We are now heading down a centuries-long path toward increasing the productivity of our natural capital – the resource systems upon which we depend to live – instead of our human capital. – Paul Hawken
The signs of accelerating global climate change are manifold. Evidence comes from reports of breathtakingly high temperatures transforming the Arctic, reports that the rate of sea level rise is effectively double estimates from only last year, ongoing wildfires of enormous scale, massive coral death worldwide, and oxygen depletion of the world’s oceans. The list is numbing, overwhelming, and for those of us who understand the science, it is evidence that climate change represents the greatest challenge in the history of our species. We are at a crossroads in our evolution.
This reality means that we must act now to manage the overall carbon budget of our planet. Because our climate emergency is accelerating out of control, we must immediately cease all investment in infrastructure, exploration, and development of fossil fuels. All new energy investments must be directed toward renewable alternatives, primarily wind, water, and solar. Although efforts at mitigation can slow down warming, ocean acidification, and attendant ecological transformations, returning to a more natural pace of change will not be possible during this century. Nevertheless, failure to significantly slow down climate change will have devastating consequences for civilization and the ecology of our planet. It is the eleventh hour and we must no longer tolerate those who deny this reality to influence our collective decision making.
The IPCC, its parent UNFCCC, and the US Global Change Research Program, and dozens of officially sanctioned science agencies throughout the industrialized world have rightly emphasized the need to drastically reduce the emissions from fossil fuels. Despite alarming developments as climate change accelerates, recent agreements to expand mitigation efforts are a reason for hope. Drastically reducing the use of fossil fuels is essential if we are to have any chance of holding the average global warming below the rather arbitrary guardrail of 2˚C relative to preindustrial times. The more ambitious aspiration adopted by overwhelming consensus at COP21 targets 1.5˚C, but achieving this will be dependent on increasing the sequestration of carbon from the atmosphere. Increased sequestration could be accomplished through intensively engineered carbon capture, or as I will argue here, through management of the biosphere to maximize biological uptake and storage of CO2.
We have no choice but to manage emissions from the biosphere as we eliminate those from fossil fuels. The rationale for this comes from two facts. First, multiple natural sources of emissions have been amplified by the current level of warming, these sources of emissions will continue to accelerate in the coming decades regardless of the degree to which we control fossil fuels. This is because the storage and exchange of energy among land, ocean, and the troposphere will drive some degree of continued warming through at least the end of the century. The impact of increasing biogenic emissions is likely to be as severe as the ongoing effects of any of the major sectors of fossil pollution.
Second, by not managing the natural capacity of our planet to capture and sequester atmospheric carbon, we discard a powerful tool in the fight to control climate change. We must include in our assessment of biogenic emissions those ecosystems managed for production, specifically agriculture and forestry. The Intergovernmental Panel on Climate Change Fifth Assessment (IPCC AR5 Working Group III) reports that agriculture, forestry, and other land uses (AFOLU) account for about a quarter of all anthropogenic emissions. Herein I provide an overview of how we might manage these resources to reduce these emissions and maximize carbon sequestration.
Biogenic emissions of greenhouse gases are accelerating
Humans have been profoundly altering the carbon cycle of the Earth for thousands of years. We are now witnessing an extreme acceleration of this process as our population has exploded and fossil fuels have been used at prodigious rates. The fact that emissions from biogenic sources are accelerating can be understood from first principles and from empirically observed trends.
It is well understood that as the Earth’s temperature increases, natural sources of CH4 and CO2 become more active. Essentially all living systems show an increased rate of respiration and CO2 production as temperature increases. Similarly, methanogenic organisms increase their activity as ambient temperatures drive their metabolism higher. Frozen biological materials become active emitters as temperatures rise above freezing for extended periods, and thus there is great concern about warming permafrost. Surprisingly, warmer wintertime temperatures may tip the balance of the carbon cycle in the far north. Northern permafrost is estimated to contain more than twice as much carbon as the entire of the atmosphere. The potential for methane clathrates to rapidly emerge from warming oceans is poorly understood, but may pose a serious threat (the so called clathrate gun hypothesis).
The interglacial periods during the 2.5 million years of the Pleistocene were periods when natural emissions amplified the warming of Earth. Interglacials were initiated and terminated mostly by variation in Earth’s interception of energy from the sun. Termed orbital forcing of the climate, variation in interception and thus temperature was driven by periodicity in Earth’s orbit. Ice cores from ~15,000 to ~850,000 years ago indicate that CO2 and CH4 emissions from natural sources increased during these interglacial periods. In turn, these greenhouse gases amplified warming and the Earth warmed considerably more than if driven solely by orbital forcing. Presently, the same process is underway, but humans are the cause of the initial warming. Both the rate and extent of emissions from fossil fuels dwarf that of the previous interglacials. Were it not for human intervention pushing CO2 levels above 240 ppm, our planet would be naturally cooling toward another glacial advance in possibly no more than two millennia.
Biogenic sources can be expected to emit at higher rates under warming conditions, and there is abundant evidence that this is underway on a large scale. It is no surprise that there are large increases in emissions from ecosystems as they are damaged by extreme weather, extended drought, flooding, storm surge along the coasts and other forms of disturbance that come with extreme events driven by climate change. Increasing size of wildfires correlates with climate change driven drought. Peat fires are more frequent, releasing huge stores of carbon. Forest dieback, infestations of tree-killing pests, and more frequent drought drive emissions from most forests around the globe. Prairies and grasslands too are emitting more as warming progresses.
We don’t know the extent to which CO2 fertilization of photosynthesis worldwide and greening of northern landscapes due to warmer temperatures and extended growing periods might offset increased emissions from the biosphere. It is clear, however, that that this process will not offset a significant fraction of projected increases in atmospheric CO2 from all sources. Moreover, because greening in the North results in a darker albedo and absorption of more sunlight relative to a snowy landscape, this process can enhance regional climate warming. A new report from the USGS shows that Alaskan ecosystems are presently a minor sink for carbon, but expanding forests will offset some of the increasing emissions from permafrost, lakes, and rivers. In contrast to the greening observed in this report, there is evidence that extreme climate events are driving Arctic browning. Expert consensus among researchers who study the northern permafrost is that it will be a global net emitter, to some degree, regardless of the extent to which we control fossil emissions.
Managing the biosphere for carbon sequestration
The biosphere removes CO2 from the atmosphere through photosynthesis and this presents us with a challenge to use this process to manage the carbon flux through living systems to increase sequestration of CO2. Although removing CO2 from the atmosphere can also be accomplished via engineered carbon capture and sequestration, the energy required for this is very large and the logistics of accomplishing this on a large scale are daunting. Short of such geoengineering approaches, the biosphere could be managed to maximize carbon uptake and minimize carbon loss using techniques and resources that are mostly already in place.
Ecologists have tools for how we might adaptively manage forests, grasslands, streams, lakes, and tundra to optimize carbon flux. Certain approaches for managing natural and semi natural systems seem obvious, including strategic management of forest productivity, reduction of forest destruction and deforestation (e.g., UN REDD+ program), fire, aggressive control of pests, wetlands, monitoring and control of keystone species with large impacts on biosphere carbon cycling, and engineering of water movement through ecosystems to maximize soil carbon and nutrient retention. However, much remains unknown about adaptively managing ecosystems, and it is difficult to predict the impact of management strategies over decades and centuries. This points to the need for development of targeted ecological research. I suggest that this research be framed as transdisciplinary sustainability science, which focuses on complex problem solving and near term application of results.
The managed ecosystems of forestry and agricultural offer the greatest opportunity for improved carbon capture and sequestration via the biosphere. Agriculture as a whole is a major source of emissions, and there is recent evidence that agriculture, rather than fossil fuel production, is becoming the dominant source of global methane emissions. In theory, carbon farming can be applied to the vast amount of land presently under cultivation or used for silviculture or pasture. Carbon farming employs targeted application of techniques to increase ecosystem carbon retention in pasture, perennial crops, annual crops, and agroforestry. While optimizing the carbon balance of these managed systems, these techniques can also improve sustained yield for many crop and tree species. Livestock can be strategically included in agroecological management schemes. While such integrated approaches are complex and by no means a panacea, they are gaining considerable respect in the scientific community as a powerful tool for managing the carbon flux of the biosphere.
Along with other experts, I am convinced that we are rapidly approaching a state shift in the Earth’s biosphere. Because of lag times built into the climate system, I believe that this is our last decade, termed Decade Zero by some activists, in which to move decisively toward a new relationship with our planet. It is my view that once this tipping point is traversed, managing biosphere carbon will likely be beyond our capacity on any time scale that can make a difference in terms of maintaining civilization in its current form. Ecosystems will be transformed and many species of plants and animals will be lost. The IPCC fourth assessment notes that at 3˚C warming, many crops will suffer major reductions in yield, and most will require new approaches for cultivation. At 4˚C many crops will no longer be viable where currently grown because of widespread, permanent drought. Beyond that point, even if we belatedly drastically curtail fossil emissions, emissions from the biosphere may drive the planet into sustained warming that will continue on the timescale of previous interglacials.
As we approach increasingly dire conditions, the temptation to massively artificially geoengineer either carbon uptake or sunlight interception, or both, will be overpowering. Carbon uptake could be engineered on a relatively short timescale through massive afforestation (planting trees where they have never occurred, in contrast to reforestation), artificial ocean upwelling (pump deep, cold, nutrient rich waters to the photosynthetic zone of the surface), ocean alkalinization (increase the CO2 uptake of the ocean by adding lime), and ocean iron fertilization (eliminate limits on phytoplankton photosynthesis). Sunlight interception by aerosols or other means could artificially cool the planet. All of these approaches have potentially large negative consequences for Earth systems and do not address the underlying problem of emissions. Perhaps most scary, some of these techniques, such as ocean fertilization and sunlight interception, could be deployed unilaterally by any large, technologically capable geopolitical power.
Management of the biosphere requires us to fundamentally restructure our relationship with nature. Many scholars argue that we must now develop a radically new and deep respect for the biosphere. This degree of change may seem out of reach while we attempt to address global poverty, population overshoot, and restructure a fossil fuel based economy. I have argued that such a transformation is not only possible, but necessary if human civilization is to mature beyond its adolescence. I suggest that we can monetize carbon management through the creation of a knowledge-based adaptation economy. Meanwhile, our political systems are intransigent and ongoing change in our economy and energy use is much too slow.
Cooperation on a massive, global scale is necessary to address large scale shifts in Earth systems. I see encouraging signs that such a sea change in our relationships with each other and the Earth has begun. It is worth noting that because of nearly universal access to information, never before in the history of humanity has such cooperation been as possible as it is now. The scholar of environment and religion, Bron Taylor, notes that a science-linked spiritual ethic about the ecology of our planet is on the rise. This contrasts with traditional religious views of the environment which are not typically grounded in science and to varying extents may obviate human responsibility. Noting our responsibility to creation, Pope Francis has issued the historic encyclical laudato si’, titled On Care for Our Common Home. I am hopeful that efforts at climate mobilization and ongoing efforts derived from the Paris climate accord will succeed before we lose our window of opportunity to salvage a livable climate for our children. It is possible that the Paris agreement will be the historical turning point ushering in a new era of sustainability and proactive mitigation and adaptation.