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We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a "Hothouse Earth" pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System-biosphere, climate, and societies-and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.
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Trajectories of the Earth System in
the Anthropocene
Will Steffen
, Johan Rockström
, Katherine Richardson
, Timothy M. Lenton
, Diana Liverman
Colin P. Summerhayes
, Anthony D. Barnosky
, Sarah E. Cornell
, Michel Crucifix
, Jonathan F. Donges
Ingo Fetzer
, Steven J. Lade
, Ricarda Winkelmann
, and Hans Joachim Schellnhuber
Edited by William C. Clark, Harvard University, Cambridge, MA, and approved July 6, 2018 (received for review June 19, 2018)
We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary
threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and
cause continued warming on a Hothouse Earthpathway even as human emissions are reduced. Crossing
the threshold would lead to a much higher global average temperature than any interglacial in the past
1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine
the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the
resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Col-
lective human action is required to steer the Earth System away from a potential threshold and stabilize it in a
habitable interglacial-like state. Such action entails stewardship of the entire Earth Systembiosphere,
climate, and societiesand could include decarbonization of the global economy, enhancement of biosphere
carbon sinks, behavioral changes, technological innovations, new governance arrangements, and trans-
formed social values.
Earth System trajectories
climate change
biosphere feedbacks
tipping elements
The Anthropocene is a proposed new geological ep-
och (1) based on the observation that human impacts
on essential planetary processes have become so pro-
found (2) that they have driven the Earth out of the
Holocene epoch in which agriculture, sedentary com-
munities, and eventually, socially and technologically
complex human societies developed. The formaliza-
tion of the Anthropocene as a new geological epoch is
being considered by the stratigraphic community (3),
but regardless of the outcome of that process, it is
becoming apparent that Anthropocene conditions
transgress Holocene conditions in several respects
(2). The knowledge that human activity now rivals geo-
logical forces in influencing the trajectory of the Earth
System has important implications for both Earth Sys-
tem science and societal decision making. While
recognizing that different societies around the world
have contributed differently and unequally to pres-
sures on the Earth System and will have varied capa-
bilities to alter future trajectories (4), the sum total of
human impacts on the system needs to be taken into
account for analyzing future trajectories of the
Earth System.
Here, we explore potential future trajectories of the
Earth System by addressing the following questions.
Is there a planetary threshold in the trajectory of the
Earth System that, if crossed, could prevent stabili-
zation in a range of intermediate temperature rises?
Given our understanding of geophysical and bio-
sphere feedbacks intrinsic to the Earth System,
where might such a threshold be?
Stockholm Resilience Centre, Stockholm University, 10691 Stockholm, Sweden;
Fenner School of Environment and Society, The Australian
National University, Canberra, ACT 2601, Australia;
Center for Macroecology, Evolution, and Climate, University of Copenhagen, Natural History
Museum of Denmark, 2100 Copenhagen, Denmark;
Earth System Science Group, College of Life and Environmental Sciences, University of Exeter,
EX4 4QE Exeter, United Kingdom;
The Beijer Institute of Ecological Economics, The Royal Swedish Academy of Science, SE-10405 Stockholm, Sweden;
School of Geography and Development, The University of Arizona, Tucson, AZ 85721;
Scott Polar Research Institute, Cambridge University, CB2 1ER
Cambridge, United Kingdom;
Jasper Ridge Biological Preserve, Stanford University, Stanford, CA 94305;
Earth and Life Institute, Universit ´ecatholiquede
Louvain, 1348 Louvain-la-Neuve, Belgium;
Belgian National Fund of Scientific Research, 1000 Brussels, Belgium;
Research Domain Earth System Analysis,
Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany;
Department of Environmental Sciences, Wageningen University & Research,
6700AA Wageningen, The Netherlands; and
Department of Physics and Astronomy, University of Potsdam, 14469 Potsdam, Germany
Author contributions: W.S., J.R., K.R., T.M.L., C.F., D.L., C.P.S., A.D.B., S.E.C., M.C., J.F.D., I.F., S.J.L., M.S., R.W., and H.J.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Published under the PNAS license.
To whom correspondence may be addressed. Email: or
This article contains supporting information online at PNAS Latest Articles
If a threshold is crossed, what are the implications, especially for
the wellbeing of human societies?
What human actions could create a pathway that would steer
the Earth System away from the potential threshold and toward
the maintenance of interglacial-like conditions?
Addressing these questions requires a deep integration of
knowledge from biogeophysical Earth System science with that
from the social sciences and humanities on the development and
functioning of human societies (5). Integrating the requisite knowl-
edge can be difficult, especially in light of the formidable range of
timescales involved. Increasingly, concepts from complex systems
analysis provide a framework that unites the diverse fields of in-
quiry relevant to the Anthropocene (6). Earth System dynamics
can be described, studied, and understood in terms of trajectories
between alternate states separated by thresholds that are con-
trolled by nonlinear processes, interactions, and feedbacks. Based
on this framework, we argue that social and technological trends
and decisions occurring over the next decade or two could sig-
nificantly influence the trajectory of the Earth System for tens to
hundreds of thousands of years and potentially lead to conditions
that resemble planetary states that were last seen several millions
of years ago, conditions that would be inhospitable to current
human societies and to many other contemporary species.
Risk of a Hothouse Earth Pathway
Limit Cycles and Planetary Thresholds. The trajectory of the
Earth System through the Late Quaternary, particularly the Holo-
cene, provides the context for exploring the human-driven
changes of the Anthropocene and the future trajectories of the
system (SI Appendix has more detail). Fig. 1 shows a simplified
representation of complex Earth System dynamics, where the
physical climate system is subjected to the effects of slow changes
in Earths orbit and inclination. Over the Late Quaternary (past
1.2 million years), the system has remained bounded between
glacial and interglacial extremes. Not every glacialinterglacial
cycle of the past million years follows precisely the same trajectory
(7), but the cycles follow the same overall pathway (a term that we
use to refer to a family of broadly similar trajectories). The full glacial
and interglacial states and the ca. 100,000-years oscillations be-
tween them in the Late Quaternary loosely constitute limit cycles
(technically, the asymptotic dynamics of ice ages are best modeled
as pullback attractors in a nonautonomous dynamical system). This
limit cycle is shown in a schematic fashion in blue in Fig. 1, Lower
Left using temperature and sea level as the axes. The Holocene is
represented by the top of the limit cycle loop near the label A.
The current position of the Earth System in the Anthropocene
is shown in Fig. 1, Upper Right by the small ball on the pathway
that leads away from the glacialinterglacial limit cycle. In Fig. 2, a
stability landscape, the current position of the Earth System is
represented by the globe at the end of the solid arrow in the
deepening Anthropocene basin of attraction.
The Anthropocene represents the beginning of a very rapid
human-driven trajectory of the Earth System away from the gla-
cialinterglacial limit cycle toward new, hotter climatic conditions
and a profoundly different biosphere (2, 8, 9) (SI Appendix). The
current position, at over 1 °C above a preindustrial baseline (10), is
nearing the upper envelope of interglacial conditions over the
past 1.2 million years (SI Appendix, Table S1). More importantly,
the rapid trajectory of the climate system over the past half-
century along with technological lock in and socioeconomic
inertia in human systems commit the climate system to conditions
beyond the envelope of past interglacial conditions. We, there-
fore, suggest that the Earth System may already have passed one
fork in the roadof potential pathways, a bifurcation (near A in
Fig. 1) taking the Earth System out of the next glaciation cycle (11).
In the future, the Earth System could potentially follow many
trajectories (12, 13), often represented by the large range of
global temperature rises simulated by climate models (14). In
most analyses, these trajectories are largely driven by the amount
of greenhouse gases that human activities have already emitted
and will continue to emit into the atmosphere over the rest of this
century and beyondwith a presumed quasilinear relationship
between cumulative carbon dioxide emissions and global tem-
perature rise (14). However, here we suggest that biogeophysical
feedback processes within the Earth System coupled with direct
human degradation of the biosphere may play a more important
role than normally assumed, limiting the range of potential future
trajectories and potentially eliminating the possibility of the in-
termediate trajectories. We argue that there is a significant risk
that these internal dynamics, especially strong nonlinearities in
feedback processes, could become an important or perhaps,
even dominant factor in steering the trajectory that the Earth
System actually follows over coming centuries.
Fig. 1. A schematic illustration of possible future pathways of the
climate against the background of the typical glacialinterglacial
cycles (Lower Left). The interglacial state of the Earth System is at the
top of the glacialinterglacial cycle, while the glacial state is at the
bottom. Sea level follows temperature change relatively slowly
through thermal expansion and the melting of glaciers and ice caps.
The horizontal line in the middle of the figure represents the
preindustrial temperature level, and the current position of the Earth
System is shown by the small sphere on the red line close to the
divergence between the Stabilized Earth and Hothouse Earth
pathways. The proposed planetary threshold at 2 °C above the
preindustrial level is also shown. The letters along the Stabilized Earth/
Hothouse Earth pathways represent four time periods in Earths recent
past that may give insights into positions along these pathways (SI
Appendix): A, Mid-Holocene; B, Eemian; C, Mid-Pliocene; and D,
Mid-Miocene. Their positions on the pathway are approximate only.
Their temperature ranges relative to preindustrial are given in SI
| Steffen et al.
This risk is represented in Figs. 1 and 2 by a planetary threshold
(horizontal broken line in Fig. 1 on the Hothouse Earth pathway
around 2 °C above preindustrial temperature). Beyond this
threshold, intrinsic biogeophysical feedbacks in the Earth System
(Biogeophysical Feedbacks) could become the dominant pro-
cesses controlling the systems trajectory. Precisely where a po-
tential planetary threshold might be is uncertain (15, 16). We
suggest 2 °C because of the risk that a 2 °C warming could acti-
vate important tipping elements (12, 17), raising the temperature
further to activate other tipping elements in a domino-like cas-
cade that could take the Earth System to even higher tempera-
tures (Tipping Cascades). Such cascades comprise, in essence, the
dynamical process that leads to thresholds in complex systems
(section 4.2 in ref. 18).
This analysis implies that, even if the Paris Accord target of a
1.5 °C to 2.0 °C rise in temperature is met, we cannot exclude the
risk that a cascade of feedbacks could push the Earth System
irreversibly onto a Hothouse Earthpathway. The challenge that
humanity faces is to create a Stabilized Earthpathway that steers
the Earth System away from its current trajectory toward the
threshold beyond which is Hothouse Earth (Fig. 2). The human-
created Stabilized Earth pathway leads to a basin of attraction
that is not likely to exist in the Earth Systems stability landscape
without human stewardship to create and maintain it. Creating such
a pathway and basin of attraction requires a fundamental change in
the role of humans on the planet. This stewardship role requires
deliberate and sustained action to become an integral, adaptive
part of Earth System dynamics, creating feedbacks that keep the
system on a Stabilized Earth pathway (Alternative Stabilized
Earth Pathway).
We now explore this critical question in more detail by con-
sidering the relevant biogeophysical feedbacks (Biogeophysical
Feedbacks) and the risk of tipping cascades (Tipping Cascades).
Biogeophysical Feedbacks. The trajectory of the Earth System is
influenced by biogeophysical feedbacks within the system that
can maintain it in a given state (negative feedbacks) and those that
can amplify a perturbation and drive a transition to a different
state (positive feedbacks). Someof the key negative feedbacks that
could maintain the Earth System in Holocene-like conditions
notably, carbon uptake by land and ocean systemsare weakening
relative to human forcing (19), increasing the risk that positive
feedbacks could play an important role in determining the Earth
Systems trajectory. Table 1 summarizes carbon cycle feedbacks
that could accelerate warming, while SI Appendix,TableS2de-
scribes in detail a more complete set of biogeophysical feedbacks
that can be triggered by forcing levels likely to be reached within
the rest of the century.
Most of the feedbacks can show both continuous responses
and tipping point behavior in which the feedback process
becomes self-perpetuating after a critical threshold is crossed;
subsystems exhibiting this behavior are often called tipping el-
ements(17). The type of behaviorcontinuous response or
tipping point/abrupt changecan depend on the magnitude or
the rate of forcing, or both. Many feedbacks will show some
gradual change before the tipping point is reached.
A few of the changes associated with the feedbacks are re-
versible on short timeframes of 50100 years (e.g., change in
Arctic sea ice extent with a warming or cooling of the climate;
Antarctic sea ice may be less reversible because of heat accu-
mulation in the Southern Ocean), but most changes are largely
irreversible on timeframes that matter to contemporary societies
(e.g., loss of permafrost carbon). A few of the feedbacks do not
have apparent thresholds (e.g., change in the land and ocean
physiological carbon sinks, such as increasing carbon uptake due
Table 1. Carbon cycle feedbacks in the Earth System that could accelerate global warming
Strength of feedback
by 2100,* °C
Refs. (SI Appendix, Table
S2 has more details)
Permafrost thawing 0.09 (0.040.16) 2023
Relative weakening of land and ocean physiological C sinks 0.25 (0.130.37) 24
Increased bacterial respiration in the ocean 0.02 25, 26
Amazon forest dieback 0.05 (0.030.11) 27
Boreal forest dieback 0.06 (0.020.10) 28
Total 0.47 (0.240.66)
The strength of the feedback is estimated at 2100 for an 2 °C warming.
*The additional temperature rise (degrees Celsius) by 2100 arising from the feedback.
Fig. 2. Stability landscape showing the pathway of the Earth System
out of the Holocene and thus, out of the glacialinterglacial limit cycle
to its present position in the hotter Anthropocene. The fork in the
road in Fig. 1 is shown here as the two divergent pathways of the
Earth System in the future (broken arrows). Currently, the Earth
System is on a Hothouse Earth pathway driven by human emissions of
greenhouse gases and biosphere degradation toward a planetary
threshold at 2 °C (horizontal broken line at 2 °C in Fig. 1), beyond which
the system follows an essentially irreversible pathway driven by intrinsic
biogeophysical feedbacks. The other pathway leads to Stabilized Earth, a
pathway of Earth System stewardship guided by human-created
feedbacks to a quasistable, human-maintained basin of attraction.
Stability(vertical axis) is defined here as the inverse of the potential
energy of the system. Systems in a highly stable state (deep valley) have
low potential energy, and considerable energy is required to move them
out of this stable state. Systems in an unstable state (top of a hill) have
high potential energy, and they require only a little additional energy to
push them off the hill and down toward a valley of lower potential energy.
Steffen et al. PNAS Latest Articles
to the CO
fertilization effect or decreasing uptake due to a de-
crease in rainfall). For some of the tipping elements, crossing the
tipping point could trigger an abrupt, nonlinear response (e.g.,
conversion of large areas of the Amazon rainforest to a savanna or
seasonally dry forest), while for others, crossing the tipping point
would lead to a more gradual but self-perpetuating response
(large-scale loss of permafrost). There could also be considerable
lags after the crossing of a threshold, particularly for those tipping
elements that involve the melting of large masses of ice. However,
in some cases, ice loss can be very rapid when occurring as
massive iceberg outbreaks (e.g., Heinrich Events).
For some feedback processes, the magnitudeand even the
directiondepend on the rate of climate change. If the rate of
climate change is small, the shift in biomes can track the change in
temperature/moisture, and the biomes may shift gradually, po-
tentially taking up carbon from the atmosphere as the climate warms
and atmospheric CO
concentration increases. However, if the rate of
climate change is too large or too fast, a tipping point can be crossed,
and a rapid biome shift may occur via extensive disturbances (e.g.,
wildfires, insect attacks, droughts) that can abruptly remove an
existing biome. In some terrestrial cases, such as widespread wild-
fires, there could be a pulse of carbon to the atmosphere, which if
large enough, could influence the trajectory of the Earth System (29).
Varying response rates to a changing climate could lead to
complex biosphere dynamics with implications for feedback
processes. For example, delays in permafrost thawing would most
likely delay the projected northward migration of boreal forests
(30), while warming of the southern areas of these forests could
result in their conversion to steppe grasslands of significantly
lower carbon storage capacity. The overall result would be a
positive feedback to the climate system.
The so-called greeningof the planet, caused by enhanced
plant growth due to increasing atmospheric CO
(31), has increased the land carbon sink in recent decades (32).
However, increasing atmospheric CO
raises temperature, and
hotter leaves photosynthesize less well. Other feedbacks are also
involvedfor instance, warming the soil increases microbial res-
piration, releasing CO
back into the atmosphere.
Our analysis focuses on the strength of the feedback between
now and 2100. However, several of the feedbacks that show
negligible or very small magnitude by 2100 could nevertheless be
triggered well before then, and they could eventually generate
significant feedback strength over longer timeframescenturies
and even millenniaand thus, influence the long-term trajectory
of the Earth System. These feedback processes include perma-
frost thawing, decomposition of ocean methane hydrates, in-
creased marine bacterial respiration, and loss of polar ice sheets
accompanied by a rise in sea levels and potential amplification of
temperature rise through changes in ocean circulation (33).
Tipping Cascades. Fig. 3 shows a global map of some potential
tipping cascades. The tipping elements fall into three clusters
based on their estimated threshold temperature (12, 17, 39).
Cascades could be formed when a rise in global temperature
reaches the level of the lower-temperature cluster, activating
tipping elements, such as loss of the Greenland Ice Sheet or Arctic
sea ice. These tipping elements, along with some of the non-
tipping element feedbacks (e.g., gradual weakening of land and
ocean physiological carbon sinks), could push the global average
temperature even higher, inducing tipping in mid- and higher-
temperature clusters. For example, tipping (loss) of the Green-
land Ice Sheet could trigger a critical transition in the Atlantic
Meridional Ocean Circulation (AMOC), which could together, by
causing sea-level rise and Southern Ocean heat accumulation,
accelerate ice loss from the East Antarctic Ice Sheet (32, 40) on
timescales of centuries (41).
Observations of past behavior support an important contri-
bution of changes in ocean circulation to such feedback cascades.
During previous glaciations, the climate system flickered between
two states that seem to reflect changes in convective activity in the
Nordic seas and changes in the activity of the AMOC. These
variations caused typical temperature response patterns called the
bipolar seesaw(4244). During extremely cold conditions in the
north, heat accumulated in the Southern Ocean, and Antarctica
warmed. Eventually, the heat made its way north and generated
subsurface warming that may have been instrumental in destabi-
lizing the edges of the Northern Hemisphere ice sheets (45).
If Greenland and the West Antarctic Ice Sheet melt in the fu-
ture, the freshening and cooling of nearby surface waters will have
significant effects on the ocean circulation. While the probability
of significant circulation changes is difficult to quantify, climate
model simulations suggest that freshwater inputs compatible with
current rates of Greenland melting are sufficient to have mea-
surable effects on ocean temperature and circulation (46, 47).
Sustained warming of the northern high latitudes as a result of this
process could accelerate feedbacks or activate tipping elements
in that region, such as permafrost degradation, loss of Arctic sea
ice, and boreal forest dieback.
While this may seem to be an extreme scenario, it illustrates
that a warming into the range of even the lower-temperature
cluster (i.e., the Paris targets) could lead to tipping in the mid- and
higher-temperature clusters via cascade effects. Based on this
analysis of tipping cascades and taking a risk-averse approach, we
suggest that a potential planetary threshold could occur at a
temperature rise as low as 2.0 °C above preindustrial (Fig. 1).
Alternative Stabilized Earth Pathway
If the worlds societies want to avoid crossing a potential threshold
that locks the Earth System into the Hothouse Earth pathway, then
it is critical that they make deliberate decisions to avoid this risk
Fig. 3. Global map of potential tipping cascades. The individual
tipping elements are color- coded according to estimated thresholds
in global average surface temperature (tipping points) (12, 34).
Arrows show the potential interactions among the tipping elements
based on expert elicitation that could generate cascades. Note that,
although the risk for tipping (loss of) the East Antarctic Ice Sheet is
proposed at >5 °C, some marine-based sectors in East Antarctica may
be vulnerable at lower temperatures (3538).
| Steffen et al.
and maintain the Earth System in Holocene-like conditions. This
human-created pathway is represented in Figs. 1 and 2 by what
we call Stabilized Earth (small loop at the bottom of Fig. 1, Upper
Right), in which the Earth System is maintained in a state with a
temperature rise no greater than 2 °C above preindustrial (a
super-Holocenestate) (11). Stabilized Earth would require deep
cuts in greenhouse gas emissions, protection and enhancement of
from the atmosphere,
possibly solar radiation management, and adaptation to unavoidable
impacts of the warming already occurring (48). The short broken red
line beyond Stabilized Earth in Fig. 1, Upper Right represents a po-
tential return to interglacial-like conditions in the longer term.
In essence, the Stabilized Earth pathway could be conceptu-
alized as a regime of the Earth System in which humanity plays an
active planetary stewardship role in maintaining a state in-
termediate between the glacialinterglacial limit cycle of the Late
Quaternary and a Hothouse Earth (Fig. 2). We emphasize that
Stabilized Earth is not an intrinsic state of the Earth System but
rather, one in which humanity commits to a pathway of ongoing
management of its relationship with the rest of the Earth System.
A critical issue is that, if a planetary threshold is crossed toward
the Hothouse Earth pathway, accessing the Stabilized Earth
pathway would become very difficult no matter what actions hu-
man societies might take. Beyond the threshold, positive (reinforcing)
feedbacks within the Earth Systemoutside of human influence or
controlcould become the dominant driver of the systems pathway,
as individual tipping elements create linked cascades through time
and with rising temperature (Fig. 3). In other words, after the Earth
System is committed to the Hothouse Earth pathway, the alternative
Stabilized Earth pathway would very likely become inaccessible as
illustrated in Fig. 2.
What Is at Stake? Hothouse Earth is likely to be uncontrollable
and dangerous to many, particularly if we transition into it in only a
century or two, and it poses severe risks for health, economies, po-
litical stability (12, 39, 49, 50) (especially for the most climate vul-
nerable), and ultimately, the habitability of the planet for humans.
Insights into the risks posed by the rapid climatic changes
emerging in the Anthropocene can be obtained not only from
contemporary observations (5155) but also, from interactions in
the past between human societies and regional and seasonal
hydroclimate variability. This variability was often much more
pronounced than global, longer-term Holocene variability (SI
Appendix). Agricultural production and water supplies are espe-
cially vulnerable to changes in the hydroclimate, leading to hot/
dry or cool/wet extremes. Societal declines, collapses, migrations/
resettlements, reorganizations, and cultural changes were often
associated with severe regional droughts and with the global
megadrought at 4.23.9 thousand years before present, all oc-
curring within the relative stability of the narrow global Holocene
temperature range of approximately ±1 °C (56).
SI Appendix, Table S4 summarizes biomes and regional bio-
spherephysical climate subsystems critical for human wellbeing
and the resultant risks if the Earth System follows a Hothouse Earth
pathway. While most of these biomes or regional systems may be
retained in a Stabilized Earth pathway, most or all of them would
likely be substantially changed or degraded in a Hothouse Earth
pathway, with serious challenges for the viability of human societies.
For example, agricultural systems are particularly vulnerable,
because they are spatially organized around the relatively stable
Holocene patterns of terrestrial primary productivity, which de-
pend on a well-established and predictable spatial distribution of
temperature and precipitation in relation to the location of fertile
soils as well as on a particular atmospheric CO
Current understanding suggests that, while a Stabilized Earth
pathway could result in an approximate balance between in-
creases and decreases in regional production as human systems
adapt, a Hothouse Earth trajectory will likely exceed the limits of
adaptation and result in a substantial overall decrease in agricul-
tural production, increased prices, and even more disparity be-
tween wealthy and poor countries (57).
The worlds coastal zones, especially low-lying deltas and the
adjacent coastal seas and ecosystems, are particularly important
for human wellbeing. These areas are home to much of the worlds
population, most of the emerging megacities, and a significant
amount of infrastructure vital for both national economies and in-
ternational trade. A Hothouse Earth trajectory would almost cer-
tainly flood deltaic environments, increase the risk of damage from
coastal storms, and eliminate coral reefs (and all of the benefits that
they provide for societies) by the end of this century or earlier (58).
Human Feedbacks in the Earth System. In the dominant climate
change narrative, humans are an external force driving change to the
Earth System in a largely linear, deterministic way; the higher the
forcing in terms of anthropogenic greenhouse gas emissions,
the higher the global average temperature. However, our anal-
ysis argues that human societies and our activities need to be
recast as an integral, interacting component of a complex, adaptive
Earth System. This framing puts the focus not only on human system
dynamics that reduce greenhouse gas emissions but also, on those
that create or enhance negative feedbacks that reduce the risk that
the Earth System will cross a planetary threshold and lock into a
Hothouse Earth pathway.
Humanitys challenge then is to influence the dynamical
properties of the Earth System in such a way that the emerging
unstable conditions in the zone between the Holocene and a very
hot state become a de facto stable intermediate state (Stabilized
Earth) (Fig. 2). This requires that humans take deliberate, integral,
and adaptive steps to reduce dangerous impacts on the Earth
System, effectively monitoring and changing behavior to form
feedback loops that stabilize this intermediate state.
There is much uncertainty and debate about how this can be
donetechnically, ethically, equitably, and economicallyand
there is no doubt that the normative, policy, and institutional as-
pects are highly challenging. However, societies could take a wide
range of actions that constitute negative feedbacks, summarized
in SI Appendix, Table S5, to steer the Earth System toward Sta-
bilized Earth. Some of these actions are already altering emission
trajectories. The negative feedback actions fall into three broad
categories: (i) reducing greenhouse gas emissions, (ii) enhancing
or creating carbon sinks (e.g., protecting and enhancing bio-
sphere carbon sinks and creating new types of sinks) (59), and (iii)
modifying Earths energy balance (for example, via solar radiation
management, although that particular feedback entails very large risks
of destabilization or degradation of several key processes in the Earth
System) (60, 61). While reducing emissions is a priority, much more
could be done to reduce direct human pressures on critical biomes
that contribute to the regulation of the state of the Earth System
through carbon sinks and moisture feedbacks, such as the Amazon
and boreal forests (Table 1), and to build much more effective stew-
ardship of the marine and terrestrial biospheres in general.
The present dominant socioeconomic system, however, is
based on high-carbon economic growth and exploitative resource
use (9). Attempts to modify this system have met with some
Steffen et al. PNAS Latest Articles
success locally but little success globally in reducing greenhouse
gas emissions or building more effective stewardship of the bio-
sphere. Incremental linear changes to the present socioeconomic
system are not enough to stabilize the Earth System. Widespread,
rapid, and fundamental transformations will likely be required to
reduce the risk of crossing the threshold and locking in the Hot-
house Earth pathway; these include changes in behavior, tech-
nology and innovation, governance, and values (48, 62, 63).
International efforts to reduce human impacts on the Earth
System while improving wellbeing include the United Nations
Sustainable Development Goals and the commitment in the Paris
agreement to keep warming below 2 °C. These international
governance initiatives are matched by carbon reduction com-
mitments by countries, cities, businesses, and individuals (6466) ,
but as yet, these are not enough to meet the Paris target. En-
hanced ambition will need new collectively shared values, prin-
ciples, and frameworks as well as education to support such
changes (67, 68). In essence, effective Earth System stewardship is
an essential precondition for the prosperous development of
human societies in a Stabilized Earth pathway (69, 70).
In addition to institutional and social innovation at the global
governance level, changes in demographics, consumption, be-
havior, attitudes, education, institutions, and socially embedded
technologies are all important to maximize the chances of
achieving a Stabilized Earth pathway (71). Many of the needed
shifts may take decades to have a globally aggregated impact (SI
Appendix, Table S5), but there are indications that society may be
reaching some important societal tipping points. For example,
there has been relatively rapid progress toward slowing or re-
versing population growth through declining fertility resulting
from the empowerment of women, access to birth control tech-
nologies, expansion of educational opportunities, and rising in-
come levels (72, 73). These demographic changes must be
complemented by sustainable per capita consumption patterns,
especially among the higher per capita consumers. Some changes
in consumer behavior have been observed (74, 75), and oppor-
tunities for consequent major transitions in social norms over
broad scales may arise (76). Technological innovation is contrib-
uting to more rapid decarbonization and the possibility for re-
moving CO
from the atmosphere (48).
Ultimately, the transformations necessary to achieve the Sta-
bilized Earth pathway require a fundamental reorientation and
restructuring of national and international institutions toward
more effective governance at the Earth System level (77), with a
much stronger emphasis on planetary concerns in economic
governance, global trade, investments and finance, and techno-
logical development (78).
Building Resilience in a Rapidly Changing Earth System. Even if
a Stabilized Earth pathway is achieved, humanity will face a tur-
bulent road of rapid and profound changes and uncertainties on
route to itpolitically, socially, and environmentallythat chal-
lenge the resilience of human societies (7982). Stabilized Earth
will likelybe warmer than any other time over the last 800,000 years
at least (83) (that is, warmer than at any other time in which fully
modern humans have existed).
In addition, the Stabilized Earth trajectory will almost surely be
characterized by the activation of some tipping elements (Tipping
Cascades and Fig. 3) and by nonlinear dynamics and abrupt
shifts at the level of critical biomes that support humanity (SI
Appendix, Table S4). Current rates of change of important fea-
tures of the Earth System already match or exceed those of abrupt
geophysical events in the past (SI Appendix). With these trends
likely to continue for the next several decades at least, the con-
temporary way of guiding development founded on theories,
tools, and beliefs of gradual or incremental change, with a focus
on economy efficiency, will likely not be adequate to cope with
this trajectory. Thus, in addition to adaptation, increasing resil-
ience will become a key strategy for navigating the future.
Generic resilience-building strategies include developing in-
surance, buffers, redundancy, diversity, and other features of
resilience that are critical for transforming human systems in the
face of warming and possible surprise associated with tipping
points (84). Features of such a strategy include (i) maintenance of
diversity, modularity, and redundancy; (ii) management of con-
nectivity, openness, slow variables, and feedbacks; (iii) un-
derstanding socialecological systems as complex adaptive
systems, especially at the level of the Earth System as a whole (85);
(iv) encouraging learning and experimentation; and (v) broaden-
ing of participation and building of trust to promote polycentric
governance systems (86, 87).
Our systems approach, focusing on feedbacks, tipping points,
and nonlinear dynamics, has addressed the four questions posed
in the Introduction.
Our analysis suggests that the Earth System may be approaching
a planetary threshold that could lock in a continuing rapid pathway
toward much hotter conditionsHothouse Earth. This pathway
would be propelled by strong, intrinsic, biogeophysical feedbacks
difficult to influence by human actions, a pathway that could not be
reversed, steered, or substantially slowed.
Where such a threshold might be is uncertain, but it could be
only decades ahead at a temperature rise of 2.0 °C above pre-
industrial, and thus, it could be within the range of the Paris Ac-
cord temperature targets.
The impacts of a Hothouse Earth pathway on human societies would
likely be massive, sometimes abrupt, and undoubtedly disruptive.
Avoiding this threshold by creating a Stabilized Earth pathway
can only be achieved and maintained by a coordinated, de-
liberate effort by human societies to manage our relationship with
the rest of the Earth System, recognizing that humanity is an in-
tegral, interacting component of the system. Humanity is now
facing the need for critical decisions and actions that could in-
fluence our future for centuries, if not millennia (88).
How credible is this analysis? There is significant evidence from
a number of sources that the risk of a planetary threshold and thus,
the need to create a divergent pathway should be taken seriously:
First, the complex system behavior of the Earth System in the
Late Quaternary is well-documented and understood. The two
bounding states of the systemglacial and interglacialare
reasonably well-defined, the ca. 100,000-years periodicity of the
limit cycle is established, and internal (carbon cycle and ice albedo
feedbacks) and external (changes in insolation caused by changes
in Earths orbital parameters) driving processes are generally well-
known. Furthermore, we know with high confidence that the
progressive disintegration of ice sheets and the transgression of
other tipping elements are difficult to reverse after critical levels of
warming are reached.
Second, insights from Earths recent geological past (SI Ap-
pendix) suggest that conditions consistent with the Hothouse
Earth pathway are accessible with levels of atmospheric CO
concentration and temperature rise either already realized or
projected for this century (SI Appendix, Table S1).
| Steffen et al.
Third, the tipping elements and feedback processes that
operated over Quaternary glacialinterglacial cycles are
the same as several of those proposed as critical for the fu-
ture trajectory of the Earth System (Biogeophysical Feed-
backs,Tipping Cascades, Fig. 3, Table 1, and SI Appendix,
Table S2).
Fourth, contemporary observations (29, 38) (SI Appendix)of
tipping element behavior at an observed temperature anomaly of
about 1 °C above preindustrial suggest that some of these ele-
ments are vulnerable to tipping within just a 1 °C to 3 °C increase
in global temperature, with many more of them vulnerable at
higher temperatures (Biogeophysical Feedbacks and Tipping
Cascades) (12, 17, 39). This suggests that the risk of tipping cas-
cades could be significant at a 2 °C temperature rise and could
increase sharply beyond that point. We argue that a planetary
threshold in the Earth System could exist at a temperature rise as
low as 2 °C above preindustrial.
The Stabilized Earth trajectory requires deliberate manage-
ment of humanitys relationship with the rest of the Earth System if
the world is to avoid crossing a planetary threshold. We suggest
that a deep transformation based on a fundamental reorientation
of human values, equity, behavior, institutions, economies, and
technologies is required. Even so, the pathway toward Stabilized
Earth will involve considerable changes to the structure and func-
tioning of the Earth System, suggesting that resilience-building
strategies be given much higher priority than at present in decision
making. Some signs are emerging that societies are initiating some of
the necessary transformations. However, these transformations are
still in initial stages, and the social/political tipping points that
definitively move the current trajectory away from Hothouse Earth
have not yet been crossed, while the door to the Stabilized Earth
pathway may be rapidly closing.
Our initial analysis here needs to be underpinned by more in-
depth, quantitative Earth System analysis and modeling studies to
address three critical questions. (i) Is humanity at risk for pushing
the system across a planetary threshold and irreversibly down a
Hothouse Earth pathway? (ii) What other pathways might be pos-
sible in the complex stability landscape of the Earth System, and
what risks might they entail? (iii) What planetary stewardship strat-
egies are required to maintain the Earth System in a manageable
Stabilized Earth state?
We thank the three reviewers for their comments on the first version of the
manuscript and two of the reviewers for further comments on a revised version
of the manuscript. These comments were very helpful in the revisions. We thank
a member of the PNAS editorial board for a comprehensive and very helpful
review. W.S. and C.P.S. are members of the Anthropocene Working Group.
W.S., J.R., K.R., S.E.C., J.F.D., I.F., S.J.L., R.W. and H.J.S. are members of the
Planetary Boundaries Research Network and the Earth LeaguesEarthDoc
Programme supported by the Stordalen Foundation. T.M.L. was supported by
a Royal Society Wolfson Research Merit Award and the European Union
Framework Programme 7 Project HELIX. C.F. was supported by the Erling
Persson Family Foundation. The participation of D.L. was supported by the
Haury Program in Environment and Social Justice and National Science
Foundation (USA) Decadal and Regional Climate Prediction using Earth
System Models Grant 1243125. S.E.C. was supported in part by Swedish Re-
search Council Formas Grant 2012-742. J.F.D. and R.W. were supported by
Leibniz Association Project DOMINOES. S.J.L. receives funding from Formas
Grant 2014-589. This paper is a contribution to European Research Council
Advanced Grant 2016, Earth Resilience in the Anthropocene Project 743080.
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| Steffen et al.
... Most anthropogenic pressures on biota have increased in recent years (IPBES, 2019), and new pressures with novel characteristics have emerged. Climate change, atmospheric nitrogen deposition (Staude et al., 2020;Stevens et al., 2018), pollution (e.g., noise, light pollution, plastic, pesticides; Halfwerk & Jerem, 2021;Sánchez-Bayo & Wyckhuys, 2019) and ocean acidification (Hoegh-Guldberg et al., 2007) are now acting everywhere, although with differing intensities and rates of change at different locations (e.g., Steffen et al., 2018;Wang-Erlandsson et al., 2022). Depending on socio-political decisions and the capacity for their implementation, the velocity of these environmental changes (Leclère et al., 2020;Loarie et al., 2009), biotic changes (Seebens et al., 2021) and species extinction rates (IPBES, 2019) are likely to increase further in the future. ...
The Anthropocene is characterized by a rapid pace of environmental change and is causing a multitude of biotic responses, including those that affect the spatial distribution of species. Lagged responses are frequent and species distributions and assemblages are consequently pushed into a disequilibrium state. How the characteristics of environmental change—for example, gradual ‘press’ disturbances such as rising temperatures due to climate change versus infrequent ‘pulse’ disturbances such as extreme events—affect the magnitude of responses and the relaxation times of biota has been insufficiently explored. It is also not well understood how widely used approaches to assess or project the responses of species to changing environmental conditions can deal with time lags. It, therefore, remains unclear to what extent time lags in species distributions are accounted for in biodiversity assessments, scenarios and models; this has ramifications for policymaking and conservation science alike. This perspective piece reflects on lagged species responses to environmental change and discusses the potential consequences for species distribution models (SDMs), the tools of choice in biodiversity modelling. We suggest ways to better account for time lags in calibrating these models and to reduce their leverage effects in projections for improved biodiversity science and policy.
... Partieron, para ello, de la reconstrucción de la singladura terrestre por el Cuaternario Tardío, caracterizada por un comportamiento cíclico entre dos estados límite: glacial e interglacial. Sus conclusiones alertan sobre la proximidad actual a una bifurcación de caminos potenciales que, de no adoptar medidas inmediatas de gestión deliberada de nuestra actuación en relación con el Sistema Tierra (básicamente a través de una reducción drástica de las emisiones de gases de efecto invernadero, pero no solo), supondría entrar en "unas condiciones climáticas más cálidas y una biosfera profundamente diferente" a la que ha conocido toda la historia de nuestra estirpe homínida14 . No es insignificante el aviso. ...
Full-text available
En un mundo complejo y amenazado, como es el nuestro, resulta preciso confiar en la ciencia, desarrollar nuestras capacidades prosociales y aplicar una ética de la solidaridad y la sostenibilidad.
... To achieve this would certainly increase greenhouse gas emissions, deplete many essential renewable resources from fish-stocks to arable soils and strain global life-support to breaking point, including the risk of triggering runaway hothouse Earth conditions. 10 We acknowledge that there are many other relevant behaviours and considerations, including genetic pre-dispositions to consume, the role of temporal, spatial and social discounting, socio-political factors (e.g. status hierarchies) and even addiction to conspicuous consumption. ...
Full-text available
Previously, anthropogenic ecological overshoot has been identified as a fundamental cause of the myriad symptoms we see around the globe today from biodiversity loss and ocean acidification to the disturbing rise in novel entities and climate change. In the present paper, we have examined this more deeply, and explore the behavioural drivers of overshoot, providing evidence that overshoot is itself a symptom of a deeper, more subversive modern crisis of human behaviour. We work to name and frame this crisis as 'the Human Behavioural Crisis' and propose the crisis be recognised globally as a critical intervention point for tackling ecological overshoot. We demonstrate how current interventions are largely physical, resource intensive, slow-moving and focused on addressing the symptoms of ecological overshoot (such as climate change) rather than the/home/sci distal cause (maladaptive behaviours). We argue that even in the best-case scenarios, symptom-level interventions are unlikely to avoid catastrophe or achieve more than ephemeral progress. We explore three drivers of the behavioural crisis in depth: economic growth; marketing; and pro-natalism. These three drivers directly impact the three 'levers' of overshoot: consumption, waste and population. We demonstrate how the maladaptive behaviours of overshoot stemming from these three drivers have been catalysed and perpetuated by the intentional exploitation of previously adaptive human impulses. In the final sections of this paper, we propose an interdisciplinary emergency response to the behavioural crisis by, amongst other things, the shifting of social norms relating to reproduction, consumption and waste. We seek to highlight a critical disconnect that is an ongoing societal gulf in communication between those that know such as scientists working within limits to growth, and those members of the citizenry, largely influenced by social scientists and industry, that must act.
Full-text available
To realize policies that benefit the youth and future generations, discussions are being held on how to give the votes of children who are currently ineligible to vote, and even future unborn generations, to their parents or voters of the present generation to vote as their proxies. To examine the effect of proxy voting on future-friendly choices, we conducted a laboratory experiment with the general public, including parents. Participants were assigned the roles of present and future generations, and the present-generation participants voted on allocating payoffs between generations. Proxy votes for future-generation participants were granted to some present-generation participants. We found that proxy voting did not increase the proportion of votes for future-friendly choices compared to the case without proxy votes, which is consistent with previous studies involving university students. We also observed that the older the participants, the more likely they were to vote for future-friendly choices. Once age was controlled for, parents were less likely than non-parents to vote for future-friendly choices. From a consequentialist perspective, these results suggest that we should add a twist to proxy voting, examine non-proxy voting methods, or explore other measures.
Geological sequestration of carbon dioxide (CO2) in depleted gas reservoirs represents a cost-effective solution to mitigate global carbon emissions. The surface chemistry of the reservoir rock, pressure, temperature, and moisture content are critical factors that determine the CO2 adsorption capacity and storage mechanisms. Shale-gas reservoirs are good candidates for this application. However, the interactions between CO2 and organic content still need further investigation. The objectives of this paper are to (i) experimentally evaluate the adsorption isotherm of CO2 on activated carbon, (ii) quantify the nanoscale interfacial interactions between CO2 and the activated carbon surface using Monte Carlo (MC) and molecular dynamic (MD) simulations, (iii) evaluate the modeling reliability using experimental measurements, and (iv) quantify the influence of temperature and geochemistry on the adsorption behavior of CO2 on the surface of activated carbon. These objectives aim at obtaining a better understanding of the behavior of CO2 injection and storage in the kerogen structure of shale-gas formations, where activated carbon is used as a proxy for thermally mature kerogen. We performed experimental measurements, grand canonical Monte Carlo (GCMC) simulations, and MD simulations of CO2 adsorption and diffusion on activated carbon. The experimental work involved measurements of the high-pressure adsorption capacity of activated carbon using pure CO2 gas at a temperature of 300 K. The simulation work started with modeling and validating an activated carbon structure by calibrating the GCMC simulations with experimental CO2 adsorption measurements. Then, we extended the simulation work to quantify the adsorption isotherms at a temperature range of 250–500 K and various surface chemistry conditions. Moreover, CO2 self-diffusion coefficients were quantified at gas pressures of 0.5 MPa, 1 MPa, and 2 MPa using MD simulations. The experimental results showed a typical CO2 excess adsorption trend for the nanoporous structures, with a density of the sorbed gas phase of 504.76 kg/m3. The simulation results were in agreement with experimental adsorption isotherms with a 10.6% average absolute relative difference. The self-diffusion results showed a decrease in gas diffusion with increasing pressure due to the increase in the adsorbed gas amount. Increasing the simulation temperature from 300 K to 400 K led to a decrease in the amount of adsorbed CO2 molecules by about 87% at 2 MPa pressure. Finally, the presence of charged functional groups (e.g., hydroxyl–OH and carboxyl–COOH) led to an increase in the adsorption of CO2 gas to the activated carbon surface. The outcomes of this paper provide new insights about the parameters affecting CO2 adsorption and sequestration in depleted shale-gas reservoirs. This in turn helps in screening the candidate shale-gas reservoirs for carbon capture, sequestration, and storage to maximize the CO2 storage capacity.
Humanity has not been able to operate a sustainable food system globally. Radical transformation in society and the economy is needed to make food production serve the well-being of all human and non-human stakeholders while respecting planetary boundaries. This paper reviews the literature on the problem of food production in the Anthropocene. It then explores how a business enterprise might also serve as a social movement and the way in which the interaction between the two can create sustainable value. The case of Green Monday, a social movement and start-up group selling plant-based food, established in Hong Kong and promoting low-carbon emissions, sustainable lifestyles, food security, and animal welfare is presented and examined. The case study provides some valuable insights into how the collaborative actions of a social movement and a related business organization can help to meet real human needs and contribute to preservation and regeneration of nature.
Arctic permafrost, the largest non-seasonal component of Earth’s cryosphere, contains a significant climate-sensitive carbon pool. Its potential for loss due to climatic changes leading to a global tipping point, where thawing accelerates with disproportionate impacts, remains debated. Here, we provide an integrative perspective on this question, building on a cross-disciplinary meta-analysis of literature supported by geospatial analyses of global data products and climate model output. Contrary to the existence of a global-scale tipping point, scientific evidence suggests a quasi-linear response to global warming, both from observation-based and model-based projections. While certain processes, such as talik development, thermokarst, thermo-erosion, and vegetation interactions, can drive rapid local permafrost thaw and ground ice loss, they do not accumulate to a non-linear response beyond regional scales. We conclude that there is no safety margin for Arctic permafrost where its loss would be acceptable. Instead, with each increment of global warming, more land areas underlain by permafrost will proportionally experience thaw, causing detrimental local impacts and global feedbacks.
This article introduces tipping points in the Anthropocene. It argues that to minimise the risk from negative climate tipping points, positive social tipping points need to be identified and triggered.
This short contribution aims to summarize the relevance and necessity of using the concept of system and the systemic approach to understand the major environmental and societal issues facing human societies in the context of the Anthropocene. After a brief historical review, the text proposes a definition of the concept of system and presents its general characteristics, refers to certain fields of application, and concludes with some reflections on the teaching and learning of systems thinking in schools.
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Carbon roadmaps and pathways are important for describing, planning and tracking the technical, managerial and behavioral changes that are consistent with the Paris Agreement. Nevertheless, roadmaps and pathways for decarbonization often gloss over a fundamental question: ‘How do deliberate social transformations happen?’ Often the social complexity of transformation processes is downplayed or ignored in favor of technical solutions and behavioral approaches. In this article, I explain why they are incomplete and unlikely to ‘bend the curves’ to reduce emissions in accordance with the Paris Agreement. I first discuss the distinction between technical and adaptive challenges and why this is relevant. I then review and describe the dynamics of social change in relation to three related and interacting ‘spheres’ of transformation: the practical, political, and personal spheres. Finally, I explore how these three spheres can be used to identify leverage points for transformations that support the 1.5°C target.
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Significance Most nations recently agreed to hold global average temperature rise to well below 2 °C. We examine how much climate mitigation nature can contribute to this goal with a comprehensive analysis of “natural climate solutions” (NCS): 20 conservation, restoration, and/or improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We show that NCS can provide over one-third of the cost-effective climate mitigation needed between now and 2030 to stabilize warming to below 2 °C. Alongside aggressive fossil fuel emissions reductions, NCS offer a powerful set of options for nations to deliver on the Paris Climate Agreement while improving soil productivity, cleaning our air and water, and maintaining biodiversity.
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International commitment to the appropriately ambitious Paris climate agreement and the United Nations Sustainable Development Goals in 2015 has pulled into the limelight the urgent need for major scientific progress in understanding and modelling the Anthropocene, the tightly intertwined social-environmental planetary system that humanity now inhabits. The Anthropocene qualitatively differs from previous eras in Earth’s history in three key characteristics: (1) There is planetary-scale human agency. (2) There are social and economic networks of teleconnections spanning the globe. (3) It is dominated by planetary-scale social-ecological feedbacks. Bolting together old concepts and methodologies cannot be an adequate approach to describing this new geological era. Instead, we need a new paradigm in Earth System science that is founded equally on a deep understanding of the physical and biological Earth System – and of the economic, social and cultural forces that are now an intrinsic part of it. It is time to close the loop and bring socially mediated dynamics explicitly into theory, analysis and models that let us study the whole Earth System.
This timely volume recognizes that traditional policy approaches to reduce human impacts on the environment through technological change - for example, emphasizing resource efficiency and the development of renewable energy sources - are insufficient to meet the most pressing sustainability challenges of the twenty-first century. Instead, the editors and contributors argue that we must fundamentally reconfigure our lifestyles and social institutions if we are to make the transition toward a truly sustainable future. © Maurie J. Cohen, Halina Szejnwald Brown and Philip J. Vergragt 2013. All rights reserved.
Christiana Figueres and colleagues set out a six-point plan for turning the tide of the world’s carbon dioxide by 2020.
Permafrost, which covers 15 million km 2 of the land surface, is one of the components of the Earth system that is most sensitive to warming. Loss of permafrost would radically change high-latitude hydrology and biogeochemical cycling, and could therefore provide very significant feedbacks on climate change. The latest climate models all predict warming of high-latitude soils and thus thawing of permafrost under future climate change, but with widely varying magnitudes of permafrost thaw. Here we show that in each of the models, their present-day spatial distribution of permafrost and air temperature can be used to infer the sensitivity of permafrost to future global warming. Using the same approach for the observed permafrost distribution and air temperature, we estimate a sensitivity of permafrost area loss to global mean warming at stabilization of million km 2 °C â '1 (1σ confidence), which is around 20% higher than previous studies. Our method facilitates an assessment for COP21 climate change targets: if the climate is stabilized at 2 °C above pre-industrial levels, we estimate that the permafrost area would eventually be reduced by over 40%. Stabilizing at 1.5 °C rather than 2 °C would save approximately 2 million km 2 of permafrost. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.