How Humans Make the Earth Their Home

How Humans Make the Earth Their Home

Laurence C. Smith [6.12.20]

Beginning in 2012, and for many summers ever since, my team and I have been helicoptering onto the Greenland ice sheet, in this fantastical melt zone. We use helicopters to string cableways over the top of rushing super glacial rivers so that we can hang this river discharge measurement technology called Acoustic Doppler Current Profiler (ADCP). We operate around the clock to collect measurements of river discharge every hour, for up to a week in duration. We have collected the world's first meltwater runoff measurements on top of the ice sheet. What we then do is simultaneously use drones and satellites to map out the upstream contributing watershed area flowing to that point where we are collecting the discharge measurements. When we know the contributing watershed area and we have the flow measurements at the bottom of the watershed, we then have a completely independent field dataset from which we can test the ability of climate models to simulate meltwater runoff from the Greenland ice sheet. And it's those models that are being used to predict the future. It's those models that are being used to estimate projected ranges of sea level rise in IPCC reports and so forth.

LAURENCE C. SMITH is the John Atwater and Diana Nelson University Professor of Environmental Studies and Professor of Earth, Environmental and Planetary Sciences at Brown University. He is the author, most recently, of Rivers of PowerLaurence C. Smith's Edge Bio Page


As an earth and climate scientist, I think a lot about the physical Earth and how it's changing, especially from climate change, but also due to human environmental impacts. As a geographer, I think a lot about how humans make the Earth their home.

If you look at the history of humanity, there's a fascinating progression of a seeming separation from nature that goes back 10,000 years and is still happening in an accelerating way today. The earliest civilizations, which got going around 10,000 years ago (their origins even earlier than that), formed along the river banks of the Tigris-Euphrates Rivers and present-day Iraq. Even before that, they formed along the Indus River in present-day Pakistan and India and the Yellow River in China. A little later, even here in North America, pre-colonial discovery, they formed along the banks of the Mississippi River, with a long-forgotten Native American civilization called the Cahokians. The Cahokians had earthen and log pyramids; they had a vast empire spreading up and down the Mississippi River Valley; and they had trade and administrative centers. These hydraulic civilizations along rivers created some of the first big societal inventions—the creation of the city-state, the creation of a ruling class, the creation of some of our earliest human institutions, like engineering, science, and law.

The first big step was the removal of our dependence on foraging for food, and being able to survive in fixed settlements due to irrigated agriculture. From there, we moved to trade, we discovered machines, the Industrial Revolution happened, and from there we moved to global food production. Our most recent trend, which has been going on for well over a century, is urbanization—this incredible movement of people from the countryside to urban cores. In fact, a little over a decade ago, in 2008, a remarkable threshold was surpassed with regard to this phenomenon. Somewhere on Earth, a baby was born—we'll never know exactly where, or who it was, or exactly when it happened—and for the first time in the history of the human species, we became urban in the majority. Never before had this happened. By that time, a decade plus ago, well over half had long since forgotten how to feed themselves, how to obtain water, how to get clothing. We long ago ceded these most basic of biological requirements to our organized society. Today, in the modern world, we rely very much on the efforts of global supply chains and multinational corporations to provide our basic biological services to us, the urban consumer.

I recently moved to New England from Los Angeles. In LA there's a very popular food chain called Trader Joe's, which many of you know. Trader Joe's is super popular with Angelinos like myself. It espouses fair trade principles, fair trade coffee, great labor practices, and good benefits for their employees. Many of my fellow Angelinos love to shop at Trader Joe's and gasp in horror at a Walmart, which has a different philosophy with regard to its labor practices and so on. The difference between these two companies is far less than they would appear, certainly to my neighbors. Both of them are reaching out around the planet to obtain goods and food items as cheaply as possible and route them via tightly scheduled global supply chains to us. They're doing the exact same thing in terms of the business model. And this model, which has been going since the 1970s, is but the latest chapter in humankind's ongoing redefinition of its relationship with the physical Earth.

It began with our move from a hunter-gatherer foraging species over 10,000 years ago to settled communities. From there, we consolidated more and more in cities, and we invented machines to do our work for us. This accelerated the departure of people from landscapes. We went from an agricultural civilization to an urban one. In the US, less than 2% of the population is engaged in agriculture today. The fields are devoid of humans and mowed by autonomous, heavy machinery guided by GPS. The advent of trade, first locally and then globally, has redistributed the way materials are circulated around the globe. Our move to a global food model only accelerated that. Now, the trend has been very much to concentrate in urban cores. While the world population is still growing, rural areas are, depending on where you look, depopulating and losing people. Depending on what happens with the land that's left behind, this can sometimes be good for nature, with rewilding of forest and the return of species that have been extirpated there in the past.

A wonderful example of this is all around me here in New England. This is a landscape that was at first dammed up everywhere—every little river and stream of any substance was damned to make mill races for the Industrial Revolution. The forests were cut down; the whole area was covered with hardscrabble farms and pasture; beavers, fish, and other forms of wildlife were extirpated. Now, in the year 2020, the place is regrown with thick forests. There are beavers all over the place. While highly suburban, most of the human activities are taking place in the city with a much milder impact upon the surrounding local environment than has happened in this area for hundreds of years.

Of course, the environmental impacts of that urban activity are now global, with climate change. This is a topic I spend most of my time on for my day job. I'm an Arctic climate change scientist, so I do a lot of work in Greenland, Siberia, northern Alaska, and so on. Looking ahead, I wonder a lot about how this relationship between humans and the physical Earth will continue to change. I wonder if we will burn the remaining reserves of fossil fuel, which is the track we're currently on, or if we will leave it in the ground. I wonder if we will defend our coasts from sea level rise or if we will retreat from them. If we do retreat, what will be the nature of that retreat? Will it happen in an orderly way or will it take major storm surge events, like Superstorm Sandy, to render areas suddenly uneconomic or unbuildable, as happened with Hurricane Katrina along many miles of the Gulf Coast? I wonder if we will geoengineer climate, for which there are a number of proposals. Just in the last ten years, even among earth scientists like myself, this idea has gone from being an outlandish concept to one that is being taken with increasing gravitas as the national and international level efforts to slow the pace of climate change continue to fumble and falter.

I wonder if humans will take control (or partial control) of evolutionary processes and begin to direct evolution through synthetic biology. My own interest in synthetic biology extends especially to the modification of plants for human food, potentially the modification of plants as a mitigator of climate change through carbon sequestration. I wonder what the implications of this may be. I am astounded to think of what kinds of life experiences my three small kids will encounter as they go through the next eighty to ninety years, particularly in this area of synthetic biology. I speculate that the changes they will see in their generation will be even more dramatic than the ones I've seen through the information revolution of the last forty or fifty years.

I wonder if we will populate the Arctic. This is a place that is continuing to warm, not that it'll ever be warm in the wintertime, of course, because it's the Arctic—the polar night will always return. But it is also a place that has a great deal of fossil fuel energy that is not currently developed. Should we stay on the path of fossil fuel development, it is an area that is likely to be accessed and used for this purpose. We're already seeing that in places like northern Siberia, the North Slope of Alaska, the oil sands, or tar sands, depending on your point of view of northern Alberta, Canada. I wonder if our long, lurching trend of global integration, which has its roots in the wreckage of post-World War II, beginning with the Bretton Woods Agreement, will stop and will reverse. Certainly, developments in recent years have suggested this is possible. Without getting into the politics of it, Brexit is a prime example. There are many indications around the world that this ideology is perhaps changing and that it is quite plausible we could deglobalize moving forward.

I wonder if the current Covid-19 pandemic will either deter or inspire the use of bio warfare. Bio warfare has long been the most untouchable and covert form of warfare. It's an old idea, of course, but it has always been considered untouchable by national actors. And I would hope it would continue to be. It is fascinating to wonder, as the Covid-19 pandemic continues—which is the biggest experiment of its kind unleashed on civilization since 1918—to what extent it could inspire bio warfare in the future, particularly along non-state actors such as terrorist groups.

Finally, looking even more broadly, I wonder whether we might in future decades consider dispersing life off of Earth. And if so, what kinds of lessons might be learned from the dispersion of life on this Earth by human hands. Those are just a few of the things I've been thinking about with all my time off.

For over twenty-five years now, my climate change research has drawn me north to the Arctic and Subarctic. These are the ice sheets and glaciers and permafrost lands and seas of Alaska, northern Canada, Iceland, Greenland, Siberia, the northernmost Nordic states. The reason my graduate students and I spend so much time working up there conducting field studies and satellite remote sensing is because the Arctic is one of the most rapidly transforming regions on Earth, both from amplification of global climate change as well as human pressures that are unique and operating within the region itself.

Let's start with the first one. The Arctic, unlike Antarctica, experiences greatly amplified increases in climate warming that are larger than the global mean temperature increase. Whenever the planet warms up by a degree on average, that one degree average is masking some profoundly different geographical contrasts around the Earth, with the Arctic experiencing well over double the global mean average rate. The reasons for this are not mysterious. We understand them quite well. There are a number of geophysical feedbacks that operate within the region that are present in the Arctic but not in Antarctica, for example. The biggest one, and most famous of these natural feedbacks, is the geography of the region.

Unlike Antarctica, which is a continent buried under over a mile of ice that is over a million years old, the geography of the Arctic consists of an ocean surrounded by massive amounts of land, with the largest landmass on the planet found in the northern high latitudes. That's where two of our biggest countries are—Russia and Canada. The fact that there is an ocean there surrounded by land, rather than a continent surrounded by ocean, gives rise to what's called the ice-albedo feedback. Meaning, the way it operates is the albedo, or reflectivity, of a dark ocean is much lower than that of ice and snow, which is highly reflective. The ocean always freezes in winter, and hopefully always will, because the polar regions will always have polar night in the wintertime. So the ice, no matter how warm it gets in the summer, will always refreeze in the winter. The Arctic Ocean freezes over in the wintertime and begins to melt back from its edges during the summertime, reaching its minimum seasonal extent in late September. The extent of that minimal summertime sea ice cover in the Arctic Ocean has been steadily declining ever since NASA first started mapping it using passive microwave satellites in the late 1970s. The maximum seasonal extent of ice cover in the Arctic Ocean has declined by over 40% since the late 1970s. This causes the reflectivity of the surface of the planet up there to decrease, because as that ice melts back, it exposes the darker ocean, which absorbs more of the incoming solar light. So rather than being reflected back to space, that energy is absorbed by the ocean, which warms the ocean water and retains heat within the system to be re-released throughout the year.

This is one of several feedbacks operating in the Arctic, which are unique to the Arctic and cause it to experience amplified climate change. Importantly, this feedback works in the opposite direction as well. So when the Earth enters periods of global cooling, such as during Ice Age oscillations, when global temperatures decrease, the Arctic's will plunge more than double the global average. It is a highly amplified system.

From a human presence and development point of view, the Arctic and Antarctica couldn't be more different. The Arctic landmasses are under the political control of eight sovereign nations. They belong to those countries, namely, the United States, Canada, Greenland, which is an autonomous region of Denmark, Iceland, Norway, Sweden, Finland, and Russia. Antarctica, in contrast, is governed by an international treaty and is shared among nations. The entry key to participation is the expenditure of funds on science and maintaining science camps in Antarctica.

Antarctica is a fascinating place because many countries want to be involved with it for geopolitical reasons, but the only allowable way in which this can manifest is through the funding of science in Antarctica. As a scientist, it's absolutely wonderful. The governance situation couldn't be more different. The Arctic, being comprised of sovereign nations, is governed by the rules of those sovereign nations, with offshores governed by a very important piece of international law called the United Nations Convention on the Law of the Sea, which governs the offshore exclusive economic zones of all signatory nations (200 nautical miles). And through a provision within this piece of international law, called Article 76, signatory nations can petition to extend their offshore sovereignty through scientific mapping and geological studies if they can establish that the sea floor is a natural extension of their continental shelf.

It just so happens, due to the geography of the Arctic Ocean—it's a fairly small ocean and very shallow—most, if not virtually all, of the Arctic Ocean either already has been or soon will be partitioned between five Arctic countries that abut onto the Arctic Ocean. Perhaps even the North Pole itself. The biggest beneficiaries of this are Russia, Canada, Greenland, the United States, Sweden, and Norway. When you couple that governance structure with the extensive potential reserves of natural gas, condensate, and oil in this region, the development prospects for this remote iconic part of the world are huge over the long term, not in the short term.

The Arctic is a very difficult place to operate—very expensive, very environmentally fraught. Many national and multinational oil companies have attempted to operate in the Arctic and have failed or have withdrawn. But over the long term, should current trends continue as they are now (and I hope they don't), there is little question that pressure to develop the fossil fuel reserves of the Arctic and subarctic will be immense. In fact, it has already begun in western Siberia, where the decades-long oil and gas development of western Siberia by the Russian Federation beginning in the sixties, when it was the USSR, have now expanded North to the Yamal Peninsula, where in 2017, the Putin administration opened up a liquefied natural gas (LNG) plant at Sabetta, on the coast of the Yamal Peninsula. So, it has already begun there. And in North America, of course, we have the ongoing bumpy development of the oil sands or tar sands.

The climate changes happening in the Arctic are more extreme than the climate changes even in Antarctica, which is also undergoing tremendous warming, and the development potential, pressures, and governance are totally different between the Arctic and Antarctica. This is why we see two asymmetric spheres of activity and interest taking place in these two very important and iconic regions. I will hasten to say, however, that the single greatest uncertainty in global sea level rise risk does come from Antarctica, which is why it is under acute scientific scrutiny and study—because a large fraction of that ice mass is grounded on the continent below sea level rise. It is also ringed by large, thick ice shelves that buttress glacial ice up on the land. If those ice shelves disintegrate, which they're prone to do when ocean water is warm, their ability to buttress the land ice up on top of the continent goes away. If you remove the plug at the bottom, then the land ice can flow right down to the ocean. This is quite a frightening possibility. We don't understand the processes involved very well. Our ice dynamics models are not well calibrated because we don't understand all of the tensile physics that are found along the interaction of the glacial bed with the overlying ice. The interaction of those physics with the buttressing effect and ocean temperatures at the ice edge are present in the models, but our models are not calibrated well enough to be able to know if and when this might happen. It creates a big error bar in our uncertainty about how fast and how high sea level may rise by the end of this century.

This collective body of wisdom gets summarized every few years with the United Nations' IPCC reports, which are notoriously conservative and slow in their assessments. That's because they are consensus documents that have to be signed off by governments. The most recent IPCC release that came out in September has significantly upgraded their risk potential for sea level rise to be as high as anywhere from 30 centimeters to 1.1 meters by the end of this century. And again, it must be kept in mind that this is a conservative document, and the reason for such a large range comes from uncertainty surrounding the stability of the West Antarctic ice sheet.

Some of the most exciting research I'm doing—together with my graduate students, postdocs, and collaborators—is improving our ability to model and predict how much sea level rise will come out of the Greenland ice sheet. The next time you look at a world map or globe, have a look at the Greenland ice sheet and look at its latitude. You should be struck by the oddity of it even existing at all. Here we have this massive ice sheet coming to quite low latitude sticking up above everything else. It's quite out of place. Unlike, say, the Antarctic ice sheet, which is perched right at the bottom of the Earth on the South Pole, the Greenland ice sheet is a relic of the last Ice Age. It survives only by virtue of its own elevation. What I mean by that is if you were to somehow magically pluck the Greenland ice sheet off the bedrock, it would not reform and grow. It just would not come back. The reason it persists at all is because it's already there and, therefore, at its higher elevations at the summit, the elevation is sufficiently high that the temperatures do not go above freezing during the summertime. Just like when you go up in an airplane and the temperatures get cold. There's a strong decrease in air temperature as you move up through the troposphere. This is what allows the Greenland ice sheet to exist.

Now, it does melt extensively around its lower elevations along the margins. This is the area that is ground zero for Greenland's contribution of meltwater runoff to the ocean, and ground zero for the single biggest component of sea level rise contribution from Greenland to the rest of the world. A little present from Greenland, if you will. The extent and intensity of this melt zone around the edges of Greenland have been dramatically increasing pretty much every year. Quite steadily. Some years are cooler, some years are warmer, but the overall secular trend is one of increasing melt and mass transfer from the Greenland ice sheet to the ocean, where it contributes about a third of global sea level rise at this time—over a millimeter per year is coming just from the Greenland ice sheet.

My team and I have been pushing this science forward by studying this melt zone. Surprisingly, until quite recently, this area received light scientific study. Most ice sheet scientists and field expeditions focus on drilling camps up at the top in the cold zone, where since it doesn't melt, the ice core record is preserved. These are amazing places to drill down into the ice and pull out a two-mile-long time machine of past climatic changes over geological history. The melt zone along the edge is a real mess. It melts every summer. Just imagine a vast slip-and-slide water park, where it snows over in wintertime, but come June, the whole place starts to melt. It's crisscrossed everywhere with torrential flowing blue streams and trickles that come together into streams, which come together into these great, branching arterial river networks flowing over the top of the Greenland ice sheet. Every single one of these torrential blue rivers in southwest Greenland, which is the most intensive area where this melting is taking place, travels for a few kilometers over the ice before breaching through the ice into a sinkhole called a moulin. From there, it tunnels under the ice and out to the ice edge where it goes right into the ocean, thus contributing to global sea level rise. This is where 90% of the runoff from the Greenland ice sheet to the ocean is coming from.

Modeling this melting process and sea level rise contribution process correctly is imperative if we are to be able to forecast with reasonable accuracy the anticipated rate of sea level rise in the future. Amazingly, until the work of our group, no testing or validation of the climate models that operate for this purpose had ever been conducted for Greenland before.

Beginning in 2012, and for many summers ever since, my team and I have been helicoptering onto the Greenland ice sheet, in this fantastical melt zone. We use helicopters to string cableways over the top of rushing super glacial rivers so that we can hang this river discharge measurement technology called Acoustic Doppler Current Profiler (ADCP). We operate around the clock to collect measurements of river discharge every hour, for up to a week in duration. We have collected the world's first meltwater runoff measurements on top of the ice sheet. What we then do is simultaneously use drones and satellites to map out the upstream contributing watershed area flowing to that point where we are collecting the discharge measurements. When we know the contributing watershed area and we have the flow measurements at the bottom of the watershed, we then have a completely independent field dataset from which we can test the ability of climate models to simulate meltwater runoff from the Greenland ice sheet. And it's those models that are being used to predict the future. It's those models that are being used to estimate projected ranges of sea level rise in IPCC reports and so forth.

The fieldwork is incredible. We pitch tents on top of the melting ice. There's water running everywhere. The tents need to be re-pitched every couple of days because the ice surface is melting all around us. The entire camp takes safety precautions very seriously. If anyone were to slip into one of these streams, they would be washed away. It's about zero degrees Celsius. They are just fast flowing chutes that have melted into the ice. There are no rocks, no trees, no branches—nothing to grab onto. And as I said before, every single one of these streams and rivers flows into a moulin, which then thunders its way down to the base of the ice sheet. So if anyone were to slip and fall into one of these things, they would not be recovered. It's quite possible to work very safely in this environment, but there are many precautions we must take.

The first thing we do is encircle the entire campsite with yellow caution tape, so no one is permitted to leave that small area of ice unless they are tethered to a rope. And this is a flat area; it's not mountaineering. The place is just flat and crisscrossed by streams. Nonetheless, when someone goes outside that camp perimeter, they wear mountaineering harnesses and latch into a rope, which a partner then feeds out line from. The scientist goes to the edge of the river where the cableway and the ADCP are and collects the measurements, towing the instrument back and forth across the river while someone else is making sure the rope is never long enough for them to even possibly fall into the river in the first place.

We've been collecting these types of measurements for several years, and the findings are just now coming out. I'll tell you some of the preliminary results. I'm working on one of the papers right now. There's good news and bad news. The bad news is that virtually all of the meltwater generated by melting across this area of southwest Greenland, unfortunately, escapes the ice sheet to the ocean. We were hoping to find that, yes, the ice melts, but the meltwater would be somehow retained up on top of the ice sheet. Maybe it would collect in little lakes and pools and just refreeze. Maybe it would soak into the cracks of the ice and refreeze and stay there. It would be wonderful from a sea level rise point of view if the meltwater that is produced by warmer temperatures over the ice would somehow remain, or be trapped, or refrozen within the ice sheet itself. In such a case, we might expect the ice sheet to lower, but also become denser and not lose all of the mass to the ocean. Unfortunately, our satellite mapping and measurements confirmed that this is not the case, and that the surface of the Greenland ice sheet is amazingly efficient at losing all of the meltwater that forms on its surface through these networks of hundreds of rivers flowing over the ice. That's the bad news.

The good news is that in study after study, we have shown that the current generation of climate models that are used in this area are, almost without exception, overestimating the amount of meltwater that is produced, by anywhere from 10% to as high as 50%. That's good news in the sense that some of the dire risk predictions of runoff contributions to sea level rise from Greenland are a little too high. We're digging right now into the reasons for this. One possibility is that the models are overestimating for reasons pertaining to energy balance. The other more likely reason is that some of the water is indeed being trapped within a rotten zone—rotten ice on top of the ice surface. It's a very fragmented, porous ice that appears to be storing and retaining some of the water. But finding that missing fraction of overestimation is what we're working on now. More generally, the take home message is that it is both exciting and scientifically critical to get boots on the ground to test and verify these climate models, which are becoming increasingly critical tools for us to project and to plan for the future.

* * * * 

I had always been interested in snow, ice, and rivers, in no small part due to my dad, who is a very highly respected earth scientist. We would spend our summers in the Canadian Rockies, visiting his field sites. He was interested in the meltwater streams and rivers draining glaciers in the Canadian Rockies. In the summertime, we would pack up the station wagon with my brother, our dog, my mom and dad, and drive from downtown Chicago—where I lived a very urban, gritty downtown life—up to the Canadian Rockies, where we would live in cabins for a couple months out of the year doing scientific fieldwork of all these beautiful meltwater streams, lakes, and rivers in the Canadian Rockies.

After a one-year stint with the US Geological Survey, after my master's degree, when I rediscovered that I liked school even better than the regular hours of a nine to five job, I applied to Cornell University's Earth Science Department and began a PhD there. It was at Cornell and the Earth Sciences Department where my real transformation as a scientist began.

First there was the access at an institution like Cornell. The access to big minds and thinkers becomes an everyday occurrence through, for example, guest lectures and colloquia from eminent visiting scientists. My second year at Cornell, I had the privilege to meet Richard Alley, a world-famous glaciologist at Penn State University who came to give a talk at Cornell and inspired me. He was speaking about his latest work, which had just come out in Nature. He would use ice cores from the Greenland ice sheet to show how North Atlantic climate, at the end of the Younger Dryas cold snap, which was a brief relapse into Ice Age temperatures that happened just as the world was pulling out of the last Ice Age—it was warming up and, almost instantly, the ice core record showed that the temperatures plunged back into cold Ice Age temperatures, stayed cold for while, then warmed, then cooled, then jumped out and continued on its warming trend. And so the temperature swings were dramatic, on the order of several degrees in a couple of years, perhaps even within a single year. It was absolutely astounding work. Richard Alley was the lead author of that work and a very famous person.

He came to Cornell and gave a lecture on it. And then, as is customary with these types of academic visits, there was a sign-up sheet to meet with him. Even lowly graduate students such as myself were permitted to spend thirty minutes with him, talking about whatever. So I nabbed one of those spots with Richard and was very much looking forward to hearing him talk about himself, and his discovery, and how he got there. To my amazement, he didn't want to talk about any of that. He insisted upon talking about me and my projects and what was I working on. At that moment, I was working on something which was very hot called wavelet transforms. It's a mathematical filter for time series analysis. I was almost embarrassed to talk to him about it, but he insisted, and before I knew it, we had run over time. We just had this very stimulating, exciting conversation.

What I learned from that encounter was how many of our greatest scientists are just perpetually curious. It doesn't matter who they speak to. They're always hungry to learn, always excited to hear new ideas, and interested in engaging and discussing them more than talking about their accomplishments, which was just fantastic.

The other formative experience I had at Cornell was running into the culture of that Earth Science Department, which at that time was populated by some towering giants in the field of tectonics, including my own advisor, Bryan Isacks. Bryan and his advisor, Jack Oliver, at Lamont-Doherty Earth Observatory, discovered plate tectonics in the 1960s. When I say "discovered" plate tectonics, what I mean is that Bryan, then a graduate student, and his advisor assembled the datasets and finally pulled together the pieces of the puzzle that revealed the existence of plate tectonics on Earth. The main datasets they looked at were magnetic reversal stripes, which have matching sets on either side of spreading ridges in the ocean and the epicenters of earthquakes.

The story, as I heard it told, was that Bryan Isacks and his advisor were standing in the advisor's office at Lamont-Doherty, sketching on a blackboard with little Xs the locations of the epicenters of earthquakes near what we now know to be a subduction zone, where one piece of tectonic crust is plunging beneath another. As Bryan and Jack were puzzling and musing over these, Bryan suddenly blurted out, "It's going down. The crosses are going down. It's [meaning the tectonic plate] getting dragged beneath the other." At that moment, it all finally became clear that the Earth's crust was being born at the spreading center ridges in the oceans, and the magnetic reversals were capturing that slow growth over time. And then they were being subsumed and plunging on the other end in the death zone where one plate was subducting beneath another. They arrived at this idea mutually and flipped a coin over who would be lead author on the paper. Bryan won and he got to be lead author on the paper that put together for the first time the theory of plate tectonics, which launched a revolution in the earth sciences that is still in the mop-up phase today.

The benefit to me from working at Cornell was that because of this legacy with Bryan Isacks and Jack Oliver, who moved to Cornell University to the Earth Science Department, they brought with them a whole cohort of big thinkers on plate tectonics who, for the first time, were looking at the Earth at the broadest possible scale to get a big-picture understanding of the Earth system. By its very nature, plate tectonics demands that kind of perspective.

When I arrived there in the 1990s, I brought with me a very small field-oriented mindset. I wanted to study a small watershed and understand all these detailed processes, and my advisor and committee pretty much beat me up over that and said, "This is Cornell University—we think big. You have to broaden yourself out." So that was the beginning of my transformation from thinking very small about the earth sciences to very broad scale theoretical and observational study of the Earth at the largest possible scales. This is one reason why my research spans everything from broad Arctic change, to societies, and to humans and the way we make the Earth our home.

The other very influential person on my career was a colleague at UCLA in the Geography Department named Jared Diamond. Jared Diamond was enormously influential on me.

My first or second year at UCLA as an assistant professor in the Geography Department, I was put in charge of the moribund colloquium program, which had few speakers and no one would attend the talks. I was told I had to revive it and that there was no money to bring in speakers. I had a budget of zero dollars. I said, all right, UCLA is a pretty good school, and there are some good speakers here. Perhaps we could invite them to the Geography Department to speak to us. I had heard of Louis Ignarro, who had just won a Nobel Prize in medicine, and I had heard of Jared Diamond, who at that time was in the medical school at UCLA. So I rang up both of their offices. A few days later, the administrative assistant for Louis Ignarro called me back and told me, yes, Dr. Ignarro would be delighted to speak to the Geography Department, for a $10,000 speaking fee. Around the same time, Jared Diamond called me back personally and said he would be delighted to speak to the Geography Department, so we scheduled him and a few weeks or months later he came and gave a talk based on Guns, Germs, and Steel, which had either just come out or was just about to come out. Many of the ideas in that book are highly geographical. The talk was great. The faculty hung around for what is probably the longest Q and A session I have ever witnessed—it went for about forty-five minutes. There was a fantastic back-and-forth between Jared and my colleagues.

A few months later, we got a query from Jared about the possibility of transferring to the Geography Department at UCLA. I was not part of those discussions, but I like to take some credit for enticing Jared to geography at UCLA and leaving the medical school. Jared left me alone until I got tenure and I established my core research working with field studies and remote sensing in west Siberia, Iceland, Alaska. After I received tenure, he really encouraged me to think a little more broadly, even beyond the hard earth sciences. I had read Jared's books and was very inspired and excited by his synthetic way of thinking. I value the way he looks across different disciplines and tries to find common threads and pull them together. He does not hesitate to learn from other fields even if they're a bit far from his core academic research. That has inspired some of my own efforts and writing outside of my core science. Those two individuals were extremely influential on me along this academic and intellectual career that I'm still on. I look forward to meeting the next person.