Of course you know these people that by now feel a bit cornered and say ‘okay, perhaps temperatures are going up. But that’s what it does, the global climate changes all the time.’
Well, to keep things simple: no, it doesn’t.
When suddenly you switch from human timescales to (paleoclimatically relevant) geological timescales – that is literally a 100,000-1,000,000 zoom difference – you get to legitimate comparisons. But always the current warming is happening at least 10 times faster than anything we can find evidence of in Earth’s fossil record.
From Geology to Quaternary Geology
There is however also a timescale in between the human timescale and that of macro scale species evolution. Within this far more recent part of our planet’s history the current disturbance of the radiative balance is unique at least over the last 20,000 years, stretching the entire Holocene up to the point where the Milankovitch cycles thought it fit to end the last ice age.
That’s what Swedish Quaternary geologist Svante Björck of Lund University writes in his Climatic Change publication (PDF) of three months ago. The many climatic fluctuations afterwards, including the Younger Dryas, the Holocene Thermal Maximum and The Little Ice Age, were all local disturbances.
On many such occasions it seems a temporary cooling on the northern hemisphere goes hand in hand with a warming on the southern hemisphere – and vice versa. This suggests the thermohaline circulation probably plays a large role in such climate hiccups – including a mechanism that is described as the bipolar seesaw.
© Rolf Schuttenhelm | www.bitsofscience.org