Since that first Earth Day, the air over major cities is cleaner. Lake Erie is healthier. So is the Cuyahoga River, which groups in Cleveland would like to turn into a centerpiece of urban life. The improvements have come with "yes, but ..." as other environmental challenges have elbowed their way to the fore. But for the most part, tools are in place to deal with them.
So, how are we doing on global warming, now widely seen as the century's most pressing environmental issue?
Most climate scientists trace global warming to the relatively rapid buildup of atmospheric CO2 from the burning of fossil fuels long sequestered deep underground.
Though only 0.04 percent of all the gases in the troposphere, where weather happens, CO2 is second only to water vapor as the most abundant greenhouse gas. And where a water molecule may remain airborne for up to 10 days before returning to the surface as rain, a newly emitted molecule of CO2 can remain in the air for centuries.
"From the grossest physical indicator, we're not getting the job done as a planet," says Alden Meyer, director of the Union of Concerned Scientists office in Washington, of the steady rise in CO2 levels.
If warming of 1.5 to 2 degrees C above preindustrial levels is the goal, he says, it's still salvageable. But time is running ou
Read more: On Earth Day 2013, a planetary report card on global warming - CSMonitor.com
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