A new study says we should be expecting an average sea-level rise in excess of 1 meter by 2100 and 5 meters by 2300 if we don’t meet current targets for the reduction of greenhouse gas emissions.

The analysis used projections compiled by over 100 international experts to estimate changes in sea levels under low- and high-emission scenarios, the team explains, in order to help policymakers have a better understanding of “the state of the science” on this threat.

The waters are coming

“The complexity of sea-level projections, and the sheer amount of relevant scientific publications, make it difficult for policymakers to get an overview of the state of the science,” says Professor Benjamin Horton, Acting Chair of Nanyang Technological University, Singapore (NTU Singapore) Asian School of the Environment, who led the survey.

“To obtain this overview, it is useful to survey leading experts on the expected sea-level rise, which provides a broader picture of future scenarios and informs policymakers so they can prepare necessary measures.”

The most optimistic scenario analyzed in this paper considered that global warming would only increase temperatures by 2 degrees Celsius above pre-industrial levels, which would translate to a rise of 0.5 meters (roughly 2 feet) by 2100, and 0.5 to 2 meters by 2300. The high-emission scenario would involve 4.5 degrees Celsius of warming and would cause between 0.6 to 1.3 meters (2 to 4 feet) sea rise by 2100, and 1.7 to 5.6 meters by 2300.

These estimations exceed those of the International Panel on Climate Change (IPCC), who set the current targets under the Paris Agreement. Researchers from The University of Hong Kong, Maynooth University (Ireland), Durham University (UK), Rowan University (U.S.), Tufts University (U.S.), and the Potsdam Institute for Climate Impact Research (Germany) took part in this study. They were chosen as they are some of the most active publishers or scientific studies on the topic (they all had at least six published papers pertaining to sea-level rise since 2014).

The large difference in sea level rise seen in this paper “provides a great deal of hope for the future, as well as a strong motivation to act now to avoid the more severe impacts of rising sea levels,” according to Dr. Andra Garner, Assistant Professor of Environmental Science at Rowan University and co-author of the study.

Still, the findings also underscore just how important it is for policy to be set in place in order to limit emissions and sea-level rise. How bad the outcome is depends entirely on how we act, and the decisions we make right now.

However, despite the sheer wealth of expertise that went into the study, there are still uncertainties. The team points to the Greenland and Antarctic Ice Sheets as the largest unknowns, as their behavior can have dramatic effects on how sea levels evolve in the future. Both of these ice sheets are key reference points for climate change and increases in sea levels, as they hold important quantities of water — and they’re both melting at much higher rates than they would naturally.

Yet, not all is lost. Climate systems have a great deal of inertia to them (as do all systems working on such scales) but taking proactive measures to limit greenhouse gas emissions would still have a significant effect.

So while the worst-case scenario definitely does seem bleak, it’s in no way out of our hands. We can choose to make things better, to limit the impact we have on the planet and the repercussions that will have on our society in the future.

The paper “Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey,” has been published in the journal Climate and Atmospheric Science.