Tuesday was Earth Day, and it reminded us how environmentalism has helped to preserve the natural habitat of the United States -- reducing the manmade pollution of our soils, air and water that is a byproduct of comfortable modern industrial life.

But now we are in a new phase of global environmental challenges, as billions of people across an interconnected and resource-scarce world seek an affluent lifestyle once confined to Europe and the U.S.

No longer are the old environmental questions of pollution versus conservation so simply framed. Instead, the choices facing us, at least for the next few decades, are not between bad and good, but between bad and far worse -- and involve wider questions of global security, fairness and growing scarcity.

One example of where these diverse and often complex concerns meet is the debate over transportation. Until hydrogen fuel cells or electric batteries can power cars economically and safely, we will still be reliant on gasoline or similar combustible fuels. But none of our current ways in which we address the problem of transportation fuel are without some sort of danger.

We can, for example, keep importing a growing share of our petroleum needs. That will ensure the global oil supply remains tight and expensive. Less-developed, authoritarian countries like Russia, Sudan and Venezuela will welcome the financial windfall, and keep polluting their tundra, coasts, deserts and lakes to pump as much as they can.

Rising world oil prices ensure that Vladimir Putin, or his handpicked successor, can continue to bully Europe; that Hugo Chavez can intimidate his neighbors; that Mahmoud Ahmadinejad can promise Israel's destruction; and that al-Qaida and its affiliates can be funded by sympathetic Middle East sheiks. Such regional strongmen and terrorists cease being mere thugs and evolve into strategic threats once they have billions of petrodollars.

The U.S., in taking advantage of a cheap dollar, may set records in exporting American goods and services this year. But we will still end up with massive trade deficits, given that we are importing every day over 12 million barrels of oil, now at over at $100 each on the world market. It takes a lot of American wheat, machinery and computer software to pay a nearly half-trillion-dollar annual tab for imported oil.

An alternative is to concentrate more on biofuels. Currently, American farmers are planting the largest acreage of corn in over 60 years. But the result is that fuel now competes with food production -- and not just here, as Europe and South America likewise turn to ethanols.

One result is higher corn prices, which means climbing food bills for cattle, pigs and poultry, and thus skyrocketing meat, pork, chicken and turkey prices. Plus, with more acreage devoted to corn, there is less for other crops like cotton, wheat, rice and soy -- and the prices of those commodities are soaring as well.

Americans' increasing use of homegrown ethanol seems to be raising the price of food for the world's poor, just as our importation of oil enriches the world's already wealthy and dangerous.

What, then, is the least pernicious alternative -- and the most environmentally, financially and ethically sound?

Unfortunately, for a while longer it is not just to trust in promising new technologies like wind and solar power; for decades to come, these will only provide a fraction of our energy needs.

Instead, aside from greater conservation, we must develop more traditional energy resources at home. That would mean building more nuclear power plants, intensifying efforts at mining and burning coal more cleanly -- and developing more domestic oil, while retooling our vehicles to be even lighter and more fuel-efficient.

Nuclear power poses risks of proper disposal of radioactive wastes. Coal heats up the atmosphere. But both can also reduce our need to import fossil fuels to run our generators, while offering electrical energy to charge efficient and clean cars of the not-too-distant future.

No one wants a nuclear plant in his county. But, then, no one wants to leave the country bankrupt paying for imported fuel, or vulnerable by empowering hostile foreign oil producers, or insensitive to the price of food for the poor.

It is also time to re-evaluate domestic oil production in environmental -- and moral --terms. The question is no longer simply whether we want to drill in the Alaskan wilderness or off the Florida or California coasts. Rather, the dilemma is whether by doing so, we can mitigate the world's ecological risks beyond our shores, deny dictators financial clout, get America out of debt, and help the poor afford food.

We may not like oil platforms off the beach or mega-tankers in Arctic waters, but the alternatives for now are far worse -- in both environmental and ethical terms.