Ecology

Fires have always burned in the planet’s temperate forests. They hasten regeneration by thinning undergrowth and fertilizing the soil. Before there were humans to flick cigarette butts into the brush, there were lightning storms and cyclical droughts.

For almost a decade, residents of some Pennsylvania counties have complained that the natural gas prospectors nearby have contaminated their water. Locals say that after the fracking for gas began, the water made them sick, that it turned brown, even that it became flammable.

Legislation like the Clean Water Act has helped check the effluent flowing into rivers and streams. Though that fight is far from over, a new, all-too-modern danger has meanwhile seeped invisibly into waters around the world: legal and illegal drugs. And their effect on the ecosystem is poorly understood.

Each year as the weather warms, crowds of families and tourists flock to the beaches. People sometimes don’t realize the risk they take when they enter the ocean, a vast aquatic habitat. Newsrooms in coastal communities are well aware that when humans and wildlife interact, the results can be tragic – especially when sharks make an appearance. Even a minor run-in with a shark can send someone to the emergency room for surgery and stitches.

Beginning in the 1940s, the “green revolution” increased crop yields around the globe through seed hybrids, increased irrigation and new fertilizers and pesticides. The result was “agricultural intensification,” getting more grain from each acre of land. While the increase in productivity is unquestioned, drawbacks exist as well — negative environmental and health consequences from pesticide use, increased water demand, reductions in biodiversity and increased vulnerability to future famines.

Just as nations have different levels of population, industrial and agricultural production, income and education, so they have varied environmental impacts. Such impacts aren’t stable over time: Countries’ use of resources and generation of wastes often rises as production grows, then may fall as cleaner technologies and better environmental practices come into use. While this trend has been theorized, empirical evidence has been mixed.