Ralph Keeling and Dad

Paul spotted this branch of the family first, in the Economist yawn and David said he had "heard of Charles David". The clan lives on!

I would have picked it up sooner if I paid more attention to my beloved New Scientist and if it came by Transporter Beam.

It's a psychological milestone. Every year in the last few decades, CO2concentrations have been going up by about 2 ppm per year. Those changes go unnoticed but people pay attention to round numbers. It gives you a bit of perspective on how far we've come – a bit like turning 40, or 50.
So how far have we come?
What did Earth look like 3-5 million years ago?
Are we in a climate danger zone?
In my view, yes. At 400 ppm, we've perturbed Earth enough already that things could unfold that will be catastrophic.
Why did he start tracking CO2 at Mauna Loa?
The early days at Mauna Loa were fraught. Power outages meant the measuring instrument had to be shut down for weeks. It would come back on reading a different level. He thought there should be a stable background, but concentrations were fluctuating. It was only when he'd gathered a year of data that he realised there was a seasonal cycle.
So levels may drop below 400 ppm again?
This article appeared in print under the headline "One minute with... Ralph Keeling"