Making Eden

by David Beerling

To be sure, the identity of the mysterious ‘doorstop’ limiting the minimum

  amount of carbon dioxide in the atmosphere is uncertain—is it some inherent

  property of Earth’s natural thermostat? Another line of enquiry suggests that

  trees and forests could be involved.57 The basic idea is that as the global atmospheric carbon dioxide concentration begins to dwindle during major episodes of

  mountain uplift, it gradually starts starving the trees and forests colonizing these uplifted terrains. As it dips towards 200 parts per million, half what it is today, carbon dioxide starvation compromises the health of the world’s forests, causing

  tree productivity to crash.58 Dead trees are unable to weather rocks actively, and

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  forests of slow-growing trees, thinned out by carbon dioxide starvation, become

  less effective at mineral weathering.59

  If this view of how the world works is broadly correct, atmospheric carbon

  dioxide concentration is a control knob regulating forest-driven weathering,

  just as it regulates climate. Trees are integral components of the natural built-in global thermostat regulated by linkages between atmospheric carbon dioxide,

  climate, and weathering. Our debt to plants is mounting. Besides food, water,

  timber, medicine, and air-conditioning our climate, trees are implicated in stabilizing Earth’s climate over millions of years by inhibiting critically low levels of carbon dioxide that would have seen Earth develop into a giant snow ball.

  We can see from this that ultimately rock weathering will remove our

  anthropogenic carbon dioxide emissions from the atmosphere and eventually

  deposit it on the seafloor as carbonate sediments. Unfortunately, in normal

  circumstances rock weathering is far too slow to help avert the threat of dangerous climate change. The basaltic terrain of Iceland is already responding to dramatic warming of the Arctic region over past decades by weathering faster,60 but this

  feedback will not save us. Our best estimates suggest natural rock weathering

  sequesters less than 2% of our annual carbon dioxide emissions from fossil fuels.

  At current rates, it will take a hundred thousand years or more for natural

  weathering processes to convert our accumulated emissions of carbon dioxide

  into anthropogenic carbonate deposits on the seafloor. Yet we find ourselves in

  far from normal circumstances, with an atmospheric carbon dioxide concentra-

  tion exceeding 400 parts per million for the first time in several million years, thanks to our combustion of fossil fuels. In 2016, our annual emissions of carbon dioxide reached 36 billion tonnes, the highest in human history and 60% higher

  than in 1990.61

  Earth’s atmospheric carbon dioxide history can be compared with what might

  happen in the future. The chart in Figure 24 show potential pathways we may fol-

  low, depending on how much fossil fuels are burned over the coming decades.

  Steep changes correspond with rapid future climate change. If we keep burning

  fossil fuels, we could soon cause higher carbon dioxide levels and faster climate change than the Earth has seen in the past 50 million years. If we burn all available fossil fuel reserves (the black ‘Wink12k’ line), the carbon dioxide concentration will exceed levels seen in the entire 420-million-year reconstruction.

  The continued accumulation of carbon dioxide and other human-caused

  greenhouse gases in the atmosphere since the pre-industrial era (i.e., from around

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  1850 onwards) has already driven global warming exceeding 1°C above the pre-

  industrial value.62 In 2016, the rise in annual global temperature was almost

  1.3°C. If warming continues at the current rate, the aspirational target of the recent United Nations Paris Agreement63 of 1.5°C will be out of reach within 20 years,

  threatening a fifth of all species with extinction. Breaking our addiction to fossil fuels and phasing over to carbon-free energy will not be easy to achieve, and

  makes even a more lenient target of 2°C difficult. Urgently phasing down carbon

  dioxide emissions is the sine qua non for fighting the threat of future climate change. There is also a growing realization that research into safe and affordable methods for extracting carbon dioxide from the air is required to augment efforts to reduce fossil fuel emissions. All such strategies are currently poorly understood , especially in terms of their environmental and ecological impacts, financial costs, and feasibility.64 But is it possible for humanity to mimic Devonian trees in

  converting huge amounts of atmospheric carbon dioxide into carbonate minerals

  to cool the planet?

  One approach proposes to deals with point sources of carbon dioxide in this

  way from power stations. Approximately 2200 coal-fired power plants in

  Europe, North America, and China release about a third of fossil fuel carbon

  dioxide emitted into the atmosphere.65 If we could retrofit these coal-fired

  plants with carbon capture and sequestration technologies, it would slow

  emissions into the atmosphere—assuming we could find somewhere to store

  it and the economics work. Perhaps we might bury the carbon dioxide by

  reacting it with basalt directly as the Earth has been doing for billions of years, aided in the past few hundred million years by trees? Basaltic rocks represent

  huge underground storage depots that are sufficiently large to accommodate

  our carbon dioxide emissions for centuries to come. Once again, researchers

  have turned to Iceland where, like Berner, they seek to exploit its remarkable

  basalt landscape.

  Located 25 kilometres east of Reykjavik, the CarbFix experiment in Iceland is

  a sequestration project assessing the potential for permanently capturing and

  storing carbon dioxide gas as carbonate minerals in basalt rock.66 In 2002,

  CarbFix injected hundreds of tonnes of carbon dioxide dissolved in ground-

  water into basaltic rocks to a depth of nearly a kilometre. Within a couple of

  years, over 95% of the carbon dioxide reacted with the basalt to form environ-

  mentally benign carbonate minerals.67 Carbonate minerals are stable residents

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  of geological strata, stable enough to lock up carbon dioxide for millions of

  years. The speed of conversion of carbon dioxide to carbonates has proved sur-

  prisingly quick. The common view was that immobilization of carbon dioxide

  in this way would take hundreds of years, if not longer. Effectively, this small-scale programme has demonstrated the initial feasibility of safely storing anthropogenic carbon dioxide emissions below ground in basaltic rocks. Further support

  comes from another pilot project, this time in the north-western United States,

  where they have already injected 1000 tonnes of pure carbon dioxide into the

  Columbia River basalt formation near the town of Wallula.68 How it might play

  out in the longer term is unknown. Could the porous basalt become plugged

  with carbonate minerals near the injection site, blocking the spread and capture of carbon dioxide? Encouraging though these findings are, a safe solution for

  permanent carbon dioxide sequestration in this way still seems a long way off.

  Even if technical hurdles could be overcome, the financial hurdles are, at pre-

  sent, impossibly high.

  Many understandably question the enormous scale of investment in infra-

  structure required to extract massive amounts of carbon dioxide from the atmos-

  phere and the burden this would place on future generations.69 Others raise

  concerns ove
r the large tracts of land that might need to be set aside for planting and harvesting bioenergy crops by the second half of the twenty-first century as a potential alternative to fossil fuels.70 And what about the water demands and

  energy costs involved in making fertilizers to grow the energy crops? Is there a

  better way? A few years ago, a team of us proposed another approach, this time

  adopting managed croplands for carbon capture and storage by utilizing them to

  weather silicate rocks and, in particular, basalt.71 Amending soils of managed

  croplands with crushed fast-reacting silicate rocks could accelerate their chemical breakdown, pulling carbon dioxide from the air into soils and, eventually, the

  oceans, to cool the planet, mimicking the bioengineering actions of trees in the

  Devonian. These processes also release nutrients that fertilize crop growth. And, as crops take up dissolved silica released from weathered rocks, they build tougher cells and prime their immune systems, giving protection against herbivore pests

  and microbial diseases. Such benefits could lower agricultural fertilizer and pesti-cide usage and costs to improve the profit margins of farmers.72

  With nearly 11% of the terrestrial surface annually managed for crop produc-

  tion, this could offer an opportunity to deploy a means of carbon sequestration

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  on a large scale within a decade or two, and also improve food security. Rapid

  deployment is important if we are to use technologies to significantly draw down

  carbon emissions by the latter part of this century. Undertaken carefully to avoid undesirable consequences, a well-designed programme might also restore soils,

  improve crop yields, and conserve geological fertilizer resources, especially rock phosphate. It could also benefit the marine environment by lowering carbon

  dioxide levels and generating soluble alkalinity to help counter ocean acidifica-

  tion, which threatens coral reefs and marine fisheries. Ocean acidification occurs when carbon dioxide dissolves in the seawater to form carbonic acid, lowering pH

  levels and making the water more acidic. Over the past thirty years, the ocean’s

  acidity has jumped by 30% and continued acidification may cost the global econ-

  omy, including loss of fisheries harvest, up to $1 trillion a year by 2100.73

  Would this ambitious and innovative scheme be feasible, or even desirable? On

  the feasibility question, arable farming is already equipped for application of lime and fertilizer granules, making annual applications of ground basalt at scale

  possible. Application rates would likely have to exceed those used in typical liming operations, but the demand for reactive silicate rocks if rolled out globally would be huge. Recycling massive quantities of freshly produced plant nutrient-containing artificial silicates74 could help meet the demand; exploiting legacy reserves that have accumulated over time would help further. These materials include basic iron and steel slag, which have a long history of farm use in place of lime.75 Increased construction and building activities in Brazil have promoted the exploit ation of basaltic reserves, and interest is growing in recycling accumulating fine basalt

  dust waste as an agricultural fertilizer. If necessary, mining wastes could be sup-plemented with substantial silicate rock resources. There is no lack of basalt formations on land. Basalt is one of the most common rock types on Earth, covering

  around 10% of the land surface.

  Like other potential large-scale strategies for removing atmospheric carbon

  dioxide, enhanced weathering on land requires further research, development,

  and demonstration. If proven effective, and environmentally sound, significant

  potential exists for meaningful large-scale deployment to capture atmospheric

  carbon dioxide. Extensive deployment of any atmospheric carbon dioxide

  removal approach has to be socially and environmentally acceptable and

  requires risk assessment, public participation, and transparency. To be clear,

  though, this will not solve the problem of climate change. Drastic near-term

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  emission reductions are required and delaying them makes the problem pro-

  gressively harder to solve.

  Taking control of the global biogeochemical cycles that have shaped Earth’s

  history to clean up our atmospheric carbon pollution and cool the planet is a

  formidable and unwanted challenge. Yet continued emissions will force society

  to consider expensive, arguably implausible, industrial-scale carbon clean-up

  operations to stabilize climate, with unknown ecological, environmental, and

  social consequences. Or face growing and alarming climate impacts including

  intensifying droughts, heat-waves, and storms. Trees began bioengineering

  planetary climate millions of years ago in the Devonian, but back then they had

  time on their hands. Our current crisis is urgent and unfolding at a time when

  global food demand will more than double before the end of the century.76 Can we

  sustainably feed a crowded planet, preserve the wonderful diversity of life on

  Earth, and stabilize the climate? These are the pressing challenges facing human-

  ity that we consider in Chapter Eight.

  8

  EDEN UNDER SIEGE

  ‘Man is everywhere a disturbing agent. Wherever he plants his foot, the harmonies of nature are turned to discord.’

  George Perkins Marsh, Man and Nature, 1864

  Peter H. Raven delivered his case in a succession of quick-fire staccato sen-

  tences, each a condensed nugget of startling information giving you pause

  for thought. He maintained his rapid-fire delivery for an hour and received a

  standing ovation for his address from an appreciative, if stunned, audience. His

  take-home message hit you straight between the eyes: the world of plants is

  beautiful and fascinating, but it is facing unprecedented threats. In fact, all of nature is in serious trouble. Worldwide, Earth’s biodiversity is declining at

  alarming rates and showing no sign of slowing.1 Vulnerable plants and animals

  are fleeing and disappearing under the continent-wide shadow of humanity.

  Raven, Director of the Missouri Botanical Garden2 for forty years, and world-

  leading advocate of biodiversity conservation, was speaking in Melbourne in

  2011, at the 11th International Botanical Congress, one of the eagerly anticipated meetings of thousands of botanists from all over the world that takes place

  every six years.3

  Put bluntly, the grim state of nature is our fault. Humans are a ridiculously successful species of primate, with our population growth tied to increasing agricultural output for over 10 000 years.4 Between 1900 and 2000, the world

  population grew from 1.7 billion to 6 billion, supported by a six-fold increase in agricultural production made possible by nitrogen fertilizers synthesized by

  the Haber–Bosch process, alongside other advances in science and medicine.5

  Nitrogen fertilizers nourish the crops, and the animals fed on crops, which we

  consume to give us nine-tenths of the essential amino acids needed to build

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  proteins. This holds true in developed and developing nations of the world including China, Egypt, and Indonesia. As the Czech-Canadian scientist and policy ana-

  lyst Vaclav Smil reminds us, ‘when you travel to Hunan or Jiangsu, through the

  Nile Delta, or the manicured landscapes of Java, remember that the children run-

  ning around or leading water buffalo got their body proteins via the urea their

  parents spread on fields, from the Haber–Bosch synthe
sis of ammonia.’

  World population is currently 7.6 billion, having increased by some 80 million

  annually for the past 40 years.6 According to United Nations forecasts,7 world

  population will increase to over 9 billion by 2050 and a little over 12 billion by 2100. Analysts suggest there is little prospect of an end to world population

  growth this century without unprecedented declines in fertility throughout sub-

  Saharan Africa, a region experiencing fast population growth. If the population

  of Africa grows by billions, it could lead to severe resource shortages, and pos-

  sibly reductions in population size through mortality or fertility effects. Globally, feeding a world population of 12 billion by 2100 brings with it daunting challenges in terms of food, water, and energy security, and an escalating threat to

  biodiversity.8

  Continued growth in the human population and our unquenchable demands

  for sybaritic lifestyles are driving unsustainable exploitation of the Earth’s natural resources. As our per capita demand rises, we degrade the vital ecosystem processes that constitute our planet’s life support system.9 No aspect of the Earth is untouched by human actions. Pressure to feed the planet by harvesting the biosphere has seen nearly 5 billion hectares of the Earth’s land surface converted to agricultural land.10 Dendritic transport networks dissect and fragment even more

  of the landscape, and ~43% of all land is now under the direct influence of

  humans—30% of wilderness areas in the Amazon have been lost and 14% in

  Africa.11 Indeed, deforestation, over-hunting, and invasive species are still the dominant drivers of species loss.12

  But alongside deforestation brought about by the continued expansion of agri-

  cultural land into pristine forests emerges the threat of climate change resulting from exploitation of fossil fuels to meet rising energy demands. Combustion of

  fossil fuels for energy releases 36 billion tonnes of carbon dioxide into the atmosphere annually,13 and has raised the concentration of carbon dioxide above 400

  parts per million for the first time in human history, and probably in over 20 million years.14 Already, the accumulation of carbon dioxide and other human-caused

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  greenhouse gases is warming the planet, melting ice sheets, glaciers, and perma-