Atmospheric CO_2 levels have risen from approximately 280 ppm in the preindustrial era to now over 400 ppm. There is scientific consensus that this rise is primarily an anthropogenic process—that it is human-caused and driven by rapid emission of greenhouse gases over this time period. The Earth's mean temperature rise relative to preindustrial values is already over 1℃ and is increasing at a rate of roughly 0.2℃ per decade. Should this trend continue past 1.5℃ and encroach on 2℃ and beyond, there is a risk (at high confidence levels) of severe, consequential transformations of global environmental systems.
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