 Thanks, Lorena. So yeah, I got my start in science, really as an engineer, working on wastewater systems and water quality systems. And actually, most of the stuff that I learned in that context was directly transferable to sort of planetary scale climate dynamics. So a wastewater treatment plan is kind of like modeling the global ocean, same sets of equations. So what I'm going to talk to you today about touches on some threads in what I think of as this synergy between three primary paradigms in science. And that is the ability to construct theory that describes the natural systems that we're thinking about, the ability to go out and observe those systems and collect empirical information about their behavior. And then finally, our ability to encode equations that describe the behavior of those systems in numerical models and directly simulate those systems and use those models as tools to advance our understanding. I am an oceanographer at the National Center for Atmospheric Research. And as an oceanographer, one might think of ships going to sea to collect observations. But here at NCAR, this is the National Center for Atmospheric Research. And so one of our primary observing platforms is this Gulfstream V aircraft. And I'm going to tell you some stories about how we've taken this airplane down to collect observations over the Southern Ocean. Most of my work is focused on modeling. And in the Climate and Global Dynamics Division at NCAR, we develop an Earth system model. It's called the Community Earth System Model. This is a climate model that couples together general circulation models that represent the circulation in the atmosphere, the full 3D circulation of the ocean, and the communication between those two systems. And then embedded within those models are representations of processes that capture the interaction of the biosphere with the physical climate system. So these are very useful tools to understanding the trajectory of climate change over the future. And also, we can use these models to interrogate geologic records of past variability in climate. So the title of my talk, Containing the Word Metabolism, Planetary Metabolism. And just to define that word for you, so we can proceed with a common understanding, here is one definition of the word metabolism. The chemical processes that occur within a living organism in order to maintain life. So I said planetary metabolism. So I'm thinking about this on the scale of Earth, the whole Earth. And this notion of energy maintaining life then becomes relevant to understanding, what am I talking about here? Well, Earth has a molten core and nuclear reactions that sustain the heat in that molten core. But this is not what I'm talking about. Very little of this energy actually leaks out to the surface of the Earth. And very little of it is actually available to support life. What I'm talking about here is this notion of ecosystems that are constructed from primary producers who are photosynthesizing at the base of the food chain and then up through secondary and tertiary consumers that harvest the energy from the primary producers. So really, the major source of energy driving this system is the sun. And we can boil that whole complex ecosystem down into sort of two primary sets of reactions. So photosynthesis harvests light from the sun. It uses that energy to split water. A byproduct of that reaction is oxygen. Heterotrophic organisms use respiration. They use that byproduct of photosynthesis, oxygen. They break apart organic matter, oxidized organic matter to develop energy and release CO2 as a byproduct. And so that forms a carbon cycle where carbon is ingested into the food chain by a photosynthesis. It's respired and exits the food chain as carbon dioxide again. So this is the planetary metabolism that we'll be talking about. So now this starts to get really interesting, because what I've just told you is that life cycles carbon dioxide. As I am sure many of you know, carbon dioxide is the most important greenhouse gas that regulates the amount of heat that escapes the atmosphere. So already we have this interesting notion that life on Earth has the capacity to interact with climate, because life on Earth is cycling carbon dioxide and potentially perturbations then, therefore in that system, have the potential to feed back onto the physical climate system. This is a picture famously called Earthrise that was taken by an astronaut on the Apollo 8 mission in 1968 on Christmas Eve. And I think I like this picture for a variety of reasons. It's a beautiful picture of our planet. But I think it's emblematic of the notion that, or the growth of an awareness of our planet at the planetary scale. Here we are, this blue dot floating in space. And indeed this picture played a significant role in the environmental movement in the late 1960s. It sort of caught people's attention that were isolated, were floating out in space as an entity. So what I'm gonna do now in the talk is present a few anecdotes from the history of science and use those anecdotes as a means of illustrating how this sort of planetary awareness developed in the field of climate science and planetary biogeochemistry. So our first starting point here is the late 1950s. And Dave Keeling, who decided to start measuring carbon dioxide at the Manila Observatory in Hawaii. And so he went out and he installed a carbon dioxide sensor on the top of the Manila Volcano. And these are some of his first data that he collected. So this is a graph on the y-axis of the graph shows the CO2 concentration measured in the atmosphere. And on the x-axis is time delineated by months of the year. Before these observations were taken, people didn't really know what to expect. There had been some Swedish measurements taken previously and the concentration of carbon dioxide seemed to bounce around from 200 to 800 parts per million PPM. So it was really exciting at the time to see these regular seasonal cycles. And Dave Keeling correctly observed the following. Nature's withdrawing CO2 from the air for plant growth during summer and returning it each succeeding winter. So at the beginning of the talk, we talked about these reactions, photosynthesis and respiration. We can see direct manifestation of these reactions in the carbon dioxide composition of the atmosphere. And indeed, now we have satellites and we can look down on the earth and make measures of greenness on land, the normalized vegetation index and DVI, or measures of the greenness of the ocean, the chlorophyll concentration in the surface ocean. And this is a picture then of the seasonal cycle of greenness of our planet that these are the same processes. This is the photosynthesis that's generating those seasonal cycles in atmospheric CO2. So Dave Keeling had a son named Ralph and Ralph has made another key contribution to our understanding of planetary metabolism in that during his PhD at Harvard, he figured out how to measure oxygen. And the measurement of oxygen is extraordinarily challenging because oxygen comprises about 20% of the atmosphere but variations in oxygen that arise due to these photosynthesis and respiration reactions are in the sixth decimal point. So we call the unit there per meg to denote that it's this tiny deviation. And look at these data. So Ralph started a global network of measuring oxygen and carried on his father's measurements of CO2 at that network. And here is some oxygen time series from about 1991 through these measurements carry on through today, but this graph only goes to 2011 or so. And this is interesting. So I showed you the seasonal cycle that Dave Keeling measured at Monteloa. And we see that in the CO2 trace from the Northern Hemisphere, this black line. But if we look at CO2 from the Southern Hemisphere, the red line, there's very little imprint of seasonality. And that's because there's not much land in the Southern Hemisphere. So most of this respiration and photosynthesis and respiration is occurring on land in the Northern Hemisphere driving seasonality in CO2. But if we look at the oxygen trace, don't worry too much about this unit. Just think of it as an anomaly in the oxygen concentration in the atmosphere. We see that we actually do have a seasonal cycle in oxygen in the Southern Hemisphere. And that's basically indicative of the fact that the ocean is contributing to seasonality in oxygen, but actually contributing very little to the seasonality in CO2. So what does that look like? Well, here's a simulation that I did with the Community Earth System model. And what we're looking at here is the surface atmosphere concentration, the surface concentration of the oxygen anomaly and the CO2 anomaly generated by exchange with the ocean. So if we just think about the seasonal patterns here, in summertime, there's a net evasion of oxygen from the ocean. The water is warm and there's photosynthesis happening in the surface ocean. So we're producing oxygen that's leaving the ocean entering the atmosphere. So we see rich oxygen concentrations, the red colors. And simultaneously, photosynthesis is pulling CO2 out of the water and pulling CO2, therefore, out of the atmosphere. And so we see a depletion in CO2 during summer and pretty much the opposite in winter. And then superimposed on that dominant seasonal pattern, we see the effect of atmospheric weather, storms passing through and stirring in these large-scale tracer concentrations. Okay, so the Keeling curve has now become something famous in that Dave Keeling's measurements continued and Ralph has continued them and a global group of scientists are continuing to measure CO2. But here's what the data looked like as of this month. So when Dave Keeling started, CO2 concentrations were in the low 300 ppm. Just recently in the last few years, we've cleared 400. So this is the inexorable rise in CO2 that's associated with human activity, primarily the burning of fossil fuel. Okay, I'd like to return to this Earthrise image and note that the dominant color of our planet is blue, right? So we've talked about signals in the atmosphere. So let's go and probe the ocean a little bit. And our anecdote for this, our touchstone for this anecdote is this textbook written or led by Wally Broker who spent his career at the Lamont Doherty Earth Observatory in Columbia, okay? And this textbook was written at an era, or you know, the culmination of a grand era of observing the global ocean, right? There was a program called Geosex. And the objective of Geosex was to go out and collect samples with a device called a CTD, a conductivity temperature depth sensor. And this is a device that is lowered in the ocean and collects temperature profiles. And each of these small cartridges, they look like cartridges that actually bottles that are lowered in the water column in an open position and then triggered to close at specific depths such that we can bring water up from the ocean abyss and measure its properties, right? And Geosex was the first time that this international cohort of scientists was able to develop comprehensive maps of properties in the ocean. So here's the first figure in this textbook, right? This is potential temperature, right? A profile at a particular location in the Pacific. And notice that this is a profile, the y-axis here is in kilometers, right? So this is a profile of temperature from the ocean surface down to nearly six kilometers, 6,000 meters in the ocean depth. Comparably a profile of salinity, the salt content of the water. A profile of oxygen and a profile of nitrate, which is a major limiting nutrient for photosynthetic organic matter production. So these types of measurements can be combined, right? And here's an example of a map. This is not a map in the 2D space that we're thinking of, sort of plan view, but a map that represents a slice through the ocean depth. So on the y-axis, we have depth. We just have a panel at the top that sort of zooms in on the top kilometer, and then a panel at the bottom that shows the full depth. What I'm showing you here is the total concentration of carbon in seawater along a transect that extends from near Antarctica in the south, sweeps past New Zealand, crosses the equator, and goes up and touches the Aleutian Island chain. This is a map then of carbon dioxide along that chain. And note that there's substantial structure in this field. This is not a homogeneous ocean filled with carbon, but rather the imprint of biology and the imprint of circulation are contained in this map. And those processes, our ability to map those properties in the ocean has been a key element of our ability to understand Earth's history. For instance, over about the last million years that have been fluctuations in glaciation in the Northern Hemisphere. The Laurentide ice sheet, for instance, at the last glacial maximum covered much of North America, and ice core measurements of CO2, shown here as purple dots, plotted against ice core derived estimates of temperature, indicate to us that these glacial interglacial cycles, fluctuations in Earth's temperature of millennial scale duration are led, are associated with changes in atmospheric CO2 of order almost 100 ppm, right? So these are natural processes in the Earth's system that are resulting in a repartitioning of Earth's carbon inventory between the ocean and the atmosphere. And the observations that were collected in the geosex era and were put together by Wally Broker in this textbook Tracers in the Sea were fundamental in enabling us to start to develop compelling hypotheses for how the ocean dynamics in the ocean primarily control these fluctuations in atmospheric CO2. Okay, now back to the modern era. And I'm gonna talk a little bit about the effect of the release of carbon dioxide through the burning of fossil fuels. So if we take that record of CO2 and just look at the last thousand years or so, here are those same purple dots, those are measurements of CO2 reconstructed from bubbles in ice core. And we see that over approximately the last thousand years, CO2 was basically constant at a pre-industrial level of about 280 ppm associated with what we think of as the interglacial period, the warm phase in Earth's history. But look, the industrial revolution kicks in and there is an exponential rise in CO2. The red line there is the Keeling curve. It's got all those seasonal wiggles in it. It's just that we're zoomed back at such a scale here we can't discern them. What we see is just this massive increase in CO2 associated with industrialization. Okay, what's the effect of increasing CO2 in the atmosphere? Well, I would argue this is the dominant effect. The ocean contains the most carbon, active carbon in the Earth's system. It is also the dominant reservoir for heat in the Earth's system. And we can very clearly say now that the ocean is accumulating anomalous heat. That's what this plot shows. The y-axis here is joules, the units are joules, which is a measure, a unit of heat. It's actually 10 to the 21st joules, right? And the x-axis is time. Each of these lines presents a different estimate, a different reconstruction of the ocean heat content anomaly. And the shading here represents our estimate of the uncertainty in the ocean heat content anomaly. So one thing you notice is that early on in the record we were not very certain about ocean heat content. But as we've continued to add observing systems to enable us to make estimates of ocean heat content, that uncertainty has narrowed. And indeed what we see is this inexorable rise in ocean heat content that's a direct manifestation of the accumulation of CO2 in the atmosphere. So if we look at the Keeling curve, and this is just another plot of that Keeling curve, there's something that is interesting to notice. If we just integrate up all the CO2 emissions, right, we should be able to match that integral, the sum of all the CO2 emissions with the CO2 that's in the atmosphere, right? But indeed that is not the case. And in fact, if we just integrate CO2 emissions, we get this solid line. And so what we see is there's actually a deficit of CO2 left in the atmosphere relative to our expectations based directly on emission. So what's going on here? Well, this is where the biosphere comes in, okay? So we have two dominant sources of CO2 emission. The biggest one is fossil fuel burning and cement production. Land use change is another significant contributor. And collectively, we have this release of CO2, only about 44% of it is actually staying in the atmosphere. The remainder is split in roughly equal proportion between the terrestrial biosphere, that's plants photosynthesizing, okay, and taking up more carbon than respiration and the absorption of CO2 by the global ocean. So this phenomena then, this notion that there's natural sinks for anthropogenic carbon, human derived CO2, is a critical thing to understand in order to be able to project the climate, right? So if we have a scenario of emissions, human emissions of CO2, and only a fraction of those emissions stay in the atmosphere and affect climate change, we need to be able to understand what controls that partitioning. And so this plot is illustrative of that exact problem. On the y-axis, we have a CO2 flux from the surface and we force a model with this red line, the fossil fuel emissions, right? So we develop a scenario that says, you know, here are the fossil fuel emissions, here's our projection of what those will be over the next approximately 100 years. We also force the model with an estimation of land use change, how much excess carbon is being generated from land use change. And then we have prognostic descriptions in the model that enable us to predict the function of the ocean and predict the function of the terrestrial biosphere such that we can predict the amount of CO2 that those two reservoirs are absorbing as a function of time, inclusive of interactions with climate, okay? So it's an imperative for a system model, therefore, to be able to represent these fluxes. But here's a problem, okay? If we look at a compilation of the air sea flux, okay, in a, in, in, in latitudinal bands and compare a variety of estimates, we see something interesting, right? And in particular, this, this plot shows four different estimates or four different ways to estimate the CO2 flux. And they all pretty much agree if we're north of about 44 degrees latitude, right? But in the Southern Ocean here, we see this significant discrepancy between the various estimates, okay? And this discrepancy has plagued the oceanographic community for more, for, for about two decades now. We've been trying to, to really dig in and understand what's going on. And indeed that, that uncertainty in the behavior of the Southern Ocean with respect to its ability to absorb CO2 was a major motivation for a aircraft campaign that we, that I, that I co-led in 2016. This was called Orcas. So the first prerequisite for being capable of planning an aircraft campaign is being good at generating acronyms for the aircraft campaign. And so, you know, Orcas turned out to be a pretty good one. We flew upon the G, the G5, the Gulfstream 5 aircraft and we were based at the tip of South America there in Punta Arenas, Chile. And we flew flights denoted by these colored lines out over the Southern Ocean to measure the distribution of CO2 and oxygen in the troposphere, the lower atmosphere, overlying it. This background color image shows you an estimate of this, a satellite-based estimate of the chlorophyll concentration. So this measure of greenness in the surface ocean where, where red colors denote very rich, waters very rich in, in chlorophyll. So our objectives here were to measure this, this distribution of CO2 in the atmosphere and try to use that distribution to make some inferences about the mechanisms affecting carbon and CO2 fluxes. This is sort of a cartoon cross-section of the Southern Ocean where we have circumpolar deepwater upwelling at the surface and then subsequently subducting to depth. So as an oceanographer, during my PhD, I actually went to sea on an ice breaker in the Southern Ocean. And I would spend, you know, a month and a half, two months at sea bobbing around on a ship, you know, taking measurements. I have to say, flying, doing oceanography by air is just far preferable, right? You can stay in a hotel, right? You get up in the morning, 9 a.m., make your way to the airport, fly all day, come home, back to the hotel, go out to dinner, you know, it's just, it's just way better than being stuck out in the middle of the Southern Ocean and bobbing around on a ship for two months. Okay, so I told you a little bit about this campaign. Now we're gonna go on a flight, okay? So what we see here is an image, a movie, from the forward-facing camera on the G5 on one of the Orca's research flights. So that's what the picture shows. Keep your eye to an extent on the map in the top right. That is the trace of where we're going in terms of geographically. And then in the bottom left, there's three lines that are being plotted directly from the data streams that are coming in on the instruments on the airplane. So the gray line shows our altitude, right? So the first thing we did was climb up to about 41,000 feet. We did a small dip to measure the top of the troposphere, okay, and then we climbed back up again. And then we've reached our target study area and we've dived down to the ocean surface to measure gas concentrations in the marine boundary layer. The red line shows the measurement of atmospheric oxygen anomaly from a sensor developed by Britt Stevens, my co-PI on this campaign, and a scientist here at NCAR. And the blue line shows the measurement of CO2 measured by some colleagues at NOAA. What we see, what we're doing now is a series of dips, okay? So we plunge the plane down to about 500 feet and then climb up to maybe 3000 feet and measure, therefore, concentrations of gases in the atmospheric boundary layer and then across the top of the boundary layer back into the free troposphere. If you look closely, what you'll see with each of those dips is that as we go to the ocean surface, oxygen concentrations are elevated and CO2 concentrations are depressed. So by now I've told you enough that you can infer the processes going on, right? Oxygen is elevated, that means we're measuring a signal associated with photosynthesis. CO2 is depressed, so that same photosynthesis actively drawing CO2 out of the air and causing a depletion in CO2 in the lower atmosphere. So on ORCA's we had different measurement objectives. What we just witnessed in these small boundary layer dips was our sort of small scale measurement objectives. But another objective was to map CO2 and oxygen distributions in the full troposphere. So now what we're doing is a northbound transect where we're taking the plane down to about 500 feet above the ocean surface and up to about 28,000 feet, right? So this is like, if you've flown on a commercial airline this is like coming in for a landing, okay? Coming back out, coming in for a landing, right? And a platform like the G5 actually makes this a lot of fun. So now we're doing our final dip at the north end of the transect. You can see us skimming the ocean surface water and eventually we're gonna climb up, climb out up into the stratosphere and just make our way back home. Okay, so on ORCA's we did about 16 research flights, similar in fashion to that. And that's what the map on the right hand side of the screen shows you, the track that the airplane took. The flight that we just witnessed was this green line here. And this panel shows the type of data we collected. So each of these little gray dots represents a measurement of CO2, the location of that measurement, in a plane now, I'm sorry, collapsing all our measurements into a single curtain through the atmosphere as a function of height, or we plotted against pressure, but you can think of this as height into the atmosphere and latitude, right? So this type, this map of CO2 in the atmosphere is what we are using now to develop inferences about what the air-sea flux of CO2 was during the summer of 2016. And we're doing a lot of work then to compare this metric of the air-sea flux to our model predictions of air-sea flux and try to understand whether the processes that we have in the model are accurate. We now actually have a means of pinning down what the air-sea flux is through this distribution of CO2. And indeed, what you see here is this deficit, this deficit of CO2 in the lower troposphere that's associated with the uptake of CO2 by the ocean. Okay, I wanna return back to this plot, the accumulation of anomalous heat in the ocean and tell another story about research that I'm actively involved in. And this story is about oxygen now, not CO2, but it's about the loss of oxygen in the global ocean. Okay, and that's what I'm illustrating here. In the top panel, we see the oxygen inventory normalized to a period in the early 1900s, 1920 to 1950. And the red line, let's just focus on the red line, is a simulation, is the results of a simulation of our earth system model out to about, out to 2100 under a business as usual warming scenario. And what you see here is that, the oxygen concentration integrated over the whole ocean is declining, moreover, the rate of decline we might expect to accelerate in the coming decades according to this model. That rate of decline is directly linked to ocean warming and indeed, if we plot this, a similar plot, but now for temperature, okay, before I showed you the accumulation of anomalous heat in the ocean as a function of joules, a metric of energy, here's just the temperature in degrees Celsius, something you're probably much more familiar with. You know, we see this strong rise in globally integrated temperature that's driving this decline in oxygen. So why do we, why does this matter? Well, I just like you to focus on the top two panels here, so the x-axis here is oxygen concentration and if you just look at the blue line, that shows you a distribution of oxygen concentration or the volume of ocean binned by oxygen concentration. So what we see is that most of the ocean is reasonably well oxygenated, but there are pockets, small pockets, in the ocean where oxygen is depleted and indeed in some cases, depleted to near zero concentrations. Well, why does this matter? Well, if we look at mortality data, right, where people have basically tortured fish and mollusks, right, in laboratory settings and determined at what oxygen concentration, excuse me, they're capable of surviving, we see that as oxygen concentrations decline, the percentage of animals capable of surviving also declines, right? And so it is a major concern at present for the health of our ocean ecosystems to understand how oxygen concentration will evolve and indeed this ocean deoxygenation trend is very likely to have significant impacts on marine ecosystems. How does oxygen in the ocean work? Well, if we look at the surface ocean, okay, oxygen is pretty much saturated or concentrations are high because of exchange with the atmosphere. But as oxygen is entrained into the ocean interior via ventilation pathways, that's a term we use in oceanography to talk about the ability of water masses to exchange properties with the atmosphere, but as water is entrained into the ocean interior, it begins to acquire a signature of respiration, right? So there's photosynthesis, production of oxygen, consumption of CO2 in the surface ocean, the organic matter that is produced via photosynthesis sinks and in the interior, there's microbial respiration, the consumption of oxygen and the production of CO2, right? And so it's that process that leaves the ocean depleted, the ocean interior depleted in oxygen, okay? But how climate warming works, right, is that at the surface, we decrease oxygen concentrations because of the temperature dependence of solubility. So think of a soda can on a warm day, you open that soda can, there's this effervescence of CO2, right? The same phenomena works for oxygen. The other factor is that as the surface ocean warms more than the ocean interior, we begin to stratify and limit the effectiveness of this ventilation pathway. And so the interior of the ocean begins to lose oxygen. This is a plot that shows a compilation of observations at the global scale and models showing the change in oxygen in a unit of concentration relative to the change in temperature. So the trend I am talking about now is observable in global reconstructions, we see this decline in oxygen as a function of increasing temperature. But note that that black dashed line is the change in oxygen we might expect if we were just dealing with oxygen, a reduction in oxygen due to decreasing solubility. That's the direct effect of temperature. The change in oxygen is actually much more significant than that solubility prediction because of the responsive ocean circulation. The ocean is becoming more stratified limiting that ventilation pathway. There's another very disturbing feature of this plot and that is the fact that our compilation of models is not capable of simulating the trend to the extent as the observations. So if we're to believe the observations and there's good reasons to be skeptical, the observations are very sparse, we're trying to infer a signal over 72% of the planet's area. So we need a lot of observations to be able to do that robustly. But if the observations are right, that indicates that the future of ocean oxygen is likely to be much worse than our models predict. So this is an area where we're working actively with a community of colleagues distributed internationally. This is of deep concern because if we go back into the history of Earth recorded in the geologic record, we see signatures of changes in oxygen concentrations in the ocean associated with warming driving significant changes in the habitability of the planet. And in particular about 252 million years ago, there was a release of CO2 from volcanism in proto-Siberia. And that accumulation of CO2 drove warming and it drove a depletion of oxygen in the ocean. About 90% of marine species perished. This event, the end permian extinction event is called the Great Dying. It is the most significant disruption in the history of life on Earth. So we're driving changes in the ocean distribution of oxygen that are comparable to what occurred on this event, but we're not gonna get to the magnitude of the end permian over the next 100 years. Maybe over the next 300 years, if we continued to emit CO2 under a business as usual scenario, we'd start to see something of the same order of magnitude as this significant event. I mentioned that we're working with a group of international colleagues to understand this. And indeed, there is consensus in the scientific community that we have reason to be deeply concerned about the trends in ocean deoxygenation. And this is just representative of that. This is the Keel Declaration. It was signed by over 500 scientists and it came from a conference on ocean deoxygen that occurred in Germany last year. So if you wanna know more about this, you can search the web and find plenty of information. Okay, I've given you a few vignettes in the context of the history of science. I've talked about some of my own research. What I'd like to do now is return to this Earthrise image and add a final piece to this talk by bringing out another point of reference from the scientific literature. Okay, and what I'd like to talk about here is an idea that was first proposed by James Loveblock and through collaboration with Lynn Margolis advanced this idea. And here is a paper that was published in 1974, Atmospheric homeostasis by and for the biosphere, the Gaia hypothesis, right? So Gaia was the mother of all life, the Greek goddess of the Earth. And let's just read this paragraph. This paper examines the hypothesis that the total ensemble of living organisms which constitute the biosphere can act as a single entity to regulate chemical composition, surface pH, and possibly also climate. I think I've basically given you the building blocks to understand that that is indeed very possibly true. The notion of the biosphere as an active adaptive control system able to maintain the Earth and homeostasis we are calling the Gaia hypothesis. So this is the idea that by virtue of climate operating as a selection pressure on the evolution of life and life operating to manipulate climate through the composition of the atmosphere we have feedback and that potential for feedback has the potential to lead to homeostasis. Life can't do stuff that disrupts the climate because if it does that, then life won't survive and vice versa, right? And so what does this organism look like? Well, the fluid spheres, I've given you examples, the seasonal cycle of CO2 in the atmosphere, the distribution of carbon in the ocean. These fluid spheres of the Earth system are Earth's circulatory systems. And what we see here is the mixing of constituents. These are not biogenic constituents per se, but this is a simulation conducted at NASA that just shows material being scooped up off the land surface and scooped up off the ocean surface and distributed in the atmosphere, right? So the visualizations we've seen earlier about the seasonal cycle of CO2 and the seasonal cycle of oxygen are reinforced by this image. So Earth is an organism, right? Now, this idea, the Gaia hypothesis, got a lot of flak in scientific literature, right? It was a little bit too new wave, right? And people for a long time didn't take it seriously. But I'd like to just present a final story from the scientific literature that to me, this was the thing that got me hooked on Earth system science, right? And it's the story of the evolution of oxygen in Earth's atmosphere. Earth is about four and a half billion years old. Life on Earth is about 3.2 billion years old, right? But when Earth first began, the atmosphere was not oxygenated. There were all sorts of crazy metabolisms when Earth first began, based on iron, based on sulfur, until a certain class of organisms developed this neat trick of photosynthesis, right? And we know about this from deposits of very old rocks. And these are called banded iron formations. What we see here are these successive layers of iron that were deposited on the sea floor as pulses of oxygen came into the atmosphere via photosynthesis and caused iron, the solubility of iron to collapse and iron precipitate out of solution in seawater. So this is our sort of best estimate of the time frame over which this happened. I mentioned Earth's about four billion years old, right? About 2.2 billion years ago, there was this great oxygenation event, okay? So organic, oxygenatic photosynthesis started to evolve, right? And there was these pulses of oxygen as the evolution of what our cyanobacteria began to leak oxygen out in the atmosphere. We get these pulses of iron at the seafloor and ultimately the system tips, the system tips. Photosynthesis takes over and the whole planet becomes oxygenated. Now this is really compelling, right? Because essentially this molten cord chunk of rock, this floating around in space, you know, developed, bootstrapped itself up, developed a set of organisms that were capable of exploiting the sunlight and the physical substrate and fundamentally change the character of the planet, right? And hence we have this profound radiation in the diversity of life, right? And indeed, you know, we ourselves are respiratory, we're heterotrophic organisms, you know, we require oxygen to breathe, our metabolisms are enabled by photosynthesis. Okay, so I've basically asserted that Earth is an organism, but you might complain, wow, it's not really an organism. It's a collection of organisms, right? Look, just, you know, here's just a picture of the diversity of life on Earth. Well, I'd like to convince you that that thought is actually misguided and we should properly consider it an organism. So Lynn Margolis had another famous hypothesis, right? And it was the hypothesis about endosymbiosis. The fact that eukaryotic cells, cells with a nucleus have organelles, right? She noticed something about those organelles, their similarity to bacteria, to cyanobacteria. And indeed, DNA evidence today has basically convinced the scientific community that she was right. The organelles in modern eukaryotic cells are derived from independent organisms. This is a symbiosis of two different or multiple different kinds of organisms living collectively as a single entity. Indeed, if we look at our own bodies, we're comprised of a society of cells, individual cells, right? That come together as a collective to build a human. And it's even more complicated than that. You know, increasingly, if you read the newspaper, you'll see discoveries about how the microbiome affects our metabolism and is an integral component of making us who we are. The microbiome affects our emotional state, right? It affects, it's a dominant factor in obesity. I read an article in the New York Times this morning. So this idea then that we can't form a single organism from multiple organisms is really misplaced. The way we should think about this is that these systems, these are complex adaptive systems, and they're subject to the laws of evolution, right? And there's a particular way in which we need to think about how evolution operates in order to understand how we can form single entities from a collective. So I'm just gonna talk about that briefly and illustrate an experiment that was conducted by William Muir, who was a professor at, I believe, Purdue in agricultural sciences, okay? And he was interested in increasing egg yields from chickens, right? And so he conducted two different experiments. He had a set of chicken coops, okay? And from his chicken coops, in his first experiment, he selected the best layers, the hens that laid the most eggs, and he bred those hens to produce, to produce, you know, to build other coops. In the second experiment, he selected the best coop, right? So the best collective. And this is the result. In this experiment, basically he selected murderous hens and egg production plummeted, right? And in fact, many of the chickens died because the society of hens was dominated by these pathological, you know, power hungry chickens, right? And in the second experiment, he increased egg yields by 160%, okay? So what's the lesson here? The lesson here is that in order to think about this notion of a collective, in the sense of a complex system, such as human society, we need to think about the level in the system at which selection pressure is exerted. William Muir artificially exerted selection pressure at the level of the individual, at the expense of the collective in this experiment to great detriment, right? And he selected, he enforced selection pressure at the level of the collective in this second experiment to yield happy productive hens. So let's pull this back. There's many examples in the natural world of social animals. Ants comprise order 10% of animal biomass in all ecosystems on earth except Antarctica. And they do that because they have exceptionally effective law rules for social organization. You know, we have this concept of hive mind, right? Ants have a super-organismal consciousness at the scale of the colony. They are able to perceive and recognize existential threats and deal with them, right? They know how to do that. Well, our species evolved on the African savannah in small group tribal units. And so we too have that capacity to operate as a collective and to perceive existential threats and as a collective understand how to deal with them, right? And we learn that through the order six million years of our species history. This is what the distribution of our species looks like now. So the Gaia hypothesis, right? Really in the context of this evolutionary theory is can be reframed as the notion that climate, planetary scale forcing drives selection pressure at the level of the collective, the collective being all life on earth, right? If we think about our society of cells, you know, there's examples on our bodies where cancer is an example where the selection pressure, the collective selection pressure is escaped, right? And the individual cells go haywire and to great detriment to our bodies, right? So the challenge we now face in this modern era that is increasingly be called the Anthropocene is develop this super-organismal consciousness at the scale at which our selection pressures being exerted, the planetary, the planetary scale. And so that's really where I'd like to leave you. I think this notion of planetary metabolism, how the planet functions as an organism provides a pretty interesting lens in which to view the modern era. And our challenge now is to really develop new perspectives on the function of the planet in this context. Fortunately, we have growing technology and scientific capabilities. This is an artist's rendition of all the satellites circling the earth and, well, they're not to scale. But, you know, our capacity to put our finger on the pulse of the system is growing increasingly. And as we continue to invest in science and continue to develop advanced understanding of the dynamics of this complex system, Earth, we will develop the capacity to manage our impact and we'll develop the capacity to manage the system at the scale commensurate with the problem. Okay, so that's where I'd like to leave you where we started, that this idea of science and the three paradigms of science forming a basis upon which we can build a sustainable future is really essential. And with that, I'm happy to take questions. Thank you.