There are two kinds of climate change

New Year ramblings or “the conversation I have sometimes with people about climate change”. Okay, let me be clear here, there is no denying anthropogenic effects on our climate. Taking CO2 as one greenhouse gas (GHG) we were emitting <5 Gigatonnes per year in 1845, by the time we starting using fossil fuels in a big way in the 1950s we were up at 10-15 Gigatonnes per year, and in 2011 we’d hit around the 37 Gigatonnes per year mark or around a 10-fold increase in 177 years.

I am not denying human created climate change (short-term) but I want to introduce to people the idea of another kind of climate change (long-term) that has nothing to do with us because this historical data is informing the way we create and sense check our anthropogenic (short-term) climate models and you don’t get to hear about it.

I’m going to be very woolly and take a big broad brush approach. I’m going to stick to CO2, temperature and sea level and be very specific about my time frame. This doesn’t mean I am unaware of other things it’s just that these three interlinked variables alone can be used to illustrate my point without methane, sulphur, carbon particles, CFCs, Milankovich cycles, solar intensity etc. (And there’s a lot of science of which I don’t know the half of).

We talk a lot about CO2 as a key GHG due to its long-term effects and its measurable-ness both now and historically. 10 years after its emitted is when its warming effect is felt and its so stable that 1,000 years later such an increase will still be being felt by the climate. What I  struggle with is if our actions to change our impact by reducing our pollution really matter because of long-term effects (let me say I think we should try though). Be aware that “human long-term” may not matter much so if we’re going to geo-engineer a solution we may as well get on with it as the planet “Earth long-term” will barely notice. Here’s the thing, most people don’t understand time frames on a planet scale.  They don’t know what the planet has already been through without our meddling.

I’m a geologist. I have been trained to think about time differently to most. For a geologist the past 50 Million years is 1% of the earth’s history and also represents, in plate tectonic terms, something similar(ish) to the configuration of the planet we now have. This is what I think of as the recent past for the Earth. Talking to non-geos the recent past may be represented as last week, or WWII or at a push the last 5,000 years when humanity started paying attention to the world around them. So for me when people say CO2 levels are rising and are now around 400ppm in the atmosphere (up from 361ppm in 1995 when the first UN climate change conference was held) I think well that’s not as high as 2,000-3,000ppm as it was during the Eocene Optimum* (a globally warm moment in time 55-45 Million years ago when there were no polar ice caps and evidence of crocodiles living at high latitudes.) Here’s the thing it is imperative to point out this period is used as a case study for current global warming models because it is the most recent period of rapid warming we know about on Earth. There are four key, data supported, ‘knowns’ I’m going to use about the last 50 Million years that I give below:

Sea level was around 70m higher in the Eocene then than it is now.

CO2 levels have, until recently, been steadily dropping for 45 Million years.

We had a Little Ice Age 20,000 years ago and the drop in global temperature between the Eocene Optimum and the Little Ice Age was around 17degC.

The Antarctic ice sheet started forming about 35Million years ago; it’s a baby geologically speaking.

A lot of media discussion centres around the speed of the ice sheets melting and sea level rise. Of course time lapse space photography can look pretty scary when viewing the loss of the ice sheets and the desperate situation of polar bears in the Arctic. Science is therefore being asked what CO2 concentration is needed in the atmosphere before the ice sheets melt? So now you know that this isn’t all ‘made up’ from models and that we have a piece of recent geological history that can help us. We know the current Polar ice sheets started forming around 35 Million years ago so what was the CO2 in the atmosphere then? Well it’s of course not that simple. Tectonic configurations were not exactly the same then and ocean currents took warmer water to Antarctica than it receives now but, the data says somewhere between 600-1,400ppm. That’s a big range. The models converge on a number for continental Antarctic ice sheet formation around 780ppm of CO2.

Science is also being asked will happen when they melt, how fast will sea level rise be? Well again we have data from the Little Ice Age. We know what happened then with de-glaciation. On average sea level went up 1.25cm a year but that rate wasn’t constant. It started off slow (0.25cm a year) and peaked at 13cm/year about 5,000 years after de-glaciation started dropping off after that. So there, that’s the context for the three variables I said I’d talk about within a particular time frame I’ve chosen. So what?

What this demonstrates is that we know from historical geological data (not just models) that the earth’s climate system is highly variable and doesn’t have an optima. What humanity has done is adapt to certain climatic conditions at a particular point in time representing a tiny fraction of the earth’s life. We have come to think of it as having an optima for us. That is fine but it is an important point to make that the planet doesn’t care what the temperature is, what the CO2 is or what sea level is – we do. So anything we do will only affect our outcome (and the rest of life on it) not the planet as a whole. Earth has been there and done that and got the T-shirt in all the colours already. So if we want to make changes to keep our self-defined optima we have to get on with it or accept the fact that we will have to adapt to survive the changes we are inflicting on the planet by our short-term actions.

Finally, bear in mind that that “high sea level, high CO2, plenty crocodiles and jungles at the Poles” moment back around 50 Million years ago that we use as a proxy for our models for what’s happening now has a cause we don’t yet understand. Global temperatures jumped up around 6degC in 20,000 years out of nowhere and while we have theories there is no definitive cause identified. We can safely say it was not an anthropogenic effect. So even if we do stop polluting and get things sorted out the planet itself is perfectly capable of throwing curved balls that will be much harder to adapt to than our own messy creations as we will have to understand what has caused them first rather than already knowing.

*Also known as the Paleocene-Eocene Thermal Maximum (PETM)