A missing bit of information in the article, Carbon dioxide at highest levels for over 2.5 million years, expert warns of 100 years of disruption, is that from about 1400 AD until about 1850 AD, the Earth was in a period called the Little Ice Age.
Climate scientists have not determined what caused this cool period. The onset was sudden. It happened over the course of about 100 years. The atmosphere was cooler during this period, by about one degree Celsius, than what it had been before 1400 AD and is only now getting back to the normal temperature for Earth in recent history.
The cold Little Ice Age, at about one degree cooler, is not a temperature that we want to return to. In 1850, the ending of the Little Ice Age, is about when thermometers were first available, and that cold time of 1850 is climate scientists’ starting point for recorded Earth temperatures.
The onset of the Little Ice Age was quite sudden, as has been its retreat. There is no explanation for it, and the level of CO2 in the atmosphere could not have caused the onset or the start of the retreat. Maybe it was related to the sun’s output.
There needs to be more investigation into the relationship between CO2 levels in our atmosphere and temperature, as the correlation between them is not as direct as climate scientists have theorized.
Earth has experienced little to no temperature increase since 1998, even as our atmospheric CO2 level has continuously risen from about 365 parts per million (ppm) in 1998 to 410 ppm today.
The current 410 ppm of CO2 in our atmosphere, even though it is higher than Earth has had in thousands of years, is still a very small concentration.