming will cause excessive sea level rise

In a previous post we discussed the warming of the oceans. We only have significant ocean temperature data since 2004, it is plotted in figure 3. It shows the temperature in the oceans is rising at about 0.003°C per year currently.

One-third to one-half of the 18 cm rise in sea level that we have seen over the past century (1914-2014, from the CSIRO record plotted in figure 2) is due to the oceans warming as we come out of the Little Ice Age. Thus, at most, only 12 cm (about 5 inches) is due to melting glaciers and ice sheets.

According to Lomborg in Cool It:

“…when water gets warmer, like everything else it expands. Second, runoff from land-based glaciers adds to the ocean water volume. Over the past forty years, glaciers have contributed about 60 percent and water expansion 40 percent of the rise in sea levels. In its 2007 report, the UN estimates that sea level will rise about a foot over the rest of the century. While this is not a trivial amount, it is also important to realize that it is certainly not outside historical experience. Since 1860, we have experienced a sea-level rise of about a foot, yet this has clearly not caused major disruptions.

The IPCC cites the total cost for U.S. national protection and property abandonment for more than a three-foot sea-level rise (more than triple what is expected in 2100) at about $5 billion to $6 billion over the century. Considering that the adequate protection costs for Miami would be just a tiny fraction of this cost spread over the century, that the property value for Miami Beach in 2006 was close to $23 billion, and that the Art Deco National Historic District is the second-largest tourist magnet in Florida after Disney World, contributing more than $11 billion annually to the economy, five inches will simply not leave Miami Beach hotels waterlogged and abandoned.” Lomborg, Bjorn. Cool It (Kindle Locations 956-977).

Sea level rose six inches during the 20th century (see figure 6) according to the Church and White dataset. If the IPCC projection for the 21st century is correct, and it rises another 12 to 16 inches, this should not be a problem. We adapted to six inches of sea level rise with more primitive 20th century technology, another ten inches will not be a problem for 21st century technology. Sea walls, barriers like the Thames Barrier and dikes and levees will be built. Or people may choose to move to higher ground. The key factor is sea level is rising very slowly and there is plenty of time to adapt.

The IPCC expects the average person in the standard future to make $72,700 in the 2080s. If the world decides to mitigate additional CO2, rather than adapt to additional CO2, the average person’s earnings would decrease to $50,600 according to Lomborg, a reduction of 30%. It is possible the environmental world would see more people flooded than the richer, less environmental world, because people would be poorer and less able to adapt. In the last century we have lost very little land to higher sea level, simply because the land was valuable enough to protect it with technology.

Figure 6, Church and White Sea Level, 20th century

Figure 7 shows the famous Thames Barrier that protects London from high tides and North Sea storm surges.

Figure 7, the Thames Barrier

The largest U.S. death toll, due to a hurricane, was in 1900. The Great Galveston Hurricane was a category 4 storm that made landfall on September 8, 1900 and killed 6,000 to 12,000 people. It is by far the deadliest hurricane in U.S. history. During much of the 19th century, Galveston was the largest city in Texas. By the time of the great storm, however, it was the fourth largest city after Houston, Dallas, and San Antonio. The 15-foot storm surge swept over the entire island and destroyed the city. The survivors mostly moved to Houston and elsewhere in Texas. The island, at the time, only had an eight-foot elevation, and 3,600 homes were washed away.

After the storm the remaining population raised the island’s elevation to 17 feet behind a concrete seawall, which was completed in 1911. The seawall has protected Galveston from most subsequent hurricanes, even the monster Hurricane Carla in 1961, which is strongest hurricane to ever hit the United States according to the Hurricane Severity Index.

Figure 8 shows the sea wall not long after it was completed.

Figure 8, The Galveston sea wall in the early 20th century, an undated public domain image.

Figure 9 is a 1905 photo of the wall under construction:

Figure 9, Galveston sea wall under construction in 1905.

Figure 10 shows what the sea wall looked like after Hurricane Ike in 2008, the first hurricane to top the wall.

Figure 10, the Galveston sea wall in 2008, shortly after Hurricane Ike (photo credit: Aurelia May)

The Army Corps of engineers estimate that $100 million of damage was averted in 1983 from Hurricane Alicia by the sea wall. Hurricane Ike (2008) overtopped the sea wall and caused a great deal of damage. Since then additional storm surge protections have been proposed, like the so-called “Ike Dike.” But, these are still in the planning stages.


It is true that glaciers are melting today as we warm up after the Little Ice Age. But, the melting glaciers provide much needed water in dry areas. Glaciers reached their maximum Holocene extent during the Little Ice Age and the glaciers today are still more extensive than they were 6,000 years ago. The melting glaciers, outside of Greenland and Antarctica, contribute 30%-50% of the expected one foot rise in sea level over the next 100 years, with thermal expansion of the ocean water contributing most of the remainder. Greenland and Antarctic are not major contributors to sea level rise, especially if Antarctica is gaining ice as claimed by Zwally, et al. and NASA.

Worldwide sea level rise over the next 100 years is not expected to be a problem. Local sea level rise is a problem for low lying communities and they should monitor it locally and build local infrastructure to ameliorate its effects. Land can be protected from sea level rise and severe maritime storms at an affordable cost, or people can move to higher ground.

When one considers that Galveston, Texas was able to protect itself and rebuild after the devastating 1900 Great Galveston Hurricane in only 11 years, imagine what we can do today, 117 years later. Imagine what we will be able to do 100 years from today. Most analyses suggest that adapting to climate change is better than trying to prevent it. The measures that have been proposed to mitigate climate change, mainly Kyoto and Paris, do very little and are very expensive. Further, we are not even sure that global warming is a problem, why fix something that may not even matter?

From an economic perspective, the “time value of money” principle tells us it is foolish to invest a serious amount of money today to fix something that may or may not be a problem over 100 years from now. The best investments will be those that benefit us now and that means adaptation. We may need that money to adapt, whether climate change is natural or man-made.

The important take-aways from this series, in my opinion, are:

  1. The data comes first, before models and predictions, especially predictions from unvalidated models.
  2. If you don’t see the problem in the data, it’s not a problem.
  3. Global warming will not destroy the planet or humans, even in the worst projections (part 1).
  4. The oceans, the Sun and the Earth’s orbit are the major controls on the climate. Human’s may have some effect, but it must be small (part 1 and here).
  5. The time value of money is critical. Spending a lot of money today to fix a possible problem in 100 years is foolish. From the standpoint of technology development, 100 years might as well be forever (post 3).
  6. Human prosperity leads to a better environment, a healthier population, more adaptability, and lower population growth (part 1).
  7. Poverty leads to a poorer environment, poorer health, and higher population growth (part 1).
  8. Cheap, widely available, and reliable energy leads to prosperity (part 3, here and here).
  9. Cold is worse than hot. Cold weather leads to more deaths and disease, warm weather leads to fewer deaths and less disease (part 5).
  10. Humans are adaptable, today we live in hot areas, cold areas, dry and wet areas, high in the mountains and in rainforests, we have already adapted, somewhere, to anything foreseen by the climate alarmists (part 5).
  11. Our food supply is growing rapidly, with no sign of slowing down, prices are stable. Population growth, on the other hand is slowing down (part 2).
  12. The rate of extinctions today is very low, we are not in a “great extinction” nor are we even close (part 4).
  13. The extreme weather trend is flat or declining (part 6).
  14. The Gulf Stream is not shutting down (part 4).
  15. Our measurements of the rate of sea level rise are so inaccurate we cannot be sure that sea level is rising at all, although it probably is at a very slow rate (Kip Hansen here).
  16. Sea level rise is not alarming, except locally, and should be dealt with as a local problem (part 7, this post).