In 2009, a paper was published that measured where humanity stood in respects to the safe operating boundaries for nine environmental parameters ( Rockström et al. 2009 ). The nine they chose were climate change, ocean acidification, stratospheric ozone depletion, rate of biodiversity loss, biogeochemical cycles (specifically, the nitrogen and phosphorus cycles), global freshwater use, change in land use, atmospheric aerosol loading, and chemical pollution. Using the Holocene as a baseline, they calculated threshold levels for each parameter that, when crossed, created a high risk for changes that would be damaging for human civilization.