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Notes:
In less than 200 years human activity has increased the atmospheric concentration of greenhouse gases by some 50 % relative to preindustrial levels. at about 372 ppm, today’s atmospheric carbon dioxide level is higher than at any time in at least the past 420,000 years; data for the past 60,000 years are shown above.
There is no previous human experience of the Earth’s atmosphere at current levels of greenhouse gases to assist us to predict the outcomes. It is likely, though, that the natural oscillating pattern of ice ages and warm periods is now being disturbed. Are we currently entering the first enduring ‘hot period’ for over 50 million years?