Matt Ridley in The Australian explains how every man and his dog is forecasting the doom of the Arctic sea ice, and not only have they been wrong year after year, but they all assume that if the ice all melts it’ll be a global disaster. But Earth’s already been-there done-that, and for years, and it was no-biggie. Polar bears obviously got through it, as did seals. Humans without protective solar panels somehow spread far and wide, and generally flourished.
I suspect the main climate refugees from the Arctic would have names like Donner and Blitzen. This is the one thing Matt doesn’t explain — in 8,000BC when the ice melted, what the heck happened with Santa?
This was a period known as the “early Holocene insolation maximum” (EHIM). Because the Earth’s axis was tilted away from the vertical more than today (known as obliquity), and because we were then closer to the Sun in July than in January (known as precession), the amount of the Sun’s energy hitting the far north in summer was much greater than today. This “great summer” effect was the chief reason the Earth had emerged from an ice age, because hot northern summers had melted the great ice caps of North America and Eurasia, exposing darker land and sea to absorb more sunlight and warm the whole planet.
The effect was huge: about an extra 50 watts per square metre 80 degrees north in June. By contrast, the total effect of man-made global warming will reach 3.5 watts per square metre (but globally) only by the end of this century.
To put it in context, the EHIM was the period during which agriculture was invented in about seven different parts of the globe at once. Copper smelting began; cattle and sheep were domesticated; wine and cheese were developed; the first towns appeared. The seas being warmer, the climate was generally wet so the Sahara had rivers and forests, hippos and people.
Barring one especially cold snap 8200 years ago, the coldest spell of the past 10 millennia was the very recent “little ice age” of AD1300-1850, when glaciers advanced, tree lines descended and the Greenland Norse died out.
It is pretty hard to measure sea-ice that might have melted 8,000 years ago. But the Greenland Ice cores show temperatures there were hotter than today, and there are some proxies to estimate the extent of the sea ice. Ridley refers to a paper (Stranne 2013) which uses 8 different proxies that suggest extended periods of hundreds of years where there was no perennial sea ice. With models (yeah, yeah) they say the Holocene warm period is all explained with extra sunlight coming in due to the orbital shift at the time (I don’t think that is controversial). They speculate that the earlier instability and temperature gyrations of 12-15,000 years ago in Greenland were due to the ice shifting from a phases of regular sea ice, to being regularly ice free. The albedo of sea ice is a reasonably important feedback.
The darker blue times in the graph below are when proxies suggest there was “low” sea ice (6,000 to 12,000 years ago).
Abstract — Stranne et al
Stranne, C., Jakobsson, M., Bjork, G. (2014) Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum , Quaternary Science Reviews, http://dx.doi.org/10.1016/j.quascirev.2013.10.022
* h/t to Craig Thomas for pointing out and that the word “global” in Graph 2, was better off not being there. h/t to Michael for spotting that the arrows on graph 2 for the MWP and LIA were incorrect. Both fixed. Thanks to both.