#253      30 min 46 sec
Sedimental journey: Probing climate's buried past to predict our future

Paleoclimatologist Prof Jonathan Overpeck describes how research into uncovering the earth’s climate history generates important insights about our climate future. Presented by Dr Shane Huntington.

"We're starting to understand what we can adapt to and what we cannot adapt to. That is a very powerful tool in guiding our mitigation discussions. In other words, if we don't think we can adapt to a temperature increase and associated drying, say beyond a two degree global warming, then we really need to be stronger advocates for keeping the earth from warming beyond two degrees." -- Prof Jonathan Overpeck




Prof Jonathan Overpeck
Prof Jonathan Overpeck

Jonathan Overpeck is a climate scientist and co-director of the University of Arizona’s Institute of the Environment, as well as a Professor of Geosciences and also Atmospheric Sciences. He received his BA from Hamilton College, followed by MSc and PhD from Brown University. Jonathan has written over 160 papers on climate and the environmental sciences, and recently served as a Coordinating Lead Author for the Nobel Prize winning UN Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (2007). Other awards include the US Department of Commerce Bronze and Gold Medals, a Guggenheim Fellowship and the Walter Orr Roberts award of the American Meteorological Society. Overpeck has active climate and paleoclimate research programs on five continents, and is also the lead investigator of the Climate Assessment for the Southwest and the Southwest Climate Science Center – two programs focused on regional climate adaptation. He has appeared and testified before Congress multiple times, is a Fellow of the American Association for the Advancement of Science, and is a Visiting Fellow of the Victorian Centre for Climate Change Adaptation Research, as well as a Visiting Scientist with the Australian Research Council’s Centre of Excellence For Climate System Science. He tweets about climate-related issues @TucsonPeck.

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Host: Dr Shane Huntington
Producers: Eric van Bemmel, Kelvin Param, Dyani Lewis
Audio Engineers: Gavin Nebauer
Voiceover: Nerissa Hannink
Series Creators: Kelvin Param & Eric van Bemmel

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VOICEOVER 
Welcome to Up Close, the research talk show from the University of Melbourne, Australia. 

SHANE HUNTINGTON 
I’m Dr Shane Huntington, thanks for joining us. Over the past 4.5 billion years, the earth's climate has changed in very significant ways. From meteor impacts to ice ages, earth's environment has been affected by both terrestrial and extra-terrestrial events. Some of these changes have led to mass extinctions, whilst others have led to explosions of new species. The earth's inhabitants and its climate history have always been intimately linked, but recent activities by humans have redefined just how intense these links can be. With the current threat of significant human-induced climate change on our planet, a detailed understanding of how the environment has shifted in the past becomes critical. Not only can we compare the rate of current changes to previous events, but we can learn a lot about what we must expect in coming decades, and how to deal with these changes. Enter the world of the paleoclimatologists who study the history of the earth's climate and the potential causes for climate shifts. One such expert who gathers ancient climate data is Professor Jonathan Overpeck, founding co-director of the Institute of Environment at the University of Arizona. Peck, as he likes to be called, joins us today to discuss paleoclimatology and its role in dispelling some of the myths about climate change. Peck is visiting the University of Melbourne as a guest of the Victorian Centre for Climate Adaptation Research. Welcome to Up Close Peck. 

JONATHAN OVERPECK
Thanks, it's great to be here. 

SHANE HUNTINGTON
I think we start with why it's actually important to study these past climate conditions. 

JONATHAN OVERPECK
Well there are a variety of reasons why paleoclimatology is becoming more and more mainstream. The first and most important thing is that the instrumental or rain gauge and thermometer record of climate change is so short that we don't really get a complete view of how climate can vary on its own. Another aspect that requires paleoclimatology is that we are using models to simulate into the future. These would be climate models, and they project future conditions. We have to see how well these models can project past changes in climate, before we can trust them to simulate future changes in climate. 

SHANE HUNTINGTON  
Right now if we look in earth orbit, there are thousands of satellites that are monitoring weather at all times. There are probably millions of sensors distributed across the globe that help us monitor various environmental conditions. But how do we go about determining climate conditions from the distant past when all this technology wasn't available? 

JONATHAN OVERPECK
Well there are not a lot of satellites up there looking at climate unfortunately. We need more. Most are doing other things. Some are doing weather and telecommunications and things. But getting back to the main topic, what we really need is to use our cleverness when we're trying to reconstruct climate going back hundreds, thousands, even millions of years. That's what paleoclimatologists are known for, is figuring out ways to use natural archives of climatic information to reconstruct past change. A good example might be using the variations in the width or density of rings in a tree. You can count these rings going back hundreds, even thousands of years in some places. These variations often reflect changes in temperature, or precipitation, or stream flow, or other variables that are very important to understand if we're going to be able to project future climates better. 

SHANE HUNTINGTON
Now when we consider some of these potential ways of determining what was going on in the past, like tree rings, each of these methodologies has a slightly different timeframe that it works on, doesn't it? Can you give us an idea of what some of them are and how far back we can actually look?

JONATHAN OVERPECK
Well there are a whole range of proxies that have annual time control. The tree rings I mentioned can do that, so can bands in corals or layers in some sediment basins, such as lakes and some marine basins. In these cases you can get paleoclimatic information with an annual or even seasonal resolution. Of course the trade-off is often you can't go back that far. If you wish to go back further, you need other types of archives that don't have that resolution nature, but have been accumulating either sediment or some kind of mineral for a long time, that has in it a biological or chemical signature of past climate variations. Some of these records, say a marine record from the deep ocean some place in the Pacific, might go back several million years. It could go back even tens of millions of years. Ice cores from Antarctica can go back nearly a million years. So there are a lot of very long records available. On land we have some lake records now that extend back over a million years. 

SHANE HUNTINGTON
Talking about lake records, in one of your recent studies you've been looking at a sedimentary record from a lake in West Africa, specifically in Ghana. What is particular about this lake that drew your attention?

JONATHAN OVERPECK
Well I've - before we go into that, I just want to say the name of the lake is Lake Bosumtwi and also that we are working with Ghanaian colleagues on this project, who have been quite instrumental not just in logistics but understanding the environment of the lake and what it might tell us. This lake's amazing. It's really worked out well to study for understanding paleoclimate, paleoenvironment more generally. What got my attention was it looked like a kind of lake that would have these annual laminations. A number of years, now decades ago, I guess [laughs], I went back, and people had studied it before but hadn't really brought modern methodologies to force on this lake and the sediments that are in the lake. We did discover that they had indeed annual laminations for the last 2500 years, and a really clever graduate student of mine, Tim Shanahan, did a marvellous job of extracting climate information over that time period. And then of course the lake had sediments that went back further. The lake formed when a meteor hit that region of Ghana 1.1 million years ago. So we have a whole team of scientists who have been working on trying to put together the million year climate record for that lake. And it's going to be coming out soon. It's very exciting to see such a long record of environmental change from Africa. 

SHANE HUNTINGTON
Talk us through how you go about that, because I can't imagine a scenario where you just dig a little bit around the bottom of the lake and learn all of this. You must be going fairly deep over an extended time frame in order to pool all this information together. How do you actually extract the material?

JONATHAN OVERPECK
Well it's a lot of work. For a lake like this, it's many visits. Many by myself, many by colleagues, many by Tim Shanahan. The two primary things we did on the lake were extract sediment cores from the bottom of the lake itself, and the lake is tens of metres deep, 70 metres roughly. In some cases we used handheld devices to bring back sediments to the boat, and then back to the laboratory in the United Stated. In other cases we actually brought in a large drill rig, and drilled to the bottom, into the bedrock under the lake, because we were also interested in how a meteorite impact leaves its record in the rock underneath the lake. So that's a big part of this. In order to get those long records we had to do seismic stratigraphy. So there's a lot of additional work and expeditions to do that work, done by colleagues at Syracuse University and led by them. A huge team though, many scientists from many places coming and going to finally put together a collection  of cores that could then be studied back in the laboratory. 

SHANE HUNTINGTON 
When you look at this core that you brought back into the lab, is there a nice linear correlation between the depth of the particular piece that that core comes from, and the time it comes from? Or is the variation more substantial depending on the climatic conditions at that particular time in history?

JONATHAN OVERPECK
Well a big trick in all of this is getting a good chronology, time control, for your cores. As you guessed, because climate is varying a lot, the processes that put sediment in the bottom of the lake change dramatically over time. So it isn't a linear relationship between depth and age. You need to have independent time control and hopefully in many cases multiple types of time control to cross check to get a good chronology. We used counting of the layers in the uppermost part of the sediment. We used radio carbon which is unprecedented number of radio carbon dates I think. We used changes in other chemical species in the lake. Then colleagues at the University of Rhode Island have put in years of effort to get what I think is going to be just about the best million year magnetic time control of a lake. And that's very exciting too. So looking actually at how the magnetic field has changed through time and left an impression on the grains of sediment in the lake. 

SHANE HUNTINGTON
Peck, how much information do we have now from this particular examination of one lake that gives us some idea of how climate was changing over the period, that's new, compared to information we had in the past?

JONATHAN OVERPECK
To me the most important things to date that we've published are those data that tell us about past hydro-climatic variability, in particular drought variability. One of the reasons we went to this lake the very first time, is because we figured it would have a very sensitive record of drought in the sub-Saharan Africa region, and made famous by the Sahel drought of the '70s, all the way up pretty much to today. When a major drought happens in that region, it affects a lot of people and in fact more and more people are moving in to the sub-Saharan region now, because of population pressures. And what we discovered, and it's pretty scary, is that the really devastating Sahel drought that we had in the twentieth century is but a small example of the kinds of droughts that can occur in that region. We found from the Lake Bosumtwi sediments that we can have droughts lasting over 100 years, and when they occur – much drier than the Sahel drought. For example, the lake dropped a couple of tens of metres and became much shallower during these droughts. We have multiple ways of using the sediment record to be sure that these past droughts were real, and therefore are a real threat in the future if they occur again. 

SHANE HUNTINGTON
I'm Shane Huntington, and you're listening to Up Close. In this episode, we're talking about paleoclimatology with Jonathan Overpeck.Peck, weather is certainly cyclical in nature, and you've mentioned areas such as drought, but what other areas do we find when we look back through these long term records where we find cycles? Is temperature one of the areas where we find these sorts of long term cycles?

JONATHAN OVERPECK
Well I'd kind of like to discourage the use of cycles when talking about climate and weather. When you look back in the paleoclimate records, there are actually very few variations that are truly cyclic. A good example of these which we see in Lake Bosumtwi sediments and many other records are quasi-periodic, so they're not purely cyclic, variations in the earth's climate, the coming and going of the ice ages is a good example, that are due to changes in the earth's orbit.As you get to faster and faster time scales, more relevant to the future, there's very few cases where past climate was cyclical. But it has varied substantially and we see the comings and goings of drier conditions in just about any continental area of the world, as well as wetter conditions. We see warmer conditions and cooler conditions. So we're trying very hard as paleoclimatologists to understand what caused those variations in the past, and to what extent they could cause similar variations in the future. 

SHANE HUNTINGTON
Do you get any information from these sorts of studies on severe weather events?

JONATHAN OVERPECK
Yeah well, certainly drought. Certainly floods another one we can get a lot of record. We have some very clever colleagues who are getting records of hurricanes or typhoons and tropical cyclones, and can look at the frequency of those storms making landfall in a particular area over very long periods of time. So we can get some records of extremes, as well as mean conditions. 

SHANE HUNTINGTON 
So there's been an apparent increase in the number of severe weather events of late, or at least the reporting of them has increased. It's hard sometimes to disentangle the two. Are these determinations at the moment valid, that there has been an increase? Or when you compare them to those past circumstances is this just the normal scenario for a planet like earth? 

JONATHAN OVERPECK
In terms of some of these extremes, we have been able to start detecting changes and attributing those changes to global warming, for example. An example of that in Australia would be the intensity of the most rapid rainfall events, short rainfall events, lasting just a matter of hours. More rain is being dumped during these events than in the past, and there seems to be a clear relationship between temperature increase and the amount of rainfall that's coming out. We call it the intensity of the rain. That is something that was predicted quite a long time ago, that should be occurring. Now we're at the point where we're starting to see that in many parts of the world including Australia. 

SHANE HUNTINGTON
Some of what we know about past climate is being used at the moment by people who don't believe that humans are playing any role in the current global warming that's occurring. An example is the use of Medieval Warm Period in their discussions. Can you give us an understanding of what is referred to here as the Medieval Warm Period, and how that argument is or is not valid?

JONATHAN OVERPECK
The Medieval Warm Period was coined decades ago by a scientist working I believe in England. He was really focused on the warmth that was apparent during Medieval times in Europe. A lot of people have been studying this interval. And a lot of people have also been using it in various ways to make their own arguments, I suppose. But we now know a lot more about it. When it comes to the global scale phenomenon, we don't call it a Medieval Warm Period anymore. We call it the Medieval Climate Anomaly. The reason we do that is indeed it was warm in some parts of the world, particularly the Northern hemisphere and Europe, but it was actually colder than today, substantially colder, in other parts of the world such as the tropical Pacific. So it really wasn't a uniformly warm event like we have now with global warming. We try and make that real clear, and of course, I think until the earth is totally cooked [laughs], there'll still be people arguing that for some reason the Medieval times were warmer, and we're gaining warmth now for the same reason. That's just a total myth. 

SHANE HUNTINGTON
One of the other areas that often comes up is this issue of solar activity and how that's affecting the weather. Is there information from paleoclimatology that sheds light on the validity of those arguments?

JONATHAN OVERPECK
You know there hasn't been a big change, not even a noticeable change, in the sun since we started recording the radiance changes using satellites, the best possible way. So we've had the most dramatic increase in global temperature over a period when the sun hasn't changed at all. But if you go back further in earth history, you do see temperature variations that can be explained in part by changes we think in the output of the sun. This effect is very small and hardly noticeable compared to say the effect of volcanic eruptions, which don't last very long but they're very pronounced when they occur, and get aerosols or dust and chemicals in the upper atmosphere or stratosphere. And they're also very small compared to variations in greenhouse gases in the atmosphere. 

SHANE HUNTINGTON 
You're listening to Up Close. In this episode we're talking about paleoclimatology with Jonathan Overpeck. I'm Shane Huntington. Peck, much like stem cell work, nuclear power and a myriad of other scientific areas that have generated public controversy over the years, climate science seems to require a very high standard of public engagement. How are you going about this and what sort of things do we need to do to make sure the public is appropriately aware of just what's going on?

JONATHAN OVERPECK
I think you're right that climate change is becoming pretty much one of the problems of our generation, and our future generations. And many very important and potentially costly decisions need to be made about how we handle climate change. For example the impacts of climate change in the United States, last year we had billions of dollars in damages due to climate extremes, such as Hurricane Sandy, but also a drought, that were in part coloured by climate change. In the case of Hurricane Sandy the rainfall amounts, the intensity of rain, was high, but also we had an elevated sea level due to climate change that made the impacts worse. Conversely, we might wish to reduce the causes of climate change rather than enduring their impacts and their economic costs there. So either way it's going to cost. And we really need to make sure that everybody that's voting and helping to decide on what to do understands the gravity of the problem, and what the options are for dealing with it. What it means to them, and what they can do as individuals or as a society to deal with the problem. For that reason I think we're seeing a lot more climate scientists coming out of the laboratory and engaging in discussions with the public and discussions with church or religious groups, with the media. Any which way that we can to have a good discussion, talk about the facts and try and counter the disinformation campaign that's being funded by the fossil fuel industry, which is causing a lot of confusion in the public. But that might not be enough. What I've learned in particular, even more so coming to Australia and spending time here, is that we really need to work more directly as scientists with practitioners in society. People for example who manage water resources or bushfire or public health, or are planning how to deal with sea level rise. We need to work with them to generate knowledge on options for example, and how to best implement those options in cost effective ways. And by doing this, working together, this co-generation of knowledge, I think what will happen is there'll be an increase on the practitioner side, the person in society, an increase in their understanding, but also trust in the scientific knowledge that they need to use to make better decisions. And I think the scientists will also learn about the reality of making better decisions, as opposed to the more academic view of things we tend to have in science. 

SHANE HUNTINGTON 
Over the last 20 or so years we seem to have moved from a position where climate change was something that might happen in the future, to one where now as you've been suggesting, it's already happening. How has the message shifted over that period, and where should it shift to in the coming years?

JONATHAN OVERPECK
Well without a doubt climate change has gone from when I was grad student 30 years ago to a hypothetical it's change that's coming, to something that's very real now. You see that in Australia in spades, you see it in the Southwest United States where I'm from. Things are certainly getting hotter, things are getting drier. We're getting more of these extremes. And you see the same thing played out around the world. The earth is certainly changing due to the burning of fossil fuels and other greenhouse gas emitting activities of humans. And a good measure of this is just how much money the fossil fuel industry and other groups are putting into disinformation campaigns. They're worried that the status quo, the way they make money at the expense of the climate and essentially the people in the world, is going to affect their status quo. And it's clear that we as a society need to have a very good debate, an open debate, about what needs to be done. 

SHANE HUNTINGTON
Peck, at what stage do we need to move from a mitigation strategy, where we're essentially trying to cap the production of greenhouse gases, to one of adaptation where we're trying to adapt to the effects of climate change? As in, this is happening, we have to live with it, how do we live with it in a way that is reasonable?

JONATHAN OVERPECK
I think we have to deal with both adaptation and mitigation. Both of those are essential to dealing with climate change. Because climate change is already occurring, it's already having big effects, people are already starting to come up with adaptation strategies. For example, water managers both here and in the United States and elsewhere around the world already are figuring out that climate change is a problem and we have to be able to endure drier, hotter conditions. And the paleo record makes it real clear that that's a good strategy even in the absence of climate change, because droughts occur. So it's a no-regrets kind of strategy. That said, as we learn to adapt and we work closely as partners, practitioners and scientists, we're starting to understand what we can adapt to and what we cannot adapt to. That is a very powerful tool in guiding our mitigation discussions. In other words, if we don't think we can adapt to a temperature increase and associated drying, say beyond a two degree global warming, then we really need to be stronger advocates for keeping the earth from warming beyond two degrees. And the way we do that is by reducing our emissions of greenhouse gases. 

SHANE HUNTINGTON
It sounds as though there is a fair degree of risk here. You mentioned that there is quite a large advocacy coming from the fossil fuel industries towards polluting that message that we currently have around mitigation. When we start moving towards that adaptation message, is there an equally likely chance that they will start polluting that as well, and push the idea that well we can adapt to this, it's not so bad?

JONATHAN OVERPECK
Well yeah, and I think it's a fair debate. And all I'm asking for is a fair debate. There are things that we should be able to adapt to, and perhaps it will just cost a lot of money to do it. And maybe the fossil fuel industry would help contribute to that or we can do that via a carbon tax or something. The important thing is if we're going adapt, we're going to have to find the money to do that. The second thing is that there are going to be limits to what we can adapt to. We have to, in an open fair discussion, identify what those limits are and have discussions about how to prevent us from crossing those limits. 

SHANE HUNTINGTON
You're an advocate for what's called no-regrets adaptation. What do you mean by that?

JONATHAN OVERPECK
Well there are things we can do regardless of what's causing climate change, how large climate change is, that makes sense. A good example would be what's going on in the United Stated right now. We're having a very bad what you could call bushfire season, we call it wildfire season. Hundreds of homes are being burned up in Colorado for example. And it's a no-regrets strategy to think of ways to not put houses and people in harm's way in forests, because we're always going to have wildfire. Climate change only makes the probability of wildfire and the severity of wildfire worse. But even without climate change, wildfire's reality and you don't want to put houses in there if you're worried about them burning up. Another example would be drought and water supply. I think in the United States we're already seeing water managers take into account these long droughts that we've seen in the paleoclimatic record, lasting decades, and thinking about how their management, water management, strategies would handle such a drought that they've never seen in their rain gauge or instrumental record of the last 100 years. One of the things I've been trying to do while I'm here in Australia is explore the extent to which this would be a good way to go in Australia. I think it's pretty clear that like North America, Australia's had these much longer droughts in recent earth history, and that it would be a no-regrets strategy to think of ways to deal with very long prolonged, very long, severe big dries. It would be no-regrets because if climate change brings on the next big drought, you're ready. If natural variability brings on the big drought, you're ready. That's why it's a no-regrets strategy. 

SHANE HUNTINGTON 
It appears that in the past we very much went with the more moral argument with regards to the pollution of our environment. We taught our kids, we taught everyone not to pollute their environment because it was just simply wrong to do it. We seem to have moved away from that to the point where we're using the 'save our own skin' argument with regards to climate change. Is that being effective, or do we need to move back towards getting society onto a more moral track of just not doing this, full stop?

JONATHAN OVERPECK
Well we have to consider both the practical socio-economic factors embedded in climate change as well as the moral. And it's been pretty clear from our discussion today that there are big costs of climate change if we let it go unchecked. Probably much larger than the costs of mitigation, that's what most of the scientists now feel, who study this for a living and write papers in the peer-reviewed literature. At the same time, you have to worry about those countries in the Pacific and the Indian Ocean for example, that will be completely submerged. Their cultures, in existence for thousands of years, their land gone, because of fossil fuel burning in places like Australia, China, North America, and Europe. The same thing holds true for a lot of indigenous populations. For example in North America I've worked with Native Americans and Inuit people up in the Northern parts of North America, in the arctic. There, there are huge changes that are taking place because of climate change - no doubt about it, melting of sea ice in summer is just unprecedented - are having big effects on the cultural traditions of these people. And there are not a lot of cultural traditions left that bring them together as a people, and they're shouting and screaming as much as they can to the international community to stifle this climate change, because it's really threatening their traditional ways of life.   And the last one that really is a moral imperative is the possibility that we could trigger a mass extinction of species on earth as we combine unprecedented climate change with all the other things we're doing to the land surface and ocean of this planet. And it's quite plausible that we would give rise to a mass extinction and in geologic history; those have only occurred when you have things like huge meteorite impacts. We could essentially duplicate that via climate change. 

SHANE HUNTINGTON 
Peck, just to finish up you're out here in Australia obviously pushing this message very strongly. Are you still optimistic about what the outcomes could be here?

JONATHAN OVERPECK
I'm always an optimistic person. Indeed there was a study just done a couple of weeks ago by an international group that indicated that we could, if we moved quickly, still limit climate change to two degrees C, this is global warming, and all the change that would go with that. That's substantially more than we have now. And of course there's nothing magical about two degrees C, some parts of our society and natural world will be able to handle more warming than that. Some will handle less probably. We're trying to get a better feel for what the regional place-specific limits are. So I'm also made optimistic because I see a lot of progress being made in the United States, in particular, and even China is starting to really change their ways to be much more aggressive about dealing with climate change. I think in the United States and in China it's as much about getting ready to capture the really strong economic market that is going to be created when everyone around the world is dealing with climate change, both adapting to climate change and mitigating climate change. It's probably going to be a market that brings a lot more economic gain to the people of the world than the fossil fuel industry that it will replace. 

SHANE HUNTINGTON 
Professor Jonathan Overpeck, founding co-director of the Institute of Environment at the University of Arizona. Thank you for being our guest on Up Close today, and talking with us about paleoclimatology and communicating climate change. 

JONATHAN OVERPECK
It's my pleasure. Thank you. 

SHANE HUNTINGTON 
Relevant links, full transcript, and more information on this episode can be found on our website at upclose.unimelb.edu.au. Up Close is a production of the University of Melbourne Australia. This episode was recorded 18 June 2013. Producers for this episode were Kelvin Param, Eric van Bemmel and Dr Dyani Lewis. Audio engineering by Gavin Nebauer. Up Close is created by Eric van Bemmel and Kelvin Param. I'm Dr Shane Huntington. Until next time, goodbye. 

VOICEOVER
You've been listening to Up Close. We're also on Twitter and Facebook. For more information visit upclose.unimelb.edu.au. Copyright 2013, the University of Melbourne. 


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