When researchers scan the global horizon, overfishing, loss of species habitat, nutrient run-off, climate change, and invasive species look to be the biggest threats to the ability of land, oceans, and water to support human well-being.
Yet "there is significant reason for hope. We have the tools we need" to chart a course that safeguards the planet's ecological foundation, says Stephen Carpenter, a zoologist at the University of Wisconsin, Madison. "We don't have to accept the doom-and-gloom trends."
That's the general take-home message in an assessment of the state of the globe's ecosystems and the impact Earth's ecological condition has on humans.
Thursday, officials released a five-volume coda to the UN's Millennium Ecosystem Assessment, an ambitious four-year attempt to explore the relationship between the environment and human development. Summary reports of the findings as they affected four international environmental treaties were released last year. These new volumes represent the detailed information that underpins the earlier reports.
In the process, it outlines four plausible ways the planet could develop politically, economically, and socially by 2050, and the effect they would have on people and the environment.
The pathways for political and economic development the authors use - ranging from a relatively wide-open global system to a circle-the-wagons, fragmented world - emerged out of discussions with political and business leaders, scientists, and nongovernmental organizations worldwide. The authors then drew on the latest research to estimate the impact of these paths. The assessment was conducted by 1,360 researchers from 95 countries.
By 2050, it estimates that the highly global approach - with liberal trade policies, and concerted efforts to reduce poverty, improve education and public health, yet respond reactively to environmental issues - could yield the lowest population growth and the highest economic growth. But the environmental scorecard would be mixed.
In a fragmented world that focuses largely on security and regional markets and takes a reactive approach to ecological problems, economic growth rates are the lowest and the population is the highest of the four pathways.
Two other paths, which place a greater emphasis on technology and a proactive approach to the environment, yield population growth rates somewhere in the middle, and economic growth rates that may be slow at first, but accelerate with time.
Even under the most environmentally beneficial paths, however, ecological trouble spots are likely to remain - central Africa, the Middle East, and southern Asia.
In the end, Carpenter says, "there is no optimum approach, no one-size-fits-all. It's all about trade-offs."
To put the planet on a sustainable path, he continues, the report makes clear that people must view Earth's ecosystems as one interlinked system, rather than as fragments. People must begin to actively manage those ecosystems in ways that ensure that they will receive the benefits those ecosystems provide - from blunting the surge from ocean storms and filtering water to feeding a hungry world. Indeed, with efforts now under way to develop worldwide observing systems to monitor the oceans, atmosphere, and land use, technology is moving into place to support such broad management efforts.
Unfortunately, humans have "badly mismanaged" the ecosystems that support them," says Walter Reid, a professor with Stanford University's Institute for the Environment and director of the assessment. "We need to manage for the full range of ecosystem benefits, not just those that pass through markets."
For instance, the report holds that to safeguard the availability of fresh water and encourage its more ecologically prudent use, governments could consider replacing their subsidies with a more market-based pricing system. To ensure that the poor aren't priced out of the system, Carpenter says, one could adapt South Africa's approach. It guarantees a minimum allotment per person. Once the meter ticks beyond that amount, market prices kick in.