What should define the start of the next ice-age?

I’ve often wondered what will be taken as the “start” of the next ice-age. Assuming the start is fairly gradual, we’d expect to see something that either has never happened before starting to happen or something that happens quite often becoming regular.
My own preferred measure would be something very simple, such as the first year in which ice remains continuously on the Scottish mountains.
However looking today I see that WUWT have an article: “4 of the 5 Great Lakes about to freeze over” and I thought that perhaps the first year of a succession when 5 of the 5 might be more likely.
Any thoughts?

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5 Responses to What should define the start of the next ice-age?

  1. Bill Illis says:

    When the snow does not melt out over the summer at Eureka Canada. This is where the ice ages start.

    • Scottish-Sceptic says:

      I take it this is the place: “Eureka is a small research base on Fosheim Peninsula, Ellesmere Island, Qikiqtaaluk Region, in the Canadian territory of Nunavut.”
      Interesting, I was imagining some text: “The current ice age started when glaciers form on”. I was going to say some place well known, but obviously if an ice-age starts they will soon be covered and no one will know what it was.

  2. TinyCO2 says:

    My WAG is that the sun does something we’ve never seen before to trigger ice ages so I’d expect that to be the first sign but maybe the behaviour of the jet streams might be a clue. There might be something big like a current switching position or speed. Or it might just be the Great Lakes reaching high levels more often over a decade than before. We could be decades into cooling before we even recognised the cooling, never mind anything more drastic.

    • Scottish-Sceptic says:

      It’ll certainly get defined in retrospect. It could be some shipping lane is blocked with ice (like the NW passage is being used to suggest warming).
      … could be another “the Thames froze?”

  3. edhoskins says:

    In my book the next ice age started about 1000BC. That is when the Holocene decline in temperature escalated from about 0.05degC / millennium 8000BC – 1000BC to about 0.5 degC / millennium.
    The ice core records from Greenland show.
    1 The last millennium of our current benign Holocene epoch 1000AD – 2000AD was the coldest of the whole current interglacial.
    2 for its first 8000 years the early Holocene, encompassing its “climate optimum” had a pretty flat temperatures on average a drop of only 0.05 degC per millennium.
    3 but the recent Holocene for the last 30o0 years since 1000BC has seen a temperature diminution at 10 times that earlier rate 0.5 degC / millennium
    4 our Holocene interglacial at about 11000 years old and it is probably drawing to its close in this century the next century or this millennium.
    5 any current warming since 1970 will eventually be seen as just noise in the longer term progress of continuing cooling.

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