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Facing the Anthropocene. Ian Angus
Читать онлайн.Название Facing the Anthropocene
Год выпуска 0
isbn 9781583676110
Автор произведения Ian Angus
Жанр Биология
Издательство Ingram
• Mass extinctions, species migrations, and replacement of natural vegetation with agricultural monocultures are changing the nature of the biosphere.
• Sea level rises may reach ten to thirty meters for each 1°C increase in temperature, and acidification of ocean water will have severe effects on coral reefs and plankton.
The combined impact of these changes “makes it likely that we have entered a stratigraphic interval without close parallel” in the Quaternary Period, but “it is too early to state whether or not the Quaternary has come to an end.” The authors conservatively concluded that the Anthropocene should be evaluated as a new epoch, not a new period.
Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change. These changes, although likely only in their initial phases, are sufficiently distinct and robustly established for suggestions of a Holocene-Anthropocene boundary in the recent historical past to be geologically reasonable….
Sufficient evidence has emerged of stratigraphically significant change (both elapsed and imminent) for recognition of the Anthropocene … as a new geological epoch to be considered for formalization by international discussion.
This tentative “yes, there is enough evidence for the subject to be considered” received a remarkably quick response. Within months, the International Commission on Stratigraphy (ICS), the committee of the International Union of Geological Sciences (IUGS) that has responsibility for the geological time scale, asked Jan Zalasiewicz, chair of the London Society’s Stratigraphic Commission, to convene an international Anthropocene Working Group to investigate and report on whether to formally define the Anthropocene as a geological epoch.
To recommend such a change, the AWG must find that there have been major, qualitative changes to the Earth System, and that geological evidence preserved in rock, sediment, or ice uniquely differentiates layers laid down in the Anthropocene from earlier times. To define when the Holocene/Anthropocene transition occurred, they must propose either a specific stratigraphic marker (often called a “golden spike”) or a specific date, or both.5
The Anthropocene Working Group includes some 38 volunteer members from 13 countries on five continents. About half are geologists; the rest have backgrounds in other earth sciences, archaeology, and history. They hope to make recommendations during the 35th International Geological Congress in South Africa in August 2016, but formalization of the Anthropocene is not a foregone conclusion. The recommendation might be that the term should remain informal, or that a decision should be delayed. If the AWG recommends formalization, the geological time scale still will not be changed unless 60 percent majorities in the ICS and the IUGS agree.
As paleontologist Anthony Barnosky says, if the Anthropocene gets through all those hoops, “it would not only be a very big deal for earth scientists—the academic equivalent of, say, adding a new amendment to the United States Constitution—but it would also underscore that people have become a geological force every bit as powerful as the kinds of forces that turned an ice-covered Earth into a warm planet, or that wiped out the dinosaurs.”6
In his first articles on the Anthropocene, Paul Crutzen suggested that the new epoch may have begun at the time of the Industrial Revolution, when large-scale burning of coal launched a long-term rise in atmospheric concentrations of greenhouse gases. That led some observers to conclude that the issue had been prejudged, and many words have been wasted criticizing or praising Crutzen and his co-thinkers for supposedly believing (as some green theorists do) that industrialization as such is the source of all environmental problems. Actually, Crutzen was opening a discussion, not declaring a conclusion: he clearly stated that “alternative proposals can be made.”7
And in fact a dozen or more proposals for dating the Anthropocene have been made to the AWG. Though they differ substantially from one another, the starting dates under serious consideration fall into two broad groups that can be labelled Early and Recent, depending on whether the proposed starting date is in the distant past, or relatively close to the present.
An Early Anthropocene?
The first Early Anthropocene proposal was advanced by American geologist William Ruddiman, who argues that the Anthropocene began when humans began large-scale agriculture in various parts of the world between eight and five thousand years ago. Those activities, he believes, produced carbon dioxide and methane emissions that raised global temperatures just enough to prevent a return to the Ice Age.8
Other Early Anthropocene arguments suggest dating the Anthropocene from the first large-scale landscape modifications by humans, from the extinction of many large mammals in the late Pleistocene, or from the formation of anthropogenic soils in Europe. One widely discussed proposal focuses on the intercontinental exchange of species that followed the European invasions of the Americas, and proposes 1610 as a transition date. Some archaeologists propose to extend the beginning of the Anthropocene back to the earliest surviving traces of human activity, which would take in much of the Pleistocene, and others have suggested that the entire Holocene should simply be renamed Anthropocene, since it is the period when settled human civilizations first developed.
This outpouring of proposals reflects humanity’s long and complex relationships with Earth’s ecosystems—many of the proposed beginnings are significant turning points in those relationships, and deserve careful study. But the current discussion is not just about human impact: “The Anthropocene is not defined by the broadening impact of humans on the environment, but by active human interference in the processes that govern the geological evolution of the planet.”9 None of the Early Anthropocene options meet that standard, and none of them led to a qualitative break with Holocene conditions.
Even if Ruddiman’s controversial claim that the agricultural revolution caused some global warming is correct, that would only mean that human activity had extended Holocene conditions. The recent shift out of Holocene conditions, to a no-analog state, would still need to be evaluated and understood. Noted climatologist James Hansen and his colleagues write:
Even if the Anthropocene began millennia ago, a fundamentally different phase, a Hyper-Anthropocene, was initiated by explosive 20th-century growth of fossil fuel use. Human-made climate forcings now overwhelm natural forcings. CO2, at 400 ppm in 2015, is off the scale…. Most of the forcing growth occurred in the past several decades, and two-thirds of the 0.9°C global warming (since 1850) has occurred since 1975.10
The idea of an Early Anthropocene has been promoted by anti-environmentalist lobbyists associated with the Breakthrough Institute, because it supports their claim that there has been no recent qualitative change and thus there is no need for a radical response. In their view, today’s environmental crises “represent an acceleration of trends going back hundreds and even thousands of years earlier, not the starting point of a new epoch.”11
As Clive Hamilton and Jacques Grinevald explain, the Early Anthropocene argument is attractive to conservatives because it minimizes recent changes to the Earth System:
It “gradualizes” the new epoch so that it is no longer a rupture due principally to the burning of fossil fuels but a creeping phenomenon due to the incremental spread of human influence over the landscape. This misconstrues the suddenness, severity, duration, and irreversibility of the Anthropocene, leading to a serious underestimation and mischaracterization of the kind of human response necessary to slow its onset and ameliorate its impacts.12
A Recent Anthropocene?
The various Early Anthropocene proposals have been considered carefully and rejected by a substantial majority of the Anthropocene Working Group. In January 2015, over two-thirds of the members signed an article titled “When Did the Anthropocene Begin?: A Mid-Twentieth-Century Boundary Level Is Stratigraphically Optimal.”