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Sep
24
2009
Scientists propose nine thresholds for a safe planet
In this week’s Nature, researchers lay out a new framework for evaluating the Earth’s environmental status. Humanity should stay within nine “planetary boundaries,” they argue – but we’ve already crossed three of them.
The boundaries are as follows: climate change, biodiversity loss, nitrogen and phosphorus cycles, ozone depletion, ocean acidification, freshwater use, land use, atmospheric particulate concentrations, and chemical pollution. For instance, the amount of phosphorus that enters the ocean should not exceed 11 million tonnes per year, the authors say. If the Earth is kept within this safe zone, they write, the environment could remain relatively stable.
As one might expect, some of the thresholds have already been crossed. Atmospheric carbon dioxide concentrations, extinction rates, and nitrogen usage have all overstepped acceptable limits, according to the authors. They warn that exceeding one threshold could affect other boundaries as well.
The team acknowledges that some of the threshold values are just initial guesses. And their argument has provoked debate, as detailed in these associated commentaries. Boundaries may be comforting, writes one scientist, “but waiting to act until we approach these limits merely allows us to continue with our bad habits until it’s too late to change them.” – Roberta Kwok
Source: Rockström, J., Steffen, W., Noone, K., Persson, A., Chapin, F., Lambin, E., Lenton, T., Scheffer, M., Folke, C., Schellnhuber, H., Nykvist, B., de Wit, C., Hughes, T., van der Leeuw, S., Rodhe, H., Sörlin, S., Snyder, P., Costanza, R., Svedin, U., Falkenmark, M., Karlberg, L., Corell, R., Fabry, V., Hansen, J., Walker, B., Liverman, D., Richardson, K., Crutzen, P., & Foley, J. (2009). A safe operating space for humanity Nature, 461 (7263), 472-475 DOI: 10.1038/461472a
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Filed Under Biodiversity, Climate change, Endangered species |
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