Safe Operating Space

A fascinating paper in Nature  (Johan Rockstrom, et al) proposes a framework of "planetary boundaries" that define a "safe operating space" for humanity with respect to the Earth system, so that environmental stability of the last 10,000 years (known as the Holocene) -- which has seen human civilizations develop and thrive -- can continue for several thousand more years. The framework involves nine planetary system processes with proposed boundaries for seven of them (the other two are TBD).

Here are the processes that have already crossed their boundaries:

Earth System Process	Parameters	Proposed Boundary	Current Status
Climate change	Atmospheric carbon dioxide concentration (parts per million by volume)	350	387
Climate change	Change in radiative forcing (watts per meter squared)	1	1.5
Rate of biodiversity loss	Extinction rate (number of species per million species per year)	10	>100
Nitrogen cycle (part of a boundary with the Phosphorous cycle)	Amount of N2 removed from the atmosphere for human use (millions of tonnes per year)	35	121

The climate change boundaries result from three reasons:

1. Current models may underestimate long-term climate change because slow reinforcing feedback loops are not included.
2. The stability of the polar ice sheets are at risk when the CO2 concentration is betweek 350 and 550 ppm (based on paleoclimate data).
3. Some subsystems (such as ice in the Arctic ocean, and Greenland/West Antarctic ice sheets) are already moving outside their stable Holocene state.

Kumar Venkat