What Difference Does 350 Make?

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350 at BU's Marsh Plaza

This past Saturday (October 24th) was the International Day of Climate Action. The “Action” chosen this year was thousands of displays of the number “350” around the globe, including the above, at BU‘s Marsh Plaza. The number refers to the carbon dioxide atmospheric load in parts per million. This commonly used metric is the independent variable upon which policymakers base their reduction targets.

There has been quite a lot of press in the run-up to the event exclaiming how 350 ppm is the maximum load under which the climate would remain stable. The number comes from Jim Hansen, the NASA climate scientist, by way of environmentalist Bill McKibben. It is something of an arbitrary number (why not 365?), but more importantly, politically untenable. The IPCC barely recognizes 350 as a possible stabilization level in its latest synthesis report, and even pro-environment lawmakers do not see this target as attainable. Continue reading