How many millions of years might that be then? Two, apparently: CO2 level ‘is greater than at any time in at least the past 2 million years’. What about earlier times? The caption to the first photo in the article reads: ‘The near future may be similar to the mid-Pliocene warm period a few million years ago.’ So natural variation is confined to history, and/or dependent on volcanoes? The article asserts: ‘the last warm period between ice ages peaked about 125,000 years ago—in contrast to today, warmth at that time was driven not by CO₂, but by changes in Earth’s orbit and spin axis.’ Now orbital factors have also switched themselves off? And so it goes on: our climate models say…
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Many numbers are swirling around the climate negotiations at the UN climate summit in Glasgow, COP26, says Phys.org.
These include global warming targets of 1.5℃ and 2.0℃, recent warming of 1.1℃, remaining CO₂ budget of 400 billion tons, or current atmospheric CO₂ of 415 parts per million.
It’s often hard to grasp the significance of these numbers. But the study of ancient climates can give us an appreciation of their scale compared to what has occurred naturally in the past.
Our knowledge of ancient climate change also allows scientists to calibrate their models and therefore improve predictions of what the future may hold.
Recent work, summarized in the latest report of the Intergovernmental Panel on Climate Change (IPCC), has allowed scientists to refine their understanding and measurement of past climate changes. These changes are recorded in rocky outcrops, sediments from the ocean floor and lakes, in polar ice sheets, and in other shorter-term archives such as tree rings and corals. As scientists discover more of these archives and get better at using them, we have become increasingly able to compare recent and future climate change with what has happened in the past, and to provide important context to the numbers involved in climate negotiations.
For instance one headline finding in the IPCC report was that global temperature (currently 1.1℃ above a pre-industrial baseline) is higher than at any time in at least the past 120,000 or so years.
That’s because the last warm period between ice ages peaked about 125,000 years ago—in contrast to today, warmth at that time was driven not by CO₂, but by changes in Earth’s orbit and spin axis.
Another finding regards the rate of current warming, which is faster than at any time in the past 2,000 years—and probably much longer.
via Tallbloke’s Talkshop
November 2, 2021 at 07:18AM