• 350 ppm CO2 = 1°C warming (a warming we can live with, see 350.org) • 400 ppm CO2 = 1.5°C warming (things get worse for an increasing number of people) • 445 ppm CO2 = 2°C warming (dangerous warming, but the best we can hope for)6
2°C warming is a guardrail beyond which changes become catastrophic • 560 ppm CO2 = 3°C warming (really bad: and positive feedbacks accelerate) • 700 ppm CO2 = 4°C warming (To be avoided at all costs)7
6. (PDF download) Hansen et al. state that 2°C warming could be dangerous.
7. (PDF download) Turn Down The Heat: Why a 4°C Warmer World Must be Avoided.
We passed 400 ppm CO2 last year.
At current emission rates that are increasing CO2 at a rate of 2 ppm/year, we will blow past the budget for staying below 2°C warming within 20 years.The only possibility for avoiding 2°C warming is for humans to alter their behavior and reduce energy use while we bring low-carbon energy sources online. The Paris Accord is one a…