Sooner we urgently stop burning fossil fuels the better.

Professor Caroline Lear, one of the report’s co-authors from Cardiff University’s School of Earth and Environmental Sciences, said:   “Atmospheric CO2 concentrations have varied naturally in the past. Although these changes were far slower than the modern changes caused by burning fossil fuels, we can use them to understand how our planet responds to changes in CO2.

Our findings tell us that we will continue to see the impacts of our emissions for thousands of years, as the planet continues to warm and sea levels continue to rise. Phasing out fossil fuels is our only option to reduce this harm, and has never been more urgent.

Professor Caroline LearDean of Research and Innovation, College of Physical Sciences and Engineering

The new assessment shows the last time CO2 was consistently higher than now was about 16 million years ago, at about 480 parts per million (ppm) – the unit used to report CO2 concentrations.

By 14 million years ago it had sunk to today’s human-induced level of 420 ppm.

The decline continued, and by about 2.5 million years ago, CO2 reached about 270 or 280ppm kicking off a series of ice ages. It was at or below this figure when modern humans came into being about 400,000 years ago, and persisted there until the effects of widespread combustion of fossil fuels by humans took effect on a grand scale about 250 years ago.

FROM -  https://www.cardiff.ac.uk/news/view/2794064-66-million-year-history-of-carbon-dioxide-shows-climate-is-highly-sensitive-to-greenhouse-gases