Carbon dioxide is the most important long-lived global warming gas, and once it is emitted by burning fossil fuels such as coal and oil, a single CO2 molecule can remain in the atmosphere for hundreds of years...
By drilling for ice cores and analyzing the air bubbles, scientists have found that, at no point during at least the past 800,000 years have atmospheric CO2 levels been as high as they are now...
For a 2009 study, published in the journal Science, scientists analyzed shells in deep sea sediments to estimate past CO2 levels, and found that CO2 levels have not been as high as they are now for at least the past 10 to 15 million years, during the Miocene epoch.
Text from
Climate Central, via
On Weather. While it's possible that there may have been transient spikes in the remote past not sampled in ice-core type data, there is no arguing about the direction of the present trend (Keeling curve at top) or the departure from historic norms.
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