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Earth - system Control Planetary boundary process variable(s) (zone of uncertainty) Land - system change (R2009: same) Freshwater use (R2009: Global freshwater use) Atmospheric aerosol loading (R2009: same) Introduction of novel entities (R2009: Chemical pollution) Global: Area of forested land as % of original forest cover Biome: Area of forested land as % of potential forest Global: Maximum amount of consumptive blue water use (km 3yr -1) Basin: Blue water withdrawal as % of mean monthly river flow Global: Aerosol Optical Depth (ACID), but much regional variation Regional: ACID as a seasonal average over a region. South Asian Monsoon used as a case study No control variable currently defined events in many regions of the world is increasing (I%); changes in atmospheric circulation patterns have increased drought in some regions of the world (I%); and the rate of combined mass loss from the Greenland and Antarctic ice sheets is increasing (36). Changes in biosphere integrity We propose a two- component approach, address- ing two key roles of the biosphere in the Earth system. The first captures the role of genetically unique material as the "information bank" that ultimately determines the potential for life to RESEARCH ( RESEARCHARTICLE Global: 75% (75 -54 %) Values are a weighted average of the three individual biome boundaries and their uncertainty zones Biome: Tropical: 85% (85 -60 %) Temperate: 50% (50 -30 %) Boreal: 85% (85 -60 %) Global: 4000 km3 yr 1 (4000 -6000 km3 yr 1) Basin: Maximum monthly withdrawal as a percentage of mean monthly river flow. For low -flow months: 25% (25 -55 %); for intermediate - flow months: 30% (30 -60 %); for high -flow months: 55% (55 -85 %) Regional: (South Asian Monsoon as a case study): anthropogenic total (absorbing and scattering) ACID over Indian subcontinent of 0.25 (0.25 - 0.50); absorbing (warming) ACID less than 10% of total ACID No boundary currently identified, but see boundary for stratospheric ozone for an example of a boundary related to a novel entity (CFCs) continue to coevolve with the abiotic component of the Earth system in the most resilient way possible. Genetic diversity provides the long -term capacity of the biosphere to persist under and adapt to abrupt and gradual abiotic change. The second captures the role of the biosphere in Earth - system functioning through the value, range, distribution, and relative abundance of the func- tional traits of the organisms present in an eco- system or biota (7). For the first role, the concept of phylogenetic species variability (PSV) (7 33, 37) would be an appropriate control variable. However, because Current value of control variable 62% -2600 km3 yr 1 0.30 ACID, over South Asian region global data are not yet available for PSV, we re- tain the global extinction rate as an interim con- trol variable, although it is measured inaccurately and with a time lag. There may be a considerable risk in using extinction rate as a control variable, because phylogenetic (and functional) diversity may be more sensitive to human pressures than species -level diversity (38). In principle, the bound- ary should be set at a rate of loss of PSV no greater than the rate of evolution of new PSV during the Holocene. Because that is unknown, we must fall back on the (imperfectly) known extinction rate of well- studied organisms over the past several SCIENCE sciencemag.org 13 FEBRUARY 2015 • VOL 347 ISSUE 6223 1259855 -5