Short-lived compounds like greenhouse gas methane stay in the atmosphere just between a year and a few decades. However, researchers have found that they can cause lingering warmth that can lead to sea levels rising for centuries long after the compounds have been cleared from the atmosphere.

In a study published in the journal Proceedings of the National Academy of Sciences, researchers from the Simon Fraser University and MIT showed that even if all greenhouse gas emissions stop tomorrow, the world will still be experiencing rising sea levels hundreds of years after.

"It's all the more reason why it's important to understand how long climate changes will last, and how much more sea-level rise is already locked in," said Susan Solomon, study author.

She used the Polynesian island nation of Tuvalu as an example. As it is located barely above sea level, is the country already doomed? Will Tuvalu still go under even if greenhouse gas emissions cease tomorrow?

Supported by NASA and the Natural Sciences and Engineering Research Council of Canada, the study also included work from Daniel M. Gilford and Kirsten Zickfeld.

Greenhouse Gases In The Atmosphere

Recent studies have shown that sea-level rise related to carbon dioxide emissions will continue for over 1,000 years. However, unlike short-lived compounds like methane, carbon dioxide's effects can be attributed to the fact that it stays long in the atmosphere, sticking around for centuries after it has been released from ground sources.

It has been established that methane has a shorter lifetime but it was not clear how exactly the greenhouse gas would affect sea-level rise on the long term. To find out, Solomon and colleagues came up with a variety of climate scenarios with the help of the Earth Systems Model of Intermediate Complexity (EMIC), a climate model simulating atmospheric and ocean circulation to create climate change projections over the course of decades, centuries and even millennia.

With the EMIC, the researchers were able to calculate average sea-level rise and global temperature in response to anthropogenic carbon dioxide and methane emissions.

Long-Term Effects Of Methane

To evaluate sea level response to methane emissions, the researchers used three years as yardsticks: 2050, 2100 and 2150. In all three, EMIC showed methane was cleared quickly from the atmosphere and there was a drop in atmospheric warming, but the greenhouse gas continued to influence sea-level rise for hundreds of years after. Additionally, the researchers observed that the longer it takes for methane emissions to be reduced, the longer sea levels remained elevated.

It's a good thing that countries are putting climate agreements in place but the researchers also saw that a past regulation on pollutants had effectively reduced emissions of ozone-depleting compounds all over the world. Ratified in 1989, the Montreal Protocol is an agreement involving 197 countries to phase out chlorofluorocarbons. It was originally developed to protect the ozone layer but it also had a hand in helping prevent sea levels from rising. Had chlorofluorocarbon use continued, it would have resulted in up to 6 inches of additional sea-level rise by 2050.

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