In 2007, the latest IPCC report predicted sea-level rise of up to 59 cm by the end of the century — plus a potential contribution of unknown magnitude from poorly understood ice dynamics in Greenland and Antarctica. Since then, researchers have published alarming sea-level projections that far exceed the range of the 2007 report (for example, Geophys. Res. Lett. 37, L07703; 2010). However, actual measurements of sea level do not back up these projections. So far, scientists have neither observed an extreme rise nor reached a consensus on the question of whether sea level has been going up more quickly in recent years. There is only one certainty: in global average terms, the water is rising.
Until 1993, the data were based only on readings from in situ tide gauges. Since 1993, satellites have also been used to measure the oceans. These have registered a rise of as much as three millimetres per year. Some studies see a recent acceleration in the rise in sea level (for example, J. Climate 22, 5772–5781; 2009). But deciding what constitutes an acceleration is not so simple, as John Church of Australia's Commonwealth Scientific and Industrial Research Organisation and head of the IPCC Sea Level Working Group points out: “The rate of rise has increased from the nineteenth to the twentieth century and during the twentieth century.” The rate of rise in recent years is larger than the twentieth century average, but whether or not this is a further acceleration is not yet clear, says Church. Eduardo Zorita of the GKSS Institute of Coastal Research confirms: “I would say that the data quality does not allow for asserting an acceleration or deceleration.” The rate of sea-level rise has slightly decreased in the last eight years, says Zorita. According to Simon Holgate, a sea-level researcher at the National Oceanography Centre in Liverpool, the rise over the past 20 years is nothing unusual in comparison to other decades of the twentieth century (Geophys. Res. Lett. 34, L01602; 2007). This state of affairs is puzzling. Melt rates in Greenland and Antarctica have been reported to be going up (Geophys. Res. Lett. 38, L05503; 2011), and faster melt should speed up the rise in sea level.
This is a preview of subscription content, access via your institution
