In 2009 a group of researchers published a paper (Rockstrom et al 2009) detailing 9 planetary boundaries which, as long as humanities activities did not result in moving the metrics describing those boundaries outside certain limits, would allow continued safe "Operating Space" for humans on our world. These nine boundaries are the following:
Climate Change
Phosphorus Flow
Ozone Depletion
Ocean Acidity
Atmospheric Aerosol Load
Fresh Water Consumption
Agricultural Land Use
Nitrogen Flow
Chemical Pollution
Biodiversity Loss
The paper identified metrics for 7 of these boundaries and the report and TED talk show where we are (as of 2009) in relation to those boundaries. As one might imagine it is not a very pretty picture. Especially give the passage of another 4 years. The paper discusses each boundary separately as well as discussing the important interactions between them. As of the writing of the paper we have exceeded the boundaries of 3 of the 7 for which the paper identified metrics; climate change, biodiversity loss and nitrogen flow. We are over the limit for nitrogen flow the most. Other boundaries where we are approaching the limits are agricultural land use, ocean acidity and phosphorus flow. The TED talk is very interesting (19min) and the paper itself is very comprehensive (it is a hard read and fairly long but worth it for those who want to see the actual work).
TED talk video here (given by the lead author):
http://www.stockholmresilience.org/planetary-boundariesAcademic paper here:
http://www.ecologyandsociety.org/vol14/iss2/art32/