Atmospheric carbon dioxide over the last 800,000 years
It has been said that the Earth has experienced climate change in the past, and that we are overreacting to a perceived crisis. Scientisis have various ways to look into that past, and one of those is to study ice cores. The better we understand the past, the better we can anticipate the future.
Polar ice caps are formed by layers of snowfall, which are compressed at depth into ice. As this occurs, air pockets in the snow get trapped in the ice, giving us a record of atmospheric greenhouse gasses going back in time, depending on the depth of the ice core sample. As well, scientists can deduce past temperature (from analysing isotopes of H and O), wind patterns, trace chemicals, and dust (such as volcanic eruptions).
We have continuous ice core data going back 800-thousand years, and there is a push to extend that to ~1 million years in Antarctica, with a multinational project led by Australia that is expected to be completed by the end of the decade (it’s a challenging project). There are other kinds of data for earlier ages, however a depth corresponding to 1 million years reaches the surface of the Antarctic continent and is therefore as far as we can go back in time at that location.
The 800-thousand year ice core data for atmospheric CO2 is plotted below (black dots). The current era is on the right of the x-axis, and time goes backwards to the left, with -800,000 years on the far-left.
The data show CO2 concentration cycling over epochs recuring about every 100,000 years, ranging between ~175–300 ppm. It is thought that this cycling pattern was driven by a subtle wobble in the Earth’s orbit around the Sun that produced glacial and inter-glacial periods that modulated CO2 release from ocean stores according to temperature.
Where are we now? That’s depicted by the red line and dot. The dot represents the present CO2 concentration of 419 ppm. The red line is vertical because on this time-scale there is not enough resolution to show the detail of our impact on CO2 concentration over recent years.
One caveat is that the paleolithic record (black) is from ice cores, and the current data (red) is from direct atmospheric measurement, so they could be disparate data. Fortunately there was a small overlap (~1960/70) when both sources of data were available. It turns out that they match quite well. So this graph is probably real. And therefore striking.
There are other ctitisms, for example ice core data suggest CO2 concentration lagged temperature changes and was thus not causal. This is true. In the past climate change has been driven by the Earth’s orbit. However, as oceans heated during inter-glacial periods, they could release more CO2 that caused more warming etc. In this feedback scenario, CO2 would be expected to lag temperature at first because it’s not the cause of it, but rather reinforced global heating. This is different to our current circumstance in which we are recklessly dumping carbon directly into the atmosphere, with global warming being the consequence. This time around it’s causal.
Life on Earth goes back ~3.5 billion years (single-cell), and even this 800 thousand year record is less than the probable 2.2 million year history of our hominin ancestors. However, our species, even in its archaic form, did not arise until 300 thousand years ago, and modern homo sapiens about 150 thousand years ago. So this graph takes in the entirety of our species. As a species, we have never experienced atmospheric carbon comparable to the present day, or had to deal with the potential consequences of that.
Those that propose climate change is not new might shrug off the perpendicular red line (and it will inevitably increase beyond 419). Perhaps the Earth, despite being faced with something on this sudden time-scale, will shrug it off too and life on Earth continue much as we want it to. Maybe the technology cavalry will come to our rescue at the last minute blowing their horns with a message of hope. Then again, maybe the last we’ll see of hope will be as it races over the nearest hill with its ass on fire.
Finally
No one living today will see that 419 ppm red dot come down by natural means. CO2 clears from the atmosphere with time-scales of centuries to millenia. It has been estimated that if all CO2 emissions were halted today, it would take over 30,000 years for CO2 concentration to return to pre-industrial levels.
We have set a new benchmark.
Further reading
800,000 year data as text file from NOAA
