SOURCE: Washington Post

DATE: December 11, 2018

SNIP: Over the last three decades of global warming, the oldest and thickest ice in the Arctic has declined by a stunning 95 percent, according the National Oceanic and Atmospheric Administration’s annual Arctic Report Card.

The finding suggests that the sea at the top of the world has already morphed into a new and very different state, with major implications not only for creatures such as walruses and polar bears, but in the long term, perhaps, for the pace of global warming itself.

The oldest ice can be thought of as a kind of glue that holds the Arctic together and, through its relative permanence, helps keep the Arctic cold even in long summers.

If the Arctic begins to experience entirely ice-free summers, scientists say, the planet will warm even more, as the dark ocean water absorbs large amounts of solar heating that used to be deflected by the cover of ice.

The new findings about the decreasing age of ice in the Arctic point to a less noticed aspect of the dramatic changes occurring there. When it comes to the icy cap atop the Arctic ocean, we tend to talk most often about its surface area — how much total ocean is covered by ice, rather than by open water. That’s easily visible — it can be glimpsed directly by satellite — and the area is, indeed, in clear decline.

But the loss of old and thick ice, and the simultaneous decline in the total ice volume, is even larger — and arguably a much bigger deal. Young and thin ice can regrow relatively quickly once the dark and cold winter sets in. But it may not add much stability or permanence to the Arctic sea ice system if it just melts out again the next summer.

Increasingly, what remains is ice that only forms after the peak warmth of the summer, usually in September, and which may not survive the following summer. This “first year ice” is more brittle, more easily tossed around by winds and waves, rendering the Arctic ice pack more mobile and prone to breaking apart.

This process of reverse-aging, scientists say, is all headed to a crucial moment — when all of the ice in the Arctic will be thin and a year old or less. When that happens — the day of maximum youth — we will be on the verge of a much feared milestone: an entirely ice-free Arctic ocean in summer.

The open ocean absorbs about twice as much sunlight as floating sea ice, explained Veerabhadran Ramanathan, a climate expert at the Scripps Institution of Oceanography. Ramanathan fears that entirely ice-free summers, if they began to occur regularly, could add another half a degree Celsius (.9 degrees Fahrenheit) of warming on top of whatever else the planet has experienced by that time.