Half Earth is half an answer

We’re not yet sentient or intelligent enough to be much of anything. And we’re not going to have a secure future if we continue to play the kind of false god who whimsically destroys Earth’s living environment, and are pleased with what we have wrought.
Wilson, Edward O. (2016-03-07). Half-Earth: Our Planet’s Fight for Life (p. 47).


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Trail near Skokie in the Canadian Rockies where the landscape was
sculpted by the last great Earth systems transformation. S. Mulkey.


E. O. Wilson’s latest work, Half Earth – Our Planet’s Fight for Life, is a characteristically elegant proposal that we expand the world’s current system of preserves to set aside half of the Earth for the preservation of biodiversity. Although Dr. Ant focuses generously on animals, it is clear that he understands the importance of intact ecosystems that form the basis of the biosphere. Wilson notes that we are presently in the sixth great extinction of life in the history of our planet, and as he has done so eloquently many times before, he articulates the compelling reasons why it is urgent that we stem the bleeding of biodiversity. Like Wilson, I was trained as an ecologist immersed in the natural history and systematics of organisms. Given my background, you might think that I would simply love this idea, and you would be right.

Unfortunately, in the era of climate change, Wilson’s idea as stated in Half Earth can be generously described as incomplete. Coming from a scientist of his stature, I find his plea for preservation both inspiring and heart wrenching. Although crafted with noble intent, he gives only superficial consideration to the biggest thing in the world that will make his plan moot. Perhaps his omission of a more thorough assessment of climate change is intentional, or simply an oversight. But, it seems plausible that E. O. Wilson does not grasp the depth of the challenge that climate change poses to the preservation of biodiversity.

The biodiversity conservation models of the 20th century are mostly inadequate because we have entered a new era of rapid and potentially cataclysmic ecological change. Although human use of resources and habitat degradation have heretofore been the principal causes of biodiversity loss, changes set in motion by climate change will inexorably become the leading cause of ecological restructuring of the biosphere.

Such impacts will occur at two functionally interdependent scales.  First, at the scale of the entire planet, the energy imbalance resulting from our emissions is transforming the oceans, atmosphere, and landscape, and this will continue to some extent for centuries and likely millennia, even after we cease the use of fossil fuels. Some Earth systems have already passed a critical point of no return beyond which their transformation is inevitable. Second, at the more regional and local scale of biological communities, we are witnessing dynamic redistributions of species and extinctions as ecosystems are affected by accelerating climate warming, extreme weather events, and a variety regional and local phenomena driven by climate change.

Earth systems transformations

Large scale shifts in Earth systems have been relatively common over the history of our planet during the ice ages. Glacial advances and retreats in the Northern Hemisphere were initiated by periodic long term variation in the Earth’s orbit known as Milankovitch cycles, referred to as orbital forcing of the climate system. When the phase of orbital forcing resulted in warming, the resulting increased biological activity produced emissions of greenhouse gases (figure 1), further amplifying warming. Associated with this warming was large scale ecosystem restructuring throughout the terrestrial biosphere as continental ice sheets retreated (figure 2). These changes occurred over approximately evolutionary timescales and thus the associated speciation and extinction processes have been accepted as part of the natural dynamics of our planet.

Many of these large scale shifts in Earth systems are again underway in the current era, but our emissions are the primary cause. In fact, without the influence of human generated greenhouse gases, orbital forcing would drive the planet into another glacial advance within a few millennia. Ongoing massive shifts in the Earth’s distribution of energy include:

  • The permafrost has passed a point of no return and will become a net carbon source to the atmosphere by 2100 regardless of emissions scenario.
  • Extreme drought across the Amazon basin may now be a regular occurrence.
  • Far sooner than expected, the Atlantic Meridional Overturning Circulation (AMOC, commonly referred to as the Atlantic thermohaline circulation or conveyor belt) off the eastern coast of North America is slowing.
  • The Arctic sea ice is in massive retreat, affecting marine and terrestrial ecosystems throughout the Arctic and beyond. For over a decade all models of Arctic sea ice continue to significantly underestimate the rate of decline.
  • Surface warming of Greenland is dramatic, widespread, accelerating, and will continue for centuries. As bad luck would have it, part of Greenland sits on top of a geothermal hot spot, which is contributing to the melting of the ice sheet from below.
  • The Western Antarctic Ice Sheet is committed to eventual collapse over the next couple of centuries. New analysis shows that the contribution of Antarctica to sea level rise could be more than 6 feet by 2100, producing more than double the current expected rate of rise.
  • Without mitigation the present emissions trajectory will result in 7.2-9˚F (4-5˚C) warming by the end of the century relative to preindustrial average temperatures. Over centuries, this will result in the eventual loss of all land based ice, resulting in 230 feet (~75 m) of sea level rise.

There are two important differences between the climate shifts of prehistory and the current era. First, the amount of CO2 and CH4 liberated to the atmosphere by human activities is vast and unprecedented in 3 million years, and possibly as long as 20 million years. Second, the rate of release is the fastest in at least 66 million years. The rate of ocean acidification is the fastest in the known history of the Earth, exceeding any rate of the paleo record over at least 300 million years.

Because CO2 is the master control for the Earth’s energy balance, such unprecedented scale of emissions implies that significant climate disruption is imminent. As shown by Michael Mann in 1999 and more than a dozen subsequent papers by different research teams, the amount and rate of warming of the current period far exceeds any over the last 1000 years (figure 3). Over any meaningful human timeframe, the climate of the preindustrial period, and indeed the 20th century, is gone forever.

Based on the paleo record, the physics of the Earth’s energy balance, and general circulation modeling, there is little reason to expect that large scale Earth systems will respond gradually over millennia as they appear to have in paleo history. Although it is impossible to know how these major transitions will play out, it is reasonable to expect unanticipated abrupt shifts as systems pass through tipping points. Extinction events and periods of recovery may occur, but it is likely that our ability to manage biodiversity at such large scales will be only indirect through efforts to mitigate greenhouse gas emissions. Perhaps the good news is that we can manage both biodiversity and emissions from natural sources on smaller, ecosystem level scales even as biological communities respond to accelerating climate change.

Vostok_420ky_4curves_insolationfigure 1. 420,000 years of ice core data from Vostok, Antarctica, research station. Current period is at left. Scale does not permit visualizing the lag between orbital driven warming and initial rise in emissions of CO2 and CH4.


Post Glacial Plant Communities2 figure 2. Reconstruction of biological communities from pollen cores as glaciers in eastern North America receded demonstrates the potential for widespread restructuring of the terrestrial ecology of Earth as warming accelerates. It is doubtful that new assemblages of species will be as stable as those in the past unless we are able to slow down and eventually halt global warming. More detailed images of biological community succession following the retreat of the last great North American glaciation can be found at  http://www.esd.ornl.gov/projects/qen/nercNORTHAMERICA.html


NH_Temp_Reconstructionfigure 3. The Hockey Stick updated. The original version published as part of the IPCC Third Assessment provoked widespread attack by the climate change denial industry. Many lay people continue to believe that it is fallacious.


Regional and local tranformations of biological communities

Dynamic shifts in species composition of biological communities at smaller scales are increasingly driven by large scale changes in Earth systems. Such regional and local responses are sometimes subtle at this point in history, but they are becoming a concern planet wide. Numerous examples of regional and local scale climate change impacts on community organization have been reviewed by several research teams, including here, here, here, and here. Climate change can directly cause or amplify the effects of drought, wildfire, coastal flooding, storm surge, extreme weather events, toxic algal blooms, atypical movement of species, desertification, and other processes influenced by energy in the atmosphere. Plant and animal populations have often recovered when such events have been relatively rare, but as they recur with increasing frequency, damage to biodiversity can be long term or permanent.

In some cases, disturbance resulting from climate change may act to increase biodiversity in the near to intermediate term, but this is unlikely to be the case for very long if ecosystems are unstable and experiencing ongoing reorganization. More often, the effect is quite the opposite. Bellard et al. 2012 state “the majority of models indicate alarming consequences for biodiversity, with the worst-case scenarios leading to extinction rates that would qualify as the sixth mass extinction in the history of the earth.”

Half Earth is possible – but not through pure preservation

The management challenges for the preservation of biodiversity by this speed and degree of change are beyond any considered by Wilson in Half Earth. While qualifying for my PhD at the University of Pennsylvania, I learned the classic theory (Wilson coauthored this cornerstone work with Robert MacArthur in 1967) behind the development of permanent nature preserves to ensure the longevity and diversity of species. Now we see that growing zones are on the move and are increasingly decoupled from regional ecologies. As this decoupling progresses we can expect many preserves to be located in climate regions that are inappropriate for their various conservation functions. Without aggressive intervention, we can expect widespread transformation and even outright failure of species interactions and functional processes within ecosystems.

We need a much more dynamic and proactive approach to biodiversity conservation than was assumed in the 20th century. Habitat corridors connecting protected areas as they transform will become an increasingly important conservation tool. Similarly, we must more fully understand the complex and controversial process of assisted colonization so that we can move species as their preferred habitat changes or degrades. We must re-examine our understanding of invasive species in this brave new ecology. In a previous essay I argued that instead of focusing on pure preservation of species, we must work to maintain ecosystem form and function, thus preserving ecosystem services. Biodiversity is precious and should be preserved, but it may not be possible to preserve species in the community milieu where they currently exist.

Ecosystems undergoing dynamic change provide an opportunity not only for saving biodiversity but also for at least partial regulation of greenhouse gas emissions and uptake from the biosphere. Without intervention, ecosystems transforming in response to climate warming and disruption will release carbon to the atmosphere and enhance greenhouse warming. Such positive feedback will cripple our efforts at mitigation focused solely on reduction of fossil fuel use. In their seminal writings of the early 70’s, the pioneers H. T. Odum and E. T. Odum understood that maintenance of ecosystem form and function is essential for supporting diverse living systems. Thus, it should come as no surprise that in virtually all cases, biological diversity is inextricably linked to the flow of carbon through ecosystems.

Many of the tools for management of ecosystem carbon flux are the same tools used for modern day management of the ecology of forests, landscapes, grasslands, wetlands, and streams. Although there is much to be learned through additional research and practice, I suggest that we know enough about carbon flux in ecosystems to begin aggressive long term management to minimize positive feedback of greenhouse gases to the atmosphere, while maximizing photosynthetic carbon fixation and carbon sequestration where possible. New research indicates that proper management of the Earth’s soils, especially agricultural soils, could sequester or reduce climate warming emissions by a significant amount. It is through management of these smaller scale ecosystem-based processes that we have the opportunity to influence the carbon balance of the atmosphere in the near to intermediate term, and at the same time gain some advantage for the preservation of species.

Wilson’s contribution to the preservation of biodiversity in Half Earth is but a beginning. It can only be taken forward in the context of a fuller understanding of the challenges created by accelerating climate change. Taken as a whole, including its impact on biodiversity, climate change is the most significant challenge in the history of our species. Throughout his career, Wilson has been a major contributor to our understanding of just what is at stake as we stride across the face of this planet with the force of a geological calamity. In preserving half of the Earth for biodiversity and including in this our best efforts to manage climate, we might also succeed in preserving civilization.

I can only imagine what turns my career might have taken had I not been influenced by E. O. Wilson. I have reverence and gratitude for his contributions to evolutionary ecology, and unlike his critics, I see him as a brilliant yet humble intellectual. I hold him in high regard for his willingness to change his mind on the utility of kin selection as an explanation for evolution of sociality, and thereby endorse a form of group selection. Two phrases that I hardly ever hear from my colleagues are “I don’t know” and “I was wrong”. I have heard both from Ed Wilson. I offer my thanks to Dr. Ant for inspiring this essay and for inspiring my professional life. His eloquent articulation of wonder and awe has contributed to my spiritual appreciation of living things. This has helped sustain me when it seemed that I was surrounded by peers incapable of affective engagement with the mystery of life.