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GLOBAL WARMING: WHAT, HOW, WHY?

The basic physics of global warming are as well understood as any scientific phenomenon. The Earth’s average surface temperature is rising unnaturally and frighteningly fast, threatening to snuff out a staggering number of plants and animals in the very near future and have far-reaching impacts on human civilization — with many endangered species already feeling the heat. Scientific consensus points squarely at human activity as global warming’s driver. But we can fight to stop a total global climate catastrophe, and understanding what’s happening is the first step.

THE PROCESS

Certain gases in the atmosphere are called greenhouse gases — specifically, carbon dioxide, methane, nitrous oxide, tropospheric ozone, and CFCs — because they allow shortwave radiation from the sun to pass through the atmosphere and warm the Earth’s surface. The energy that then radiates out from the surface, longwave radiation, is trapped by the same greenhouse gases, warming the air, oceans, and land. This process, appropriately dubbed “the greenhouse effect,” is how global warming occurs. Black carbon, a particle rather than a gas, also has a very large warming impact.

The greenhouse effect itself isn’t a bad thing. In fact, Earth could never have become warm enough to sustain life without it. But in the late 18 th century, the advent of fossil fuels set off a chain reaction. When coal, oil, and natural gas are burned, they release enormous amounts of greenhouse gases — especially carbon dioxide, or CO2, which is by far the most prevalent. The gases add up much faster in the atmosphere than natural processes can absorb them, and thereby wreak havoc on Earth’s complex climate system. After the Industrial Revolution changed everything from goods manufacturing to land use to lighting and heating methods, fossil fuel combustion increased dramatically — and then came cars, which now join coal-burning power plants as one of the top emitters of greenhouse gases. Combined with massive population growth and the effects of large-scale deforestation and industrial agriculture, the widespread combustion of fossil fuels has made greenhouse gas concentrations in the atmosphere climb to levels never seen before in the more than 200,000-year history of the human subspecies.

Humans have added so dramatically to the atmospheric blanket of greenhouse gases that the greenhouse effect that first made life possible now threatens the world as we know it.

THE NUMBERS

According to the Intergovernmental Panel on Climate Change, a scientific group tasked with assessing the risk of anthropogenic or human-caused climate change, the concentration of atmospheric carbon dioxide swelled from 280 parts per million (ppm) prior to industrialization to 379 ppm in 2005. Now we’re at 385 ppm, and we’ll reach 550 ppm by mid-century if current trends continue. Leading scientists warn we must reduce the atmospheric carbon dioxide level to below 350 ppm if we want to avoid runaway global warming with catastrophic impacts.

THE CONSEQUENCES

The Intergovernmental Panel on Climate Change projects that temperatures at the Earth’s surface will increase by as much as 11.5 degrees Fahrenheit over the next 100 years, snow cover and permafrost will be lost entirely in many places, and sea ice at the poles will continue to melt away. To date, warming and melting of the Arctic has occurred far faster than was projected, leading some scientists to conclude that the Arctic could be ice free in the summer as early as 2012. If the Greenland ice sheet were to melt completely, sea level would rise about 20 feet, leaving hundreds of millions of coastal residents — people, plants, animals — homeless. And severe weather events like hurricanes, droughts, and heat waves, already on the rise, will occur more frequently than ever. Countless other disastrous outcomes, many of which can’t be precisely modeled for predictive purposes, make climate change a looming threat.

Perhaps the most overarching consequence of global warming is its devastating effect on biodiversity as it threatens to wipe out an astounding number of Earth’s plants and animals. From the Arctic, where polar bears, ice seals, and walruses are losing their sea-ice habitat, to the oceans, where greenhouse gas-caused ocean acidification threatens all marine life, crucial habitat is changing dramatically, and species that can’t adapt to new conditions or migrate out of harm’s way will die. According to one landmark study, if we let current trends continue, by 2050 this will amount to 35 percent of all plant and animal life currently in existence — at least a million species.

THE TIME TO ACT

Projections of what will happen if we continue on our present course paint a stark picture of the future. And, in fact, global warming constitutes the greatest threat yet faced by human societies. But it’s not too late to act swiftly to save the planet and the species that call it home. Slashing our carbon dioxide emissions is absolutely essential for fighting climate change in the long term, and cutting down immediately on emissions of black carbon and methane, which remain in the atmosphere for much shorter time periods than CO2, is a way to buy ourselves time to perfect other strategies. Solutions must be enacted individually, locally, nationally, and internationally if we want to curb the emissions that cause global warming in order to save millions of species (including our own).

Bearded seal photo © David S. Isenberg