New Milestone on the Climate Wayback Machine

9 05 2013
Another guest post by Mark Cochrane…….

We are currently flirting with 400ppm on the atmospheric CO2-meter. We’ll be popping above and below this arbitrary value for the next year or two but it is nice to point out the sights along the way. The planet has been here before, about 3 million years ago. Of course humans weren’t around then since Australopithecus sp. had just made the scene (link).

 

The geological period was called the Pliocene. So what was life like at the time? Well the USGS has been studying just that question (Project Website).

The USGS homed in on the mid-Pliocene as a good analog for modern Earth’s changing climate. The agency considered data from 100 sites and a distinct period of time, making the first and only geospatial reconstruction of the Pliocene.

In the last five years, a more complete and detailed picture of the epoch has emerged.

The mid-Pliocene was about as warm as climate models predict it will be by 2100, or about 3.6 degrees F (2 degrees C) above current global mean temperatures, the Geological Survey said.

Sea levels were as much as 70 feet higher than they are now. Florida would have been a narrow strip instead of a broad peninsula, Washington, D.C., might have offered oceanfront views and much of Bangladesh would have been under water. Greenland, now covered in melting glaciers, had forests growing on its northern slope.

Animals and plants would have looked familiar to 21st century eyes, as newly formed grasslands attracted long-legged grazers. The dinosaurs were long gone, and the mountains were basically built. Two-footed ancestors of homo sapiens probably walked the Earth.

Carbon dioxide levels in the atmosphere were between 350 and 400 parts per million (that is, between 350 and 400 carbon dioxide molecules for every million molecules of air), said Pagani, who called the estimates “a pretty good ballpark figure.” (link)

Take notice that we are now passing out of the Pliocene analogue CO2 range as we head to >400ppm levels, even though the planet’s temperature still hasn’t caught up yet to the forcing that we have already put in place (the ice and oceans delay the response). The picture laid out above is roughly what we could expect ‘ if ‘ we stopped adding to the greenhouse gas forcing now. We are not stopping though, we aren’t even slowing down so the next point of interest as we reminisce will be the Miocene. At that time, South America hadn’t connected to North America yet and the Himalayas were just getting started. This is the period when ‘ice ages’ really got going. North America’s fauna looked like this.

Happy travelling…

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3 responses

9 05 2013
Greg Bell

Do we know if CO2’s effect is linear, or if it rolls off above a certain value and other factors become dominant?

9 05 2013
mikestasse

Hi Greg….. we do actually know that it is not linear. The problem lies in the fact that there are so many feedbacks that come with warming, like the ice melting increasing the albedo of the planet, and the subsequent release of methane from under that ice and melting permafrost. The models can only guess at just how bad those feedbacks will be…… but while the guesses are still not that accurate, they all point in the same direction, and that’s up.

20 06 2013
Pier

Hi, Are you aware of last year finding of lake El’ gygytgyn research?

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