photo credit : http://www.wdm.org.uk


Finding A Balance
by Jo Abbess
10th April 2008

Today is the second time I have started to read James Hansen's report "Target Atmospheric CO2 : Where Should Humanity Aim ?" :-

http://www.columbia.edu/~jeh1/2008/TargetCO2_20080407.pdf

From the Abstract alone, I can tell that this is report is going to be very hard for some people to comprehend.

"Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago, large scale glaciation occuring when CO2 fell to 425+/-75 ppm..."

CO2 = Carbon Dioxide; ppm = parts per million

Now I know exactly what the Climate Obstructionists (Deniers, Skeptics, Sceptics, Warmistas, Delayers) will say.

"Oh look ! When the CO2 levels were at 450 ppm, give or take a bit, the Earth entered an Ice Age ! So that level of CO2 is responsible for Global Cooling, then, not Global Warming !"

It's sad, but that is exactly what they will say. They will try to sneak up on it and jump it, and try to beat it into submission, and yet they will have failed to understand.

One of the great principles of the appliance of heat is that there are a number of mechanisms for the take up of the heat by the heated object.

There's convection. There's conduction. There's radiation and re-radiation and reflection. But there's an underlying principle that has to always be considered : time lag.

If I light a fire under your seat, which I won't, because I'm a pacifist, it will take some time for you to experience the heating effect and jump up and start stamping the flames, and throwing your expensive wool jacket on the conflagration to keep the oxygen out.

Same is true of the Earth's warming response to the Global Warming signal from a change in Greenhouse Gases. There is a time lag between cause and effect.

There is always a delay before the heat of the sun's rays focussed on the shard of glass in the forest litter causes the grass underneath to reach Fahrenheit 451 or whatever exact temperature, and start the burn that will wipe out the trees.

And there's the impact of the speediness of the heating. If I'm cooking, and I turn up the electric dial to 11, then the pan really fries fast. If I have the dial on 5, it takes longer.

Increasing atmospheric Carbon Dioxide causes what is known in the Climate trade as "radiative forcing".

It ensures that more heat from the Sun is trapped within the Earth atmosphere, by not allowing the rays to bounce back out again as easily as before. There is a net heating-up effect.

And, logically, if you decrease the atmospheric Carbon Dioxide, you create a cooling-down effect.

And it takes time for these effects to make their mark on the Earth system temperature.

Plus, over time, there is a "levelling out" process, where the Earth moves to a stable configuration, appropriate to the given level of Carbon Dioxide in the atmosphere.

So, if you rapidly increase Carbon Dioxide for a hundred or two hundred years, you will see a warming effect that will build up, after a time lag, to its peak warming, and then after that point the warming effect will diminish until the system is stable again, albeit at a higher average global temperature.

Let me try to explain it this way : you're riding a bicycle, and trailing behind you you have a box on wheels, attached to the bike by a rope that's a couple of metres long. You might have a large quantity of stinking manure in the trailer box, and that's why you want to keep it far away behind you.

So, you need to turn a corner, so you turn the handlebars in the new direction, and the bike moves round. But the trailer takes time to change its course. After all, it's not had something to push its wheels around.

And think of this : a line of rollerskaters, all linking arms, and some at one end of the line start to change direction. At first the line does not respond as one, and when it does start to change direction, it can swing wide and wild, before settling into the new direction.

There is what you might call "Climate Inertia", and "Climate Momentum". If something is heating or cooling the Earth, it will take some time to work up to getting hotter or colder. And when it does start heating or chilling, and the forcing effect is halted, it will take some time to stop changing.

And the correction after the swing may even take the temperatures in the opposite direction, because regaining balance depends on the exact levels of Greenhouse Gases up there.

This is what James Hansen is talking about : the Carbon Dioxide levels in the atmosphere were very high before about 50 million years ago, and then they started to decrease, and the effect of decreasing Carbon Dioxide in the atmosphere was Global Cooling of such an intense nature that it kicked off glaciation.

But it would not have ended there. The Global Cooling was an overshoot. If the CO2 levels had remained the same after their fast reduction to 450 (give or take) ppm, then after the necessary time lags, the Earth would have readjusted from that violent cooling swing to the relevant average heat for that CO2 level. And that would have been high. Higher than today.

James Hansen is saying that if you look at the change in the levels of CO2 roughly 50 million years ago, and looking at the temperature swing that the sharp dip in CO2 caused, then you can use that to work out the the temperature swing out for the sharp rise in CO2 we are now experiencing.

He says that this historical data can be used to calculate what happens at the end of the swing, as well.

Here's what he says (with his colleagues) :-

"Equilibrium sensitivity, including slower [...] feedbacks, is [of the order of] 6 degrees C for doubled CO2..."

Equilibrium, that point at which the time lags are over and the swing is finished and come back to a balanced point, appropriate to the level of CO2 in the sky.

Sensitivity, that total change of global temperature in response to the CO2 signal.

Six degrees is a very high number in Climate terms.

Increasing the levels of Carbon Dioxide in the atmosphere causes the Earth to heat up. About that there is no longer any doubt, scream and rant though you may.

The speed of the increase in temperature, the wildness of the temperature swing and the eventual temperature equilibrium were thought to be hard to decide upon.

However, James Hansen and his colleagues have sought to indicate what this could be by looking at periods in the dim and distant past where they could establish the data : six degrees Centigrade higher than today.

For those North Americans who have read this far : that's over 40 extra degrees of Fahrenheit.

That, my British friends, is the difference between average Spring and Summer temperatures in England.

Basically, with an extra six degrees, Spring will be like Summer is now, and you can expect double Summer heating. Very little will survive this.

My advice is, you better start understanding this and reacting to it.


The College of Global Change was formed to provide a platform for thinkers and writers on Energy, Environmental and Economic Change. The Change College aims to encourage information and opinion exchange in the science, policy and education communities, and to offer commentary to the media about Global Change news. The College hopes to promote sound systems thinking for policymakers at all levels of government, and practical action for social structures and corporate organisations. The Change College is a private, non-partisan, non-profit network and is free to join. The online resources are offered at no charge to readers, and contributors are not paid. Contact us by e-mail at change dot college at google mail dot com.