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•   Current levels of atmospheric carbon dioxide are probably sufficient to trigger large-scale permafrost carbon feedbacks and global warming that human effort would be unable to contain.
• The time to slash emissions was a long time ago but now is still much, much better than later, which may, as new studies suggests, simply become too late.

Two future climate impacts above all others will overwhelm human efforts to mitigate global warming should temperatures and carbon dioxide levels reach critical levels, which in the latter case we are already close to achieving.     The last time carbon dioxide levels were apparently as high as they are today – and were sustained at those levels – global temperatures were 3 to 6 degrees Celsius higher than they are today, the sea level was approximately 25 to 40 metres higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland.