- JoNova - http://joannenova.com.au -

Arctic Sea Ice — it all melted before and it didn’t matter

Posted By Jo Nova On August 30, 2016 @ 4:58 pm In Global Warming | Comments Disabled

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?

Ice scares aren’t all they’re cracked up to be

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.

 

Greenland Ice Cores, GISP, Holocene Temperature, Arctic.

UPDATE: This graph shows the ice-core data up until 1855. The last 150 years (1705 to 1855) are highlighted in red to show the warming as the Earth began coming out of the LIA.

GISP, Greenland, ice cores, Cuffy, Clow, 1997, Holocene temperatures, graph.

Created by Cuffy and Clow in 1997, and based on Greenland ice core records, this chart shows global temperatures for the past 15,000 years.  |  h/t Don Easterbrook. *

Source: iceagenow.

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).

Holocene, graph, Arctic, proxies, sea ice. Stranne.

Stranne et al (2013) Click to enlarge. H/t to The HockeySchtick

Abstract — Stranne et al

Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (∼6000–10,000 years Before the Present) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth’s orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere–sea ice–ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bølling–Allerød period (c. 12,700–14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.

H/t GWPF

REFERENCE

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.

VN:F [1.9.22_1171]
Rating: 9.3/10 (66 votes cast)

Article printed from JoNova: http://joannenova.com.au

URL to article: http://joannenova.com.au/2016/08/arctic-sea-ice-it-all-melted-before-and-it-didnt-matter/

Copyright © 2008 JoNova. All rights reserved.