We are very near passing a milestone. The CO2 levels will likely soon reach 400 ppm at the Mauna Loa Observatory in Hawaii. The curve of course is named after Charles Keeling who started the measurements in 1958. They started it because even then there was concern that we might be dangerously interfering with our climate by burning fossil fuels. They just did not know, and when scientists do not know, they ask questions and make measurements.

Using ice cores you can compare the last 300 years:

and the last 800,000 years…

The daily readings are available from their Twitter feed here: https://twitter.com/@keeling_curve

Readings are also taken at the South Pole at Amundsen Scott Station. (Been there and bought the t-shirt). I even have a flask of air from the observatory. The readings go up and down each year as the seasons change in the Northern Hemisphere (where most of the plants are) so we will touch it and then drop back for a while, but eventually we will always be above it….The only question now is whether we will do something about it before we reach 500 ppm.

There’s a GIGANTIC mountain of scientific evidence now that says we’d better….

Andy Revkin and Greg Laden have good quality info on this as well.