This article says that we might have an ice-free Arctic in summer for the first time in millions of years. How can we be sure of that? Arctic ice floats and moves, so we cannot take ice cores. So how do we know the Arctic wasn’t ice-free at some point in the more recent past, say the Medieval Warm Period or the Holocene Maximum? Or in the previous interglacial when at one point England hosted lions and cheetah?
I’m not interested in debate, just looking for a fact check.
This Nature article abstract at least list a short summary of the reason for believing that the ice has been thicker for the past 1500 years, altough it would be nice to have access to the full article. But for millions of years, I have no idea how they estimate that.
If it wasn’t for Dating Arctic Ice I wouldn’t date at all.
Not that I date Arctic ice, but it seems to me the presence or non-presence of remains of plankton in the sediment is how long term ice coverage is determined.
Maybe this is the full article?
Yeah, that looks like the thing. Thanks for finding that.
Here’s the data used in the Nature article:
That article doesn’t make sense: it says that ice cover decreased during the Little Ice Age and the Dark Age Cold Period, which is counter-intuitive.
You need to take into account that there is very little evaporation from perennial ice, as opposed to open water, resulting in very little precipitation onto the ice. Pleistocene ice advances seem to have occurred when a relatively open Arctic allowed for relatively high relative humidity, resulting in net precipitation on on land. Snow buildup turned into ice and expanded, increasing albedo in a positive-feedback cycle. When this chilled the Arctic enough that it froze again, the cycle reversed, and there was net evaporation over precipitation, and meltback. You need the reservoir of open water feeding the humidity of cold air to get the cycle started.
One needs to realize that the Medieval Warm Period wasn’t global, or warmer than current conditions:
That said, it was warmer than it was up until the mid-20th Century.
Also, for the comment about less ice coverage and colder conditions during the Little Ice Age, one notes that recent extreme winters (although not colder overall, either globally or year-round for local conditions) have been linked to sea ice decline, which as noted sounds counter-intuitive but is due to the altering of weather patterns, a warming of several degrees in the Arctic still leaves it much colder than normal weather further south (as sea ice continues to decline, eventually the link will break down).
As far as the “millions of years” statement goes, it is much less certain for obvious reasons, although current global temperatures (with much greater warming in the Arctic, although I suppose that was also true in the past) are now approaching mid-Pliocene (~3 million years ago) levels if the figure on page 13 here is any indication, although the warmest part of the last interglacial (Eemian) may have been warmer at its peak (although it includes a caveat that the graph exaggerates warming above Holocene levels).