Four of the nine planetary boundaries identified by scientists in 2009 have now been exceeded, according to research published in Science.
The boundaries consist of: climate change; loss of biodiversity (renamed as biosphere integrity to better reflect the effect humans have on the functioning of ecosystems); ozone depletion; ocean acidification; biogeochemic to reflect flows (the flow of nitrogen and phosphorus); land-system change (deforestation); freshwater use; atmospheric aerosol loading; and chemical pollution.
The four that have been crossed are: extinction rate (one of two indicators for biosphere integrity); deforestation; atmospheric carbon dioxide (an indicator for climate change); and the flow of nitrogen and phosphorus.
Scientists believe that crossing planetary boundaries increases the risk of the Earth system moving to a much less hospitable state for human civilisation than the current one, which is known as the Holocene epoch.