Is Sea Level Rise Accelerating?

Monday 15th Jun 2015 by theWeather Club

For most of the 20th century sea level rise may have been overestimated by as much as 30%. However, the bad news is  if this is the case, then sea levels since 1990 have started to accelerate more sharply than anyone had ever expected - and this has implications for future projections.

The research published in Nature found annual sea level rise from 1901 to 1990 was about 1.2 mm, roughly 0.3 to 0.6 mm less than the projected for that time period. However, there has been nearly a threefold annual increase in global sea levels over the last quarter of a century - with an average global sea level rise of 3 mm a year  since 1990.  Therefore major coastal cities and island communities may be at a higher risk than previously thought.

Robert Kopp, a senior scientist on the study said, “As you go back through the 20th century, the tide gauge record becomes sparser. One of the things we’re interested in is global mean sea level – the volume of water in the ocean.” Previous research did not account for “gaps” in tide gauge data, leading to the discrepancy.

Estimating and accounting for global mean sea level (GMSL) rise is critical to characterising current and future human-induced changes.

“We know that sea level is changing for a variety of reasons,” said Dr Carling Hay, post-doctoral fellow in Harvard’s Department of Earth and Planetary Sciences (EPS). “There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present day melting of land-ice − all of which result in unique patterns of sea level change. These processes combine to produce the observed global mean sea level rise.”

If sea level rise has indeed been overestimated then this has implications for models calibrated using these estimates and therefore calls into question the accuracy of future projections for sea level change.