Peter Clack writes on X:
A common climate myth is that modern CO₂ is rising faster than anything in 800,000 years.
The truth is, no one can ever know. And this is where the science rubber really hits the road. There’s no way to measure the speed of previous warming episodes. This means no one can say modern warming is ‘unprecedented’.
The truth comes from science, the laws of physics and ice core studies for more than a century. Before snow turns into solid ice, it exists in what is known as the ‘firn’. This refers to the porous, packed layer of snow that eventually settles into glacial ice. But this doesn’t happen overnight.
These ice bubbles are not sealed from the surrounding air. So the air moves freely through this layer for decades or even centuries before the weight of new snow finally crushes the pores shut. This gas-age/ice-age difference is why a single slice of ice contains air that is significantly younger than the ice surrounding it.
Because the air can circulate during those 50 to 200 years (depending on the site’s snowfall rate), a single bubble doesn’t represent a year. It can represent a rolling average of a century.
If a massive CO₂ spike occurred 10,000 years ago but only lasted 40 years, the ice core would smooth it out. The spike would be averaged into the surrounding centuries of lower data, making it appear as a tiny, invisible bump.
Comparing a 20-year satellite trend to a 200-year ice core average is like comparing a high-definition photograph to a smudge of charcoal.
