MUCH of today’s discourse about environmental problems revolves around the need to reduce greenhouse gas (GHG) emissions. But, according to the Stockholm Resilience Centre, that’s not nearly enough. The Earth is facing environmental tipping points along planetary boundaries, which revolve around not just climate change, but also stratospheric ozone, biodiversity, chemicals dispersion, ocean acidification, freshwater consumption, land system change, nitrogen and phosphorus discharge and atmospheric aerosol emissions. These boundaries represent load-bearing limits on human activity.

In order to avoid catastrophic tipping points, people need to start now to effectively manage key Earth system processes. Whether or not humanity will be able to stabilize climate within safe levels depends upon its ability to reduce emissions and constructively manage a number of critical natural systems on the planet.

The planetary boundaries hypothesis is based on the idea that humanity has been able to flourish during the stable conditions on Earth of the last 10,000 years, a period known as the Holocene epoch. Hence human society needs to make sure that those stable biophysical conditions don’t get disrupted.

The boundaries need to be quantified because there is a need to avoid unacceptable environmental change. Three of the boundaries, climate change, biodiversity loss and global nitrogen, have already been crossed. Freshwater use, ocean acidification and global phosphorous are close to being crossed. Boundaries for aerosol loading and chemical pollution remain undefined, and land use change is seen as something that ought to have limits but has no natural boundary or tipping point.

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