During the 20th century, the world’s population nearly quadrupled, from 1.6 billion people in 1900 to 6 billion by century’s end. In that same period, the world’s gross domestic product ballooned from $1.98 trillion to over $28 trillion (both in 1990 dollars), according to author John R. McNeill.

Throughout this period of unprecedented economic expansion and population growth, humanity also transformed the earth. “This is the first time in human history that we have altered ecosystems with such intensity, on such scale, and with such speed,” writes Mr. McNeill in his book “Something New Under the Sun.”

Vertebrate numbers are down by one-third since the 1970s, according to the WWF. And between 20 and 30 percent of plants and animals are in danger of extinction with the temperature increases that are likely this century, says the Intergovernmental Panel on Climate Change.

The plight of other living things aside, scientists worry that humanity’s demands on – and disruption of – natural systems threaten their very ability to support people. Scientists increasingly stress the need for active conservation – not just putting bits of nature off limits, but restoring degraded ecosystems. The question is: Can ecosystems recover after such major disturbances?

A new analysis in the June issue of the journal PLoS ONE finds that, if societies commit to cleanup and restoration, ecosystems can recover faster than previously thought.

Surveying 240 studies, scientists at the Yale School of Forestry & Environmental Studies found that the speed of recovery depended upon the type of ecosystem and the growth rate of the organisms within it. Forests recovered within 42 years, but ocean floors in less than a decade. Polluted ecosystems – those plagued by oil spills, mining, trawling, or invasive species – could recover in just five years. Only 15 percent were deemed beyond recovery.

The findings seem to contradict the popular notion that ecosystems take centuries or even millenniums to recover – boosting the rationale for proactive conservation.