Climate change created by human activity is seen as a relatively recent phenomenon. But is it?
There is general agreement that we now live in an epoch called the Anthropocene (or “the Age of Man”), in which there has been a new and accelerating human impact on Earth’s ecology due to industrial civilization.
Many scientists peg the era’s starting point as 50, or perhaps 250, years ago. But Erle Ellis, a professor of geography and environmental systems at UMBC, is among those who argue that the Anthropocene wasn’t born yesterday.
“Human engineering of ecosystems, which changed the biosphere at globally significant levels in order to sustain human populations, likely began 3,000 years ago or earlier,” he says.
Long before the emergence of agriculture, Ellis explains, human populations had adapted to denser populations by increasing the productivity of their land use systems, burning forests to attract game, consuming broader diets, and propagating favored species. The emergence of agriculture only continued the trend.
“We have been pushing past natural limits as long as we have been a species,” he observes.
Ellis and other colleagues have been publishing about the extended Anthropocene era and its possible implications in journals including Proceedings of the National Academy of Sciences and Trends in Ecology and Evolution.
Some of the ripple effects from taking a longer view of the Anthropocene may be surprising. Ellis observes that rises in agricultural productivity mean that humans are using far less land per person than even a century ago. As populations level off and concentrate within cities, land is increasingly being returned to other species- a process that might ultimately allow biodiversity to recover worldwide.
Widening the time frame through which we examine human effects on the biosphere and climate offers a very different view of the planetary changes we humans are responsible for.
Some observers, for instance, frame the question of global environmental change as a recent crisis: are humans now causing changes in Earth’s ecosystems that might soon trigger a global tipping point? Is the Anthropocene biosphere accelerating towards a point of no return?
While global tipping points can be difficult to recognize, Ellis points out, ecological tipping points at the local level are well studied.
“If you add nutrients to a lake,” he explains, “it will continue on as before until you surpass a certain level of nutrients. Then the lake’s ecosystem will suddenly shift to a new state – it will have reached its tipping point. The lake will go from having very clear water to very turbid water, the kinds of fish will change and the chemistry and the ecology of the lake will change almost completely. It is then very hard to get that lake back into its previous state.”
Such a planetary tipping point in Earth’s ecosystems might occur if systems across the planet responded to the same human pressures in similar ways, or if there were strong connections across continents and ecosystems that enabled ecological responses to be transmitted rapidly across the planet. Yet Ellis and other researchers have shown that there is virtually no precedent or current evidence for such processes in the Earth system.
Our planet’s animals, plants, microbes and ecosystems are greatly limited in their ability to interact at global scales by distance and barriers such as oceans and mountain ranges, and their responses to human pressures, including rapid climate change, depend largely on local conditions. As a result, even rapid changes in global climate are unlikely to produce a coherent global shift in ecology because local ecosystems respond so differently to changes in climate and other human pressures.
“Essentially, local changes aren’t acting to push each other over the edge, as is the case with tipping points,” Ellis says. “They are simply adding up to cause long-term global changes in ecology.” His work on long-term human changes in the terrestrial biosphere shows clearly that while these changes are massive, they have been sustained for millennia. While recent changes are more rapid and dramatic than ever, the longer view shows that these represent less of a crisis than a continuation of human transformation of the Earth.
Ellis argues that the big picture of human effects on the terrestrial biosphere calls for a renewed emphasis on managing ecosystems at the local and regional levels. “The overwhelming disadvantage of thinking in terms of global tipping points,” says Ellis, “is that if you think you are far from the brink, no need to act, and if you think you’ve passed the tipping point you might as well give up.” “The real question is – how can we all work together to create the planet that future generations will be proud of.”
– Nicole Ruediger