<Oxygen was discovered in 1774. Testing the atmosphere for trace chemical elements came much later, yet here we have "the highest level for at least 420,000 years and probably for 20m years."

Oh yes, it's certain for 420,000 years - the 20m years is just probably!



To be fair, there are many methods for measuring atmospheric content other than directly, including gases locked in glaciers and many others. But I see you noticed the "mays," "coulds" and "probablies" that tend to be scattered through reports on these subjects.

That CO2 is increasing has been measured by many scientists. The graph published by environmentalists usually looks something like the following:

As with most statistics, clever use of the axis scales can make something look a lot worse than it is. We see here CO2 going from 315 ppm to 360 ppm, or to put it another way, from 3.15/10,000 to 3.6/10,000.

More information can be found here, including this graph over a longer time period:

The red line is a guess, based on the increases not changing any other variables. The rest of the site is worth browsing for methodology.

Note that the scientists can find out WHAT the climate was doing, but they still don't know WHY.

...We cannot instrument the past; the complex atmospheric processes can not be measured. The climate system must remain a black box

They still don't know exactly what's going on, which makes the red line on the graph kind of iffy.

Another informative article can be found here. Note the percentage of fossil fuel CO2 vs. the natural amounts in the cycle (its about 5 percent of it). Note also the "missing sink," which appears to be increasing along with the CO2, showing that we still don't have all the variables in hand.

IMO, if CO2 is a problem, the solution is not to destroy technology, but to advance it. Nuclear-powered production of hydrogen for a fuel-cell economy would be a damn good start. Environmentalists never balance the human effects of a few degrees in temperature rise against the human effects of wrecking the world economy. Damage can be done in more ways than one.