Table 1 The updated control variables and their current values, along with the proposed boundaries and zones of uncertainty, for all nine planetary boundaries.

In the first column, the name for the Earth-system process used in the original PB publication (R2009, reference 1) is given for comparison.

Earth-system
process
Control
variable(s)
Planetary boundary
(zone of uncertainty)
Current value of
control variable
Climate
change
(R2009:
same)
Atmospheric CO2
concentration, ppm
Energy imbalance
at top-of-
atmosphere, W m-2
350 ppm CO2 (350-450 ppm)
+1.0 W m-2 (+1.0-1.5 W m-2)
398.5 ppm CO2
2.3 W m-2
(1.1-3.3 W m-2)
Change in
biosphere
integrity
(R2009:
Rate of
biodiversity
loss)
Genetic diversity:
Extinction rate
Functional diversity:
Biodiversity
Intactness Index (BII)
Note: These are
interim control
variables until more
appropriate ones are
developed
< 10 E/MSY (10-100 E/MSY)
but with an aspirational goal of
ca. 1 E/MSY (the background
rate of extinction loss). E/MSY =
extinctions per million species-years
Maintain BII at 90% (90-30%)
or above, assessed
geographically by biomes/large
regional areas (e.g. southern
Africa), major marine
ecosystems (e.g., coral reefs) or
by large functional groups
100-1000 E/MSY
84%, applied to
southern Africa
only
Stratospheric
ozone
depletion
(R2009: same)
Stratospheric O3
concentration, DU
<5% reduction from pre-
industrial level of 290 DU
(5%–10%), assessed by
latitude
Only transgressed
over Antarctica in
Austral spring
(~200 DU)
Ocean
acidification
(R2009:
same)
Carbonate ion
concentration,
average global
surface ocean
saturation state with
respect to aragonite
arag)
≥80% of the pre-industrial
aragonite saturation state of
mean surface ocean, including
natural diel and seasonal
variability (≥80%– ≥70%)
~84% of the
pre-industrial
aragonite
saturation state
Biogeochemical
flows: (P and
N cycles)
(R2009:
Biogeochemical
flows: (interference
with P and N
cycles))
P Global: P flow
from freshwater
systems into the
ocean
P Regional: P flow
from fertilizers to
erodible soils
N Global: Industrial
and intentional
biological fixation
of N
11 Tg P yr-1 (11-100 Tg P yr-1)
6.2 Tg yr-1 mined and applied to
erodible (agricultural) soils
(6.2-11.2 Tg yr-1). Boundary is a
global average but regional
distribution is critical for
impacts.
62 Tg N yr-1 (62-82 Tg N yr-1).
Boundary acts as a global
‘valve’ limiting introduction of
new reactive N to Earth System,
but regional distribution of
fertilizer N is critical for
impacts.
~22 Tg P yr-1
~14 Tg P yr-1
~150 Tg N yr-1
Land-system
change
(R2009:
same)
Global: Area of
forested land as %
of original forest
cover
Biome: Area of
forested land as %
of potential forest
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%)
62%
Freshwater
use
(R2009:
Global
freshwater
use)
Global: Maximum
amount of
consumptive blue
water use (km3yr-1)
Basin: Blue water
withdrawal as % of
mean monthly river
flow
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%)
~2600 km3 yr-1
Atmospheric
aerosol
loading
(R2009:
same)
Global: Aerosol
Optical Depth
(AOD), but much
regional variation
Regional: AOD as
a seasonal average
over a region. South
Asian Monsoon
used as a case study
Regional: (South Asian
Monsoon as a case study):
anthropogenic total (absorbing
and scattering) AOD over
Indian subcontinent of 0.25
(0.25-0.50); absorbing
(warming) AOD less than 10%
of total AOD
0.30 AOD, over
South Asian
region
Introduction
of novel entities
(R2009: Chemical
pollution)
No control variable
currently defined
No boundary currently
identified, but see boundary
for stratospheric ozone for an
example of a boundary
related to a novel entity (CFCs)