This article was written by Alex Steffen in January 2008. We're republishing it here as part of our month-long editorial retrospective.
The difference between greenhouse gas (GHG) stabilization levels and GHG peak targets is one we've failed to adequately explain. I may make a botch of this, but here goes:
Stabilization levels are our long-term goals: when Jim Hansen says we need a concentration of carbon dioxide in the atmosphere no more than 350 ppm, he's discussing where we need to end up in a certain time frame (many use the time frame 2050 or 2100 -- I'm not sure what Hansen's time frame here is). Though we're already over that level, with concerted effort and widespread innovation, we could bring CO2 concentrations down.
Peak target is another kind of measurement, a threshold above which we should stray. The consensus opinion here seems to be hovering around 450 ppm: meaning that if we exceed that amount of CO2 (and other GHGs) in the atmosphere, we're running serious risk of quickly crossing catastrophic tipping points.
I imagine an engine. For optimal performance and longevity, we should only run it so fast. It can be run faster, but wear and tear (and the possibility of break down) increase rapidly the longer we run it at faster speeds. Some speeds, however, are just too fast: above those speeds, we're likely to just burn the engine out altogether.
Stabilization level is the fastest speed at which we believe we can safely run the engine over time: peak target is the red zone, the speed at which the engine should never go.
(Thanks to Tariq Banuri for pointing out this key concept.)
Stabilization and Peak Targets: Understanding CO2 Numbers is part of our month long retrospective leading up to our anniversary on October 1. For the next four weeks, we'll celebrate five years of solutions-based, forward-thinking and innovative journalism by publishing the best of the Worldchanging archives.
"Peak target is another kind of measurement, a threshold above which we should stray."
I believe this should be "should not stray," yes?