The lives of billions of people, for centuries to come, will be at stake when world leaders and government negotiators meet at the United Nations Climate Change Conference in Paris at the end of the month. The fate of an unknown number of endangered species of plants and animals also hangs in the balance.

At the “Earth Summit” in Rio de Janeiro in 1992, 189 countries, including the United States, China, India, and all European countries signed on to the U.N. Framework Convention on Climate Change, and agreed to stabilize greenhouse-gas emissions “at a low enough level to prevent dangerous anthropogenic interference with the climate system.”

So far, however, no such stabilization has taken place, and without it, climate feedback loops could boost rising temperatures further still. With less Arctic ice to reflect sunlight, the oceans will absorb more warmth. Thawing Siberian permafrost will release vast quantities of methane. As a result, vast areas of our planet, currently home to billions of people, could become uninhabitable.

Earlier conferences of the UNFCCC signatories sought to reach legally binding agreements on emission reductions, at least for the industrialized countries that have produced most of the greenhouse gases now in the atmosphere. That strategy faltered -- partly owing to U.S. intransigence under President George W. Bush -- and was abandoned when the 2009 Copenhagen conference failed to produce a treaty to replace the expiring Kyoto Protocol (which the U.S. never signed). Instead, the Copenhagen Accord merely asked countries for voluntary pledges to cut their emissions by specific amounts.

Those pledges have now come in, from 154 countries, including the major emitters, and they fall far short of what is required. To fathom the gap between what the pledges would achieve and what is required, we need to go back to the language that everyone accepted in Rio.

The wording was vague in two key respects. First, what would constitute “dangerous anthropogenic interference with the climate system”? And, second, what level of safety is assumed by the term “prevent”?

The first ambiguity has been resolved by the decision to aim for a level of emissions that would cap the increase in average surface temperature at 2 degrees Celsius above the preindustrial level. Many scientists consider even a lower increase dangerous. Consider that even with a rise of only 0.8 degrees Celsius so far, the planet has experienced record-high temperatures, more extreme weather events, and substantial melting of the Greenland ice sheet, which contains enough water to cause a 7-meter rise in sea levels. In Copenhagen, the pleas of representatives of small island states (some of which will cease to exist if sea levels continue to rise) for a target of 1.5 degrees Celsius went unheeded, essentially because world leaders thought the measures required to meet such a target were politically unrealistic.

The second ambiguity remains. The London School of Economics’ Grantham Research Institute has analyzed the submissions made by all 154 countries and concluded that even if they are all implemented, global carbon emissions will rise from their current level of 50 billion tons per year to 55-60 billion tons by 2030. But, to have even a 50 percent chance of keeping to the 2 degrees Celsius limit, annual carbon emissions need to come down to 36 billion tons.

A report from Australia’s National Center for Climate Restoration is no less alarming. The level of emissions in the atmosphere today already means that we have a 10 percent chance of exceeding 2 degrees Celsius, even if we stopped adding further emissions right now (which is not going to happen).

Imagine if an airline slashed its maintenance procedures to a level at which there was a 10 percent chance that its planes would not safely complete their flights. The company could not claim that it had prevented dangerous planes from flying, and it would find few customers, even if its flights were much cheaper than anyone else’s. Similarly, given the scale of the catastrophe that could result from “dangerous anthropogenic interference with the climate system,” we ought not to accept a 10 percent chance – if not many times higher – of exceeding 2 degrees Celsius.

What is the alternative? Developing countries will argue that their need for cheap energy to lift their people out of poverty is greater than rich countries’ need to maintain their often wasteful levels of energy consumption – and they will be right. That is why rich countries should aim at decarbonizing their economies as soon as possible, and by 2050 at the latest. They could start by closing down the dirtiest form of energy production, coal-fired power stations, and refuse licenses to develop new coal mines.

Another quick gain could come from encouraging people to eat more plant-based foods, perhaps by taxing meat and using the revenue to subsidize more sustainable alternatives. According to the U.N. Food and Agriculture Organization, the livestock industry is the second largest source of greenhouse-gas emissions, ahead of the entire transport sector. This implies great scope for emission reductions, and in ways that would have a smaller impact on our lives than ceasing all fossil-fuel use. Indeed, according to a recent World Health Organization report, a reduction in the consumption of processed and red meat would have the additional benefit of reducing cancer deaths.

These proposals may sound unrealistic. Anything less, however, would be a crime against billions of people, living and yet to be born, and against the entire natural environment of our planet.

By Peter Singer

Peter Singer is Professor of Bioethics at Princeton University and Laureate Professor at the University of Melbourne. His books include “Animal Liberation,” “The Life You Can Save” and, most recently, “The Most Good You Can Do.” --Ed.

(Project Syndicate)