Statistical significance test of the intrinsic secular trends of (a) the global mean sea level (GMSL) time series, (b) the GMSSL time series, and (c) the global ocean mass change time series. The gray lines in each panel show the secular trend derived from randomly generated AR(1) red noise with the lag-1 auto-correlation ranging from 0 to 0.99 (in order from light gray to dark gray). The coloured lines show the secular trend of each sea level time series, which is normalized by the standard deviation of the linear detrended time series. The dashed lines show the two-standard-deviation of the secular trend derived from randomly generated AR(1) red noise with the corresponding lag-1 auto-correlation coefficient, as indicated in the legend. Graphic: Chen et al., 2017 / Nature Climate Change

By Alister Doyle
26 June 2017
OSLO (Reuters) – The rise in global sea levels has accelerated since the 1990s amid rising temperatures, with a thaw of Greenland’s ice sheet pouring ever more water into the oceans, scientists said on Monday.The annual rate of sea level rise increased to 3.3 millimeters (0.13 inch) in 2014 – a rate of 33 centimeters (13 inches) if kept unchanged for a century – from 2.2 mm in 1993, according to a team of scientists in China, Australia, and the United States.Sea levels have risen by about 20 cms in the past century and many scientific studies project a steady acceleration this century as man-made global warming melts more ice on land.Until now, however, scientists have found it hard to detect whether the rate has picked up, is flat or has fallen since 1990. The study found that early satellite data had exaggerated the rate of sea level rise in the 1990s, masking the recent acceleration.The confirmation of a quickening rise “highlights the importance and urgency” of working out ways to cut greenhouse gas emissions and to protect low-lying coasts, the scientists wrote in the journal Nature Climate Change. [more]

Global sea level rise accelerates since 1990, study shows
Monthly mean time series of Greenland and Antarctic ice sheet mass losses. Blue line is the data available at http://imbie.org/data-downloads from the and red line is the data from GRACE record. Black dots denote the joint time series in 2003. Graphic: Chen et al., 2017 / Nature Climate Change

By John Church, Christopher Watson, Matt King, Xianyao Chen, and Xuebin Zhang
27 June 2017
(The Conversation) – Contributions to the rate of global sea-level rise increased by about half between 1993 and 2014, with much of the increase due to an increased contribution from Greenland’s ice, according to our new research.Our study, published in Nature Climate Change, shows that the sum of contributions increased from 2.2mm per year to 3.3mm per year. This is consistent with, although a little larger than, the observed increase in the rate of rise estimated from satellite observations.Globally, the rate of sea-level rise has been increasing since the 19th century. As a result, the rate during the 20th century was significantly greater than during previous millennia. The rate of rise over the past two decades has been larger still.The rate is projected to increase still further during the 21st century unless human greenhouse emissions can be significantly curbed.However, since 1993, when high-quality satellite data collection started, most previous studies have not reported an increase in the rate of rise, despite many results pointing towards growing contributions to sea level from the ice sheets of Greenland and Antarctica. Our research was partly aimed at explaining how these apparently contradictory results fit together.

Changes in the rate of rise

In 2015, we completed a careful comparison of satellite and coastal measurements of sea level. This revealed a small but significant bias in the first decade of the satellite record which, after its removal, resulted in a slightly lower estimate of sea-level rise at the start of the satellite record. Correcting for this bias partially resolved the apparent contradiction.In our new research, we compared the satellite data from 1993 to 2014 with what we know has been contributing to sea level over the same period. These contributions come from ocean expansion due to ocean warming, the net loss of land-based ice from glaciers and ice sheets, and changes in the amount of water stored on land.Previously, after around 2003, the agreement between the sum of the observed contributions and measured sea level was very good. Before that, however, the budget didn’t quite balance.Using the satellite data corrected for the small biases identified in our earlier study, we found agreement with the sum of contributions over the entire time from 1993 to 2014. Both show an increase in the rate of sea-level rise over this period.The total observed sea-level rise is the sum of contributions from thermal expansion of the oceans, fresh water input from glaciers and ice sheets, and changes in water storage on land. IPCCAfter accounting for year-to-year fluctuations caused by phenomena such as El Niño, our corrected satellite record indicates an increase in the rate of rise, from 2.4mm per year in 1993 to 2.9mm per year in 2014. If we used different estimates for vertical land motion to estimate the biases in the satellite record, the rates were about 0.4mm per year larger, changing from 2.8mm per year to 3.2mm per year over the same period.

Is the whole the same as the sum of the parts?

Our results show that the largest contribution to sea-level rise – about 1mm per year – comes from the ocean expanding as it warms. This rate of increase stayed fairly constant over the time period.The second-largest contribution was from mountain glaciers, and increased slightly from 0.6mm per year to 0.9mm per year from 1993 to 2014. Similarly, the contribution from the Antarctic ice sheet increased slightly, from 0.2mm per year to 0.3mm per year.Strikingly, the largest increase came from the Greenland ice sheet, as a result of both increased surface melting and increased flow of ice into the ocean. Greenland’s contribution increased from about 0.1mm per year (about 5% of the total rise in 1993) to 0.85mm per year (about 25% in 2014). [more]

Greenland’s ice largely responsible for the accelerating pace of sea-level rise

ABSTRACT: Global mean sea level (GMSL) has been rising at a faster rate during the satellite altimetry period (1993–2014) than previous decades, and is expected to accelerate further over the coming century1. However, the accelerations observed over century and longer periods2 have not been clearly detected in altimeter data spanning the past two decades3, 4, 5. Here we show that the rise, from the sum of all observed contributions to GMSL, increases from 2.2 ± 0.3 mm yr−1 in 1993 to 3.3 ± 0.3 mm yr−1 in 2014. This is in approximate agreement with observed increase in GMSL rise, 2.4 ± 0.2 mm yr−1 (1993) to 2.9 ± 0.3 mm yr−1 (2014), from satellite observations that have been adjusted for small systematic drift, particularly affecting the first decade of satellite observations6. The mass contributions to GMSL increase from about 50% in 1993 to 70% in 2014 with the largest, and statistically significant, increase coming from the contribution from the Greenland ice sheet, which is less than 5% of the GMSL rate during 1993 but more than 25% during 2014. The suggested acceleration and improved closure of the sea-level budget highlights the importance and urgency of mitigating climate change and formulating coastal adaption plans to mitigate the impacts of ongoing sea-level rise.

The increasing rate of global mean sea-level rise during 1993–2014