Dr Philip Pogge von Strandmann
Climate change:
lessons learnt from the past
Dr Philip Pogge von Strandmann is an isotope geochemist at University College London’s
Department of Earth Sciences. His current research is reshaping our understanding of past
climate change events so that we are better equipped to deal with global warming today
chemical weathering is Earth’s dominant natural
CO2 removal process, it becomes critical to
understand how weathering has changed in
response to global temperatures, and how this
has affected climate and life. Ultimately, this
project is trying to understand weathering, and
thus CO2 withdrawal and climate stabilisation
mechanisms, and the consequences for life,
though periods of extreme climate change in
Earth’s history.
How important is an understanding
of the role played by continental silicate
weathering in controlling and moderating
climate, and its link to atmospheric
CO2 levels?
Could you reflect on how you became
involved in this area of research? What is
your ultimate goal for this project?
Trying to understand how atmospheric CO2
is controlled is clearly an important question.
The Earth’s climate has changed considerably
during its history, so ideally we can use
these changes to limit the consequences of
anthropogenic climate change. Given that
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Continental silicate weathering is thought
to account for more than 80 per cent of
Earth’s natural removal of atmospheric CO2.
In addition, silicate weathering is likely to
provide a climate stabilisation feedback: if
atmospheric CO2 concentrations are high, the
greenhouse effect will increase temperature.
Because chemical reactions are faster at higher
temperatures, silicate weathering will increase
and remove more CO2, allowing the climate
to cool. The reverse is also true, and therefore
silicate weathering may be the mechanism
that has moderated Earth’s climate, and kept
it within the narrow bands necessary for life.
The alternative would have been for an Earth
without an active hydrological cycle to end up
in a runaway greenhouse state like Venus, or a
runaway icehouse state like Mars.
Through the use of lithium (Li) isotopes,
what can be learnt from examining large
climate fluctuations in Earth’s history?
Can this knowledge be applied to today’s
climate issues?
Looking at Li isotopes through periods of large
and rapid climate change tells us how silicate
weathering changed as the climate warmed
and cooled. In turn, this tells us how weathering
responds to temperature change, and if
weathering could be the climate-moderating
process that has kept the Earth habitable for life.
At first, I will be examining periods of largescale global climate change, but as the method
is refined, smaller events can also be targeted.
The more we understand about how the Earth’s
climatic system recovers from extreme change,
the more we understand about climate change
in general. Without complete comprehension of
Dr Philip Pogge von Strandmann
natural climate change mechanisms, we cannot
predict the consequences of manmade global
warming particularly well.
What has your work revealed about the time
period for the climate to be brought back
under control through weathering?
Silicate weathering has always been thought
to be able to moderate and control climate,
but only on timescales greater than about
1.5 million years. My research is showing
that weathering can cause the climate to
recover from perturbations much faster – in
about 300,000 years. While that is still
too long to have much climate impact on
human timescales, it provides critical new
information on the time periods in the Earth’s
past that we are using to predict what will
happen in the future.
Looking ahead, what plans do you have for
the future of this research? How do you hope
that the results will affect future climate
change policy?
Understanding natural climate change and
response mechanisms has always been critical
for predicting future climate change. Hence
the more we can understand about periods of
climate change in the Earth’s past, the better. My
research aims to gradually progress from looking
at the huge past events to ones that may be
more similar to what we will experience in the
next few hundred years. This is also interesting
because it might be possible to artificially
increase the weathering rate to remove CO2
on human timescales. This would be a form of
geoengineering by, for example, grinding silicate
material to a fine grain size and distributing it
onto fields or into the oceans. Then the natural
weathering processes would take over and
sequester CO2. We need to understand more
about the consequences of this process before
we actually implement it.
Silicate weathering
and climate stabilisation
Research into the underlying processes behind history’s most catastrophic
climate change events is shining new light on the impacts of global
warming. Using novel geochemical tracers of weathering has shown how
the Earth maintains a stable climate and recovers from extreme warming
The atmosphere plays a vital role in
sustaining life on the planet; in order to survive,
we need the climate to remain within a narrow
range of conditions. Today, global warming is
changing the atmosphere at an increasing rate,
but predicting the consequences for life on Earth
remains a major challenge. Geological records
divulge the potentially fatal consequences of
sudden climate change. During the PermoTriassic warming which occurred 250 million
years ago, 96 per cent of marine life was wiped
out along with 70 per cent of vertebrate land
species. Yet, the Earth can regulate and recover
from atmospheric changes and the more we
understand about past climate change, the
better we can predict its future.
Scientists are delving deep into history to fill the
gaps in knowledge about how atmosphere is
regulated. It is known, for example, that 80 per
cent of the removal of CO2 from the atmosphere
occurs through the chemical erosion of the
land and rocks that make up our continents,
but it is not fully understood how this process
is controlled. Dr Philip Pogge von Strandmann,
a geochemist at University College London’s
Department of Earth Sciences, is investigating
the role of continental silicate weathering in
maintaining our climate and how this process
is affected by changes in temperature and
mountain building. If this weathering does prove
to be temperature-controlled, it could be the key
to Earth’s natural ability to maintain a climate
conducive to life.
Chemical weathering
Chemical weathering of silicate rocks like granite
or basalt on the continents is responsible for
the majority of the removal of CO2 from the
atmosphere. However, as Strandmann explains,
this process does not necessarily remove the
CO2 permanently: “For the CO2 to be removed
permanently, it has to be transported as
bicarbonate in rivers across the continents to
the oceans. Once in the oceans, it is locked
up in limestone”. Some of the dissolved rock
ends up forming clay or soils in river water
rather than being carried to the ocean.
Strandmann is therefore trying to measure
the proportion of CO2 that remains on the
continent as clay or soil, and is locked away in
the ocean in order to calculate how much CO2 is
removed permanently.
Initially, Strandmann’s research will focus on
several major past climate change events that
led to the widespread extinction of marine
and terrestrial life. These include the PermoTriassic warming, the Ordovician ice age which
happened 445 million years ago, and parts
of the Cretaceous which occurred roughly 90
million years ago. Samples of marine calcium
carbonate from each period will be analysed to
build up a record of ocean chemistry which, as it
is directly linked to atmospheric conditions, will
reveal how rates of weathering changed with
variations in temperature. Once these major
events have been examined and modelled, it
will be possible to study smaller episodes of
climate change that are more comparable to
today’s global warming.
Tracing Li isotopes
This research exploits a relatively new
geochemical tracer of weathering; lithium (Li)
isotopes. Geochemical tracers have long been
used to reveal information about the history
of the Earth’s climate, but Li isotopes offer a
number of advantages over traditional tracers.
They respond to the intensity of weathering so,
for the first time, we will be able to detect past
variations in weathering rates. When combined
with information gathered through other
tracers, it is possible to model the changing
marine and atmospheric conditions throughout
Earth’s history.
This research will thus overcome some of the
major barriers faced by geologists in the past.
Lithium is only significantly present in silicates,
whereas most other elements are present in
both silicate and carbonate rocks. Since it is the
weathering of silicates that affects atmospheric
CO2 levels, Strandmann is confident that this
novel methodology will considerably advance
our comprehension of long-term climate
change: “Unlike other geochemical tracers
of weathering, Li isotopes are independent
of the rock-type undergoing weathering,”
he reflects. “Consequently, changes in the Li
isotope composition of seawater (which is
controlled by river water) reflect chemical
weathering processes and are not complicated
by differences in lithology.”
The studies completed so far have resulted in
some interesting findings. In one, Strandmann
www.researchmedia.eu
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Testing the control of
weathering on CO2 – evidence
from extreme climate events
OBJECTIVES
• To determine how silicate weathering
rates, and therefore atmospheric CO2
concentrations, respond to changes in
temperature and mountain building
• To discover if silicate weathering is the
process that has sustained the Earth
within narrow climatic bands
KEY COLLABORATORS
Dr Hugh Jenkyns,
Lecturer,
University of Oxford, UK
Dr André Desrochers,
Associate Professor,
University of Ottawa, Canada
Dr Christoph Korte,
Lecturer,
University of Copenhagen, Denmark
Funding
Natural Environment Research Council
(NERC)
CONTACT
Dr Phillip Pogge von Strandmann
Department of Earth Sciences
University College London
Gower Street
London
WC1E 6BT
UK
T +44 1865 272027
E p.strandmann@ucl.ac.uk
Dr Philip Pogge von
Strandmann is a Senior Lecturer
in Earth Sciences at University College
London (UCL) and Birkbeck, University
of London. Formerly he was a NERC
Research Fellow at the University of
Oxford. His research focuses on using
novel isotope systems to understand
present and past biogeochemical cycling
and CO2 controls.
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and his colleagues investigated the processes
behind the Ocean Anoxic Event (OAE) 2 that
occurred over 93 million years ago and led to
mass extinction. The researchers used Li isotope
measurements from across the 440,000-year
period to determine the role played by silicate
weathering. Their work suggests that this event
was triggered by high levels of CO2 emissions
from volcanic activity which led to rapid global
warming. As temperatures increased, so did
the rate of weathering; in fact, Strandmann
estimates that within 300,000 years,
weathering had removed roughly half of the
CO2 from the atmosphere, allowing the oceans
and climate to recover much more quickly than
was previously thought possible.
What is perhaps most pertinent about this
study is that the levels of CO2 emitted initially
were around 10 gigatonnes per year, not far
below today’s emissions. The link Strandmann
has found between rising temperatures, the
acceleration of the weathering process and the
burial of organic carbon shows how the Earth
can recover from extreme climate change and
stabilise the atmosphere. Unfortunately the
timescales involved are way beyond human
lifespans; even if we were to stop emitting now,
the Earth would still warm and take several
hundred thousand years to recover.
Learning from history
These results will be shared widely with other
geologists, not least through the American
Geophysical Union (AGU) and Goldschmidt
conferences, and will surely inspire further
investigations. The work already completed
has gone some way to explaining the complex
feedback mechanisms that make the climatic
Monitoring location for glacial weathering, VatnajÖkull icecap,
East Iceland. A location of significant CO2 withdrawal.
Once these major events have
been examined and modelled, it
will be possible to study smaller
episodes of climate change that
are more comparable to today’s
global warming
conditions on Earth so amenable to life. For
Strandmann, learning from history remains the
best way to gain concrete evidence about the
consequences of global warming: “The more we
can learn about the effects of warming on the
climate and on life, the better we can predict
what will happen in the future,” he affirms.
This knowledge will have a variety of
applications; from prompting further scientific
research to informing policy. There have already
been interesting suggestions for practical
ways to use this research to manage today’s
changing climate. If we know that increasing
the rate of chemical weathering removes more
CO2 from the atmosphere, then exciting new
possibilities for geoengineering are opened
up. One potential application is the spreading
of silicate materials on fields or in the oceans
to accelerate this process. Without further
research the full potential of such concepts
will of course remain hypothetical, but this
work nonetheless represents an important step
forward in our attempts to understand and
tackle climate change.