Glabal Sea Level Rise

By -
GLOBAL SEA LEVEL RISE
Summary
  • The average rate of sea level rise from 1880 to 2013 is 1.6 mm/year
  • The rate of sea level rise is not constant. It is increasing at 0.014 mm/year/year.
  • Superimposed on the rising sea levels is a cyclical component with a periodicity of about 50 years which is synchronous with the Atlantic Multidecadal Oscillation.
CSIRO Estimate
Sea levels have risen more than 100 m since the end of the last ice age and they are still rising. This post looks at the rate of rise over the last century or so and, based on sea level data, and answers the question "Is the rate of level rise increasing?",

The CSIRO provide one of the main estimate of global mean sea levels (Church, J. A. and N.J. White (2011), Sea-level rise from the late 19th to the early 21st Century. Surveys in Geophysics, doi:10.1007/s10712-011-9119-1.). The data run from 1880 to 2013. They are available as monthly or annual values. The annual values have been analysed here.

This chart shows the CSIRO sea level data. The data are in millimeters relative to an arbitrary datum. The data show that global sea levels have risen by just over 200 mm in the period 1880 to 2013. Plotting a trend line through the graph gives an average rate of rise of 1.6 mm/year. This is 160 mm  century, much less than most of the climate change projections.








The above chart gives just one rate of sea level rise - the one for the whole period. So what if we look at year-on-year sea level change.

Year-on-year rate of sea level rise

The next chart plots the difference between the value of sea level in the given year and the value in previous year, for each year from 1981 to 2013. So, the first value is the difference between sea level in 1881 and in 1880, and so on. Looking at the chart there is a lot of year-to-year variation, from minus 17 mm/year to plus 21 mm/year. A trend line through the data shows that the rate of sea level rise has increased, by 0.0141 mm/year/year. That means the underlying rate of sea level rise was 1.9 mm/year higher in 2015 than it was in 1880. In other words, the rate of sea level rise is increasing.



Smoothed rate of sea level rise

One way of observing underlying trends more clearly when the data have a lot of year-on-year variation is to use a moving average. This takes the average of the values of the data for a number of years before and after each point plotted. As the data are so variable a long period has been used for averaging, 31 years. The first point plotted is for 1896 and is the average of the sea level from 1881 to 1911, the next is the average from 1882 to 1912 and so on.

This chart confirms that the rate of sea level rise is increasing but not in a uniform way. From a peak of 1.66 mm/year in 1900 to fell to minimum of 0.51 mm/year in 1920. It then rose to another peak of 2.2 mm/year in 1946 before falling to to a minimum of 1.33 mm/year in 1978. The rate of sea level rise then increased again to another peak of 2.84 mm/year 1997.

The trend line on the chart gives a slightly different value for the rate at which the rate of sea level rise in increasing, 0.0117 mm/year/year, to that in the chart above. This is due to effect of the averaging.



Cyclical component to sea level rise

The final chart plots the difference between the rate of sea level rise and the trend line. This is described as the detrended rate of sea level rise. For example, the peak in 1946 was 2.20 mm/year, the value on the trend line for that year was 1.63 mm/year so the value plotted was the difference between them 0.57 mm/year.

This chart shows that the rate of sea level rise has two components. The first is the underlying increase in the rate of sea level rise, this is 0.0141 mm/year/year as seen in the first chart. The second is a cyclical component with an amplitude of plus or minus 0.6 mm/year and a periodicity of around 50 years.





And the orange line? Climate scientists have detected a number of cycles in observed climate data. One of these is called the Atlantic Multidecadal Oscillation (AMO). It is based on sea temperatures in the northern part of the Atlantic Ocean. When the values of this oscillation are plotted along with the detrended rate of sea level rise they show a high degree of synchronicity. It cannot be argued that the AMO causes the variation in the rate of sea level rise. On other hand, it could be argued that both phenomena share an unknown forcing agent.

Comments

Post a Comment

Popular posts from this blog

Climate Change Impact - Part 8 - Samoa

By -
Image
Climate Change Impact Part 8: Example – Samoa Summary Some of the roads on Samoa had been damaged in recent storms and the objective of the project was to prepare the rehabilitation taking account of climate change. Climate data, including rainfall at a 10-inute time step for two stations were obtained. The data showed that there was a significant increase in rainfall with elevation (which might explain why the most severe damage to the roads was at highest elevations). A methodology was developed to estimate the storm intensity for a range of durations and return period taking account of climate change. Introduction Samoa consists of two main islands shown on the following map. Both islands have a road network. On Upolo there are roads around and across the island. On Savai’I the roads run around the island. There is a third island, to the east of and smaller than these two, which is a US territory. Figure  1  Map of Samoa The main aim of the proje
Read more

It's a Cop Out

By -
Image
Conference of the Parties Since 1995 the self-proclaimed great-and-good of the climate movement have met to discuss measures to combat climate change. The meetings have taken place every year, except for the COVID hit year of 2020. Each meeting is referred to a Conference of the Parties. The Conference of the Parties, usually shortened to COP, is the supreme decision-making body of The United Nations Framework Convention on Climate Change (UNFCCC). It works in parallel with the International Panel on Climate Change (IPCC) which produces regular Coupled Model Intercomparison Project (CMIP) reports. The latest is CMIP6. In brief, the IPCC produce projections of climate change (with emphasis on temperature) and the UNFCCC proposes measures to moderate those changes. The following chart shows the number of participants at each of the annual meetings of the COP. COP 26 The two largest meetings were those at Paris in 2012 (COP 21) and in Glasgow in 2021 (COP 26). Participants are classed in
Read more
By -
Image
Global Snow and Ice A recent post called "Water Behaving Badly" by Willis Eschenbach looked at the change in sea ice at the poles. He concluded that the change were marginal when both Arctic and Antarctic ice were considered. In this post I have taken this a stage further looking at global sow and ice cover.  The main data sets I have used are the NSIDC sea-ice data set and the global snow cover from Rutgers University. The first of these deals with snow lying on ice and the second deal with snow lying on land. In both case I have used the monthly data. The following chart shows the global snow and ice cover from the end of 1978 to the near present.  Add caption The chart has monthly values and a 12-month moving-average. The main message from the chart is that snow cover area is, indeed, tending to reduce. However, it is difficult to argue that the rate is is any way approaching catastrophic. The trend line plotted through the 12-month average values represen
Read more