Climate note #2: "The carbon budget"
In climate note #1, we noted this global consensus:
If humans are to avoid a massive die-off - and even steer well clear of possible human extinction - then within a single single human lifetime, net global carbon emissions from human activity must reach 0, and then go below 0.
To better understand what is required, scientists have asked this question:
How much CO2 can we add to the atmosphere before we have locked in temperatures beyond our best-hope 1.5°C limit?
Today we are adding carbon to the atmosphere very quickly. Each year, human activity adds about 42 billion metric tonnes of CO2 (aka "42 GtCO2") to the atmosphere.[1]
The consensus understanding today is that we will have a slightly better than a 50-50 chance of staying below the 1.5°C limit if we add not more than an additional 580 GtCO2. This is probably an optimistic estimate.
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