Good Night Sunshine -- Geo-engineering Solutions to Climate Warming?

The goal of last year’s Paris accord to limit global warming to 2°C (=3.6°F), if not 1.5°C (=2.7°F), is admirable, but it’s unlikely that these aspirational goals can be reached with voluntary greenhouse gas emission reductions alone.  Already, we are nearing the 1.5°C global warming level, with predictions for reaching 2°C not far into the future.  The implications of global warming are recognized widely, both in short-term events like coastal inundation and extreme weather, and long-term in the form of permanently shifting climate zones and higher sea level.  The range of our actions, however, is not limited to greenhouse gas generation only.

Building on humanity's remarkable history of engineering approaches to overcome challenges--from early use of fire to create stronger tools, to modern manufacturing and construction-- climate engineering techniques should be included as viable solutions for reducing the impacts of global warming.  Investigations of geo-engineering approaches have been around for several decades, but have grown especially since the 2006 publication of Dutch Nobel Laureate Paul Crutzen’s editorial essay on reducing solar influence, called “Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?”

Climate engineering takes two approaches: (1) Carbon dioxide removal (CDR), and (2) solar radiation management (SRM).  CDR addresses the cause of climate warming by removing greenhouse gas from the atmosphere ("treat the illness").  SRM offsets the warming effects of greenhouse gases by allowing Earth to absorb less solar radiation ("treat the symptoms").  Reduction of greenhouse gas emissions, as proposed in the Paris Accord, is desirable, but is not a prerequisite for climate engineering.  Among the range of techniques, SRM, the focus of Crutzen’s essay, is the main source of professional and public anxiety and has mostly remained taboo.  There are concerns about unintended consequences, local applications with global consequences, runaway effects, and even climate warfare.

Given that climate engineering remains highly controversial, a set of thoughtful research papers and scientific commentaries have been published on this in AGU’s open-access journal Earth's Future, introduced by Boettcher and Schäfer (2017).  This thematic collection examines the techniques and risks of climate engineering, from specific methodologies to socio-political dimensions.  The contributions highlight our much improved understanding of the environmental, political and societal risks and benefits of climate engineering, but they also recognize that the current state of our knowledge is insufficient for reliable deployment.  Computer modeling and integrated assessments have advanced the positive and negative aspects of various techniques, allowing for an informed public debate and eventual decision-making.  Some nations more than others are advancing this understanding and are considering some implementation.  However, more extensive scientific efforts and social study that includes real-world, outdoor experimentation will be needed to adequately assess near-term deployments and their impact.

Climate engineering has unquestionable potential to limit global warming when coupled with currently available technologies, but the scientific, social and ethical dimensions of implementation are not sufficiently examined.  Given the worldwide impact of most deployment approaches, planning should occur on a global scale, involving all nations, both rich and poor, and not be limited to a few technologically advanced, wealthy stakeholders.  We know we must limit the impacts of global warming, but we also know that warming will continue for decades or centuries even with radical reductions in greenhouse gas emissions. This situation generates an urgent need to invest in research and impact analysis of climate engineering approaches.  Judging by the resilience of today’s human society to global environmental change, ignoring the potential of climate engineering solutions does not seem prudent nor realistic.

Ben van der Pluijm, University of Michigan-Ann Arbor, USA.
Guy Brasseur, Max Planck Institute for Meteorology, Hamburg, Germany.

Crutzen +10: Reflecting upon 10 years of geoengineering research.  Earth's Future Special Collection (2016/17).  http://agupubs.onlinelibrary.wiley.com/hub/issue/10.1002/(ISSN)2328-4277.GEOENGIN1/
Photo credit: Abode Stock #113493276. Art credit: Kiel Earth Institute

Modified from American Geophysical Union's Editors’ Vox.

Here comes the Anthropocene

Two excellent papers examine the meaning and formalization of an Anthropocene Epoch, a geological era in which humans have a major impact on surface processes and the environment. Steffen et al. (2016) take an Earth Systems approach while Williams et al. (2016) focus on biospheric signals.  Both papers are informative and data-based, and are required reading for anyone interested in this proposed change to the Geologic Timescale, but also those of us interested in global change (that is, all of us).

The field of stratigraphy is explicitly recognized in each analysis, as it provides the foundation of Earth’s geologic timescale.  A quick primer on stratigraphy: for the past 2.5 million years, we have lived in the Cenozoic Era’s Quaternary Period, which started with the Pleistocene Epoch and, currently, the Holocene Epoch.  The addition of an Anthropocene Epoch into the geological time scale is a key motivation behind these papers, which will be decided by the International Commission on Stratigraphy, supported by an Anthropocene Working Group that includes the leads and several authors of these two papers.  Steffen and colleagues use Earth Systems science to describe our planet’s evolution from an evolving Precambrian environment into a life-dominated Phanerozoic one (since ~540Ma).   They conclude that today’s Earth system has undergone a substantial transition away from the Holocene (interglacial) state, toward a world with much less polar ice, changed atmospheric composition, and accelerated plant and animal species extinction.  Williams and colleagues’ biotic approach emphasizes that modern humans are changing the planet’s relationship through human consumption of Earth’s resources, with major consequences for the ecosphere and a change in evolutionary state.  Using different perspectives, both papers reach the same conclusion of an Anthropocene state that is unlike the Holocene, supporting the need for a new epoch.  Both also favor a chemical tracer from mid-20thC nuclear activity as its lower boundary, though that, I believe, seems less compelling from their descriptions.

The stratigraphic foundation of the Phanerozoic Eon’s geologic timescale is the preservation of hard-bodied life.  Extinctions, a relatively sudden, large decline of species, punctuate the record with five major events (excluding today) and multiple smaller events, providing global markers for stratigraphic boundaries in the geologic record.  Some extinctions were relatively fast (kyr), while others reflect longer times (myr).  The species extinction of modern time, which started with the rise of humans as the planet’s dominant consumer of resources can likewise become the base of the Anthropocene.  This latest (6th) major extinction is already underway, and continuing for decades to centuries, perhaps even culminating in human extinction.  Life, notably the radiation of species, offers another global stratigraphic marker in the tradition of the geologic timescale.  Humans exploring and conquering the world transported other life, including plants and seeds, small animals (like insects and rodents), and even large animals (like horses) that since became entrained as fossils in modern depositional strata.  This biomarker would place the start of the Anthropocene well before the 20th century, as far back as 15th century, following Medieval times.  Arguably, the current 6th extinction also started around that time.  Unlike the Holocene, which started ~12,000 years ago as a garden-variety interglacial, the Anthropocene involves vast and fast changes on a global scale, affecting life, atmosphere, land and oceans.

These patterns are not mere extensions or accelerations of the Holocene interglacial.  The Anthropocene signature is unlike that of our planet’s past icehouse-greenhouse system, leading to my earlier, alternative suggestion to adopt a Pleistocene-Anthropocene boundary that reflects this fundamental change in Earth System from an externally-driven (or Milankovitch) state to a human-driven state.  As we move toward a decision on the timescale, these papers make a compelling case for an Anthropocene Epoch, while reminding us of the large changes in environmental conditions that are already underway.

Steffen, W., Leinfelder, R., Zalasiewicz, J., Waters, C. N., Williams, M., Summerhayes, C., Barnosky, A. D., Cearreta, A., Crutzen, P., Edgeworth, M., Ellis, E. C., Fairchild, I. J., Gałuszka, A., Grinevald, J., Haywood, A., Sul, J. I. d., Jeandel, C., McNeill, J.R., Odada, E., Oreskes, N., Revkin, A., Richter, D. d. B., Syvitski, J., Vidas, D., Wagreich, M., Wing, S. L., Wolfe, A. P. and Schellnhuber, H.J. (2016).  Stratigraphic and Earth System Approaches to Defining the Anthropocene. Earth's Future, 4: 324–345. doi:10.1002/2016EF000379.
http://onlinelibrary.wiley.com/doi/10.1002/2016EF000379/full

van der Pluijm, B. (2014). Hello Anthropocene, Goodbye Holocene. Earth's Future, 2: 566–568. doi:10.1002/2014EF000268.
http://onlinelibrary.wiley.com/doi/10.1002/2014EF000268/full

Williams, M., Zalasiewicz, J., Waters, C. N., Edgeworth, M., Bennett, C., Barnosky, A. D., Ellis, E. C., Ellis, M. A., Cearreta, A., Haff, P. K., Ivar do Sul, J. A., Leinfelder, R., McNeill, J. R., Odada, E., Oreskes, N., Revkin, A., Richter, D. d., Steffen, W., Summerhayes, C., Syvitski, J. P., Vidas, D., Wagreich, M., Wing, S. L., Wolfe, A. P. and Zhisheng, A. (2016).  The Anthropocene: a conspicuous stratigraphical signal of anthropogenic changes in production and consumption across the biosphere. Earth's Future, 4: 34–53. doi:10.1002/2015EF000339. http://onlinelibrary.wiley.com/doi/10.1002/2015EF000339/full

Modified from AGU Editors’ Vox; https://eos.org/editors-vox/here-comes-the-anthropocene.