Sea level
Although sea level is rising in many regions of the oceans, in other places it is falling. At NOC we study the causes of sea level change and how sea level will change globally and regionally over the next few decades to centuries. By 2050 it is expected that 2 billion people (over 20% of the global population) will live within 100 km of the coast, many of them in megacities with populations in excess of 20 million. Coastal communities will be at increasing risk of flooding linked to rising sea level and storms. Against this backdrop it is vital to improve predictions of regional sea level change to inform future coastal planning and to develop more reliable flood forecasting systems.
Causes of sea level change
Sea level varies on a wide range of time scales, from minutes to millions of years. Sea level rise is a combination of ocean volume and ocean mass changes.
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Measuring sea level change
Mean sea level has risen at approximately 1.8 mm per year over the last 55 years, according to observations from 177 coastal tide gauges with near global coverage (and correcting for vertical land movements due to the elastic recovery from the last ice age).
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Tides
Tides are caused by the combined effects of gravity and the revolution of the Earth-moon system about its common centre of mass. At this point (which lies within the solid Earth) the gravitational attraction between Earth and moon exactly balances the forces required to maintain the moon’s orbit. Elsewhere the two forces are not in balance and give rise to the so-called tide generating force. This explains why there are two tides per day at most places around the globe – described as semidiurnal tides
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Tide gauges
Tide gaugesare instruments that allow us to measure the movement of the sea surface and they have been used to do this in the UK since the mid-19th century. Due to technological advances, there are now many different types of tide gauge.
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