During Hurricane Harvey, the Houston neighborhood of Harrisburg-Manchester didn’t flood as much as some other parts of the city. But if greenhouse gas emissions continue unchecked, it won’t be so lucky: the area will eventually be permanently under water because of sea level rise.
A new study and a series of visualizations show the long-term consequences of global warming on sea levels in cities around the world. Most research on sea level rise has focused on what might happen, decade by decade, this century. “That’s extremely important work, because it helps us with our immediate planning,” says Benjamin Strauss, CEO and chief scientist at the nonprofit Climate Central, and the lead author of the new paper in Environmental Research Letters. “But we wanted to highlight the big picture here, and the hundreds of years of unremitting sea level rise that we set in motion depending on what we do.”
If the average global temperature rises 3 degrees Celsius, something that is likely to happen by the end of the century if we continue on the current trajectory, ice sheets will melt enough water to eventually cover an area of land where 10% of today’s global population currently lives. In China alone, 43 million people now live on land that will be under water after 3 degrees of warming. After 4 degrees of warming, 50 major cities will be on a path to face unprecedented exposure and will either have to invest in massive protection or abandon some areas. Many small island nations, like the Bahamas, face near total loss of the areas where most of the population lives now, the study says.
The study doesn’t project the timing of that sea level rise. Past research has looked at timeframes ranging from as long as 2,000 years to as little as 200 years. “Ice takes time to melt,” says Strauss. “The big ice sheets on the planet haven’t yet come close to catching up to the warming that we’ve already caused.” While the exact timing is challenging to project, it’s easier to say what the eventual consequences will be: There’s a certain amount of water trapped in ice sheets now, and whenever it does completely melt, low-lying coastal cities will flood in predictable ways. The sea level rise will be irreversible, even if we cool the planet down.
If emissions drop steeply right now, reaching net zero by the middle of the century (and giving us a chance of limiting warming to 1.5 degrees Celsius instead of 3 degrees), the difference in sea level rise won’t be immediately obvious. But it could reduce the worst extents of it by about 50%. It would also slow down the rate sea level rise, giving cities more time to adapt. “I don’t believe there’s ever been a time in human history when people could understand that the actions they took across 10 years would have consequences for 1,000, or 10,000 years. If, on one hand, that’s a really heavy responsibility, and on the other hand, it’s a really huge opportunity to make a difference for so many generations of people all around the world. there’s a real choice here, and how we’re going to be remembered in the history books. People who are alive today.”
The visualizations, which look at the impacts of sea level rise at specific locations, are designed to help make the problem more tangible. “I think when we talk about climate change, we so often get wrapped up in abstractions,” he says. “And this is a way to make it as simple as a poster. As simple as, you know, do you choose Door A or do you choose Door B? And here’s what they look like.”