Commentary in 2009

Despite their political popularity, carbon tariffs will be next to impossible to implement effectively, and as such will do little to solve the climate problem.

Policymakers must aim to avoid a 2 °C temperature rise, but plan to adapt to 4 °C.

Climate policy should aim to limit the rate of warming, as well as setting a cap on total allowable emissions.

In their efforts to make climate information more useful for adaptation decisions, scientists will need to be clear about the limits of climate prediction.

Humanity must learn to live within a stable Holocene environment, but the boundary limit for land use depends on more than the amount of surface covered.

Ocean acidification has impacts other than simple changes in pH, and these may need boundaries too.

Five per cent is a reasonable limit for acceptable ozone depletion, but it doesn't represent a tipping point.

For nitrogen deposition as for other pollution, waiting until we approach the limits of environmental degradation merely allows us to continue our bad habits until it's too late to change them.

Setting a limit on long-term atmospheric carbon dioxide concentrations merely distracts from the much more immediate challenge of limiting warming to 2 °C.

A global limit on water consumption is necessary, but the suggested planetary boundary of 4,000 cubic kilometres per year is too generous.

A boundary that expresses the probability of families of species disappearing over time would better reflect our potential impacts on the future of life on Earth.

National targets give virtually no chance of constraining warming to 2 °C and no chance of protecting coral reefs.

An oft-forgotten source of food security and livelihoods, fisheries must be included in ongoing discussions of how the world’s most vulnerable can adapt to climate change.

Emissions targets must be placed in the context of a cumulative carbon budget if we are to avoid dangerous climate change.