Gavin Schmidt investigated
the source of the specific claim that tide gauges on islands in the Pacific Ocean show no sea level rise, and found that the data show a rising sea level trend at every single station. But what about global sea level rise?
A common error in climate debate is drawing conclusions from narrow pieces of data while neglecting the whole picture. A good example is the recent claim that sea level rise is slowing
. The data cited is satellite altimeter measurements of global mean sea level over the past 16 years (Figure 1). The 60 day smoothed average (blue line) seems to indicate sea level peaked around the start of 2006. So one might argue that sea levels haven't risen for 3 years. Could one conclude that the long term trend in sea level rise has ended?
Figure 1: Satellite altimeter measurements of the change global mean sea level with inverse barometer effect (
University of Colorado
To answer this question, all one has to do is view the entire 16 year dataset. A noisy signal is imposed over the long term trend of sea level rise. These fluctuations mean there will be short periods where sea level shows no trend. For example, 1993 to 1996 or 1998 to 2000. In other words, there have been several short periods of several years over the last 16 years of steady sea level rise where sea level appears not to rise.
This is inevitably the case when you have a noisy signal imposed over a long term trend. We see exactly the
same phenomenon occur in the temperature record
(which is why we also see the same erroneous conclusions). The lesson from this is to treat with skepticism anyone who concludes long term trends from several years of a noisy signal (after all, skepticism should cut both ways).
In addition to this, Figure 1 is a particularly noisy signal because it displays unfiltered data. Sea level is subject to the "Inverse Barometer" Effect. This is where sea level is depressed in areas of high atmospheric pressure, and raised in areas of low pressure. When barometric pressure effects are filtered out, the result is a less noisy signal and a clearer picture of what's happening with sea level.
Figure 2: Satellite altimeter measurements of the change global mean sea level with inverse barometer effect filtered out (
University of Colorado
A broader view of sea level rise
Global mean sea level (eg - the global average height of the ocean) has typically been calculated from tidal gauges. Tide gauges measure the height of the sea surface relative to coastal benchmarks. The problem with this is the height of the land is not always constant. Tectonic movements can alter it, as well as Glacial Isostatic Adjustment. This is where land which was formerly pressed down by massive ice sheets, rebounds now that the ice sheets are gone.
To construct a global historical record of sea levels, tide gauge records are taken from locations away from plate boundaries and subject to little isostatic rebound. This has been done in
A 20th century acceleration in global sea-level rise (Church 2006)
which reconstructs global sea level rise from tide gauges across the globe. An updated version of the sea level plot is displayed in Figure 3:
The fantasy of accelerating sea level rise just got hosed
/ February 4, 2018
We’ve been told over an over again that global warming would melt the icecaps, and melt Greenland, and that would result in catastrophic sea level rise flooding cities
. We’ve also been told that “sea level rise is “accelerating” but in an investigation done here on WUWT by Willis Eschenbach, Putting the Brakes on Acceleration,
he noted in 2011 that there seems to be no evidence of it at all, and notes that sea level was rising faster in the first half of the record.
Figure 1. Satellite-measured sea level rise. Errors shown are 95% confidence intervals. Data Source.
The smaller trend of the recent half of the record is statistically different from the larger trend of the first half. Will this reduction continue into the future? Who knows? I’m just talking about the past, and pointing out that we sure haven’t seen any sign of the threatened acceleration in the satellite record. Quite the opposite, in fact.
Pierre Gosselin, of “No Tricks Zone” has this excellent summary
of what’s been going on since then. Excerpts below.
Over the past months a spate of scientific papers published show sea level rise has not accelerated
like many climate warming scientists warned earlier. The reality is that the rise is far slower than expected, read here
The latest findings glaringly contradict alarmist claims of accelerating sea level rise. For example the National Oceanic and Atmospheric Administration (NOAA) here
wrote sea levels would “likely rise for many centuries at rates higher than that of the current century”
, due to global warming.
In 2013 The Potsdam Institute for Climate Impact Research (PIK) wrote here
sea-level rise in this century would likely be 70-120 centimeters by 2100″ (i.e. 7 – 12 mm annually) and that 90 experts in a survey “anticipated a median sea-level rise of 200-300 centimeters by the year 2300”
(i.e. on average circa 7 to 10 mm every year).
Using these modelled estimates, the globe should now be seeing a rapid acceleration in sea level rise. Yet no evidence of this can be found so far. In fact the real measured data show the opposite is happening: a deceleration in sea level rise is taking place.
Instead of the 7 – 12 mm annual sea level rise the PIK projected in 2013, a recent study appearing in the Geophysical Research Letters
in April 2017 corrected the satellite measured sea level rise downwards from 3.3 mm annually to just 3.0 mm over the past 24 years – or less than half what PIK models projected.
In another newly published paper by Frederiske et al. 2018
just this year, oceanographers estimate that global sea levels rose at a rate of only 1.42 mm per year between 1958 and 2014. That figure closely coincides with the results of Dr. Simon Holgate from 2007
. According to the Holgate study: “The rate of sea level change was found to be larger in the early part of last century (2.03 ± 0.35 mm/yr 1904–1953), in comparison with the latter part (1.45 ± 0.34 mm/yr 1954–2003).”
The Holgate result was confirmed by another 2008 paper authored by Jevrejeva et al
, which found the fastest sea level rise during the past 300 years was observed between 1920 – 1950 with maximum of 2.5 mm/yr.
In other words: global sea level rise has decelerated since the 1950s.
By the mid-Holocene period, 6000-5000 years ago, glacial melting had essentially ceased, while ongoing adjustments of Earth's lithosphere due to removal of the ice sheets gradually decreased over time. Thus, sea level continued to drop in formerly glaciated regions and rise in areas peripheral to the former ice sheets. At many low-latitude ocean islands and coastal sites distant from the effects of glaciation, sea level stood several meters higher than present during the mid-Holocene and has been falling ever since. This phenomenon is due to lithospheric responses to changes in ice and water loading. Water is "siphoned" away from the central equatorial ocean basins into depressed areas peripheral to long-gone ice sheets. Loading by meltwater that has been added to the oceans also depresses far-field continental shelves, tilting the shoreline upward and thus lowering local sea level. Over the past few thousand years, the rate of sea level rise remained fairly low, probably not exceeding a few tenths of a millimeter per year.
Twentieth century sea level trends, however, are substantially higher that those of the last few thousand years. The current phase of accelerated sea level rise appears to have begun in the mid/late 19th century to early 20th century, based on coastal sediments from a number of localities. Twentieth century global sea level, as determined from tide gauges in coastal harbors, has been increasing by 1.7-1.8 mm/yr, apparently related to the recent climatic warming trend. Most of this rise comes from warming of the world's oceans and melting of mountain glaciers, which have receded dramatically in many places especially during the last few decades. Since 1993, an even higher sea level trend of about 2.8 mm/yr has been measured from the TOPEX/POSEIDON satellite altimeter. Analysis of longer tide-gauge records (1870-2004) also suggests a possible late 20th century acceleration in global sea level.
Recent observations of Greenland and the West Antarctic Ice Sheet raise concerns for the future. Satellites detect a thinning of parts of the Greenland Ice Sheet at lower elevations, and glaciers are disgorging ice into the ocean more rapidly, adding 0.23 to 0.57 mm/yr to the sea within the last decade. The West Antarctic Ice Sheet is also showing some signs of thinning. Either ice sheet, if melted completely, contains enough ice to raise sea level by 5-7 m. A global temperature rise of 2-5°C might destabilize Greenland irreversibly. Such a temperature rise lies within the range of several future climate projections for the 21st century. However, any significant meltdown would take many centuries. Furthermore, even with possible future accelerated discharge from the West Antarctic Ice Sheet, it highly unlikely that annual rates of sea level rise would exceed those of the major post-glacial meltwater pulses.
Is there anything about the loco collective that isn't bogus??