Rising seas and climate change: Everything you need to know

Oceans rose and fell hundreds of metres over many millenniums. How is our current situation different?

While it is true that sea levels have shifted radically over geologic time, they have actually been relatively stable in most places for the past 5,000 years. U.S. oceanographer John Englander, who spent the past decade raising awareness about rising sea levels, said humanity enjoyed this stability because the Earth's climate was transitioning from a warming period to a cooling period.

That era is over. Tide gauges (and more recently, satellite observations) reveal that the world's oceans have risen gradually since the mid-19th century. "The records show that sea level rose over the 20th century, between one and two millimetres per year," said Thomas James, a research scientist at Geological Survey of Canada, which is part of Natural Resources Canada. "But in the last two, two-and-a-half decades, sea level has been rising at more than double that. It's now in excess of three millimetres per year." This acceleration is expected to continue, translating into seas changing at rates not observed in millenniums.

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