Satellites trace sea level change

Jonathan Amos in the BBC: A major reassessment of 18 years of satellite observations has provided a new, more detailed view of sea-level change around the world. Incorporating the data from a number of spacecraft, the study re-affirms that ocean waters globally are rising by just over 3mm/yr.

But that figure, according to the reassessment, hides some very big regional differences - up and down. The Philippine Sea, for example, has seen increases in excess of 10mm/yr . Part of that signal reflects the great fluctuation in winds and sea-surface temperature across the Pacific Ocean known as the El Nino/La Nina-Southern Oscillation.

"The trend map is really a way of looking at average field changes over the 20 years," explained Steven Nerem of the University of Colorado, US. "The places where you see high trends probably won't have high trends in another 20 years. A lot of this is decadal variability that will average out over the longer time series, which is why we need more missions to understand where this variability is."

Paolo Cipollini from the UK's National Oceanography Centre added: "Many of the features in the trend map correspond to long-term variations in the ocean currents."

This is evident if you look for some of the well-established mass movements of water - such as the Gulf Stream arching across the North Atlantic from the eastern US, or the Kuroshio Extension reaching out from Japan into the Pacific....