Ecosystems, species, wild populations, local varieties and breeds of domesticated plants and animals are shrinking, deteriorating or vanishing. The essential, interconnected web of life on Earth is getting smaller and increasingly frayed. This loss is a direct result of human activity and constitutes a direct threat to human well-being in all regions of the world. Once we’re over the threshold…you’re dealing with how the Earth works, and it goes on its own ride.
CURRENT GLOBAL RESPONSE INSUFFICIENT; TRANSFORMATIVE CHANGES NEEDED
Human activities are transforming Earth’s atmosphere, ocean and land surfaces at a scale and magnitude not previously seen during the past several thousand years of human history. These changes threaten healthy planetary functions and socioeconomic well-being.
Many global change stresses on terrestrial and marine ecosystems affect not only ecosystem services that are essential to humankind, but also the trajectory of future climate by altering energy and mass exchanges with the atmosphere.
The ecological consequences of these changes are apparent in individual organisms, the communities they inhabit, and the ecosystems in which they function.
TRESHOLDS
The continuous accumulation of carbon dioxide in the planet’s oceans—which shows no sign of stopping due to humanity’s relentless consumption of fossil fuels—is likely to trigger a chemical reaction in Earth’s carbon cycle similar to those which happened just before mass extinction events
The Earth System may be approaching a planetary threshold that could lock in a continuing rapid pathway toward much hotter conditions—Hothouse Earth. This pathway would be propelled by strong, intrinsic, biogeophysical feedbacks difficult to influence by human actions, a pathway that could not be reversed, steered, or substantially slowed.
Where such a threshold might be is uncertain, but it could be only decades ahead at a temperature rise of ∼2.0 °C above preindustrial, and thus, it could be within the range of the Paris Accord temperature targets. The impacts of a Hothouse Earth pathway on human societies would likely be massive, sometimes abrupt, and undoubtedly disruptive.
Avoiding this threshold by creating a Stabilized Earth pathway can only be achieved and maintained by a coordinated, deliberate effort by human societies to manage our relationship with the rest of the Earth System, recognizing that humanity is an integral, interacting component of the system. Humanity is now facing the need for critical decisions and actions that could influence our future for centuries, if not millennia.
COMPLETELY TERRIFYING
There is significant evidence for the risk of trespassing a planetary threshold and thus, the need to create a divergent pathway should be taken seriously:
- the complex system behavior of the Earth System in the Late Quaternary is well-documented and understood. The two bounding states of the system—glacial and interglacial—are reasonably well-defined, the ca. 100,000-years periodicity of the limit cycle is established, and internal (carbon cycle and ice albedo feedbacks) and external (changes in insolation caused by changes in Earth’s orbital parameters) driving processes are generally well-known.
- we know with high confidence that the progressive disintegration of ice sheets and the transgression of other tipping elements are difficult to reverse after critical levels of warming are reached.
- insights from Earth’s recent geological past suggest that conditions consistent with the Hothouse Earth pathway are accessible with levels of atmospheric CO2 concentration and temperature rise either already realized or projected for this century.
- the tipping elements and feedback processes that operated over Quaternary glacial–interglacial cycles are the same as several of those proposed as critical for the future trajectory of the Earth System.
- contemporary observations of tipping element behavior at an observed temperature anomaly of about 1 °C above preindustrial suggest that some of these elements are vulnerable to tipping within just a 1 °C to 3 °C increase in global temperature, with many more of them vulnerable at higher temperatures (Biogeophysical Feedbacks and Tipping Cascades).This suggests that the risk of tipping cascades could be significant at a 2 °C temperature rise and could increase sharply beyond that point. A planetary threshold in the Earth System could exist at a temperature rise as low as 2 °C above preindustrial.
- the diversity within species, between species and of ecosystems, as well as many fundamental contributions we derive from nature, are declining fast. Tens to hundreds of times: the extent to which the current rate of global species extinction is higher compared to average over the last 10 million years, and the rate is accelerating
- up to 1 million: species threatened with extinction, many within decades
- the average abundance of native species in most major land-based habitats has fallen by at least 20%, mostly since 1900. More than 40% of amphibian species, almost 33% of reef-forming corals and more than a third of all marine mammals are threatened. The picture is less clear for insect species, but available evidence supports a tentative estimate of 10% being threatened. At least 680 vertebrate species had been driven to extinction and more than 9% of all domesticated breeds of mammals used for food and agriculture had become extinct by 2016, with at least 1,000 more breeds still threatened.
- 75%: terrestrial environment severely altered to date by human actions (marine environments 66%)
- 47%: reduction in global indicators of ecosystem extent and condition against their estimated natural baselines, with many continuing to decline by at least 4% per decade
- +/-60 billion: tons of renewable and non-renewable resources extracted globally each year, up nearly 100% since 1980
- 15%: increase in global per capita consumption of materials since 1980
- >85%: of wetlands had been lost by 2000 – loss of wetlands is currently three times faster, in percentage terms, than forest loss.
A NEW ERA
The Holocene lays behind us and our species is embarking upon a new period in this planetary voyage. This period is more than simply an Anthropocene; a Stabilized Earth trajectory requires deliberate management of humanity’s relationship with the rest of the Earth System if the world is to avoid crossing a planetary threshold. Many of the global change stressors that terrestrial and marine ecosystems face need to be understood not only for their impacts on ecosystem services that are essential to humankind, but also as processes that affect the magnitude and trajectory of climate change.
Humanity’s challenge then is to influence the dynamical properties of the Earth System in such a way that the emerging unstable conditions in the zone between the Holocene and a very hot state become a de facto stable intermediate state. This requires that humans take deliberate, integral, and adaptive steps to reduce dangerous impacts on the Earth System, effectively monitoring and changing behavior to form feedback loops that stabilize this intermediate state.
Technically, ethically, equitably and economically challenging it takes normative policy and institutional leadership to steer the Earth System toward Stabilized Earth. While reducing emissions is a priority, much more could be done to reduce direct human pressures on critical biomes that contribute to the regulation of the state of the Earth System through carbon sinks and moisture feedbacks, such as the Amazon and boreal forest and to build much more effective stewardship of the marine and terrestrial biospheres in general.
The negative feedback actions fall into three broad categories: reducing greenhouse gas emissions, enhancing or creating carbon sinks (e.g., protecting and enhancing biosphere carbon sinks and creating new types of sinks), modifying Earth’s energy balance (via solar radiation management) and considering eco- bioengineering technologies ( Intervention Ecology, Assisted Evolution, Genetic Rescue). For example, since coral in the Great Barrier Reef is in terminal decline, research is ongoing into how to release heat-resistant zooxanthellae, the photosynthesising symbiote of coral polyps, into the ocean.
The present dominant socioeconomic system, however, is based on high-carbon economic growth and exploitative resource use. Attempts to modify this system have met with some success locally but little success globally in reducing greenhouse gas emissions or building more effective stewardship of the biosphere.
Incremental linear changes to the present socioeconomic system are not enough to stabilize the Earth System. Widespread, rapid, and fundamental transformations will likely be required to reduce the risk of crossing the threshold and locking in the Hothouse Earth pathway; these include changes in behavior, technology and innovation, governance, and values.
Biodiversity and nature’s contributions to people are our common heritage and humanity’s most important life-supporting safety net. But our safety net is stretched almost to breaking point