Peak global mean temperature, atmospheric CO2, maximum global mean sea level (GMSL), and source(s) of meltwater. Light blue shading indicates uncertainty of GMSL maximum. Red pie charts over Greenland and Antarctica denote fraction (not location) of ice retreat. Graphic: Dutton, et al., 2015

By Ari Phillips
10 July 2015

(Climate Progress) – A major new analysis on the impact melting polar ice sheets could have on sea level rise has given rise to some worrisome conclusions.

Researchers found that sea levels increased some 20 feet during three warming periods of 1.8 to 3.6°F (1 to 2°C) that took place at different interglacial periods over the past three million years. The study’s findings mean that the planet could be in for major sea level rise even if warming is kept to 2°C — a limit that the world is set to exceed without major action on climate change.

Published in the journal Science, the review compiled more than 30 years of research from scientists around the world to show that changes in the planet’s climate and sea levels are closely linked. It found that even a small amount of warming can lead to significant sea level rise.

Andrea Dutton, a geochemist at the University of Florida, led the study. She told ThinkProgress that her team looked at periods of time that took place 125,000, 400,000, and three million years ago in order to get a range of possibilities, as no one will be a perfect analog to the warming period the Earth is experiencing now.

“What’s important to note is that the ice sheets appear to be out of equilibrium with the climate based on what’s happened in the past,” she said.

Last year was the warmest on record — a record that 2015 is on pace to break. The International Energy Agency recently warned that temperatures could jump by as much as 7.7°F (4.3ºC) by 2100 — more than double the amount that caused sea level to rise 20 feet in previous eras. Global average temperatures have already risen almost 1.8°F (1ºC) since the 1880s. […]

“People always talk about the year 2100 when they talk about sea level rise,” she said. “It’s not going to stop then; it will keep rising after. It’s important to realize the decisions we make today will influence that trajectory.”

Sea level rise of 10 or 20 feet could impact hundreds of millions of people living in coastal areas around the world. Many major urban centers — New York City, Hong Kong, Tokyo, Bangkok — would be overcome by the elevated seas. The authors of the study point out that most of Florida has an elevation of 50 feet or less, and Miami averages just six feet about sea level. Dhaka, the capital of Bangladesh, has some 15 million residents all inhabiting the low-lying coastal delta. […]

When sea levels rise, there are other corollary impacts, including storm surge, erosion and inundation, according to Anders Carlson, an Oregon State University glacial geologist and paleoclimatologist, and co-author of the Science study.

Carlson also said that we are starting to see these changes already.

“It takes time for the warming to whittle down the ice sheets,” he said. “But it doesn’t take forever. There is evidence that we are likely seeing that transformation begin to take place now.”

Carlson told ThinkProgress that “we are nearing one degree Celsius warming,” and that the “worst case scenario is what we are already on.” [more]

Study: We’re Already In The ‘Worst Case Scenario’ For Sea Level Rise

ABSTRACT: Interdisciplinary studies of geologic archives have ushered in a new era of deciphering magnitudes, rates, and sources of sea-level rise from polar ice-sheet loss during past warm periods. Accounting for glacial isostatic processes helps to reconcile spatial variability in peak sea level during marine isotope stages 5e and 11, when the global mean reached 6 to 9 meters and 6 to 13 meters higher than present, respectively. Dynamic topography introduces large uncertainties on longer time scales, precluding robust sea-level estimates for intervals such as the Pliocene. Present climate is warming to a level associated with significant polar ice-sheet loss in the past. Here, we outline advances and challenges involved in constraining ice-sheet sensitivity to climate change with use of paleo–sea level records.

Sea-level rise due to polar ice-sheet mass loss during past warm periods



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