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Sep
24
2009
Scientists propose nine thresholds for a safe planet
In this week’s Nature Buy viagra overnight delivery, , 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, Kopen goedkope viagra, biodiversity loss, nitrogen and phosphorus cycles, ozone depletion, ocean acidification, Osta viagra online, freshwater use, land use, Pharmacy viagra, atmospheric particulate concentrations, and chemical pollution. For instance, the amount of phosphorus that enters the ocean should not exceed 11 million tonnes per year, cheap viagra from canada, the authors say. If the Earth is kept within this safe zone, För viagra online, they write, the environment could remain relatively stable.
As one might expect, some of the thresholds have already been crossed. Atmospheric carbon dioxide concentrations, Arizona AZ Ariz. , extinction rates, and nitrogen usage have all overstepped acceptable limits, Buy viagra without prescription, 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, buy viagra overnight delivery. And their argument has provoked debate, as detailed in these associated commentaries. Boundaries may be comforting, viagra pills, 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
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