The Dust Bowl. During the 1930s, a period of severe dust storms engulfed the American and Canadian prairie lands. The cause: a severe drought coupled with decades of land misuse that left topsoil susceptible to the wind. The so called "black blizzards" forced hundreds of thousands of people in Oklahoma, Texas, New Mexico, Colorado, and Minnesota to abandon their farms, exacerbating the dire economic conditions of the Great Depression. This image shows a dust storm approaching Stratford, Texas, on April 18, 1935. NOAA/MCT/Newscom/File
The Great Smog. From December 5 to December 9, 1952, London was shrouded in a thick layer of smog, caused by windless conditions and cold weather that prompted Londoners to burn more coal to keep warm. Visibility was reduced to only a few feet, and car, bus, and air transport ground to a halt. A Ministry of Health report estimated that 4,075 died as a result of the poor air quality and another 100,000 were sickened; more recent research suggests that the Great Smog, as it became known, killed 12,000 people. Newscom/File
The 'Kill a Sparrow' campaign. In 1958, Chinese Communist Party chairman Mao Zedong ordered peasants to begin killing sparrows, which ate grain seeds and disrupted agriculture. The people complied, destroying nests, breaking eggs, and frightening the birds away by banging pots and pans. What Mao failed to consider was that sparrows also ate insects: the resulting locust swarms helped lead to the Great Chinese Famine, in which some 36 million people starved to death. In this March 1, photo, a sparrow stands in the snow in Tiananmen Square.
Cuyahoga River. The northeast Ohio river, whose name means "crooked river" in the Iroquois language, first caught fire back in 1868. The largest river fire in 1952, shown here, caused over $1 million in damage. The river's oily surface combusted at least a dozen since then, until a June 1969, fire caught the attention of a reporter for Time Magazine. "Chocolate-brown, oily, bubbling with subsurface gases," the reporter wrote, "[the Cuyahoga] oozes rather than flows." The 1969 fire prompted a raft of environmental legislation, including the Clean Water Act.
Love Canal. In 1976, news emerged that the Love Canal neighborhood in Niagara Falls, New York, was sitting on 21,000 tons of toxic waste that had been buried decades earlier by the Hooker Chemical Company. Those living in the neighborhood saw a high rate of miscarriages and birth defects. Public outrage led to the Superfund Act, which holds polluters accountable for their damages. This photo shows empty lots that once held low income houses over the toxic dump. Ari Denison/CSM/File
The Bhopal disaster. Early in the morning on Dec. 3, 1984, a holding tank at a pesticide plant owned and operated by Union Carbide, released a large volume of poisonous gases into the city of Bhopal, India. Thousands died immediately, and an estimated 20,000 have died since then, apparently from gas-related symptoms. Another 100,000 to 200,000 people are thought to have been severely sickened by the gas. Union Carbide, now owned by the Dow Chemical Company, maintains that the gas leak was caused by deliberate sabotage, although company officials have been warned of repeated safety violations beforehand. To date, nobody has been prosecuted. In this photo, activists in Bhopal demonstrate on the 25th anniversary of the disaster. Altaf Qadri/AP/File
Chernobyl. On April 26, 1986, reactor number four at the Chernobyl plant in the Ukrainian Soviet Socialist Republic suffered a meltdown. About 50 plant workers and firefighters died initially after heavy radiation exposure. The radiation plume spread, forcing large areas of Ukraine, Belarus, and Russia to be evacuated. Today, the Zone of Alienation, as the 19 mile exclusion zone around the plant is known, has been largely reclaimed by nature, with wildlife flourishing. This 2006 photo shows an amusement park in Pripyat, Ukraine, a city of 50,000 that was completely evacuated 36 hours after the meltdown. Residents were told they were being taken away for just 3 days.
The Exxon Valdez spill. On March 24, 1989 the single-hulled oil tanker Exxon Valdez, loaded with crude oil bound for California, struck a reef in Alaska's Prince William Sound, and dumped some 11 million gallons into the sea. According to the BBC, the oil killed about 250,000 seabirds, nearly 3,000 sea otters, 300 harbor seals, 250 bald eagles, up to 22 killer whales, and left the pristine beaches befouled to this day. In 2008, the US Supreme Court drastically reduced the damages that Exxon had to pay, a ruling that then-Gov. Sarah Palin called "tragic."
Gulf War oil spill. On January 21, 1991, as they retreated from Kuwait, Iraqi forces deliberately dumped millions of gallons of oil into the Arab Gulf in an attempt to slow a landing by US Marines. The exact amount of oil is unknown, but it is widely regarded as the largest oil spill in history, although the long-term damage appears to be minimal. This May 1991 photo shows the oil-slicked Manifah Bay, Saudi Arabia.
Kingston Fossil Plant coal fly ash slurry spill. On December 22, 2008, an earthen wall holding back 1.1 billion gallons of coal fly ash slurry ruptured at the Tennessee Valley Authority's Kingston Fossil Plant in Roane County, Tennessee. The toxic sludge spread over 300 acres, poisoning river water and decimating the marine wildlife population.