According to scientists studying global environmental change, the Earth is moving out of the Holocene — the period of remarkably stable climate that began roughly 12,000 years ago — into the Anthropocene, an era in which a single species, humans, are driving the Earth’s systems.
“Can we return to the nice, steady Holocene stage where we know humanity can survive or will we be able to transition to a new, much hotter state?” asked Will Steffen, executive director of the Australian National University’s Climate Change Institute, on the first day of the Planet Under Pressure Conference in London. “We are at the cusp of some big changes. Can we turn the ship around or are we going to an uncertain future on a much hotter planet?”
The Holocene has been an era with a “nice, steady” climate, but from 1950 to 2000 scientists have graphed steep increases in carbon dioxide in the atmosphere, which is driving average global temperatures higher. When the Planet Under Pressure moderator asked for a show of hands from an audience that included 2,000 scientists, decision-makers, and others knowledgeable about global change, most were pessimistic about the future. (She didn’t poll the additional 2,000 people attending the conference online.)
But pessimism was mixed with hope, if only because of the gathering itself. Eleanor Ostrom, 2009 Nobel laureate in Economics, opened the Planet Under Pressure proceedings arguing that the conference can move the world forward to address global environmental problems, “because we have scientists from all across the sciences — biophysical and social — as well as humanities and from over 100 countries.” Three years of planning preceded the conference, intended to gather and generate science and knowledge “to navigate the Anthropocene.” The conference steering committee selected parallel sessions (about a dozen in each time slot over four days) that offer a mix of social and biophysical research, a focus on solutions to complex problems, and a broad geographic range.
As Steffen outlined in a series of slides, it’s an uphill push. Not only is CO2 in the atmosphere cutting a sharp upward curve, but average global temperatures have continued to rise, though not as steeply in the last decade. Although greenhouse gas emissions dropped during the recent recession, global emissions have fully returned to previous and rising levels.
Oceans absorb 80-90 percent of the additional heat, so the oceans too are heating. Not only are scientists worrying about carbon, they have found that the nitrogen cycle has changed even more dramatically than the carbon cycle, pouring nitrogen from fertilizer into rivers and oceans causing algae blooms and even dead zones in the ocean, and contributing to air pollution as well as global warming.
But to know whether we can return to a more stable climate, we need to know where the tipping points are and whether we have reached them. Tipping points are thresholds — if we overstep them, we move into a different condition. The Anthropocene is likely to be an era with uncomfortably warmer temperatures and extremes: draughts, coastal flooding, increased storms, loss of biodiversity.
In short, humans are creating conditions that make it difficult if not impossible for many species to adapt. “Arctic sea ice is the tipping point we’ve already lost,” Steffen explained. “The Arctic Ocean will be ice-free sometime this century.” We don’t know yet where the tipping point is for loss of the ice sheets on Greenland or the Antarctic. Steffen called them “great refrigerators slowing down the warming of the planet.” He explained that the overall ice balance on the Greenland ice sheet has been dropping from the 1990s and could reach the tipping point within the next few decades. The Antarctic ice sheet appears stable, but the west Antarctic appears to be losing mass over the last decade.
Scientists also worry about where the tipping points might be for retention of the Amazon forest and permafrost in the high latitudes. Loss of either of these will magnify the effects of global warming. Most models of the Amazon rainforest predict loss of rainfall in the coming century and with drying out of the rainforest, fires increase adding to CO2 in the atmosphere.
As for permafrost, the colder high latitudes are warming much more quickly than the temperate mid-latitudes, and as permafrost there melts, methane that has been locked in the frozen soil could be released. A 2010 paper by Catherine M. Luke and Peter M. Cox explains how further heating from microbial respiration in the soils could lead to a tipping point where the heat produced would build up faster than it can be dissipated, producing a “compost bomb.”
From the vantage point of Diana Liverman, professor of geography and development at the University of Arizona, there are some reasons for optimism. In her plenary talk, she highlighted areas of progress in slowing global climate change: “Population growth, often thought of as a key threat, is now slowing as fertility rates drop.” Energy use, while still growing, has become less carbon intensive per capita. Forests are expanding in China, south Vietnam and elsewhere in places where gross domestic product is growing (although some forest destruction has been displaced to neighboring Laos and Cambodia).
While the results of more geographically focused case studies suggest that climate impacts may be reversible, these locally positive results become lost in the global averages.
Can we reverse the loss of sea ice or avoid the tipping points on ice sheets or the Amazonian rainforest? Action to reverse the trend should have started a decade or two ago, according to Steffen, but the clock hasn’t expired. “This is the critical decade.”
For its part, the global-change research community is attempting to forge a more effective scientific voice to speak on these matters.
The organizers of Planet Under Pressure have already forwarded nine policy briefs (on topics including water, energy, food security, global health, human well-being, and governance and institutions) to government ministers who will attend the Rio+20 United Nations Conference on Sustainable Development in mid-June. They will also launch Future Earth, an umbrella organization for research on global sustainability to better connect the social and biophysical sciences into global change research, to unify the major existing global change research bodies, to work with major science funders and to link this research community with business, nongovernmental organizations, and civil society. Via Miller-McCune