Following is a transcript of the video.
Narrator: Ninety-nine percent of all freshwater ice on Earth is sitting on top of Greenland and Antarctica, and each year, a little more of it melts into the ocean. Normally, it would take hundreds to thousands of years for it all to melt away. But what if something happened that caused a massive global melt overnight?
As we slept, sea levels would rise by a whopping 66 meters. Coastal cities like New York, Shanghai, and London would drown in the apocalyptic mass flood, forcing up to 40% of the world's population out of their homes. While all this chaos ensues aboveground, something equally sinister is happening below. All that rising saltwater will infiltrate groundwater reserves farther inland, forcing its way into nearby freshwater aquifers. You know, the ones that supply our drinking water, irrigation systems, and power-plant cooling systems? All those aquifers would be destroyed. Not good.
On top of that, the ice on Greenland and Antarctica is made of freshwater, so when it melts, that's about 69% of the world's freshwater supply that's going straight into the oceans. This will wreak havoc on our ocean currents and weather patterns. Take the Gulf Stream, for example. It's a strong ocean current that brings warm air to northern Europe and relies on dense, salty water from the Arctic in order to function. But a flood of freshwater would dilute the current and could weaken or even stop it altogether. Without that warm air, temperatures in northern Europe would plummet, and that could spawn a mini ice age, according to some experts.
That's not even the worst of it. Take a look at what will happen when that last 1% of freshwater ice that's not part of Greenland or Antarctica thaws. Some of that 1% is sitting in glaciers farther inland. The Himalayan glaciers specifically pose one of the largest threats because of what's trapped inside: toxic chemicals like dichlorodiphenyltrichloroethane, or DDT. Scientists discovered that glaciers like this can store these chemicals for decades. But as they thaw, those glaciers release the chemicals into rivers, lakes, and groundwater reserves, poisoning each one as they go.
The rest of that 1% is hanging out underground, mostly in the Arctic tundra, as something called permafrost. Permafrost is organic matter that's been frozen in the ground for two-plus years. Now, one of the most immediate problems with thawing permafrost would be mercury poisoning. That's right: There are an estimated 15 million gallons of mercury stored up in the Arctic permafrost. That's almost equal to the amount of mercury everywhere else on Earth. On top of that, the organic matter in permafrost is a tasty meal for microorganisms. After they digest it all, they fart out two of the most potent greenhouse gases out there, carbon dioxide and methane. Scientists estimate this could double the current levels of greenhouse gases in the atmosphere, and potentially cause global temperatures to rise by 3.5 degrees Celsius compared to today.
That might not sound like much, but say goodbye to that mini European ice age, and even rivers and lakes around the world. They'd evaporate from the higher temperatures and cause mass droughts and desert-like climates. And all that extra water vapor in the atmosphere would fuel more frequent and stronger storms, floods, and hurricanes. So all of that newly established coastline on the eastern US would be one of the last places you'd want to live. Instead, there would be mass migrations to Canada, Alaska, the Arctic, and even what's left of the Antarctic.
And you're right, this is probably never going to happen. After all, there's enough ice right now to cover the entire continent of North America in a sheet a mile thick. So the next time you hear about record-breaking heat or ultra-powerful hurricanes, at least you know that it could be worse. But scientists estimate that if we don't take action and global temperatures increase by just 1 degree Celsius, the effects of climate change we already see today will be irreversible. So yes, it could be worse, and it will be if we're not careful.
EDITOR'S NOTE: This video was originally published in September 2019.