On May 9 CO2 reached 400 ppm at the National Oceanic and Atmospheric Administration’s (NOAA) monitoring centre at Muana Loa and at at the Scripps Institution of Oceanography in San Diego, California. This is what’s been happening over the last 130 years in broad terms:
It seems many news organisations, for example the BBC, and some scientists are stressing that the last time concentrations were so high was 3 to 5 million years ago. In the linked article Michael Mann, director of the Earth System Science Center at Penn State gives a different view:
Mann said the last time scientists are confident that CO2 was sustained at the current levels was more than 10 million years ago, during the middle of the Miocene Period.
Back then, global temperatures were hotter, ice was sparse and sea level was dozens of meters higher than it is today.
This graph gives an idea of how the temperatures played out over the last 65 million years:
I don’t think you can directly compare what the sea level would have been then with now because the shape of the ocean basins were possibly significantly different. Also I understand the error margins in ascertaining what it would have been then are quite high.
Nevertheless it’s no comfort that back then there would have been no Greenland ice sheet (worth 6-7 m) and little West Antarctic ice sheet (5-7 m). The East Antarctic ice sheet would have been smaller (59 m in all) and most likely there were no land glaciers and ice caps elsewhere (0.5 m). Thermal expansion would have also seen sea levels higher. So 25 to 30 metres seems about right.
Actually Aradhna Tripati and colleagues had a look at this back in 2009. They put equivalent CO2 concentration levels back 15 million years, but their story on ice and sea levels is much as I’ve just described. They put temperatures 5 to 10F (roughly 3-5C) higher. They produced this graph comparing palaeontological CO2 levels with IPCC forecasts:
This graph from the Mauna Loa site shows how the concentrations have stepped up over time:
James Hansen’s Iowa testimony (p39) tells us that during the Cenozoic era CO2 levels changed at the rate of 100 ppm per million years, that’s 0.0001 ppm each year. Now we are doing it about 25,000 times faster.
As Michael Mann said:
“There is no precedent in Earth’s history for such an abrupt increase in greenhouse gas concentrations.”
Finally there are other greenhouse gases. CO2e or CO2 equivalent covers what is sometimes known as the ‘Kyoto six’ under the Kyoto Protocol. The main ones other than CO2 are methane and nitrous oxide. This image from the World Resources Institute gives the mix as of 2005:
Unfortunately I can’t find current levels or historical graphs, but on that basis CO2e would now be 519. That can’t be good!
The only way forward now is back: to retrace our steps and seek to return atmospheric concentrations to around 350ppm
George is his usual pessimist/realist self.
He sees our chances of preventing climate breakdown as close to zero.
So here stands our political class at a waystation along the road of idiocy, apparently determined only to complete the journey.
Update: Andrew Glikson has an interesting article at The Conversation. He’s an earth and paleo-climate scientist and as as such compares present CO2 levels with the Pliocene. With the temperature 2-4C higher and sea levels about 25m higher, it was a different place:
Life abounded during the Pliocene. But such conditions mean agriculture would hardly be possible. The tropical Pliocene had intense alternating downpours and heat waves. Regular river flow and temperate Mediterranean-type climates which allow extensive farming could hardly exist under those conditions.
I love that photo of earth from Voyager 1: