Environment / Global Warming

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Outside Boston’s Faneuil Hall, where American revolutionaries first began clamoring for independence in the 1770s, the water is nowhere in sight. Tourists click photos, office workers hurry across the cobblestone paths, and everyone is perfectly dry. As I look around, I try to imagine a different Boston—a Boston of the future, a city that has to fear the ocean.

This is not an easy scene to conjure. The edge of Boston Harbor is several blocks to the east, on the far side of a small green park on a low hill, held back by a seawall of kelp-covered concrete. When I look over the edge at low tide, the water is a good 15 feet below the bulwark. Even at extreme highs, it never reaches the top. Yet the sea level here is slowly but steadily rising. If the trend continues as predicted, ocean waters could climb several feet in the next hundred years. It would then take only one big storm surge to breach the seawall, just as hurricane Katrina sent floodwaters racing past New Orleans’s levees. Faneuil Hall would be inundated by six feet of water, and Boston would temporarily turn into a series of small island neighborhoods.

Extreme flood risk is just one of many dramatic changes that will come with a warmer planet. The average summer temperature in Boston stands to increase by as much as 14 degrees Fahrenheit by 2100, bringing with it a sharp rise in the number of deadly hot spells. In the 1970s this city experienced only 
one 100-degree day per year. By the 2070s, forecasts call for at least 24 such hellish days annually.

I’m interested in Boston because my family lives here, but many cities across the United States and around the globe would suffer far worse in a warmer world. The extremely flat coastline of Florida is particularly 
vulnerable to rising sea levels and violent storms; 8 percent of the state, including much of the Everglades aquifer, lies less than five feet above sea level. Warmer, wetter weather there is already fueling an increase in mosquito-borne tropical diseases such as dengue fever. The outlook is even bleaker in Southeast Asia, where overpopulation, poverty, and hot temperatures stand to exacerbate the impacts of climate change.

At this point you may be thinking, “Yes, we’ve heard all this before.” Such doomsday warnings seem almost cliché today because of the rush of books, movies, TV specials, and articles illustrating the most dire climate-change forecasts. For a while, many scientists doubted that such worst-case scenarios would come to pass, because they assumed governments would act to reduce emissions of carbon dioxide and other gases widely believed to be causing global warming. The 2007 International Panel on Climate Change (IPCC), the most authoritative source of climate science, spelled out the likely consequences of inaction, including extreme heat and precipitation, droughts, and rising seas. Some amount of continued warming is inevitable. But with an international ceiling on greenhouse gases, scientists argued, we could limit the rise to no more than two degrees Celsius (about 3.5 degrees Fahrenheit). Even at that level we would face challenges. A two-degree spike could create freshwater short­ages, dry out arable regions, and increase the severity of extreme cyclones, but the challenges would largely be manageable (see "The Planet Fixers").

Four years after the IPCC report, there is no international agreement, however. The drive to curb carbon emissions has waned further in the wake of financial meltdowns, global instability, and slumping public confidence in the science of climate change. All the while, the mercury keeps rising. Last year tied 2005 for the hottest year since 1880, when record-keeping began, marking the 34th straight year with global temperatures above the 20th-century average. Climate researchers now find themselves staring down an unsettling reality: In this century, average global temperature may increase more than two degrees C­­—possibly quite a bit more. Limiting climate change to two degrees is now “a very, very difficult target to achieve,” says Mark New, a climatologist at the Tyndall Centre for Climate Change Research at the University of Oxford.

For reasons researchers are still trying to sort out, four degrees appears to be a tipping point beyond which the human risks increase dramatically. Added sea-level rise, shifts in precipitation, and jumps in local temperatures could lead to vast water and food shortages. Nearly 200 million people could be displaced, and many of our standard methods of adaptation to weather extremes—developing new crops, bolstering freshwater supplies in advance of heat waves, responding to disasters after the fact—could have little effect. “In moving from two to four degrees you really do see, in all our best estimates, a major increase in the level of action required,” says climate-adaptation expert Mark Stafford Smith, science director for Australia’s national science agency. “Suddenly, dramatic adaptation is going to be needed.”

The concept of rapid, full-scale mobilization against global warming is a hard sell; dramatic actions are normally driven by immediate threats, not distant, uncertain trends. To most climate scientists, though, the changes are real and upsetting, even if they are years or decades away.