Timothy M. Lenton & Hans
Joachim Schellnhuber talk with ScienceWatch.com
and answer a few questions about this month's New Hot Paper
in the field of Geosciences. The authors have also
sent along images of their work.
Article Title: Tipping elements in the Earth's
TM;Held, H;Kriegler, E;Hall, JW;Lucht, W;Rahmstorf,
Journal: PROC NAT ACAD SCI USA
Year: FEB 12 2008
* Univ E Anglia, Sch Environm Sci, Norwich NR4 7TJ,
* Univ E Anglia, Sch Environm Sci, Norwich NR4 7TJ,
* Tyndall Ctr Climate Change Res, Norwich NR4 7TJ, Norfolk,
* Potsdam Inst Climate Impact Res, D-14412 Potsdam,
* Carnegie Mellon Univ, Dept Engn & Publ Policy,
Pittsburgh, PA 15213 USA.
(addresses have been truncated)
Why do you think your paper is highly
Our paper captures the Zeitgeist of a growing group of climate scientists
and commentators who perceive that human activities are already pushing
Earth's climate past regional "tipping points." This concern has been
heightened by recent observations of abrupt climate change in the Arctic.
For the first time, our paper defines a climate "tipping point" and pulls
together a comprehensive list of what we christen the policy-relevant
"tipping elements" in the climate system—those subsystems that may
pass a tipping point this century due to human activities, committing them
to changes in state that are sometimes rapid and often irreversible.
The resulting map of tipping elements provides an iconic image of some of
the most vulnerable parts of the planet, and it is being widely reproduced
at scientific meetings and in the popular media.
By identifying the common dynamics underlying quite different
systems—including tropical monsoons, the Amazon rainforest, ocean
circulation, Arctic sea-ice, and the great ice sheets of Greenland and West
Antarctica—our work helps bring together the interests and concerns
of specialists in quite different fields including climatology, ecology,
oceanography, and glaciology.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Our paper describes a new synthesis of knowledge regarding the potential
tipping points in the climate system. We present new definitions of a
climate tipping point and a tipping element. Also, for the first time, we
use a process of expert elicitation to assess the proximity of a subset of
tipping points and the uncertainty surrounding their status.
Would you summarize the significance of your paper
in layman's terms?
Coauthor: Hans Joachim
Map of tipping
We have been living under the illusion that climate change will be a smooth
process of global warming: yes, there will be some unfortunate victims, but
the changes should be manageable and some of us might even benefit from
them. Our paper shatters that illusion: large regions of the planet may
undergo profound changes in state that in some cases are rapid and often
are irreversible, with impacts on many millions of people.
These climate tipping points are inherently difficult to forecast, making
managing them and their consequences that much harder. However, the
situation is not without hope: we do see some prospects for early warning
of tipping points, and with grassroots social pressure forcing substantive
international political action, we can still avoid the worst scenarios.
How did you become involved in this research, and
were there any problems along the way?
One of us (Hans Joachim Schellnhuber) introduced the overall tipping-points
concept into the scientific community dealing with climate change around
the year 2000, through a 2001 Linacre lecture in Oxford, coauthored by
The specific research generating the paper in question began with us and
our coauthors organizing a workshop at the British Embassy in Berlin in
October 2005, which brought together both UK and German scientists to
debate and begin to identify the potential tipping points in the climate
A process of eliciting responses from a wider international group of
experts (led by Elmar Kriegler and Jim Hall) started at this workshop and
continued through the following year, whilst one of us (Tim Lenton) led a
comprehensive review of the literature. The greatest challenge along the
way was reconciling the inputs from a diverse group of coauthors, an even
wider pool of expert opinions, and a huge body of literature.
Where do you see your research leading in the
The next steps are to try and provide societies with some early warning of
approaching tipping points, to identify the policies and activities
necessary to avoid them (where possible), and, for those tipping points
that cannot be avoided, to identify ways to make societies more resilient
to the consequences.
We are actively researching the potential early warning signals for
not-too-distant tipping points and are finding some promising, generic
indicators. In the future, we hope to translate this theoretical work into
the design and deployment of actual early warning systems for specific
We are also beginning to identify the policies and technologies that can
help avoid climate tipping points. A strong international deal to reduce
greenhouse gas emissions in Copenhagen in December 2009 will help (if it
ensures that global warming is confined to no more than 2°C), but may
not be enough for avoiding the transgression of some tipping points.
Hence we are actively researching the potential for creating carbon dioxide
sinks by careful management of the biosphere. We are also evaluating
whether "geo-engineering," a reduction in the amount of sunlight absorbed
by the Earth, could help protect some regional tipping elements, and
whether it will threaten others.
Finally, we plan to research the possible social "tipping points" that
could tip societies onto more sustainable trajectories that help
avoid—or at least better cope with—climate tipping points.
Do you foresee any social or political implications
for your research?
The economic and political implications of our research are profound. If we
do pass some of the tipping points in the climate system, the impacts on
societies will be huge. Equally, the policy changes needed to avoid or
better cope with climate tipping points are substantial.
These implications are being recognized. Our study received widespread
coverage in the international media, it was awarded the Times
Higher Education Award for Research Project of the Year, 2008, and there
are signs that it is beginning to influence the international policy
Professor Tim Lenton
School of Environmental Sciences
University of East Anglia
Professor Hans Joachim Schellnhuber
Potsdam Institute for Climate Impact Research (PIK)
KEYWORDS: ANTARCTIC ICE-SHEET; ATLANTIC THERMOHALINE
CIRCULATION; ASIAN SOUTHWEST MONSOON; WEST-AFRICAN MONSOON; SEA-LEVEL
CHANGE; EL-NINO-LIKE; MODEL SIMULATIONS; EXPERT JUDGMENTS; CAP
INSTABILITY; FOREST DIEBACK.