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The Anthropocene and the nine thresholds
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Energy and agriculture are pushing the Earth to its limits.
The Stockholm Resilience Center published a report which outlines nine Earth systems thresholds that humanity is in danger of crossing. "The result could be irreversible and, in some cases, abrupt environmental change, leading to a state less conducive to human development." (Time)
Critics of the report noted that the notion of planetary boundaries are 'devoid of serious content' because they may lead to giving readers the idea that scientists understand the way the biosphere functions better than we actually do; the truth is that we cannot replicate any of the biosphere's functions adequately. Rockstrom's intentions, though, are rooted in opening up a discussion surrounding humanity's colletive impact upon the global biosphere. "We have reached the planetary stage of sustainability, where we are fiddling with hard-wired processes at the global Earth-system scale". He then goes on to ask, "What are the Earth-system processes that determine the ability of the planet to remain in a stable state?"
Scientific American reports, "The scale of mankind's impact on the globe is becoming more and more apparent: We have achieved a species extinction rate to rival great extinction events of all geologic time as well as a rapidly acidifying ocean, dwindling ice caps, and even sinking river deltas, a new study from scientists at the University of Colorado at Boulder reveals. No wonder then that some geologists and other scientists have dubbed the modern epoch the Anthropocene".
Rockstrom is part of a team of 28 international scientists that began making the point that "we have to conceive of many tipping points at once". They create, what they call, a 'safe operating space' within planetary boundaries that if humanity continues to push up against will result in planet-scale catastrophes on a multitude of levels.
The report outlines nine thresholds. The idea behind the nine thresholds is "to say, ‘Let’s put up some guardrails,’” says Robert Costanza of the University of New Hampshire. “Maybe the guardrails are for a slope we could have taken and survived, but maybe not. We owe it to human civilization to be more careful." Here are the nine thresholds: (from Yale Environment 360 and Scientific American):
Climate change: The report found that we should keep carbon dioxide levels no higher than 350 parts per million. Before the Industrial Revolution, the concentration was at about 280 parts per million, but today we’re up to 387. 350 ppm is equal to a total increased warming of one watt per meter squared; current warming is roughly 1.5 watts per meter squared. Current CO2 levels are higher than they’ve been in at least the past 800,000 years. Ice caps and glaciers are retreating.
Ocean acidity: As we release carbon dioxide into the atmosphere, some of it goes into the oceans and makes it more acidic. According to recent surveys, the ocean is now acidifying 100 times faster than at any time during the past 20 million years. Ocean acidification may have serious impacts on coral reefs and associated ecosystems. In addition, the large scale depletion of aragonite-forming organisms (corals, many molluscs, as well as single-celled plankton) would be a major disturbance in marine ecosystems, the consequences and impacts of which are highly uncertain. The Nature study estimates that we have not yet reached the point where acidity may cause ecological collapse, but we are close.
The ozone layer: Humanity nearly crossed this threshold by destroying the ozone layer with chlorofluorocarbons, but we recognized the crisis in time and banned chlorofluorocarbons through the Montreal Protocol, allowing the ozone layer to slowly recover. However, the Antarctic ozone hole is expected to exist for some decades, and Arctic ozone losses may continue for the next decade or two. On balance, the case of stratospheric ozone is a good example where concerted human effort and wise decision making seem to have enabled us to stay within a planetary boundary. Some people use this success story as an example of what humanity can do when they put their collective minds to it.
Freshwater use: An estimated 25% of the world’s river basins run dry before reaching the oceans, due to use of freshwater resources in the basins. Global manipulations of the freshwater cycle affect biodiversity, food and health security, and ecological functioning such as provision of habitats for fish recruitment, carbon sequestration, and climate regulation, undermining the resilience of terrestrial and aquatic ecosystems. Threats to human livelihoods due to deterioration of global water resources are threefold: First, the loss of soil moisture resources (green water) due to land degradation and deforestation, threatens terrestrial biomass production and sequestration of carbon; second, use of and shifts in runoff (blue water) volumes and patterns threaten human water supply and aquatic water needs; and third, impacts on climate regulation due to a decline in moisture feedback of vapor flows (green water) affects local and regional precipitation patterns. The remaining safe operating space for water may be largely committed already to cover necessary human water demands in the future.
The movement of nitrogen and phosphorus: As we spread fertilizer on farmland and burn coal, we are pumping far too much nitrogen into the environment. Human activity releases 140 million tons of nitrogen, much of which ends up polluting rivers, lakes, and oceans potentially pushing their ecosystems into irreversible changes. At most, the scientists argue, less than 35 million tons of nitrogen would be a safe boundary. Phosphorus, the scientists claim, is not so pressing of an issue.
The amount of land used for crops: Feeding the world's 6.7 billion people, heading towards nine billion by 2050, is already straining the Earth's ecosystems. Humanity may be reaching a point where further agricultural land expansion at a global scale may seriously threaten biodiversity and undermine regulatory capacities of the Earth System (by affecting the climate system and the hydrological cycle). As a planetary boundary we propose that no more than 15% of the global ice-free land surface should be converted to cropland. As more people in the developing world begin to eat more like people in the developed world more land and fertilizer will be needed. Then there's the impact that biofuel production will have on land use. In this area, we don't have much room to spare.
Biodiversity: During most of the history of life, species have become extinct at a slow, fairly regular pace. As old species have become extinct, new ones have been evolving. There have been times when many species have become extinct at a much faster rate, and these pulses have sometimes ushered in a global collapse of ecosystems. The Nature paper proposes that to avoid collapse, the extinction rate cannot rise above 10 times the long-term background rate. Today, however, scientists estimate that the extinction rate is 100 to 1,000 times higher than the long-term background rate.
Aerosols (haze and other particles): The complexity of aerosols, in terms of the large variety of particles involved, with different sources, impacts, and spatial and temporal dynamics, makes it difficult to define a planetary boundary above which effects may cause unacceptable change. The details of this section are still to be determined by the report.
Chemical pollution: Primary types of chemical pollution include radioactive compounds, heavy metals and a wide range of organic compounds of human origin. Chemical pollution adversely affects human and ecosystem health, which has most clearly been observed at local and regional scales but is now evident at the global scale. Details here are also TBD.
The scientists say that we have already crossed the threshold for climate change, the movement of nitrogen, and biodiversity and are heading toward unknown phenomena related to these issues; the other areas of concern highlighted in the report show humanity quickly approaching the thresholds associated with freshwater use, ocean acidity, and land use with a certain crossing over in the 21st century if no action is taken to limit humanity's impact.
The idea that Earth is an interwoven unit of interrelated systems is not a new idea, but thinking about humanity's impact on a planetary scale taking into account all of our actions is quite new. Instead of just thinking about climate change in terms of CO2, we need to start considering emissions in relation to ocean acidification and then relating both to biodiversity collapse. When we think about energy production, we need to consider water use as a dominant factor. Agriculture expansions need to consider not only water use, but also the nitrogen fertilizers that are creating additional strains. We have already started questioning the use of land to produce fuel for our cars as not the best use of resources.
Are we capable of preventing the collapse of the environment that supports our species' existence; are we truly an intelligent species?
The scientists who produced this report hope that we are, which is why they prepared protective guardrails to keep us within bounds. They have acknowledged that their figures will be open to interpretation over the coming months as the facts and figures are reviewed by peers, but they hope that they have opened up a discussion around humanity's full impact upon the planet.
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