Study suggests policy makers ask what level of sea level rise is reasonable, and then limit greenhouse gas emissions accordingly.

COURTESY OF THE NATURE CONSERVANCY - The Pacific Ocean glistens below Cascade Head on the Oregon Coast.
A new study co-authored by Oregon State University researchers argues the world should start to measure the impact of climate change by gauging the rise in sea levels as well as rising temperatures.

"One way to begin looking at it from a policy standpoint is to ask the question, 'how much sea level rise can we tolerate?' "

says Peter Clark, an OSU climate scientist and lead author on the study.

"The more carbon we emit, the more sea level rise we are committed to," Clark said. "We need to ask if there is a target for sea level rise – much like the 2-degree threshold that was established for global warming."

The study appeared this month in the scientific journal Nature Climate Change.

"When we pump more carbon into the atmosphere, the effect on temperature is almost immediate," Clark stated in a news release about the new study. "But sea level rise takes a lot longer to respond to that warming."

Ice sheets take time to melt, "so the resulting sea level rise will continue for hundreds to thousands of years after we're done emitting carbon," Clark said.

Roughly one billion people live in coastal areas that could be upended by a major rise in sea levels.

The Paris climate agreement set goals for greenhouse gas emissions based on projected increases in temperature.

If humans continue to burn fossil fuels so that temperatures meet the 2-degree Celsius threshold outlined in the Paris Agreement, global mean sea level rise may reach nearly 30 feet, though it will take many years to get there, the study notes.

The researchers say that keeping sea level rise to 3 to 9 meters – roughly 10 to 30 feet – over several thousand years is likely too optimistic, unless society finds ways to quickly reach zero emissions and then lower the greenhouse gases in the atmosphere.

Since the beginning of the Industrial Revolution, people have emitted roughly 600 billion tons of carbon dioxide or its equivalents into the atmosphere, resulting in an increase of roughly one degree Celsius in overall global temperature. But if cumulative CO2 emissions rise to 3,000 billion tons, the study shows that will result in a sea level rise of between 30 and 40 meters.

"The sea level rise we've seen thus far is just the tip of a very large iceberg," said Alan Mix, an OSU oceanographer and another co-author of the study. "The big question is whether we can stabilize the system and find new energy sources. If not, we're on the way to a slow-motion catastrophe. The question becomes: What do we owe our grandchildren, and their grandchildren?"

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