Now there is a similar challenge: global warming. The steady deterioration (恶化) of the very climate of this very planet is becoming a war of the first order, and by any measure, the U.S. is losing. Indeed, if America is fighting at all, it's fighting on the wrong side. The U.S. produces nearly a quarter of the world's greenhouse gases each year and has stubbornly made it clear that it doesn't intend to do a whole lot about it. Although 174 nations approved the admittedly flawed Kyoto accords to reduce carbon levels, the U.S. walked away from them. There are vague promises of manufacturing fuel from herbs or powering cars with hydrogen. But for a country that tightly cites patriotism as one of its core values, the U.S. is taking a pass on what might be the most patriotic struggle of all. It's hard to imagine a bigger fight than one for the survival of a country's coasts and farms, the health of its people and the stability of its economy.
The rub is, if the vast majority of people increasingly agree that climate change is a global emergency, there's far less agreement on how to fix it. Industry offers its plans, which too often would fix little. Environmentalists offer theirs, which too often amount to na; ve wish lists that could weaken America's growth. But let's assume that those interested parties and others will always be at the table and will always demand that their voices be heard and that their needs be addressed. What would an aggressive, ambitious, effective plan look like—one that would leave the U.S. both environmentally safe and economically sound？
Halting climate change will be far harder. One of the more conservative plans for addressing the problem calls for a reduction of 25 billion tons of carbon emissions over the next 52 years. And yet by devising a consistent strategy that mixes short-term solutions with far-sighted goals, combines government activism with private-sector enterprise and blends pragmatism (实用主义) with ambition, the U.S. can, without major damage to the economy, help halt the worst effects of climate change and ensure the survival of its way of life for future generations. Money will do some of the work, but what's needed most is will. "I'm not saying the challenge isn't almost overwhelming," says Fred Krupp. "But this is America, and America has risen to these challenges before."
What does the passage mainly discuss？

A. Human wars.
B. Economic crisis.
C. America's environmental policies.
D. Global environment in general.