We narrowly missed a new ice age, and now we won’t see one for a long time.
by Scott K. Johnson - arstechnica.com
13 January, 2016
Before fossil fuels rendered this moot, conditions were nearly right.
Recorded human history has played out within one type of climate—an interglacial period. During the glacial periods of the last million years (commonly referred to as “ice ages”), great ice sheets grew to cover Canada and some points south, as well as Northern Europe and much of Russia.
In the 1970s, we learned there was a consistent 100,000-year heartbeat to this back-and-forth cycle governed by subtle patterns in Earth’s orbit. The thing is, it’s about time for the next heartbeat. We’re at the part of the cycle where the interglacial period should be wrapping up and the slow but inexorable descent into another ice age would begin.
But that hasn’t happened, and it’s not going to any time soon. Our current breakneck emissions of greenhouse gases will see to that. Still, the scientific question is worth asking: what, exactly, does it take to start off an ice age?
We are currently at a low point in summer sunlight reaching the northern high latitude region, which is how the orbital cycles turn into glacial cycles. Because there are several orbital cycles involved, the peaks and valleys in that sunlight are complex—it’s not as simple as a sine wave oscillating between a constant high and a constant low. But there were two interglacial periods in the last million years (one 400,000 years ago and one 800,000 years ago) with a similar combination of orbital cycles. Both crossed the threshold into an ice age when they hit this low point in sunlight.
Now we're going to have a super-long interglacial period for at least 50,000 years, perhaps 100,000 years. And it might include a second Permian Exstinktion [sic!].