Greenland's ice sheet is melting as fast as at any time in the last 12,000 years, study shows

Meltwater carves into the ice sheet near the Sermeq Avangnardleq glacier in Greenland in August 2019.

(CNN)We've known for some time now that Greenland's ice sheet is melting at an alarming rate.

Greenland lost more ice last year than in any year on record, and the melting has accelerated rapidly since the 1990s.
But in the context of Earth's 4.5 billion-plus year history, melting in any one year or even a few decades amounts to the blink of an eye.
    Whether the rapid disintegration we're seeing on Greenland today compares to anything that has happened in the past is a question on which the science is not completely clear.
    Now, a new study published in the journal Nature provides some answers, and it is not good news: The rate of melting we're seeing today already threatens to exceed anything Greenland has experienced in the last 12,000 years.
    Over the last two decades, Greenland's ice sheet has melted at a rate of roughly 6,100 billion tons per century, a rate approached only during a warm period that occurred between 7,000 and 10,000 years ago.
    "We know there's a lot of year-to-year variability, so what we were interested in doing is capturing the more meaningful trends over decades and maybe up to a century," said Jason Briner, a professor of geology at the University at Buffalo and the lead author of the study. "And when you do that, and think about the direction that Greenland is heading this century, it's pretty clear we're in quite anomalous times."
    A chart provided by the study authors shows how rapidly Greenland's melt has accelerated, and how unprecedented it is compared to rates that occurred over the last 12,000 years.
    The big difference between now and then? The influence of human activity.
    The melting seen today is driven primarily by greenhouse gas emissions, whereas the warming that occurred thousands of years ago was a result of natural climate variability, Briner said.
    How much Greenland melts going forward is up to us.
    Under a scenario where humans continue to raise concentrations of heat-trapping gases in the atmosphere, Greenland's ice loss could reach unprecedented levels, with more than 35,900 billion tons of ice potentially lost by the end of this century.
    Right now, Briner says current melt rates track closely with this worst-case scenario.