How Do We Calculate Rising Sea Levels
Driven by climate change, sea level rose 11–16 cm in the twentieth century. Even with sharp, immediate cuts to carbon emissions, sea levels could rise another 0.5 m this century. Under higher emissions scenarios, twenty-first century rise may approach 2 m.How do we know the sea level is rising – and how do we measure it How do we measure these sea-level changes? In this educational film from the European Space Agency’s (ESA), Kelsea Brennan-Wessels explains.
What Causes Sea Level Rise?
Sea level rise is caused primarily by two factors related to global warming: the added water from melting ice sheets and glaciers and the expansion of seawater as it warms. The graph, derived from coastal tide gauge data, shows how much sea level changed from about 1870 to 20132Facts Sea Level, NASA.What causes sea level rise
Polar Ice Melt
A large fraction of the Earth’s fresh water is frozen: It’s stored in glaciers all around the world, and in both the Greenland and Antarctic ice sheets. When this ice melts or calves off, the water flows into the oceans and sea levels rise. If all glaciers and ice sheets melted, global sea level would rise by more than 60 meters3Understanding Sea level – Ice melt, NASA
Thermal Expansion
The warming of Earth is primarily due to accumulation of heat-trapping greenhouse gases, and more than 90 percent of this trapped heat is absorbed by the oceans. As this heat is absorbed, ocean temperatures rise and water expands. This thermal expansion contributes to roughly one-third of the global sea-level rise4Understanding Sea level – Thermal Expansion, NASA.
Other Sea Level Rise Factors
The oceans form an integral part of the global water cycle: precipitation, evaporation, and rivers move large amounts of water between land and the oceans. Since the amount of water on Earth doesn’t change, a change of the amount of water in one component must be offset against the other. For example, heavy rains over Australia, Southeast Asia, and the Amazon Basin — and the subsequent storage of large amounts of water on land — caused a drop in global sea level of 1 centimeter during the 2010-2011 La Niña cycle.
Humans also directly change the amount of water on land, and thus the amount of water in the oceans. The global construction of large dams in rivers has led to the impoundment of an amount of water equal to 3 centimeters of sea level5Understanding sea level rise – landwater storage, NASA.