As average global temperatures have steadily increased over the past four decades (Figure 1) eustatic sea levels have also risen. Since 1993, when satellite measurements began, sea levels have risen by just under 10 cm. Since the 1880s, when reliable record-keeping of tides began, they’ve gone up by more than 23 cm (Figure 2). The Intergovernmental Panel on Climate Change (IPCC) predicts that sea levels will continue to rise at an ever-increasing rate.
These figures hide some large regional differences. Dynamic ocean currents plus differences in temperature and salinity mean that sea levels vary significantly around the globe. At the same time land levels away from the equator are still rising and falling in response to ice loading during glaciations that occurred tens of thousands of years ago. Land levels also change owing to extraction of natural resources and drainage activities by humans.
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