Climate change: World on course for 'metres of sea level rise', scientists warn

Past predictions of sea level rises have turned out to be "on the money", with scientists now warning we're on track for "metres of sea level rise" close to the worst-case scenarios they can think of.

The Intergovernmental Panel on Climate Change has outlined three different potential outcomes this century - one of emissions resulting in 2C of warming (called RCP2.6), one in which the world fails to take any meaningful action whatsoever (RCP8.5) and something in-between these two (RCP4.5). 

"The analysis of the recent sea level data indicate the world is tracking between RCP4.5 and the worst-case scenario of RCP8.5," said John Church, a climate scientist at the University of New South Wales.

Australian and Chinese researchers looked at predictions made by the IPCC using computer modelling, and found they were "closely consistent with observations on both global and regional scales" made between 2007 and 2018.

"Our analysis implies that the models are close to observations and builds confidence in the current projections for the next several decades,"  said Prof Church.

"If we continue with large ongoing emissions as we are at present, we will commit the world to metres of sea level rise over coming centuries."

Just how much of that rise will happen in our lifetimes remains to be seen. While the observations place us on a trajectory between the middle- and worst-case scenarios, that could quickly change as unexpected feedback loops come into play.

"While the confirmation of the projection trends gives us confidence in current understanding of near future sea-level change, it leaves open questions concerning late 21st century non-linear accelerations from ice-sheet contributions," the study, published in journal Nature Communications, reads.

In other words, it's possible climate change could speed up - less ice means more trapped methane being released, as well less of the sun's energy being reflected into space, both heating up the planet.

How predictions have aligned with reality.
How predictions have aligned with reality. Photo credit: Nature Communications

"A cycle of self-reinforcing processes is established," one study concluded last year. "The process is self-sustaining, at least until all carbon is released from permafrost and all ice is melted."

Another non-linear acceleration is water vapour - as the atmosphere heats, more water evaporates into vapour, which itself is a strong greenhouse gas - leading to more warming.

"There remains a potential for larger sea level rises, particularly beyond 2100 for high emission scenarios," said Prof Church. "Therefore, it is urgent that we still try to meet the commitments of the Paris Agreement by significantly reducing emissions."