We live in a profoundly unnatural world. Since the start of the industrial revolution, and rapidly accelerating throughout the twentieth century, the actions of humans have begun to influence the flow of energy and materials in the Earth’s biosphere on a global scale. Earth’s current human population and standard of living are made possible entirely by industrial production of nitrogen-based fertilisers and crop plants bred to efficiently exploit them. Industrial production of fixed (chemically reactive) nitrogen from the atmosphere now substantially exceeds all of that produced by the natural soil bacteria on the planet which, prior to 1950, accounted for almost all of the nitrogen required to grow plants. Fixing nitrogen by the Haber-Bosch process is energy-intensive, and consumes around 1.5 percent of all the world’s energy usage and, as a feedstock, 3–5% of natural gas produced worldwide. When we eat these crops, or animals fed from them, we are, in a sense, eating fossil fuels. On the order of four out of five nitrogen molecules that make up your body were made in a factory by the Haber-Bosch process. We are the children, not of nature, but of industry.
The industrial production of fertiliser, along with crops tailored to use them, is entirely responsible for the rapid growth of the Earth’s population, which has increased from around 2.5 billion in 1950, when industrial fertiliser and “green revolution” crops came into wide use, to more than 7 billion today. This was accompanied not by the collapse into global penury predicted by Malthusian doom-sayers, but rather a broad-based rise in the standard of living, with extreme poverty and malnutrition falling to all-time historical lows. In the lifetimes of many people, including this scribbler, our species has taken over the flow of nitrogen through the Earth’s biosphere, replacing a process mediated by bacteria for billions of years with one performed in factories. The flow of nitrogen from atmosphere to soil, to plants and the creatures who eat them, back to soil, sea, and ultimately the atmosphere is now largely in the hands of humans, and their very lives have become dependent upon it.
This is an example of “geoengineering”—taking control of what was a natural process and replacing it with an engineered one to produce a desired outcome: in this case, the ability to feed a much larger population with an unprecedented standard of living. In the case of nitrogen fixation, there wasn’t a grand plan drawn up to do all of this: each step made economic sense to the players involved. (In fact, one of the motivations for developing the Haber-Bosch process was not to produce fertiliser, but rather to produce feedstocks for the manufacture of military and industrial explosives, which had become dependent on nitrates obtained from guano imported to Europe from South America.) But the outcome was the same: ours is an engineered world. Those who are repelled by such an intervention in natural processes or who are concerned by possible detrimental consequences of it, foreseen or unanticipated, must come to terms with the reality that abandoning this world-changing technology now would result in the collapse of the human population, with at least half of the people alive today starving to death, and many of the survivors reduced to subsistence in abject poverty. Sadly, one encounters fanatic “greens” who think this would be just fine (and, doubtless, imagining they’d be among the survivors).
Just mentioning geoengineering—human intervention and management of previously natural processes on a global scale—may summon in the minds of many Strangelove-like technological megalomania or the hubris of Bond villains, so it’s important to bear in mind that we’re already doing it, and have become utterly dependent upon it. When we consider the challenges we face in accommodating a population which is expected to grow to ten billion by mid-century (and, absent catastrophe, this is almost a given: the parents of the ten billion are mostly alive today), who will demand and deserve a standard of living comparable to what they see in industrial economies, and while carefully weighing the risks and uncertainties involved, it may be unwise to rule out other geoengineering interventions to mitigate undesirable consequences of supporting the human population.
In parallel with the human takeover of the nitrogen cycle, another geoengineering project has been underway, also rapidly accelerating in the 20th century, driven both by population growth and industrialisation of previously agrarian societies. For hundreds of millions of years, the Earth also cycled carbon through the atmosphere, oceans, biosphere, and lithosphere. Carbon dioxide (CO₂) was metabolised from the atmosphere by photosynthetic plants, extracting carbon for their organic molecules and producing oxygen released to the atmosphere, then passed along as plants were eaten, returned to the soil, or dissolved in the oceans, where creatures incorporated carbonates into their shells, which eventually became limestone rock and, over geological time, was subducted as the continents drifted, reprocessed far below the surface, and expelled back into the atmosphere by volcanoes. (This is a gross oversimplification of the carbon cycle, but we don’t need to go further into it for what follows. The point is that it’s something which occurs on a time scale of tens to hundreds of millions of years and on which humans, prior to the twentieth century, had little influence.)
The natural carbon cycle is not leakproof. Only part of the carbon sequestered by marine organisms and immured in limestone is recycled by volcanoes; it is estimated that this loss of carbon will bring the era of multicellular life on Earth to an end around a billion years from now. The carbon in some plants is not returned to the biosphere when they die. Sometimes, the dead vegetation accumulates in dense beds where it is protected against oxidation and eventually forms deposits of peat, coal, petroleum, and natural gas. Other than natural seeps and releases of the latter substances, their carbon is also largely removed from the biosphere. Or at least it was until those talking apes came along….
The modern technological age has been powered by the exploitation of these fossil fuels: laid down over hundreds of millions of years, often under special conditions which only existed in certain geological epochs, in the twentieth century their consumption exploded, powering our present technological civilisation. For all of human history up to around 1850, world energy consumption was less than 20 exajoules per year, almost all from burning biomass such as wood. (What’s an exajoule? Well, it’s 10^18 joules, which probably tells you absolutely nothing. That’s a lot of energy: equivalent to 164 million barrels of oil, or the capacity of around sixty supertankers. But it’s small compared to the energy the Earth receives from the Sun, which is around 4 million exajoules per year.) By 1900, the burning of coal had increased this number to 33 exajoules, and this continued to grow slowly until around 1950 when, with oil and natural gas coming into the mix, energy consumption approached 100 exajoules. Then it really took off. By the year 2000, consumption was 400 exajoules, more than 85% from fossil fuels, and today it’s more than 550 exajoules per year.
Now, as with the nitrogen revolution, nobody thought about this as geoengineering, but that’s what it was. Humans were digging up, or pumping out, or otherwise tapping carbon-rich substances laid down long before their clever species evolved and burning them to release energy banked by the biosystem from sunlight in ages beyond memory. This is a human intervention into the Earth’s carbon cycle of a magnitude even greater than the Haber-Bosch process into the nitrogen cycle. “Look out, they’re geoengineering again!” When you burn fossil fuels, the combustion products are mostly carbon dioxide and water. There are other trace products, such as ash from coal, oxides of nitrogen, and sulphur compounds, but other than side effects such as various forms of pollution, they don’t have much impact on the Earth’s recycling of elements. The water vapour from combustion is rapidly recycled by the biosphere and has little impact, but what about the CO₂?
Well, that’s interesting. CO₂ is a trace gas in the atmosphere (less than a fiftieth of a percent), but it isn’t very reactive and hence doesn’t get broken down by chemical processes. Once emitted into the atmosphere, CO₂ tends to stay there until it’s removed via photosynthesis by plants, weathering of rocks, or being dissolved in the ocean and used by marine organisms. Photosynthesis is an efficient consumer of atmospheric carbon dioxide: a field of growing maize in full sunlight consumes all of the CO₂ within a metre of the ground every five minutes—it’s only convection that keeps it growing. You can see the yearly cycle of vegetation growth in measurements of CO₂ in the atmosphere as plants take it up as they grow and then release it after they die. The other two processes are much slower. An increase in the amount of CO₂ causes plants to grow faster (operators of greenhouses routinely enrich their atmosphere with CO₂ to promote growth), and increases the root to shoot ratio of the plants, tending to remove CO₂ from the atmosphere where it will be recycled more slowly into the biosphere.
But since the start of the industrial revolution, and especially after 1950, the emission of CO₂ by human activity over a time scale negligible on the geological scale by burning of fossil fuels has released a quantity of carbon into the atmosphere far beyond the ability of natural processes to recycle. For the last half billion years, the CO₂ concentration in the atmosphere has varied between 280 parts per million in interglacial (warm periods) and 180 parts per million during the depths of the ice ages. The pattern is fairly consistent: a rapid rise of CO₂ at the end of an ice age, then a slow decline into the next ice age. The Earth’s temperature and CO₂ concentrations are known with reasonable precision in such deep time due to ice cores taken in Greenland and Antarctica, from which temperature and atmospheric composition can be determined from isotope ratios and trapped bubbles of ancient air. While there is a strong correlation between CO₂ concentration and temperature, this doesn’t imply causation: the CO₂ may affect the temperature; the temperature may affect the CO₂; they both may be caused by another factor; or the relationship may be even more complicated (which is the way to bet).
But what is indisputable is that, as a result of our burning of all of that ancient carbon, we are now in an unprecedented era or, if you like, a New Age. Atmospheric CO₂ is now around 410 parts per million, which is a value not seen in the last half billion years, and it’s rising at a rate of 2 parts per million every year, and accelerating as global use of fossil fuels increases. This is a situation which, in the ecosystem, is not only unique in the human experience; it’s something which has never happened since the emergence of complex multicellular life in the Cambrian explosion. What does it all mean? What are the consequences? And what, if anything, should we do about it?
(Up to this point in this essay, I believe everything I’ve written is non-controversial and based upon easily-verified facts. Now we depart into matters more speculative, where squishier science such as climate models comes into play. I’m well aware that people have strong opinions about these issues, and I’ll not only try to be fair, but I’ll try to stay away from taking a position. This isn’t to avoid controversy, but because I am a complete agnostic on these matters—I don’t think we can either measure the raw data or trust our computer models sufficiently to base policy decisions upon them, especially decisions which might affect the lives of billions of people. But I do believe that we ought to consider the armanentarium of possible responses to the changes we have wrought, and will continue to make, in the Earth’s ecosystem, and not reject them out of hand because they bear scary monikers like “geoengineering”.)
We have been increasing the fraction of CO₂ in the atmosphere to levels unseen in the history of complex terrestrial life. What can we expect to happen? We know some things pretty well. Plants will grow more rapidly, and many will produce more roots than shoots, and hence tend to return carbon to the soil (although if the roots are ploughed up, it will go back to the atmosphere). The increase in CO₂ to date will have no physiological effects on humans: people who work in greenhouses enriched to up to 1000 parts per million experience no deleterious consequences, and this is more than twice the current fraction in the Earth’s atmosphere, and at the current rate of growth, won’t be reached for three centuries. The greatest consequence of a growing CO₂ concentration is on the Earth’s energy budget. The Earth receives around 1360 watts per square metre on the side facing the Sun. Some of this is immediately reflected back to space (much more from clouds and ice than from land and sea), and the rest is absorbed, processed through the Earth’s weather and biosphere, and ultimately radiated back to space at infrared wavelengths. The books balance: the energy absorbed by the Earth from the Sun and that it radiates away are equal. (Other sources of energy on the Earth, such as geothermal energy from radioactive decay of heavy elements in the Earth’s core and energy released by human activity are negligible at this scale.)
Energy which reaches the Earth’s surface tends to be radiated back to space in the infrared, but some of this is absorbed by the atmosphere, in particular by trace gases such as water vapour and CO₂. This raises the temperature of the Earth: the so-called greenhouse effect. The books still balance, but because the temperature of the Earth has risen, it emits more energy. (Due to the Stefan-Boltzmann law, the energy emitted from a black body rises as the fourth power of its temperature, so it doesn’t take a large increase in temperature [measured in degrees Kelvin] to radiate away the extra energy.)
So, since CO₂ is a strong absorber in the infrared, we should expect it to be a greenhouse gas which will raise the temperature of the Earth. But wait—it’s a lot more complicated. Consider: water vapour is a far greater contributor to the Earth’s greenhouse effect than CO₂. As the Earth’s temperature rises, there is more evaporation of water from the oceans and lakes and rivers on the continents, which amplifies the greenhouse contribution of the CO₂. But all of that water, released into the atmosphere, forms clouds which increase the albedo (reflectivity) of the Earth, and reduce the amount of solar radiation it absorbs. How does all of this interact? Well, that’s where the global climate models get into the act, and everything becomes very fuzzy in a vast panel of twiddle knobs, all of which interact with one another and few of which are based upon unambiguous measurements of the climate system.
Let’s assume, arguendo, that the net effect of the increase in atmospheric CO₂ is an increase in the mean temperature of the Earth: the dreaded “global warming”. What shall we do? The usual prescriptions, from the usual globalist suspects, are remarkably similar to their recommendations for everything else which causes their brows to furrow: more taxes, less freedom, slower growth, forfeit of the aspirations of people in developing countries for the lifestyle they see on their smartphones of the people who got to the industrial age a century before them, and technocratic rule of the masses by their unelected self-styled betters in cheap suits from their tawdry cubicle farms of mediocrity. Now there’s something to stir the souls of mankind!
But maybe there’s an alternative. We’ve already been doing geoengineering since we began to dig up coal and deploy the steam engine. Maybe we should embrace it, rather than recoil in fear. Suppose we’re faced with global warming as a consequence of our inarguable increase in atmospheric CO₂ and we conclude its effects are deleterious? (That conclusion is far from obvious: in recorded human history, the Earth has been both warmer and colder than its present mean temperature. There’s an intriguing correlation between warm periods and great civilisations versus cold periods and stagnation and dark ages.) How might we respond?
Atmospheric veil. Volcanic eruptions which inject large quantities of particulates into the stratosphere have been directly shown to cool the Earth. A small fleet of high-altitude airplanes injecting sulphate compounds into the stratosphere would increase the albedo of the Earth and reflect sufficient sunlight to reduce or even cancel or reverse the effects of global warming. The cost of such a programme would be affordable by a benevolent tech billionaire or wannabe Bond benefactor (“Greenfinger”), and could be implemented in a couple of years. The effect of the veil project would be much less than a volcanic eruption, and would be imperceptible other than making sunsets a bit more colourful.
Marine cloud brightening. By injecting finely-dispersed salt water from the ocean into the atmosphere, nucleation sites would augment the reflectivity of low clouds above the ocean, increasing the reflectivity (albedo) of the Earth. This could be accomplished by a fleet of low-tech ships, and could be applied locally, for example to influence weather.
Carbon sequestration. What about taking the carbon dioxide out of the atmosphere? This sounds like a great idea, and appeals to clueless philanthropists like Bill Gates who are ignorant of thermodynamics, but taking out a trace gas is really difficult and expensive. The best place to capture it is where it’s densest, such as the flue of a power plant, where it’s around 10%. The technology to do this, “carbon capture and sequestration” (CCS) exists, but has not yet been deployed on any full-scale power plant.
Fertilising the oceans. One of the greatest reservoirs of carbon is the ocean, and once carbon is incorporated into marine organisms, it is removed from the biosphere for tens to hundreds of millions of years. What constrains how fast critters in the ocean can take up carbon dioxide from the atmosphere and turn it into shells and skeletons? It’s iron, which is rare in the oceans. A calculation made in the 1990s suggested that if you added one tonne of iron to the ocean, the bloom of organisms it would spawn would suck a hundred thousand tonnes of carbon out of the atmosphere. Now, that’s leverage which would impress even the most jaded Wall Street trader. Subsequent experiments found the ratio to be maybe a hundred times less, but then iron is cheap and it doesn’t cost much to dump it from ships.
Great Mambo Chicken. All of the previous interventions are modest, feasible with existing technology, capable of being implemented incrementally while monitoring their effects on the climate, and easily and quickly reversed should they be found to have unintended detrimental consequences. But when thinking about affecting something on the scale of the climate of a planet, there’s a tendency to think big, and a number of grand scale schemes have been proposed, including deploying giant sunshades, mirrors, or diffraction gratings at the L1 Lagrangian point between the Earth and the Sun. All of these would directly reduce the solar radiation reaching the Earth, and could be adjusted as required to manage the Earth’s mean temperature at any desired level regardless of the composition of its atmosphere. Such mega-engineering projects are considered financially infeasible, but if the cost of space transportation falls dramatically in the future, might become increasingly attractive. It’s worth observing that the cost estimates for such alternatives, albeit in the tens of billions of dollars, are small compared to re-architecting the entire energy infrastructure of every economy in the world to eliminate carbon-based fuels, as proposed by some glib and innumerate environmentalists.
We live in the age of geoengineering, whether we like it or not. Ever since we started to dig up coal and especially since we took over the nitrogen cycle of the Earth, human action has been dominant in the Earth’s ecosystem. As we cope with the consequences of that human action, we shouldn’t recoil from active interventions which acknowledge that our environment is already human-engineered, and that it is incumbent upon us to preserve and protect it for our descendants. Some environmentalists oppose any form of geoengineering because they feel it is unnatural and provides an alternative to restoring the Earth to an imagined pre-industrial pastoral utopia, or because it may be seized upon as an alternative to their favoured solutions such as vast fields of unsightly bird shredders. But as David Deutsch says in The Beginning of Infinity, “Problems are inevitable“; but “Problems are soluble.” It is inevitable that the large scale geoengineering which is the foundation of our developed society—taking over the Earth’s natural carbon and nitrogen cycles—will cause problems. But it is not only unrealistic but foolish to imagine these problems can be solved by abandoning these pillars of modern life and returning to a “sustainable” (in other words, medieval) standard of living and population. Instead, we should get to work solving the problems we’ve created, employing every tool at our disposal, including new sources of energy, better means of transmitting and storing energy, and geoengineering to mitigate the consequences of our existing technologies as we incrementally transition to those of the future.
Morton, Oliver. The Planet Remade. Princeton: Princeton University Press, 2015. ISBN 978-0-691-17590-4.
Here is a one hour talk by Oliver Morton about geoengineering as a strategy for coping with rising levels of atmospheric CO₂.