Methane remains in the atmosphere for only about ten years. But short-lived greenhouse gases like methane may have centuries-long impact on the rise of sea levels, according to a new study published in the journal Proceedings of the National Academy of Sciences. There are two key factors driving sea levels to rise: the additional water from melting land ice, and the thermal expansion of seawater as it absorbs the atmospheric heat.
Heat expands the volume of water
Humans have been pumping large amounts of greenhouse gases into the atmosphere for more than a century. These gases cause the air temperatures to rise. Some of the atmospheric heat is absorbed by oceans. Anyone who has made a cup of tea on the stove knows that hot water expands in volume, said lead author Susan Solomon of the Massachusetts Institute of Technology (MIT). This process is called “thermal expansion.”
Though most climate scientists take thermal expansion into account when modeling their projections, they may not have previously realized how long the process lasts. The new study shows that even short-lived greenhouse gases like methane can drive sea level rise for centuries. It means even if we stop emitting greenhouse gases right now, the expansion effect would be irreversible in our lifetimes.
Why greenhouse gases have such a lasting impact
The effects last so long because of the way the ocean water moves. Warm water moves from the equator to the poles, where it cools down, goes to the bottom, and flows back to the equator, reports The Washington Post. As a result, the heat is carried throughout the world. Susan Solomon said in a statement that it might take hundreds of years before the heat is released back into the atmosphere.
Scientists studied several scenarios to analyze the impact of greenhouse gases on the thermal expansion of oceans. If it remains business as usual with high emissions through 2050 before the emissions stop abruptly, their effects will remain in the oceans for hundreds of years. For the study, researchers took into account the emissions of carbon dioxide, nitrous oxide, methane, halocarbons, chlorofluorocarbons, and hydrofluorocarbons.
Effects of carbon dioxide remains for more than 750 years
Their climate model suggested that 100 years after the emissions stop, about 75% of peak thermal expansion caused by methane – which stays in the atmosphere for just a decade – would persist. About 40% of peak thermal expansion still persists after 500 years. Scientists urged the global community to curb emissions at the earliest.
Carbon dioxide remains in the atmosphere for more than 200 years. If we stop emitting carbon dioxide in 2050, about 50% of the gas would remain in the atmosphere for at least 750 years.