As 2015 looks increasingly to be the hottest year in recorded history, 150 heads of state are descending on Paris in order to push for an international agreement on climate change.
Negotiators from nearly 200 countries will spend the next two weeks brokering a deal on how to keep global temperatures from rising 2 degrees Celsius (3.6 Fahrenheit) above pre-Industrial Age levels — a threshold that many scientists say, if passed, could unleash dangerous disruptions to Earth's climate, which could jeopardize coastal cities with sea level rise, usher in more frequent, more intense extreme storms, and heightening the risk of human conflict over food and water resources.
In the lead-up to the talks, 183 countries have submitted plans explaining how they will reduce their levels of greenhouse gas emissions. Taken together, those plans keep the world within 2.7C of warming, at best, which is why thousands of people on Sunday defied a French ban on protests imposed after the Paris terror attacks to demand that world leaders do better.
Police fired tear gas into the crowd and arrested 280 demonstrators. Greenpeace executive director Kumi Naidoo was unbowed. "We'll be keeping up the pressure," he said. "They want a climate deal that keeps temperature rises in the safe zone."
But against this dramatic backdrop, several key negotiators and close trackers of the talks say that potential for a positive outcome in Paris remains high. Though the national plans now on the table can't on their own prevent dangerous levels of atmospheric warming, those plans are "only part of the Paris moment," said Jennifer Morgan, head of the climate program for the World Resources Institute, a global research organization that's been working on climate issues for more than two decades.
If the delegates gathered in a converted airport in the city's north can agree that global prosperity no longer depends on fossil fuels and set up a timetable for rapidly eliminating them, she said, that could provide the "certainty and clarity" many investors need to shift towards a low-carbon economy.
"[It] would help keep that two degrees goal still within sight," Morgan added.
Fergus Green, a researcher at the London School of Economics & Political Science, said social and economic systems rarely change in a linear way.
"Change can happen very quickly once a certain tipping point is reached," he said.
Green thinks that the world may be experiencing such a tipping point in its use of coal, the single largest contributor to climate change. This month, the United Kingdom proposed a phase out all its coal plants over the next ten years. It was soon followed by a similar pledge from the Canadian province of Alberta. China could cap the amount of coal it burns in 2020 and coal consumption in the United States has dropped significantly.
The reason such promises are feasible is because the economics of coal are in rapid decline at the same time that clean energy is becoming more and more competitive.
Evidence of that shift can be seen in the fact that in 2013 the world installed 143 gigawatts worth of clean energy capacity, compared to 141 gigawatts from oil, coal and gas. Earlier this fall, Moody's Investors Service estimated that half of the world's coal reserves aren't profitable enough to extract at today's prices. And Goldman Sachs has advised its clients that "peak coal is coming sooner than expected" — likely by the year 2020. Meanwhile, the cost of solar energy in the United States has fallen by 70 percent since 2009.
"These trends have been gathering momentum and have come to a point now where they're having kind of an unstoppable force," Green said.
Until now that force hasn't been strong enough to keep the world with 2C of warming, which is why a coalition of major companies and investors called We Mean Business is urging negotiators in Paris to make it stronger by eliminating subsidies for fossil fuels and enacting a global price on carbon. If governments head the call of these businesses — and the tens of thousands that have taken to the streets in cities around the world — then they could bring the world "within range of achieving the 2 degree goal and ensuring a smoother transition to a zero-carbon economy," said Morgan.
But that scenario is far from assured. A global price on carbon, for instance, would make it more expensive for petro-states like Saudi Arabia and other Persian Gulf economies to produce oil. There has been so much pushback against the policy from fossil-fuel producing nations that UN special advisor Brice Lalonde has argued that it's unlikely carbon pricing will end up in the final agreement.
Supporters of putting a price on carbon pollution gained an ally this October when the Liberal Party's Justin Trudeau was elected Canada's prime minister. Despite the fact that Canada remains a major exporter of oil to the United States, the country's new environment minister Catherine McKenna said in Paris on Sunday, "We need to have a price on carbon."
A major conflict point in negotiations is whether or not any final agreement should be legally binding.
US Secretary of State John Kerry thinks the final agreement should be voluntary — an outcome vigorously opposed by European Union negotiators. Yet there's zero chance a Republican-controlled Congress would approve legally binding targets.
For its part, China has pledge to make potentially deep cuts in emissions, which is why lead US negotiator Todd Stern is pushing for a Paris agreement that would force countries to renegotiate stronger targets of their choosing every five years. "This could actually enhance ambition," he said.
Morgan remains weary of voluntary targets. She thinks it's important that the targets countries agree to in Paris should be enshrined in international law. "That sends a signal of seriousness," she said.
But she agreed with Stern that the climate talks starting this week have potential to make the climate reductions already promised by 176 countries even stronger. And that in turn could mean the 2C goal remains "within sight."
"What's really possible in Paris is to create a durable long-term agreement that could be the tipping point," she said, "that would make it clear that the low carbon renewable economy is going to become the norm."
Follow Geoff Dembicki on Twitter: @GeoffDembicki