Brazil is similarly finding reforming energy subsidies a rocky road. In the West, Brazil often is portrayed as an environmental success story. It gets about 80% of its electricity from an essentially carbon-free source: water coursing through dams. It has made major strides in combatting deforestation. And roughly 20% of the automotive fuel it uses is ethanol, made from sugarcane. Yet Brazil’s government-controlled oil company, Petroleo Brasileiro SA, known as Petrobras, long has sold gasoline domestically at below-market prices. Now, as Petrobras tries to extinguish that subsidy, it’s sparking a political blowback.

The subsidy, which Petrobras doesn’t officially acknowledge but which is openly discussed in Brazil, is a creature of the Brazilian government’s desire to minimize inflation. But the subsidy is causing billions of dollars in annual losses in Petrobras’s refining division, analysts estimate. Late last month, in response to investor pressure, Petrobras announced it would phase out the subsidy over what the company called “an appropriate period” of time. That didn’t satisfy investors, who expected a firmer move and who promptly hammered Petrobras’s share price. Smarting from that investor drubbing but leery of stoking Brazilian motorists’ ire, Petrobras has declined to specify how quickly or how significantly it will cut the subsidy.

Hard as it is to pull back these direct fossil-fuel subsidies in poor countries, it’s at least easy to quantify them. Not so for the indirect fossil-fuel subsidies that analysts say the US and other wealthy nations proffer in massive quantities. These subsidies, the IMF says, arise in large part because rich as well as poor countries are failing to tax fossil fuels enough to pay for the environmental and health consequences of burning them — everything from climate change to respiratory disease, things that economists call “externalities.” In Washington and beyond, the argument that the failure to boost the price of energy to cover these factors amounts to a subsidy is stirring a fierce ideological debate.

The IMF estimates that, in 2011, the most recent year it analyzed, indirect fossil-fuel subsidies from both developed and developing countries amounted to about $1.4 trillion. That’s nearly three times the $480 billion the IMF says came through direct fossil-fuel subsidies, which occurred overwhelmingly in developing countries. The IMF reached the larger figure after making various assumptions about the cost of addressing fossil fuels’ environmental and health effects. One of them: that rectifying the global-warming damage wrought by burning fossil fuels will cost $25 for every ton of emitted carbon dioxide. According to the IMF, levying that price on CO2 emissions would raise the price of gasoline or diesel by about 20 cents per gallon.

This penalty has come to be known in many political and academic circles as the “social cost of carbon.” Everything about it elicits debate: not just the general premise that energy should be taxed to penalize carbon emissions, but, even more, the attempt to nail down a specific dollar amount per ton. Some critics, typically those on the right, say the IMF’s $25-per-ton estimate is too high. Others, typically on the left, say it’s too low. Each side cites dueling evidence. In Europe, which has regulated carbon-dioxide emissions since 2005, a permit to emit one ton of CO2 is trading today for only about $5. In the U.S., in an announcement that so far has drawn only limited attention, the Obama Administration last month issued a revised estimate of the social cost of carbon pegging it at $37 per ton of emitted CO2.

The drive to curb fossil-fuel subsidies is sputtering uphill. If one side is right in the dispute over the cost, it’s a few hundred billion dollars. If the other side is right, it’s a few trillion dollars. That gap is no longer academic. It’s about real money. And increasingly, it appears that someone, somewhere, sometime, is going to pay.