Sea Level Rise

By | February 9, 2009

 sea level rise

 

 
[Illustrations, footnotes and references available in PDF version]

 

The scare: An article published in early February 2009 by Jonathan Leake, the environment editor of The Times of London, said “The ice caps are melting so fast that the world’s oceans are rising more than twice as fast as they were in the 1970s.”

The Times said that “scientists” had used satellites “to track how the oceans are responding as billions of gallons of water reach them from melting ice sheets and glaciers”, an effect “compounded by thermal expansion". The article said that in the past 15 years “sea levels have been rising at 3.4mm a year, much faster than the average 1.7mm recorded by tidal gauges over the past 50 years.” A scientist was quoted as saying, “This rate, observed since the early 1990s, could reflect acceleration linked to global warming.” The article added that figures from the UK Meteorological Office suggested that sea level in the tidal reaches of the River Thames could rise by as much as 6ft 6in by 2100.
 
The truth: First, there is nothing new in this article. Ever since the TOPEX/JASON sea-level monitoring satellites began transmitting data in 1993, they have shown sea level as rising at a near-linear rate equivalent to 1 ft/century, compared with the 8 in/century previously estimated for the 20th century by the use of tide-gages. However, it is thought likely that the apparent increase in the rate of sea-level rise is chiefly an artifact of the change in mensuration from tide-gages to satellites in 1993. Furthermore, in response to the very sharp global cooling of the last few years, the rate of increase in sea level appears to have slowed somewhat, though it is not yet clear whether the trend will continue, and no data from the JASON satellite has been published since the late summer of 2008. In 2007 the UN reduced its high-end estimate of sea-level rise from 3 ft to less than 2 ft over the 21st century. The mean rate of sea-level rise over the past 10,000 years has been 4 ft/ century, though The Times was very careful not to provide this perspective in its article.
 
There is little scientific basis for the article’s assertion that “the ice-caps are melting fast”. There has been some decline in sea-ice extent in the Arctic, but this decline is well within natural climate variability and cannot be attributed to anthropogenic “global warming”, because the mere fact of warming (which, in any event, has not occurred for 13 years) tells us nothing of the cause of the warming. In the Antarctic, however, sea-ice extent has recently reached a record high, and the current accumulation of land-ice at the South Pole is 8850 feet deep, increasing annually. The Times somehow failed to mention the Antarctic in its article.
 
For most of the past 10,000 years – most recently in the Roman and medieval warm periods – temperatures were up to 3 Celsius degrees (5.5 Fahrenheit degrees) warmer than the present. Each of the past four interglacial periods was up to 6 Celsius degrees (11 Fahrenheit degrees) warmer than the present. Humankind cannot have been to blame.
 
End of scare.