My first degree about 35 years ago was in earth sciences. And one of my lifelong passions has been reading the history, prehistory, and evolutionary history of humans. I picked up the classic habit of those skills – a better appreciation of timescales than individual lifetimes. Which is what makes me rather cynical about the farcical attempts of humans to stop crapping in our narrow evolutionary space over the last century.
In measuring paleoclimates over the medium term (ie less than a few million years and more than the human evolutionary history), the major two natural factors are greenhouse gases and aerosols. Over the medium term timescales, they are generated by the average levels of vulcanism, but are persisted by the ability of the volatile surface of the earth to wash them into sediments. That has a cyclic trigger (measured in tens of thousands of years) driving it due to planetary orbital and axial positions and the resulting insolation effects on the northern land masses.
There are also slower changes due to the continential landmasses drifting into different parts of the globe and their effects on vulcanism, planetary insolation and ocean currents. There are also very long term changes in the suns overall output. However these effects tend to act over tens of millions of years, and for me, are less interesting because they are outside even our evolutionary history. Of course the scientific illiterates do blather on about these – see some of a links and discussion of pseudo-science in “Record heat despite a cold sun“. But basically they operate on too long a timescale to be of much interest over the next couple of centuries.
Persistent climate effects over thousands of years are mainly buffered by the accumulated changes in greenhouse gases in the volatile gases and liquids in the few kilometres at the earth surface. That is because, unlike atmospheric particulates and aerosols, some of the greenhouse gas effects are remarkably persistent. CO2 in particular is both persistent in the atmosphere and gets replenished because it accumulates in ocean water, getting released decades or centuries later.
Human societies since the development of wide scale agriculture over the past five thousand years have acted like persistent volcanic eruptions. They have managed to cause a shift in the pattern in the usual post glacial pattern, apparently largely due to the clearing land for crops and the greenhouse effects of their crops on climate – probably especially rice production.
In the last 200 years, the human effect of forcing the earth to regurgitate vast amounts of sequestered greenhouse gases in the form of hydrocarbons and other carbonates like limestone has been occurred at an unprecedented rate. It has been way in excess of any natural geological effect because of the speed at which it has happened. However the effect of pumping greenhouse gases into the atmosphere and oceans is well known in geological history – everything is going to heat up.
Just to give an idea of the scale of human intervention, have a look at the last 4 million years of CO2 levels while modern humans have been evolving.
Proxy (indirect) measurements of atmospheric CO2.
Data Source: Reconstruction from ice cores at NASA.
Credit: NOAA
Broadly speaking over the last 4 million years, until humans started interfering, the CO2 goes up and down based on glacial periods. Those glacial periods are largely triggered by orbital and axial shifts with a bit of vulcanism thrown in to replenish the greenhouse gases.
Note that I didn’t refer to glacial periods as “ice ages”. They aren’t. We have been in an ice age continuously for at least the last 40 million years. Ever since Antarctica slid into the south axial polar region while dinosaurs were still the dominant animal phyla 65 million years ago. After Antarctica built a substantive icecap it dropped the world into a deep freeze compared to the ‘normal’.
Humans and all of the other primates evolved over the last 66 million years in a frigid planet. It is a world that we and most species on earth are adapted for. The rapid and now inexorable human driven rise of temperatures in all of our world wide habitats over the next thousand years will cause all species to have problems with most of the places we currently live.
Living on an high latitude ocean island with temperature buffering water around us as we do in NZ is just about optimal. But it is hard to see how humans can live with the kinds of temperatures and climate that I’m expecting in the inland tropics. We’re on track for an average 4-6C increase worldwide in the next 100 years (as far as I can see there is nothing to prevent it – se my last paragraph).
But it is likely to be a lot higher in the tropical interiors because of changes in how those ecosystems handle increased temperatures.
We will see even higher temperatures in the polar and sub-polar areas as increased precipitation in the polar deserts causes more melt directly or via glacial movement.
This year’s 15-20C above normal temperatures in the Arctic is probably just going to be normal in a few years as the northern ice store disintegrates.
East Antarctica will take more time to drop out of its deep freeze simply because it is so dry that precipitation of snow will take a lot of time to build up. That will limit glacial movement because of the geography.
However where warmer oceans touch ice as they did for most of the 20th century in the Antarctica peninsula, then expect rapid melting. Changes to wind and the repair of the ozone hole have slowed the ice melt there for the last decade, but further warming and melting is inevitable over the coming decades.
West Antarctica over the past decade has started to get the rapid effects of warming oceans and more precipitation giving faster movement of ice to the melt.
In a few hundred years, we have melted the worlds polar and sub polar fridges and may have a place to put the few remaining people from the burning tropics. But that really assumes some rationality we have come to not expect from humans. Like markedly reducing the burn of fossil stores of carbon – something that isn’t happening.
About the only thing that is good is that the rate of increase is reducing. However that still means that vastly more greenhouse gases are going into the atmosphere and oceans than are being removed. Most of that will keep coming back again and a again over the following few thousand years.
It is the barbaric culture that treats the worlds fragile ecosphere as a free-to-dump zone that is really the problem. It appears to have forgotten the basic rule of life. If something appears too good to be true – then it isn’t good. Start looking for the gotcha.
With the amount of fossil carbon released from hydrocarbons and limestone already the gotcha genie is out of the bottle and starting to get mischievous. I can’t seen any political way of actually substantially reducing the rate of fossil carbon release in the next few decades. It’d need to drop to something like a quarter of the current level to have much of a long term effect. So I may live to see the level of atmospheric CO2 to hit double the pre-industrial level of 280ppm (depending on how the stent+drugs holds out). At that kind of level, at best, we can expect to see 4-6 degrees Celsius average sea-level temperature rise by centuries end. I’m glad that I don’t have kids. While I’m pretty sure that humans will survive complete with their society, this century is going to be a lot harder than the one I spent most of my life in.
I am uninterested in having discussions with people who don’t read my post and respond to that. If you want to push your own unsubstantiated and unlinked beliefs then use OpenMike to push your own barrow. If you want to place links into the discussion – then make sure they are relevant to the post. If I look at them and I don’t think they are not or I find people who clearly haven’t read down to this, then I will hand out educational bans. Stay on the post topic – there is more than enough in there to piss many people off.
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