Climate change will bring and has already brought a wide variety of threatening destruction to human existence. Some of these are wellknown and already operative, like the wildfires racing along California's freeways or the permanent droughts that have been upsetting Mediterranean farmers. But are these all terrible disasters we can come up with that are brought about by climate change?
Absolutely not. None of the challenges posed by our warming climate has appeared larger in the popular imagination than sealevel rise, as global populations and wealth are heavily concentrated in lowlying coastal cities.The best available models suggest that 37 million people currently live in places that will be below high tide by 2050—in an optimistic lowcarbonemissions scenario (设想).
Or rather, that's what such models suggested before this week. On Tuesday，a new study revealed that those alarming statistics were wildly inaccurate. The actual impacts of sealevel rise are going to be much, much worse.
Previous estimates of the impact that rising tides would have on coastal cities relied on essentially a threedimensional map of Earth obtained from satellite readings. But those readings were fundamentally unreliable because they often measured the planet's upper surfaces—such as treetops and tall buildings—rather than its ground level. These mistakes led scientists to overestimate the elevation (海拔) of many regions of Earth.
In a new study published by the journal Nature Communications, scientists from Princeton University detail this methodological problem，then use artificial intelligence to determine the previous literature's error rate.Their research yields some amazing updates to our conventional understanding of what the next century has in store for our coastlines.
In its optimistic scenario, the Princeton study projects that lands currently occupied by 150 million people will lie below high tide in 2050.But as warming destroys many of the world's agricultural regions, climate change could accelerate migration from rural areas to coastal cities.
The new study does include one piece of slightly encouraging news. While previous models suggested that 28 million humans currently live in places that already lie below high tide, the actual number is closer to 110 million—which means seawalls and other barriers have proven sufficient to keep many cities dry even as sea levels have risen around them. Still, the scale of barrier construction necessary to save lowlying cities from collapse is now, apparently, far greater than previously understood when the task already looked terribly expensive，particularly for developing countries.
If the Princeton researchers' projections are correct, avoiding mass death and suffering in the coming decades will require not only rapidly reducing carbon emissions and strengthening construction of seawalls but also furthering mass migrations away from lowlying cities and islands and toward higher ground.
