Andy May
We are constantly told that the rate of global mean sea level (GMSL) rise is accelerating. Yeah? How certain is the evidence? If it's accelerating, why? Is it dangerous to speed up?
The common assumption is that its rise is largely due to man-made global warming and the melting of glaciers and polar ice caps. Really? We'll examine the evidence and see what we can find out.
Dangendorf et al. The report said:
“We find that the GMSL has continued to accelerate since the 1960s and show that this is largely (about 76%) related to sea level changes in the Indo-Pacific and South Atlantic. We show that the onset of the acceleration in the 1960s is associated with the southern hemisphere westerlies The strengthening is closely related to the basin-scale equatorial shift, leading to increased ocean heat absorption, which in turn leads to an accelerated rise rate of GMSL through changes in circulation.
Sea level is not the same in each ocean basin in terms of absolute elevation, due to the shape of the ocean basin, the temperature of the individual ocean basins, and the strength and direction of the basin's prevailing winds. Therefore, the acceleration of sea level change in each basin is different, global mean sea level is the combination of all changes in each basin, and simply reporting (or discussing) GMSL masks many complexities.
Dangendorf et al. observed a continued acceleration in global mean sea level since the 1960s and concluded that the acceleration was due to changes in prevailing winds in the Southern Hemisphere, rather than melting ice. In fact, they found that melting ice contributed significantly to the rapid rise in sea levels in the 1930s, when greenhouse gas emissions were much lower than today, but “contributed zero or more to the acceleration coefficient between the 1940s and early 1990s.” is negative”.
They also report that the modern (1968-2015) “global” sea level acceleration is not global at all, it is largely an acceleration of sea level rise in specific regions. No acceleration was detected in the eastern Pacific or Arctic oceans, and deceleration was detected in the Southern Ocean. As a result, the regions most affected by melting ice—the Arctic and the Southern Ocean—are not experiencing acceleration.
This suggests that the currently observed acceleration is due to changes in atmospheric circulation and not to global warming or greenhouse gas emissions. Major changes in global wind circulation occur every 65 years, and these changes lead to global temperature changes, as shown in Figure 1.
Although the AMO index is not exactly the same as the 60-70 year global climate oscillation (often called climatological stadium waves), it is similar, and the AMO is an important component of stadium waves (Wyatt MG, 2012c) and (Wyatt & Library Li, 2014). Note that the AMO shows minima between 1910 and 1925 and between 1970 and 1980, and these minima coincide approximately with the lows after detrending the HadCRUT4 global mean surface temperature.
Figure 2 shows various estimates of sea level rise, including those of Dangendorf et al. estimate.
The first thing we notice in Figure 2 is that from 1900 to 2000, all long-term rates of sea level rise were fairly linear, ranging from 1.4 to 2.0 millimeters per year, or 5 to 8 inches per century. The second thing we noticed is that there is a similar cyclic pattern of sea level rise acceleration in all reconstructions. All show an acceleration from around 1920 to around 1950-1960, then a deceleration to the early 1990s, and then accelerating again after the 1990s. Coincidentally, satellite records begin when the cyclical acceleration begins in the early 1990s.
According to Dangendorf et al., the acceleration in sea level rise rates observed since the 1960s (near the peak of the cycle) is not significantly greater than the acceleration noted in the 1920s and 1930s. The natural climate patterns in Figure 1 appear to have a strong influence on sea level rise acceleration during both acceleration periods. Figure 3 shows a comparison of the accelerations from 1960 to 2016 reconstructed by the Dangendorf mixture model and the Jevrejeva tide gauge with the observed accelerations from 1920 to 1950.
It is clear from Figure 3 that the Jevrejeva sea level rise record is more detailed and less processed than the complex hybrid Dangendorf reconstruction, but both show similar accelerations during their respective periods. The largest acceleration is the Jevrejeva rate from 1920 to 1950, and the smallest is the Dangendorf rate for the same period. The acceleration of the Hyundai Dangendorf is moderate and less than that of the Hyundai Jevrejeva.
As pointed out by Dangendorf et al. Accelerations between 1920 and 1950 were similar to those in the modern period, and Jevrejeva data from 1920 to 1950 show higher accelerations in this period than in the modern period. Since the beginning of 20th The rate of acceleration this century is likely unaffected by greenhouse gas emissions, and there is no reason to believe that the rate of acceleration in the modern period is any different.
Greenhouse gas emissions were higher from 1950 to 1990 than from 1920 to 1950, but the acceleration of sea level rise was lower and probably negative, as shown in Figure 4.
After extensive processing, Dangendorf et al. Sea level records show lower accelerations between 1950 and 1991, but Jevrejeva tide gauge records actually show slow down period.
Discussion and conclusion
As shown by the AMO index in Figure 1, there are specific breakpoints in the climate trend around 1912 and 1972, which can also be seen in the detrended HadCRUT4 global mean surface temperature record. More information about Climate Breakpoints, AKA climate change See here , here and here .
As shown in Figure 2, there is also a break in the sea level rise rate, but with a slight shift, around ±1928 and ±1991. All sea level rise records in Figure 2 show these breakpoints with varying degrees of clarity.
It's unclear why the climate changes at these times or whether these changes are related to changes in the rate of sea level rise. This is an area that needs more research. But these figures show that the acceleration of sea level rise varies with a 60-70 year cycle. These changes follow similar patterns to rates of change in global surface temperature and the Atlantic Ocean's multidecadal oscillation.
Dangendorf et al. Believe 20th Changes in the acceleration of sea level rise over the past century are closely related to changes in atmospheric circulation, especially in the Pacific and Southern Ocean. We see no reason to disagree with this view. Accelerating changes in sea level rise appear to have nothing to do with greenhouse gas emissions or human activity.
What if there is no slowing acceleration period or any real deceleration of sea level rise this century? In other words, what if the current rate of acceleration in nature’s “juicing” since 1960 continues into 2100? How much will global mean sea level rise? Table 1 is calculated using data from each global sea level reconstruction discussed in this article. The functions used in the Jevrejeva and Dangendorf calculations are shown on the left side of Figure 3 . For additional features used, see the supplemental spreadsheet linked at the end of this article.
As shown in Table 1, if the observed acceleration in each reconstruction since the most recent rise around 1960 is extrapolated to the year 2100, sea level rise would be only 16 to 33 inches. This is lower than the global average daily tide and should not be a problem for anyone. The natural acceleration since 1960 is unlikely to continue into 2100, and it should soon return to a slower acceleration, as it did sometime between 1955 and 1965.
A spreadsheet containing the information used to create the chart can be downloaded here.
Download bibliography here.
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