While the 400 ppm mark is somewhat symbolic (as the increase in warming between 399 ppm and 400 ppm is small), it is a large increase from pre-industrial CO2 concentrations, which were around 280 ppm. The progressively earlier occurrence of these high CO2 levels — not seen in somewhere between 800,000 and 15 million years — points to the inexorable buildup of heat-trapping gas in the atmosphere as human emissions continue unabated. That increase in CO2 and other greenhouse gases has raised Earth’s average temperature by 1.6°F since the beginning of the 20th century. Some scientists say that to avoid the worst consequences of climate change, that warming needs to stay under 2°C, or 3.6°F.
We’ve lived so long under the spell of hierarchy—from god-kings to feudal lords to party bosses—that only recently have we awakened to see not only that “regular” citizens have the capacity for self-governance, but that without their engagement our huge global crises cannot be addressed. The changes needed for human society simply to survive, let alone thrive, are so profound that the only way we will move toward them is if we ourselves, regular citizens, feel meaningful ownership of solutions through direct engagement. Our problems are too big, interrelated, and pervasive to yield to directives from on high.
—Frances Moore Lappé, excerpt from Time for Progressives to Grow Up