It’s true the Earth has experienced periods of global warming in its past. The largest such warming event in the past 90 million years – since the time dinosaurs roamed Earth – was the Paleocene–Eocene Thermal Maximum, about 56 million years ago. Average global temperatures increased by 4–5°C over a period of 3,000–10,000 years. Human beings were definitely not walking the Earth back then, but today scientists are able to piece together evidence of how and why this ancient global warming happened.
Spoiler alert? It was caused by greenhouse gas emissions, likely stemming from carbon cycle feedbacks – the processes that unlocked and released more and more CO2 from the Earth’s surface as it warmed, and volcanism – the eruption of volcanoes.
Dustin Harper is a marine geologist postdoctoral researcher in the Department of Geology and Geophysics at the University of Utah. He, along with U Geology professor Gabe Bowen, published a study where they examined tiny, microscopic shell fossils taken from drilling cores in the ocean floor, that revealed important information about ancient sea surface temperatures and the levels of atmospheric CO2 . They found sea surface temperatures were closely linked with levels of atmospheric CO2 during this period.
This helps us to understand the sensitivities of our planet and the feedback mechanisms that can kick in during periods of rapid global warming triggered by greenhouse gas emissions, which is what we are experiencing today – with anthropogenic climate change – albeit at a much faster rate. Like, 4 to 10 times faster than occurred during those ancient hyperthermal events
To kick off our conversation, I asked Dustin Harper to share how he got into the geosciences in the first place.
(Featured image: Dustin Harper with other members of an International Ocean Discovery Program inspecting ocean sediment core samples aboard a research vessel during an expedition. Credit: Sandra Herrmann)
Listen to the Interview:
Transcript:
Dustin Harper
Well, yeah, I had a kind of roundabout path. I think many people that go into geosciences do. I really liked science and mathematics as a K-through-12 student, and I ended up going to college, pursuing pre-medical credentials so I could go into medical school. But the class size was overwhelming. And I took a geology course, and it was a class of 15 people. And we got to go outside, and I got to use similar types of science and mathematics in geology. And so that was really attractive to me. You know, I also I grew up in a really small town. So, you didn’t really know what other avenues there were in terms of STEM science.
Ross Chambless
Where did you grow up?
Dustin Harper
I grew up in in Northern California, in the Sierra Nevada foothills. And there weren’t too many other geologists wandering around in that. The town had less than a thousand people. And I always was out collecting insects and classifying different things with my Audubon Society books. And so, it was kind of a natural fit because I do a little bit of that collecting of organisms or fossilized organisms now and classifying them. So, I kind of fell in line.
Ross Chambless
So, now you’re in the department of Geology and Geophysics, but your specific interests are around marine geology?
Dustin Harper
So I got interested in marine geology when I first started my undergraduate work at UC San Diego, and the geology program was Scripps Institution of Oceanography. They were in charge of the undergrad geology program. So, it was all marine geologist professors. And I got looped into research during undergraduate studies looking at paleo magnetism. So, magnetism in the past. And then I got really interested in the past and went down that route. I really liked chemistry though, so I decided to pursue sedimentary geochemistry and have stuck with it since then, since the master’s that I stayed on to do there at Scripps.
Ross Chambless
Okay. So, you recently were the primary author of a study that examines sea surface temperatures with levels of atmospheric carbon dioxide over a 6-million-year period. And kind of going off the summary of this study, but you’re covering hyperthermals. Can you first describe what is a hyperthermal, and why are you studying them?
Dustin Harper
Yeah. So, hyperthermal events are global warming events that happened in the geologic past. So, the ones that we’re really interested in were happening 55 million years ago or so. And these events we have roughly similar magnitudes of carbon released to the different scenarios that we’re facing with anthropogenic climate change. So, they they’re really useful in terms of case studies of the climate system.
The global warming events in the past, these are different background conditions that they were taking place over. So that’s an important consideration. But lots of environmental change is happening. Temperatures are increasing, oceans are acidifying, the hydrologic cycle is shifting based on an intensification, a heat driven intensification. And we’re able to look at all of this environmental change and start to kind of diagnose the sensitivities of these different responses to the forcing of carbon being released into the atmosphere and ocean.
Ross Chambless
I see. So, specifically there was two events. There’s one called the Paleocene-Eocene Thermal Maximum (PETM), which is approximately 56 million years ago. And then there’s another one, the Eocene Thermal Maximum 2 (ETM-2) approximately 54 million years ago. So, these were all happening way before human beings were really around?
Dustin Harper
That’s right. Yeah.
Ross Chambless
Okay. And so, different from our current period, these events were happening sort of because of, you could say, natural causes – in quotes. But why were these events happening in those times?
Dustin Harper
So, there are a number of theories. And the study that we recently published addresses some of those theories. And one way that we can understand what was causing the carbon release is by looking at how much CO2 changed and by looking at other measurements within the carbon cycling of surface reservoirs of carbon.
And so, the leading hypothesis is that we have a number of things happening. We have in the North Atlantic this volcanism that is that is going off. But we also have a number of responses, feedback responses in the carbon cycle. So, and it is my thought that volcanism was a contributor, in order to generate this rapid release of carbon. What our study is showing is that you really need to invoke other sources of carbon, organic carbon primarily, as well as carbon derived from methane dissociation of methane into CO2. And those two types of carbon have really distinct signatures. And so, we were able to piece apart that signature using our reconstruction.
And it’s an important takeaway, because those sources of carbon, they’re responding to warming. So, it’s this positive feedback in which it warms more, and the earth system is responding in a way in which organic carbon is going from the sediments and being released into the ocean and atmosphere as well as methane that is in marine sediments.
Ross Chambless
So, this is kind of an important part of your research finding, that with these emissions of carbon dioxide and methane, you were seeing temperatures rise at the same time.
Dustin Harper
Yeah, exactly.
Ross Chambless
And you could determine that even though this happened many, many millions of years ago?
Dustin Harper
Yeah. So, we use a couple of different geochemical tools to do that. And we call them proxies because in essence, they’re a proxy measurement of the past environment. So, we’re able to reconstruct the physical and chemical properties of seawater, including temperature, and pH, to diagnose the degree of warming and ocean acidification using these microscopic shells.
Ross Chambless
Yeah. So, that’s what I also wanted to ask about. Tell me about these microscopic shells and why were these important for helping to determine as evidence how this happened?
Dustin Harper
These are one of our best archives as paleoclimatologists. We have a number of different materials, geologic materials that we can look at, that I work with. You can look at soils that were deposited in the past, for instance, on land. But in the oceans, we have these little single-celled calcium carbonate, So calcite-making protists, and they’re called foraminifera. And those foraminifera, they lived really throughout the sea, throughout the seawater, both the shallow and deeper depths, as well as the sediment water interface. The ones we’re really interested in, those were the ones living at the sea surface. And we’re interested in those because they’re in this constant flux or equilibrium with the atmosphere in the upper ocean. So, we’re able to use them as a proxy for atmosphere. And that’s because these shells, they’re making their shells in this specific seawater. So, they’re in essence recording the seawater chemistry and physical properties when they’re taking up different elements to make that shell.
Ross Chambless
So, how did you go about collecting these shell samples?
Dustin Harper
Yeah, it is a coordinated effort. So, for the last many decades now, 40 plus years, the U.S. has been involved in the international collaborations of scientific ocean drilling. Some of those collaborations are unfortunately wrapping up and we’re looking at the next phase of scientific ocean drilling. But this involved going out on two-month long expeditions at sea where we’re on a 400-foot-long drill ship with a 100 plus foot derrick. And we take sediment cores out of the deep ocean. And we’re targeting these open ocean sites because, once again, they’re in equilibrium with the atmosphere. If we go too close to shore, there’s going to be some other dynamic processes that could influence the chemistry of their shells. And by looking in the open ocean, we’re able to collect more pristine record of the atmosphere potentially.
So, it takes a lot to do this because we’re drilling in thousands of meters of water depth and pulling up hundreds of meters of core below the sediment-water interface at the seafloor. So, there are 120 people on board that range from, you know, experienced drillship operators to scientists. There’s 25 or so scientists on board. And all the techs and staff that you need to be at sea for two months.
Ross Chambless
So, was this primarily an international crew?
Dustin Harper
Yeah. It’s all international participants. Some of the techs, a lot of them are based out of Texas A&M because they run the ship. But for the most part, it was a diverse range of people, especially a science party, which was a great part of part of being involved with this.
Ross Chambless
Well, I was reading. So, you were kind of located in the North Pacific, sort of east of Japan?
Dustin Harper
So, these samples from this study, I didn’t have the opportunity to sail on this expedition. This expedition, my advisor for my Ph.D., he sailed on the expedition, so the samples were ready for me when I arrived. But during my Ph.D., I got to go out on an expedition. Then a couple of years ago, I went out on my second one for other research.
Ross Chambless
Okay. You now, when you’re looking at something that happened in the ancient past, there might be some conjecture, or certain levels of uncertainty around that. So, how accurate would you say we can determine is the data is coming from these samples?
Dustin Harper
I would say that we’re doing a pretty good job, in my belief, on accuracy. Precision is a kind of different beast, right. So, that’s why we are part of this study. We’ve been developing these statistical models to interpret the data in the most robust way possible. And so, these models, they allow us to translate from the geochemical measurement to the past environment. And when we do that translation there’s a number of places where we can incorporate uncertainty into those estimations. Just even the measurement that we’re making, there’s some uncertainty on with the mass spectrometers. So, we can incorporate all of that uncertainty into these models, and then we can report a range of values to give a sense of the precision with which we’re estimating the past.
Ross Chambless
Okay. So, just kind of stepping back, it seems like this research is really important because it helps scientists to understand these past carbon release events and forecast its consequences for our modern time, correct? I mean, that’s generally the overview. What did you seem to learn about the sensitivity of the Earth’s climate through this?
Dustin Harper
One kind of interesting finding was that pardon me over, over the shorter timescales that these events are taking place, and we’re talking thousands of years, and I’d just like to highlight that these events are slower than modern climate change, orders of magnitude in order of magnitude or more. So, we’re releasing carbon more than ten times as quickly, but they still represent some of our best analogs. And it’s encouraging to see that the sensitivity of the climate temperature to carbon release was similar for the two different events. And that was about five degrees Celsius for each doubling of CO2. And when we looked over the longer-term interval of the whole record, the 6-million-year long record and we looked at how much climate had changed over that time period and how much CO2 had changed over that time period, the sensitivity was slightly less.
So, that’s pointing towards other mechanisms that are driving these higher sensitivities during abrupt global warming events compared to a longer-term climate which might be influenced by other climate drivers other than CO2 like tectonics, for instance, is active on multi-million-year timescales. And that can change ocean circulation and influence the climate.
Ross Chambless
Maybe say more about that. So, you’re saying that the sensitivity as far as how the planet was reacting to these events wasn’t going way off the charts as far as the temperature. But this was also happening over a longer period of time?
Dustin Harper
It’s the sensitivity on these shorter timescales is more closely related to what we will experience than on these longer timescales.
There are no tectonic drivers that will be occurring over the next sub million years. So, by looking at these events, we’re able to say something about the consistency of the sensitivity of the climate to carbon release. And this has all been normalized to the amount of carbon that’s going into the system. So, it’s not that both of the events had five degrees of warming, it’s that they both experienced roughly five-degree degrees of warming for a doubling of CO2.
And so, as we continued to release carbon into the atmosphere and it gets incorporated in the ocean as well, we might be experiencing similar magnitudes of climate sensitivity. There are some other complicating factors and things have changed over the last 50 million years that can drive to more sensitive climate versus lower sensitive climate. And so, this contribution kind of falls in with a number of other contributions that have looked at the climate sensitivity and how that has evolved over geologic time and gives us a kind of a new baseline understanding for these important case study events.
Ross Chambless
And so, what do we know about the Earth’s environmental changes after these massive carbon release events? I mean, what do we understand about the conditions of the planet during those times? I mean, to has to be a conjecture because, you know, human beings weren’t around then, but what do we know happened to the flora and fauna across the planet? What happened to the globe? What was Earth like if we could go back in time and experience it?
Dustin Harper
Yeah, so, this time period, on top of these global warming events it was already a pretty warm interval. So, we’ve evolved into, over the last 66 million years we’ve developed major ice sheets at the poles, which weren’t there at the time. There were also rapid changes that occurred during the events. So, you already had a pretty warm climate to start. And then you increase global temperatures by five or six degrees C and you start having palm plants in Antarctica and at the poles. There are records of pollen of these palms and fossils of palms through this interval. You have extreme temperatures in these lower latitudes. I mean, we’re talking average temperatures over 40 degrees C in the surface ocean, which is really hot.
Besides, it’s also a dynamic period for evolution, for biology. During these events, we have some smaller scale extinctions. They’re not like the big extinction events that you hear about, like the Dinosaur K-Pg Extinction or the Permian–Triassic, but species are responding to this environmental change. And some of the species that are most affected are the deep ocean calcifiers, the ones that make their shells out of calcium carbonate. Because by putting CO2 into the system, you’re acidifying it. And it’s making it harder for those calcifiers to make shells. So that’s a big one.
It’s also a time period where you have diversification of mammals. This is just after the extinction of the dinosaurs and mammals are on the rise in terms of evolution. And there are certain adaptations that they’ve developed in order to deal with some of those warm climates.
Ross Chambless
Yeah. So fascinating, I mean, I was thinking of when you’re studying our planet on these scales, I wonder how that affects one’s perspective of our current moment on this planet? In our very short lives and all the day-to-day stuff that we get worked up about. Our very minute, momentary existence, when looking at the global scale… I mean, it must be very unique as a geo-scientist, your worldview.
Dustin Harper
Yeah. I mean, you nailed it. I think about these things a lot. I think about, you know, this is just a blip. But this blip that we’re in, we have this massive amount of carbon emissions, like the rate of carbon is still… We can go back in time and look for these analogue case studies, and we can find our best candidates like the Paleocene-Eocene Thermal Maximum. But that doesn’t mean that you know what we’re doing today, that we can completely understand what’s happening by looking at these events. We can start to piece apart how the carbon cycle works and how certain feedbacks work as we warm the planet. But there’s still a lot of unknown. And it gives a little perspective on just how different the world can look in the past. And how that can be driven by changing the CO2 levels in the atmosphere. That is abundantly clear when we look at these events and we see massive environmental change, and decreases in pH, and intense precipitation events. It kind of brings it all into focus that what we’re doing in a couple hundred years maybe is equivalent to some of the biggest dynamic changes of the planet in its geologic history over millions, if not hundreds of millions of years.
Ross Chambless
Yeah, puts it in perspective for sure. I was going to ask you, are there other schools of thought as far as understanding what triggered these hypothermal events, within this field?
Dustin Harper
Yeah. I think there are. There are a number of different ideas. I think that we’re all kind of moving towards it has to be a mixture, and there has to be some sort of interplay between the different carbon reservoirs as you start to heat up the planet. And that’s really based on these kinds of studies and other modeling studies that look at how the carbon cycle might be affected in the past. And so, I mentioned this North Atlantic Igneous Province volcanism. That was the expedition I sailed on three years ago. Now that was the target was to drill into some of the volcanism and the complexes associated with the volcanism that might be linked to the PETM. And I think there’s a good link. We found pretty strong evidence that some of these hydrothermal vent systems that are being generated in the sediments above this volcanic rock, it is releasing carbon right at the PETM, right at the Paleocene-Eocene boundary where the Paleocene-Eocene Thermal Maximum is. So, I think that is a strong candidate as at least a contributor.
But as I mentioned before, based on what we’re finding in this study, it can’t be the only thing contributing. And there are these feedbacks. By saying organic carbon reservoir, that can mean anything from organic carbon that’s being deposited into sediments and trapped in sediments that might be more able to oxidize and come to the surface. But it can also be permafrost deposits that are breaking up and releasing organic carbon from the soils. And there are a number of other mechanisms like wildfires that might be coming into play there too.
So, we know that all of those things are happening today. And we can see these things happening today. And so it’s difficult to go into the past and not invoke some of those mechanisms, those feedback mechanisms. And theory would predict that they should be involved if we look at the modeling results. And so, this is an observational study that’s a way to kind of ground truth those modeling studies, that theory. And tell us that more than likely those other processes were at play. And it wasn’t just this volcanism.
Another one of the first hypotheses for the PETM driver is this methane that’s stored in the marine sediments, and it’s trapped in ice. And it sometimes you’ll hear it called gas hydrate. It’s ice, that you can light on fire, in essence. It’ll burn. This methane, it’s really sensitive, you can imagine, to temperature change since it’s locked in these frozen reservoirs in the seafloor. And so, we would expect those to be released as we start to warm the planet. And that methane changes in the CO2 in the ocean. And then it can be emitted as CO2.
So, that is still a candidate for a contributor based on our work. And then there’s also, on top of that, we’re looking at timescales where we have these what we call “orbital cycling” of the Earth, right. That natural cycling of climate variability in the past, something that drives glacial-interglacial periods. The past ice age, for instance. So, this natural variability, also comes into play, and may be tied to some of these events where the event could have been driven by an extreme configuration, and the Earth’s orbit that would have allowed for these feedbacks to be invoked in for carbon cycle and CO2 to run away.
Ross Chambless
Interesting. So, these are sort of these hills and valleys that you see when you look at the very long-range history of the planet’s temperatures and CO2 levels?
Dustin Harper
Exactly. Over tens of thousands of years’ time scales. So, they really don’t have a huge impact on modern climate in terms of, I mean it affects where we are in terms of the baseline where we started before, we started releasing CO2. But the timescale of change for that, given the timescale of change for human released carbon, is much longer. So, it won’t be it won’t be as influential as carbon emissions in the past.
Ross Chambless
Yeah, well it sounds like it’s sort of like detective work.
Dustin Harper
Definitely.
Ross Chambless
Sort of Sherlock Holmes. I mean, you have all this evidence, and you’re trying to piece together the story of what happened and make sense of it. That that seems like that could be very intriguing, very exciting?
Dustin Harper
Yeah. I like working on time intervals in the past where there’s a lot of unknowns. Because there’s a lot of discovery yet to be made. So, I think that’s one of the more exciting aspects of what I get to do. You know, not only going out on these expeditions and discovering. Maybe you get an event, and you can see a change in the sediment with your bare naked eyes pulling up a new core, but also just that you get to make these discoveries by piecing together all of these findings that have been established over the last 50 plus years, and try to make sense of them. Or make the most sense you can at the time with them and incorporate what we don’t know when we do that as well.
Ross Chambless
Yeah. And just a few more questions. Just kind of stepping back, what do you hope to achieve with your research?
Dustin Harper
Yeah, I really hope to achieve, in terms of kind of a broader impact, I would hope that this research provides non-scientists with a perspective on what climate variability looks like, and what the earth can look like, and how the Earth can respond, and how the Earth responds to CO2 emissions.
I think it’s a perspective that sometimes is brought up even by climate skeptics or climate deniers. So, I think it’s really important that we actually can understand and look at what the leading science is telling us about past climate variability and how that relates to modern change. So, I think that is my ultimate goal in terms of the broader impact of my research.
I’m also just really a curious person when it comes to understanding the past. I mean, thinking about these past climate states is fascinating. And thinking about where you live today and the world looking vastly different than what you’re experiencing. It’s an interesting thought experiment. And that curiosity, it’s been a driver in my research where I want to better inform our understanding of modern change. But at the same time, it’s really interesting just to be able to reconstruct the evolution, the history of Earth. You know, it’s important not only in terms of curiosity, but I think it’s also important to understand biological evolution and how the environment has changed side by side with biological evolution, and what drives that change and how has biology responded.
Ross Chambless
I can sense that. It really pushes people to use their imaginations much more fully than sometimes where we’re able to.
Well, finally, what do you do for fun? What do you do when you’re not doing research?
Dustin Harper
Yeah. I’ve been in Utah a couple of years now. It was a playground for me. So, I’m happy to be here. I love getting to the mountains and mountain biking and backpacking, and hiking, and snowboarding. And I love… and this might sound a little dorky… but I also like rockhounding. So, going out and searching for rocks in the desert is something I’ve been doing for a number of years. And I really enjoy cooking. That’s another side passion of mine.
Ross Chambless
Well, as a marine geologist, you’re pretty far from the ocean. But maybe that gives you some balance. Maybe it’s just a change of scenery?
Dustin Harper
Yeah. But you know, if you go back to the Cretaceous, we did have a seaway going through North America.
Ross Chambless
It’s fascinating to see the sort of geological mapping of that can show what this place was many millions of years ago.
Dustin Harper with the Department of Geology and Geophysics. Thank you so much.
Dustin Harper
Thank you so much for having me, Ross.