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CO2 concentrations in our atmosphere are now higher than at any time in the past million years, and perhaps higher than in the past 15 million years.

There are lots of reasons to be concerned about this trend, not the least of which is the amplification of global warming through a positive feedback. (Since ice is a lot more reflective of sunlight than ocean water, melting sea ice allows more heat from the Sun to be absorbed instead of reflected, causing temperatures to rise more rapidly, thus melting more ice, and so forth, creating a positive feedback and raising the Earth’s reflectivity, also known as its albedo.)