6 Ways We're Already Geoengineering Earth

Scientists and policymakers are meeting this week to discuss whether geoengineering to fight climate change can be safe in the future, but make no mistake about it: We’re already geoengineering Earth on a massive scale. From diverting a third of Earth’s available fresh water to planting and grazing two-fifths of its land surface, humankind has […]
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Scientists and policymakers are meeting this week to discuss whether geoengineering to fight climate change can be safe in the future, but make no mistake about it: We're already geoengineering Earth on a massive scale.

From diverting a third of Earth's available fresh water to planting and grazing two-fifths of its land surface, humankind has fiddled with the knobs of the Holocene, that 10,000-year period of climate stability that birthed civilization.

The consequences of our interventions into Earth's geophysical processes are yet to be determined, but scientists say they're so fundamental that the Holocene no longer exists. We now live in the Anthropocene, a geological age of mankind's making.

"Homo sapiens has emerged as a force of nature rivaling climatic and geologic forces," wrote Earth scientists Erle Ellis and Navin Ramankutty in a 2008 Frontiers in Ecology paper, which featured their redrawn map of the human-influenced world. "Human forces may now outweigh these across most of Earth's land surface today."

Draining the Rivers

Of all the fresh water accessible in lakes, rivers and aquifers – what scientists call "blue water" – humankind uses about one-third every year. A fourth of Earth's river basins run dry before they reach the sea.

At local scales, this changes weather patterns. The Three Gorges Dam on China's Yangtze River for example, seems to be causing temperatures in its valley to drop, which in turn reduces rainfall. The draining of Kazakhstan's once-vast Aral Sea has made regional temperatures hotter in summer and colder in winter, and rain now rarely falls.

Whether regional changes in turn have global consequences remains to be seen.

Images: 1) Aral Sea in 2006/European Space Agency. 2) Aral Sea in 1973/U.S. Geological Survey.

Painting Earth Black

In 500 million households, mostly in Asia and Africa, cookfires are fed by wood, coal and animal dung. Smoke carries particles of what is known as "black carbon" into the atmosphere, where they form a heat-absorbing layer; raindrops form around the particles, and when they fall, black carbon ends up absorbing heat on the ground, too.

It's estimated that half of a 3.4-degree-Fahrenheit rise in Arctic temperatures over the last century is a result of black-carbon pollution, and it may also have altered weather patterns in a way that's reduced rainfall over South Asia and West Africa. Black carbon is also causing Himalayan glaciers to melt, threatening water supplies for hundreds of millions of people.

Image: Purple indicates areas of high black-carbon density, August 2009/NASA

The Infinite Farm

About 12 percent of Earth's land surface is now used for crops. Some of the consequences are difficult to predict. It's hard to know, for example, how agriculture in the Great Plains has affected weather. Other consequences are more obvious. Deforestation of the Amazon rain forest disrupts regional cycles of evaporation and condensation, raising the possibility that Earth's lungs could become a savanna. Should the Amazon rain forest lose much of its carbon dioxide-absorbing capacities, planetary temperatures will rise.

More immediately, fertilizers used in farming have injected vast amounts of nitrogen and phosphorus into regional environments. About 120 million tons of nitrogen are removed from the atmosphere each year and converted into fertilizer-friendly "reactive" forms, while 20 million tons of phosphorus are mined from the ground. In both cases, that's far more than would enter the biosphere naturally, and most of it is carried by streams and rivers to the sea, where it fuels rapidly growing marine dead zones.

Image: The conversion of southeastern Amazon rain forest (red) to farms and ranches (green)/NASA

Wiping Out Reefs

Of all the extinctions now taking place, perhaps the most dramatic is that of coral reefs, the rain forests of the oceans and a foundation of many marine ecosystems. As a result of pollution, climate change, overfishing and ocean acidification, one-quarter of global reef cover has been lost in the last 50 years and one-third of reef species are endangered.

The loss of corals and the animals that depend on them doesn't just threaten fishing. From a geophysical perspective, ecosystems are biological mechanisms that regulate flows of nutrients and energy. Stripped-down ecosystems — like the once-rich northwest Mediterranean, now dominated by bacteria and jellyfish — can't always do the job. Some scientists think that massive ocean extinction events in the past caused Earth's carbon cycle to fluctuate wildly for millions of years afterwards. Marine ecosystems lost their regulatory abilities, and changes in climate and weather followed.

There have been five planetary extinction events in the last half-billion years. The sixth is happening now.

Image: Coral bleaching in Australia's Great Barrier Reef/Matt Kiefer, Flickr

The Plastic Revolution

Human industry has led to the invention of chemicals that were unknown in Earth's history, and can remain active in the environment for thousands of years. These include compounds used in pesticides, and especially in plastic, some 60 billion tons of which are produced every year.

At high doses, these chemicals can disrupt animal endocrine systems, cause cancer and alter reproduction. At low doses, their effects aren't known, but may involve subtle and widespread stresses that ultimately change the composition of ecosystems.

The United Nations estimates that there are 47,000 pieces of plastic in every square mile of Earth's oceans. Low levels of organic pollutants and plastic-derived endocrine disruptors have been measured all over the world, even in areas where they've never been used, such as Antarctica.

Image: Plastic inside a decomposing Laysan albatross chick/Duncan Wright

Altering the Atmosphere

The economic engine of the Anthropocene is literally fueled by pulling carbon-rich materials from the ground, and burning them. As a result, about 40 billion tons of carbon dioxide are sent into the atmosphere every year, making fossil fuel consumption the biggest of all humankind's unwitting geoengineering experiments.

With atmospheric levels of heat-trapping carbon dioxide higher than at any time in the last 15 million years, global weather patterns are changing and average temperatures rising. Some of this carbon dioxide is absorbed by ocean water, altering the proportion of hydrogen and carbonate ions, and making the water more acidic. Corals, plankton and shellfish may literally dissolve.

Over the next several centuries, oceanic pH may change more than it has in the last 300 million years.

Image: John Norton/Flickr

See Also:

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.