The statistics are grim. Collectively, the Antarctica and Greenland ice sheets are losing around 466 tons of ice an average of one year. That is more than 1.1 billion tons every day. The water from these liquefying ice sheets flows into the oceans and the sea level rises higher and higher.
There is little evidence that the melting of the ice sheets will slow down anytime soon. In any case, it will get exponentially faster, scientists say. Like the glaciers themselves, it is a process that starts slowly but carries terrifying momentum.
The ice sheets store 99 percent of all fresh water on Earth. It's a staggering amount of water, and the meaning is immediately apparent if you've ever stood on the shores of one of North America's Great Lakes and gazed at the watery horizon. All that water, enough that it appears to be an inland sea, is only a fraction of what is transported in the solid mass of Antarctica.
Together, the ice in Antarctica and Greenland would raise Earth's sea levels by about 70 feet if everything melted. The seas would eat up a significant portion of the planet's current land, drowning coastal cities like New York, Los Angeles and Houston. Low-lying Florida would just disappear. And once a snowy wasteland, Antarctica would become a rocky archipelago, free of the overlying ice and partially submerged by rising seas.
But an Earth that is completely ice-free won't happen in our lifetimes, or probably even in the next few thousand years. By most projections, sea level rise will be about 12 inches by 2100 – much less than is possible. By the next century, Earth's ice sheets will still be firmly in place, when they are reduced in size.
The last thing we need to take away from that fact, however, is a sense of complacency. Even small changes in sea level have serious consequences. That one foot of sea-level rise could devastate low-lying coastal cities and force massive migrations inland. And melting glaciers can alter ocean currents, which could change global weather patterns in unpredictable ways.
The icy earth
The ice sheets that adorn Earth's north and south poles are so ingrained in our mental geography that their presence is often little more than an afterthought. Even preschoolers know to splash some white on the top and bottom of a drawing of the Earth. But turn the clock back some 40 million years, and those icy promontories disappear. Indeed, for most of Earth's existence, the poles have been ice-free.
In the time before our current Ice Age (which simply refers to the fact that there is permanent ice on the surface), dinosaurs roamed Antarctica and alligators swam in Alaska. Even in more recent times, the planet has been significantly warmer and wetter than it is today.
During the mid-Pliocene, about 3 million years ago, temperatures were 5 to 9 degrees Fahrenheit warmer than they are today, and the seas were as much as 50 feet, to over 75 feet, higher.
It's not uncommon for the ice sheets to be smaller and sea levels significantly higher than today. But, as with global temperatures, rapid changes in our natural world have serious consequences for the ecosystems and organisms that depend on it.
Less ice means more ocean
Most of the sea level rise today is the result of two things: melting ice and expanding water. As the water heats up, it becomes less dense, and some estimates suggest that as much half the sea level rise this decade is due to warmer ocean waters taking up more space. But with the rate of melting expected to only increase, disappearing ice sheets will become the main factor in sea level rise in the future.
The melt water that makes the oceans rise comes from the ice sheets of Greenland and Antarctica. While the Arctic ice sheet is also getting smaller, it's not contributing to sea level rise, because that ice is already floating in the ocean – it takes up all the space it can.
Estimates of how much the melting ice of Greenland and Antarctica is contributing to sea level rise vary, although scientists have consistently improved their models. One study estimates that since the satellite record began in the 1990s, the two ice sheets Have contributed a total of 17.8 millimeters to sea level rise. Another recent paper says Antarctica alone has contributed 0.36 millimeters per year to the rise in sea level, and a total of 14 millimeters since 1979. During that period, the ice sheet lost mass at an accelerating rate – from 44 billion tons per year between 1979 and 1990 to just as much 277 billion tons per year in 2017.
Although sea level rise is now measured in millimeters, that may soon change. Most studies indicate that ice loss and sea level rise will increase in magnitude over time. A study finds a noticeable tipping point in 2030, where under the worst-case scenario, the ice sheets start adding tens of millimeters to sea level every decade, ending with more than a foot of sea-level rise. That's about the same sea level rise per decade as we've seen in the past 30 years.
One reason for this could be that ice sheets are entering the ocean at an increasing rate. As warmer ocean water eats away at their base, the huge glaciers that stretch out of the mountains in Antarctica and Greenland and extend far into the ocean hold them back less.
The result is ice that falls into the ocean, where it can melt faster and faster. For example, a glacier in Greenland recently doubled its speed in just five years. In Antarctica, there are multiple ice sheets that scientists say are at high risk of collapse, including Thwaites Glacier, also called the & # 39; Doomsday Glacier & # 39; mentioned. Should it collapse and melt, it can raise sea levels by up to 90 cm.
Once started, it will probably be difficult to stop the process of the ice sheet breaking up. In fact, that means getting our emissions under control and putting a stop to global warming may not prevent the ice caps from melting
And while some evidence has shown that Antarctica may be gaining more ice than losing, as wetter conditions increase snowfall, more Recent research say that's not true. While some parts of the continent have seen more precipitation, Antarctica has lost ice on average since we started monitoring it.
So while the ice sheets won't disappear, that's largely irrelevant. There is so much water on Earth trapped in ice that the release of even a small portion of it can cause major changes. We just need to look back in time to see what to expect. During the last interglacial period, just over 100,000 years ago, Earth's temperatures were about 3 degrees warmer than they are today. That's about as warm as the The planet is expected to be in 2100, if we're lucky. Despite that relatively small change in temperature, it may have been sea level 10 feet higher than they are today. Is it a glimpse of our future? Time will tell.