When researchers scan the global horizon, over fishing, 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.

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. Last week, 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 on the issue.

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 emerged out of discussions with political and business leaders, scientists, and NGOs 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 around the globe. By 2050, it estimates that the highly global approach 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.

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. People must begin to manage ecosystems in ways that ensure they will receive the benefits ecosystems provide. “But, 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.” — The Christian Science Monitor