We’ve heard a lot about the so called “pause” in global temperatures over the recent decade – a misnomer, since temperatures have continued to rise, just not as rapidly as during, say, 1991 to 2006, to cherry pick an era of faster-than-projected rise.
Scientists were pretty sure that those rapid rises were part of natural variability, and would not be sustained, and that’s what’s happened. So not a big revelation in what we are seeing today.
Stefan Rahmstorf at Real Climate:
And a reminder: The warming trend of the 15-year period up to 2006 was almost twice as fast as expected (0.3°C per decade, see Fig. 4 here), and (rightly) nobody cared. We published a paper in Science in 2007 where we noted this large trend, and as the first explanation for it we named “intrinsic variability within the climate system”. Which it turned out to be.
The notion that climate science is “based on computer models” is a false one, but comes up a lot, recently on the Senate floor in a rant by denialist Senator Jeff Sessions. No experienced scientist is surprised when the planet doesn’t conform exactly to what a particular model run shows – and moreover, many indicators of planetary change are moving well ahead of projections made not too long ago – notably arctic sea ice loss, melting ice sheets, and subsequent sea level rise.
Above, in a recent interview, Atmospheric scientist Ken Caldeira, talks about key areas where climate models have been very much spot-on – and helped confirm the “fingerprints” of human caused global change.(this interview ties in with John Cook’s MOOC – Massive Online Open Course, “Making Sense of Climate Denial”)
At the bottom, I’ve also embedded my interview with Mike MacCracken, and clips from his 1982 talk at Sandia Labs, where he outlined the changes that scientists, using models, expected to see decades ago, all of which are now part of our emerging reality.
Now a new study of the Pliocene, a period of the not too distant geological past that many scientists compare to our own, shows that climate sensitivity, the response of the planet to carbon dioxide levels during that era, was very much like what our current best estimates tell us.
New evidence showing the level of atmospheric CO2 millions of years ago supports recent climate change predications from the Intergovernmental Panel on Climate Change (IPCC).A multinational research team, led by scientists at the University of Southampton, has analysed new records showing the CO2 content of the Earth’s atmosphere between 2.3 to 3.3 million years ago, over the Pliocene.
During the Pliocene, the Earth was around 2ºC warmer than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years.
By studying the relationship between CO2 levels and climate change during a warmer period in Earth’s history, the scientists have been able to estimate how the climate will respond to increasing levels of carbon dioxide, a parameter known as ‘climate sensitivity’.
The findings, which have been published in Nature, also show how climate sensitivity can vary over the long term.
“Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming,” says Southampton’s Dr Gavin Foster, co-author of the study.
“Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5ºC increase per CO2 doubling summarised in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions.”
More here on the Pliocene, and its warning for our world today.







