Do you understand Foraminifera?

A funny question you think. But these microscopic sea creatures that form shells form one line of evidence for what level of CO2 is a safe level for today. If you realy want to know about this try Hansen’s book, Storms of my grandchildren. But for those who don’t want to wade through a long book, I have a short explanation here.

You have probably heard of the ice cores? Well, they can tell us about the earths climate for around the last 800,000 years. When they die, foraminifera fall to the bottom of the ocean and their shells can tell us about the climate for the last 65,000,000 years. They are collected by coring the bottom of the ocean — Ocean Sediment Cores.

But what does the graph tell us about what happened since the dinosaurs died out and about what we can expect from our interferance in todays climate?

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see at… http://www.columbia.edu/~jeh1/ or http://www.columbia.edu/~mhs119/Storms/Storms_Fig.18.gif

The graph shown was developed by Hansen and Sato from data provided by Zachos. It shows the temperature calculated from the proportion of Oxygen18 in the foraminifera samples. The data has been also adjusted for the variation in O18 fraction when the planet developes ice as this changes the proportion of O18.

The graph shows the temperature of the deep ocean waters which reflect the surface temparatures of winter high latitude surface waters. So the first thing to notice about the graph is the average winter temperature in the arctic around 50,000,000 years ago was 12 degrees warmer than today. This would make the global average temperature much hotter than today, perhaps as much as 12 C (global average temperature around 27 C).

At that time there were tropical conditions in places like Alaska and no ice cap on Antarctica. Temperatures at the tropics might have been very warm, but forests appear to have extended across the entire planet.

So why the rise in temperature from 58 to 50 Ma and then the fall through to 33Ma?

Certainly the position of the continents contributed with Australia separating from antarctica around 45 Ma and allowing a circulpolar cold current to develope as it drifted north. Hansen explains that the Indian sub-continent travelling across the “Indian” ocean to collide with Asia was travelling quite fast (20 cm/yr). This released carbon deposits from the ocean floor rocks at a faster rate than could be absorbed by normal weathering of rocks. CO2 concentrations rose to 2000 ppm around 50 Ma.

Once India pushed into Asia and began to force up the Himalayers the release of ocean floor carbon deposits ceased (as the sub-continent was no longer travelling over the ocean crust). Instead, the fresh rocks exposed in the mountain building began to absorb more carbon than was occurring before. Thus after around 50 Ma the amount of CO2 in the atmosphere (and of course in the ocean) began to fall, reaching around 450 ppm (plus or minus 100 ppm) at the time the Antarctic ice sheet began to form (33 Ma).

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See at… http://commons.wikimedia.org/wiki/File:Climate-change_70ma.png

Other continental movements added to the cooling: Antarctica moved over the southern pole, the Arctic ocean became largly enclosed by continental masses and north and south America became joined. The formation of large ice sheets further reduced temperature by increasing the reflectivity of the earths surface (it’s albeido).

As we entered the period of ice ages, the motion of the earth’s wobble and the eccentricity of its orbit (Milankovitch Cycles) led to the oscilation between cold and warm periods (glacial and interglacial). We are currently in an interglacial period. During the ice ages (last 3 million years) CO2 has been around 180 to 280 ppm. Remember, all these changes occurred over very long periods of time. Much, much slower changes than are occurring now due to our burning of fossil fuels.

So that’s how we got to where we are today, but what does that mean for human interferance? It is very significant that the ice sheet began to form on Antarctica when CO2 dropped below 450 ppm. Long term CO2 levels must not rise above this level if we expect to retain ice on the planet in the long term. Sea Level Rise of 75 m would not be acceptable to our decendants.

I will quote from Hansen here…

The source of CO2 emissions from the solid earth to the surface reserviors, when divided among the surface reservoirs, is a few ten thousandths of 1 ppm per year. The natural sink, weathering, has a similar magnitude. The natural source and sink can be out of balance, as when India was cruising through the Indian Ocean, by typically one ten thousandth of 1 ppm per year. In a million years such an imbalance changes atmospheric carbon dioxide by 100 ppm, a hugh change.

But humans, by burning fossil fuels, are now increasing atmospheric carbon dioxide by 2 ppm per year. In other words, the human climate forcing is four orders of magnitude –ten thousand times– more powerful than the natural forcing. Humans are now in control of future climate, although I use the phrase “in control” loosely here.”

The foraminifera has given us a better understanding of our climate. It is yet another line of evidence as to the sensitivity of our climate to CO2. It is very clear from this that we are forcing our climate way beyond conditions experienced naturally over many millions of years.

This makes it even more urgent that we cease use of fossil fuels as soon as we practically can. It would be feasible to completely replace our energy systems over a 20 to 30 year period. But we have to start immediately with strong cuts in order to avoid catastrophic damage.

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