Living on a carbon budget. Or, you can’t always get what you want.

Is it possible to have any fun at all without burning fossil fuels? On a Saturday afternoon in my rural neighborhood, the woods reverberate with the sounds of ATVs and dirt bikes—or, in winter, snowmobiles. Even here, in an area on the Oregon-Washington border renowned for human-powered sports such as windsurfing, mountain biking, and skiing, people often drive a considerable distance to begin their recreation.

These activities may be more thrilling than low-carbon alternatives such as playing cards, making music, or tossing a Frisbee. Trouble is, Earth’s carbon budget—the remaining amount of fossil fuels that scientists calculate can be burned without destroying the climate—will last only about 30 years at the rate we’re going. It will be extremely difficult to make the budget stretch until fossil fuels can be replaced with cleaner alternatives. So how do we divvy up carbon “spending” in a way that’s fair?

This is a question that should move from the fringes of the energy debate to its very heart. Economists and energy experts shy away from issues of equity and morality, but climate change and environmental justice are inseparable: It’s impossible to talk intelligently about climate without discussing how to distribute limited energy resources. It’s highly unlikely that the world can safely produce almost five times as much electricity by 2035 as it does now—which is what it would take to provide everyone with a circa-2010 American standard of living, according to a calculation by University of Colorado environmental studies professor Roger Pielke Jr. The sooner policy makers accept this reality, the sooner they can get to work on a global solution that meets everyone’s needs. First, though, they need to understand the difference between needs and wants.

Energy “requirements.” In a recent online discussion about how to quantify carbon emissions, McGill University environmental economist Christopher Green wrote: “The important question is how the world’s huge and growing energy requirements are going to be met.” This is a common framing of the climate problem, but note that Green uses the word “requirements” rather than energy “demands.” They are not exactly the same. A requirement is a necessity, an obligation. A demand, in economics, is more like a request: It’s negotiable, and you might not get everything you ask for. It’s a function of the number of people who wish to buy a particular good.

Most economists and energy policy makers, though, proceed from the assumption that energy requirements and energy demands are synonymous. That’s certainly how the oil and gas industry views the situation. For example, in a speech that Shell CEO Peter Voser gave a couple of years before his December 2013 retirement, he said: “We must continue heavy investment to develop and deliver new energy supplies. This is not optional. We estimate the world will need to produce 40 million barrels of oil a day by 2020 from fields we haven’t even developed yet, due to the combination of increasing demand and falling production rates.”

Wow. Not optional. Because, you know, people need that oil.

Needs vs. wants. My friend Warren started his own boat-design business years ago, when he had a wife and young sons to support. I recently asked him how he found the courage to do it. He told me that he and his wife learned, early on, how to tell the difference between wants and needs.

Making this distinction will be critical in dealing with climate change, too. People need energy to provide for their families. But do they “need” to ride around on motorized vehicles in their leisure time? That’s the kind of uncomfortable question that policy makers prefer to avoid. But if need does not become a central part of the climate discussion, there is little hope of a serious solution. The experts might as well be out in the woods doing wheelies.

The key question is not how we will meet future energy demands—a framing that justifies a never-ending search for new energy sources and assumes that a growing and increasingly affluent global population should get whatever it asks for. Everyone must have his or her needs met—food, water, shelter, health. But all of us may have to forego wants. The more fundamental questions are how the world will distinguish between wants and needs, and whether energy will be shared and conserved in such a way that everyone has enough to meet basic needs. Policy makers should have learned everything they need to know about sharing in kindergarten; but since then they’ve clearly forgotten those lessons—or at least forgotten that they are as important for climate change as they are for slicing a cake.

Rights and responsibilities. In any discussion of climate justice, developing countries quickly point out two basic realities: First, they aren’t responsible for most of the emissions that have taken place since the beginning of the industrial revolution. And second, their citizens have a right to the same quality of life that Americans already enjoy. These are both completely valid points, but they lead inevitably to stalemate, allowing richer nations to argue that progress is impossible without a multilateral agreement to reduce emissions.

For example, despite the recent joint announcement that both the United States and India are committed to working toward a successful outcome at the international climate negotiations in Paris next year, Indian prime minister Narendra Modi was conspicuously absent from the UN climate summit in New York in September. India’s environment minister Prakash Javadekar said that his nation’s priority was relieving poverty, not climate change, and that the country’s emissions would continue to rise for at least the next 30 years. Emissions cuts, Javadekar told the New York Times, are “for more developed countries. The moral principle of historic responsibility cannot be washed away.”

No, it can’t, but neither can the world afford any free passes in 2014. India recently overtook the European Union as the world’s third-largest emitter of greenhouse gases, and China already emits more greenhouse gases annually than any other nation, although the United States—in second place—outsources many of its emissions to China and India by importing goods manufactured there. And even as the United States exhorts these countries to choose clean energy over coal, carbon dioxide emissions from US coal-burning power plants are inching upward, and recent reports suggest that switching from coal to natural gas won’t do much to reduce US emissions.

Climate justice or climate capitalism? The blame game accomplishes little and hinders discussion of how the world’s nations can work together to solve the climate crisis fairly. If the global carbon budget is allocated according to how much carbon each nation is currently emitting, a strategy that Michael R. Raupach and colleagues refer to as “inertia” in their recent Nature Climate Change paper, North America would have a 19 percent share. Under an “equity” scenario, in which carbon is allocated according to population, the North American share would be only 5 percent. A compromise “blended” approach—which would provide developing countries with access to energy and development opportunities, without imposing extremely high mitigation demands on developed countries—would allocate 12 percent of the world’s carbon budget to North America. Of course, such allocations are entirely dependent on a willingness to share, and North America possesses more fossil reserves than any other region.

As Naomi Klein writes in her new book, This Changes Everything, “the really inconvenient truth is that [global warming] is not about carbon—it’s about capitalism.” Convincing millions of Americans to sacrifice their wants for the needs of others will be a huge political, economic, legal, and ethical challenge. As Klein acknowledges in the October 6 issue of The Nation, “if climate justice carries the day, the economic costs to our elites will be real—not only because of the carbon left in the ground, but also because of the regulations, taxes, and social programs needed to make the required transformation.”

It won’t be easy, but climate justice is, to borrow a phrase from former Shell CEO Voser, not optional. Humans require a livable climate. In the years to come, the energy wants of the world’s wealthiest people must be weighed against the energy needs of their poorer fellow human beings. Some people may need ATVs to survive; most probably don’t.