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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 12 International innovation 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 13 Intelligence 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 [email protected] 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. 14 International innovation 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.