(Jan. 14th, 2010) Ongoing extinctions of other animal and plant species may not excite much interest in ordinary citizens, but what about their own extinction? Could mankind so completely unbalance the planetary biosphere as to threaten its own survival? In this final report, Jeremy Garwood presents research defining the limits to viable life on earth as we know it, and the risk that Homo sapiens may become extinct for lack of future vision.
Worrying about the loss of many thousands of animal and plant species is a source of concern for people who value diversity of life on earth, whether for economic, scientific, or ethical reasons. But could the manmade processes that drive other species to extinction also take the whole terrestrial biosphere with it, consuming mankind along the way?
The 2009 UN Climate Change Conference in Copenhagen tentatively addressed the question of carbon dioxide emissions and the hope that effective coordinated action by the world’s nation states might stabilise the projected rise in temperature at the Earth’s surface. However, scientists have also been looking at other geochemical and biological parameters that have shown dramatic changes during the last two centuries of human industrialisation.
SECURING THE PLANETARY BOUNDARIES
A recent overview by Johan Rockström of the Stockholm Resilience Centre discussed the limits to “A safe operating space for humanity” (Nature, 2009, vol 461, 472-75; presented in greater detail in Ecology and Society, 2009, vol 14.32). It proposes a framework based on nine ‘planetary boundaries’ that define “safe operating” limits for the Earth’s biophysical subsystems.
The main argument is that although Earth’s complex systems sometimes respond smoothly to changing pressures, they can also react in a nonlinear, abrupt, way, rendering them particularly sensitive around threshold levels for certain key variables. “If these thresholds are crossed, then important subsystems, such as a monsoon system, could shift into a new state, often with deleterious or potentially even disastrous consequences for humans.”
The 9 processes “for which we believe it is necessary to define planetary boundaries” are: climate change, biodiversity loss, the nitrogen/phosphorus cycles, ozone depletion, acidified oceans, freshwater, land use, chemical pollution, and the amount of dust suspended in the atmosphere.
“Humanity has already transgressed three planetary boundaries.”
Of these nine subsystems, Rockstrom identifies three that are already beyond reasonable “safe” limits.
1) Climate change
Obviously, this has been the most discussed environmental parameter of the decade with heated scientific, political, economic and social debates and disputes. Rockstrom et al. distinguish two measurable factors for manmade (“anthropogenic”) climate change: the great hot air generator - atmospheric carbon dioxide concentration - estimated to have been at a pre-industrial value of 280 parts per million (ppm) by volume, and currently at around 387 ppm. Anyone who is even vaguely aware of ‘global warming’ will know, this is considered to be beyond a reasonable threshold for short-term climate stability. A proposed boundary limit of 350 ppm already requires direct changes to industrial practices, but not all nations appear to agree on the economics of such action. The second parameter for climate change is ‘radiative forcing’, expressed as watts per metre squared. Here, they measure the rate of energy change per unit area of the globe at the top of the atmosphere. Taking a pre-industrial level of zero, the current value is 1.5, but should be reduced to a boundary threshold of 1.
2) Rate of biodiversity loss
Part 1 of this series outlined the concerns that current levels of species extinction might be equated with a ‘sixth mass extinction event’. Rockström quotes a historical background extinction rate for marine animals of 0.1 to 1 extinction per million species per year, and for mammals, of 0.2 to 0.5. Current estimates are at least 100 extinctions per million species per year. However, as the authors modestly explain, “from an earth boundary perspective, setting a boundary for biodiversity is difficult.” Although it is now accepted that a rich mix of species underpins the resilience of ecosystems, little is known quantitatively about how much and what kinds of biodiversity can be lost before this resilience is eroded. However, they set a boundary at ten times the background rate (i.e. 10 extinctions per million species per year) since “we can say with some confidence that Earth cannot sustain the current rate of loss without significant erosion of ecosystem resilience.”
3) Interference with the Nitrogen and Phosphorus cycles
The rise of modern agriculture has been built on the use of chemical fertilisers. However, at the planetary scale, the amounts of nitrogen and phosphorus activated by humans are so large that they significantly perturb the global cycles for these two elements. Manufacturing fertilizers for food production and cultivation of leguminous crops currently converts around 120 million tonnes of nitrogen gas in the atmosphere into reactive forms – more than the combined effects of all Earth’s terrestrial processes! Much of this reactive nitrogen ends up in the environment, polluting waterways, accumulating in land systems and adding gases to the atmosphere – after carbon dioxide, nitrous oxide is one of the principal greenhouse gases. Freshwater and marine ecosystems have been heavily disrupted – clear water becomes turbid due to abundant growth of algae and microorganisms, lack of dissolved oxygen (anoxia) kills off fish etc. Rockstrom suggests a boundary limit for fixation of atmosperic nitrogen at 35 million tonnes, barely a quarter of current levels.
Meanwhile, phosphorus is a fossil mineral, mined from rock, used in fertilisers, washing powders, toothpastes, etc. Of the 20 million tonnes mined annually, around 9 million tonnes end up in the oceans – some 8-fold the natural background rate. A major concern here is that, associated with the excessive influx of reactive nitrogen, a critical threshold of phosphorus may be reached that results in large-scale anoxic events due to uncontrolled microbial growth, that eventually kill off most marine life. For a change, the planetary boundary is higher than existing rates, but not by much – 11 million tonnes a year - representing 10-fold the pre-industrial levels.
RISING NEWCOMERS
The remaining six boundaries are also a cause for concern, not least for lack of scientific data.
4) Ocean acidification
This is measured by the global mean saturation state of aragonite (crystalline calcium carbonate) in surface sea water. Human industrial activity has raised overall ocean acidity resulting in a fall in aragonite concentrations to 85% of pre-industrial levels. The clearest result of this is the conversion of coral reefs into algae-dominated ecosystems. Other ecosystem effects from changes in the marine carbon sink are still uncertain but a boundary is suggested at no lower than 80% of pre-industrial levels.
Global freshwater use
Humans are now the dominant factor in the global freshwater cycle, adjusting river flow, and the spatial patterns and seasonal timings of vapour flows. The flow of freshwater is critical to many ecosystems but also affects rainfall levels through moisture feedback. Human withdrawal of freshwater from the global cycle already affects many ecosystems. It is currently around 2600 cubic km per year, representing upto a fifth of total available blue water. A critical boundary level is proposed at 4000 cubic km per year.
5) Change in land use
Primarily for agriculture. Currently 12% of global land cover is converted to cropland. A planetary boundary of 15% is proposed.
6) Chemical pollution
Everyday sees more news about the potentially toxic effects of a wide range of chemicals both on human health and upon the general environment. The US Environmental Protection Agency estimates that there are over 80,000 different chemicals commercialised in the global market. We are a long way from establishing data for the toxicity levels of all these chemicals in all the forms in which they may be presented to the environment. However, some chemicals are persistant pollutants with clear toxic effects, like mercury, dioxins, or the pesticide, DDT, for which limits have already been set. But, perhaps an alternative measure and response would be to identify the unacceptable, long-term, large-scale effects of chemical pollution on living organisms.
7) Atmospheric aerosol loading
The global concentration of most aerosols has doubled since the pre-industrial era, affecting Earth’s radiation, cloud formation and moisture levels. For example, there has been a shift in the seasonal timing and location of the Asian monsoon rains. There are also direct effects on human health through exposure to fine dust particles. However, since these are subject to large regional rather than global variations, a planetary limit has not yet been determined.
8) A positive note: Stratospheric ozone depletion
This measures the amount of ozone in the upper atmosphere that protects us all from lethal doses of UV radiation. The global response to this represents a major environmental success! “The appearance of the Antarctic ozone hole was a textbook example of a threshold in the Earth System being crossed—completely unexpectedly.” The subject of intensive scientific research during the 1980s, it was accepted that the major cause for this was the human use of ozone-depleting substances. Unusually rapid international collaboration resulted in the complete removal of such substances from industrial use. By 2005, the stratospheric concentration of ozone-depleting gases had decreased by 9% from their peak values in 1992–1994, halting declines in ozone levels from latitudes 60°S to 60°N. However, once started, it can take time for global processes to readjust – ozone losses in the Antarctic and the Antarctic ozone hole seem likely to continue for several decades. Nevertheless, this planetary boundary has stabilised at a ‘safe’ level.
9) Feeding Humanity
A planetary boundary not presented in Rockstrom’s analysis is that for a healthy, well-fed human population. Just how many people can planet Earth support? And with what kind of lifestyle? Constant pressures to grow ever more food for a growing human population is intimately linked to several of Rockstrom’s boundaries – notably nitrogen/phosphorus cycles, the appropriation of freshwater and land, and the loss of biodiversity through extinction.
Development economist, Jeffrey Sachs, has been prominent in advocating the goal of a halving of extreme human poverty by 2015. However, in a recent article in Science, he and a host of distinguished co-authors discuss the inveitable links between human poverty alleviation and the reduction in the rate of biodiversity loss (“Biodiversity Conservation and the Millenium Development Goals”, 2009, vol 325, 1502-3). For example, “reducing population pressure by promoting voluntary reductions in fertility in impoverished regions could support conservation of biodiversity and faster poverty alleviation.”
However, the political and economic factors that affect food production and distribution in the poorest countries often increases the vulnerability of ecosystems, like rainforests. Hence their call for an urgently-needed ‘Intergovernmental Platform on Biodiversity and Ecosystem Services’ to complement the existing ‘Intergovernmental Panel on Climate Change’ in coordinating the global efforts of scientists, economists and policy-makers towards a coherent and effective range of solutions.
What price Human Survival?
What happens if it all goes wrong? In “Reducing the Risk of Human Extinction” (Risk Analysis, 2007, vol 27, 1335-44), Jason Matheny from John Hopkins University, reminds us that the greatest fear of human extinction during the last century came from ‘uncontrolled’ (and uncontrollable) warfare. At the height of the US-Soviet ‘Cold War’, there was a very real possibility that a rash decision or error of judgement would see the entire planet getting very hot, very fast!
Although the threat of nuclear war has since been modified (and dispersed…), Matheny lists other disasters that worried observers fear could result in the extinction of the human species. Notably, bioterrorism (formerly referred to as ‘biological warfare’)– e.g. the deliberate manipulation of a virus that would possess a lethality beyond anything previously seen. In 2007, US biodefense received $5 billion “to develop and stockpile new drugs and vaccines, monitor biological agents and emerging diseases, and strengthen the capacities of local health systems to respond to pandemics.”
Nevertheless, Earth’s last Mass Extinction Event was likely due to the random collision of a huge asteroid into Mexico (discussed in Part 1). Although this happened some 65 million years ago, stargazers are passing sleepless nights convinced that another big rock could arrive any day now.
However, despite all these threats, Matheny says that “virtually nothing has been written about the cost effectiveness of reducing human extinction risks. Maybe this is because human extinction of reducing seems impossible, inevitable, or beyond our control. Maybe human extinction seems inconsequential compared to the other social problems to which cost-effectiveness analysis has been applied, or maybe the methodological and philosophical problems involved seem insuperable.”
Cost-effectiveness analysis might be applied to the proposed solutions for reducing extinction risk. Several of these solutions have already featured in science fiction, notably the colonisation of other planets to spread the risk that an asteroid (or other threat) might wipe out life on Earth. “More cost effective” might be the construction of a very strong survival bunker here on Earth that could resist “nuclear war, asteroid strikes, and climate change”. With space for say, a hundred young survivors, equipped with enough food, water and air, perhaps the species could hold on long enough for a return to a less hostile environment.
But just how much money are we prepared to invest in preventing human extinction? What really worries Matheny is the economic “discounting” of future generations: “disagreement does not center on whether future lives matter, but on how much they matter.” In economic theory, a good enjoyed in the future is worth less than a good enjoyed now. This is because “there is diminishing marginal utility from consumption” meaning that we discount the value of something the further we project into the future, knocking a few percent off its value each year. Okay, says Matheny, this idea may hold true for intergenerational transfers of most economic goods, but surely here we can make an exception, since “there is no diminishing marginal utility from having ever existed.”
However, such ‘discounting’ could be justified by our uncertainty about the ongoing existence of future generations: “If we knew for certain we would all die in 10 years, it would not make sense for us to spend our money on asteroid defense. It would make more sense to live it up, until we become extinct. A discount scheme would be justified that devalued (to zero) anything beyond 10 years.”
In conclusion, he notes that extinction risks are market failures where an individual enjoys “no perceptible benefit from his or her investment in risk reduction”. This means that prevention of human extinction, like climate change, biodiversity loss, and alleviation of human poverty is one of those topics that cannot effectively be dealt with by standard economic reasoning – it needs to be discussed by the largest possible intergovernmental forums in the hope that the ‘common good’ can overcome the limitations of short-term economic interests.