By JEFFREY BALL

Leaders of the Group of Eight major industrialized economies, meeting in Japan, issued their first long-term target for cutting global-warming emissions. But their pronouncement failed to address the two toughest questions: How will the world do it, and who will pay?

The answer to the money question is clear: Consumers will pay -- at the gasoline pump, at the car dealership and on the monthly electric bill. If the campaign against global warming gets serious, it will transform today's esoteric environmental threat into a fundamental pocketbook issue for people from Boston to Beijing.

But how much it will cost and how much it will do for the planet depend on the gritty details of how policy makers decide to attack greenhouse-gas emissions. Those details were in short supply this week, because the diplomats disagree -- and because nobody knows.

G-8 leaders on Tuesday set a goal to halve greenhouse-gas emissions by 2050. The most common manmade greenhouse gas, carbon dioxide, is belched out whenever fossil fuel -- such as oil, natural gas or coal -- is burned. Slashing the current level of greenhouse-gas emissions without injuring the global economy would likely require a range of technologies that today are still in the lab.

A separate diplomatic group that met on Wednesday and that included representatives from developing nations declined to endorse even the G-8's broad goal. Fast-growing countries like China and India don't want to commit themselves to an emissions-cut target, saying rich countries should ante up first.

Reaching the G-8's goal would go a long way toward preventing dangerous consequences from global warming but not all the way, according to many scientists. Some have called for even deeper cuts.

Many studies have tried to quantify what this would cost. A United Nations panel, for instance, said last year that reducing greenhouse-gas emissions enough to avoid the worst consequences could cut projected global economic output in 2030 by as much as 3% below the level it would otherwise reach that year.

Whether that is a reasonable price is a matter of debate. But even those who think the cost is worth it admit such studies have two whopping caveats.

The studies assume the world will cut emissions in the most economically rational way. And the studies acknowledge that the cost will hit some countries, companies and consumers harder than others.

The cost is "meaningful, but not devastating, to the economy," says Scott Nyquist, a director and co-head of the energy practice at consulting firm McKinsey & Co., which recently has issued several studies of the cost of curbing emissions. "But the point is, there are individual parts of the world that get hit harder." Consumers in countries -- or regions within them -- that rely more heavily on coal, for example, would likely face bigger increases in energy prices.

Two hints that consumers will significantly bear the costs of fighting global warming have cropped up in recent weeks.

One came from California, which proposed new rules in late June to cut its greenhouse-gas emissions to 1990 levels by 2020. Among the measures California is considering is a fee of between $10 and $50 per ton of carbon dioxide that is emitted. Translation: a potential increase in the wholesale price of gasoline of between 10 cents and 50 cents per gallon, the state said.

Congress also recently acknowledged that it will have to provide financial help for consumers if it is to make cutting greenhouse gases politically feasible.

In early June, the Senate considered and rejected what broadly amounted to a mandatory U.S. version of the G-8's nonbinding global pledge. The bill sought to cut U.S. emissions about 65% from current levels by 2050. Included in the bill was a provision for tax relief for Americans whose bills for coal-fired electricity would rise as a result.

Among the few specifics in the G-8 proposal was for more research and development of new technologies to burn coal more cleanly. Many of the world's biggest economies have huge stores of coal buried within their borders. As energy prices soar, these countries intend to burn more of that coal than ever before.

That suggests the debate over what to do about global warming is about to get a lot more personal for consumers, says Billy Pizer, a senior fellow at Resources for the Future, a Washington think tank that focuses on energy issues. The relatively easy step is setting broad goals for emission cuts decades hence. But whatever progress that represents doesn't answer the stubborn question, he says: "What are we actually going to do?"