Earth’s atmosphere seems to have found a way to get back at the human race. For almost three centuries, we humans have been filling the air with carbon dioxide, methane and other greenhouse gases. Now, it turns out, the climate change these emissions have wrought is turning people against one another.

So says a review, published today, of 60 studies on how climate change helps spark conflict throughout the world. The researchers found a surprisingly close link between climate change and civil wars, riots, invasions and even personal violence such as murder, assault and rape.

Rising temperatures are especially provocative. A shift toward greater warmth of one standard deviation caused personal violence to increase by 2.5 percent and intergroup conflict by 24 percent. (One standard deviation varies from place to place; in an African country, for example, it could amount to a warming of 0.6 degrees Fahrenheit for a year.)

Why? The science so far doesn’t answer this question, though it’s easy enough to imagine how subsistence farmers could come into greater conflict with one another as their croplands become less productive. Or how, in the face of rising sea levels, coastal dwellers could come to blows over shrinking habitable land. The scientists who did the review point as well to many psychological and economic studies that show people simply behave more aggressively or violently when temperatures are higher.

Unfortunately, humans also fight, if nonviolently, over climate change itself ― specifically, over how, and how quickly, to reduce our destructive emissions. This makes the necessary reductions difficult. The United Nations Framework Convention on Climate Change, for example, originally aimed to have an accord setting firm greenhouse-gas-reduction targets for all countries by 2009. It is now hoping to accomplish this task by 2015. Meanwhile, in the U.S., President Barack Obama has been forced to act outside Congress, through the Environmental Protection Agency, to limit carbon-dioxide pollution from coal-fired power plants. Republicans in the House have predictably introduced legislation to forbid any such action.

This resistance is especially frustrating because the longer we wait, the harder it becomes to lower emissions. Delaying the start of action just five years, from 2020 to 2025, would drastically dim any hope of limiting the rise in global mean temperature to 3.6 degrees Fahrenheit (2 degrees Celsius) ― long considered the point at which it becomes significantly more difficult to adapt. Chances of success would fall to just 34 percent from 56 percent, new research shows. On the other hand, starting to take action in 2015 would improve humanity’s chances to 60 percent.

Even if the temperature target can be met, the ocean will still grow more acidic, cropland will still become less productive, and sea levels will still gradually rise ― according to new research, by 4.8 meters (15.7 feet), or almost twice the height of Hurricane Sandy’s peak storm surge at Battery Park in New York City. And as we continue emitting greenhouse gases, we lock in an underwater future for hundreds of U.S. cities and towns.

Climate scientists use a bathtub analogy to explain the problem: Greenhouse gases are like water flowing from a faucet into a tub with a limited drain ― the trees, plants and oceans that soak up the gases. With the faucet wide open, the tub quickly fills to the point at which the concentration of carbon in the atmosphere reaches 450 parts per million, and the only way to prevent overflow is to shut the tap entirely. By slowing the stream now, we would allow ourselves the relative luxury of reducing emissions gradually.

Turning the tap slowly is something we know how to do ― by increasing energy efficiency, developing renewable energy sources and, as Obama plans, subjecting carbon dioxide to the same kind of limits we put on mercury, arsenic and other pollutants. The alternative is to let the tap run and leave the overflow for the next generation to deal with.

(Bloomberg)