After months of planning, the People’s Climate March began rolling through a large swath of Midtown Manhattan on Sunday, taking public frustration over stalled efforts to curb carbon emissions to the streets in a noisy, vivid display of unity.

At 11:30 a.m., the march began moving east along 59th Street from Columbus Circle, proceeding along a circuitous, two-mile route, and drawing labor and immigrant groups, students and politicians, scientists and religious leaders. The march will turn south on Avenue of the Americas, head west on 42nd Street to 11th Avenue and finish at 34th Street.

The protest comes two days before a climate summit at the United Nations, which will be attended by President Obama. The meeting is expected to create a framework for a potential global agreement on emissions late next year in Paris.

The timing of the march is significant in another regard. Last week, meteorologists at the National Oceanic and Atmospheric Administration announced that this summer — the months of June, July and August — was the hottest on record for the globe, and that 2014 was on track to break the record for the hottest year, set in 2010.

“Climate change is no longer an environmental issue; it’s an everybody issue,” Sam Barratt, a campaign director for the online advocacy group Avaaz, which helped plan the march, said on Friday.

“The number of natural disasters has increased and the science is so much more clear,” he added. “This march has many messages, but the one that we’re seeing and hearing is the call for a renewable revolution.”

Mayor Bill de Blasio of New York, whose administration announced this weekend a sweeping plan to overhaul energy efficiency standards in all city-owned buildings, is among the high-profile participants expected to join the march, including the United Nations secretary general, Ban Ki-moon; former Vice President Al Gore; the actors Leonardo DiCaprio and Mark Ruffalo; at least two United States senators; and one-third of the New York City Council.

Additionally, nearly 2,700 climate events are planned in more than 150 countries to coincide with the march, considered the centerpiece of the international protest. They range from a small rally in Tanzania, to major demonstrations from Berlin to Bogata.

On Sunday morning, participants from across the country began to arrive at the staging area near the American Museum of Natural History. Rosemary Snow, 75, stretched her legs after a nearly 14-hour bus drive from Georgia.

“I thought we’d have a lot of younger people on the bus,” said Ms. Snow, who made the trip with her grandson. “There’s a really great mix of people.”

Ms. Snow had traveled with dozens of others who came from different parts of the state, including Valdosta, Savannah and Atlanta.

A professor at the University of Georgia, Chris Cuomo, from Decatur, Ga., said the group was organized by the Georgia Climate Change Coalition.

She said she hoped their presence at the rally would “let the rest of the world know that people from small-town America, urban America, rural America care about climate change.”

Nearby, Ahni Rocheleau of Santa Fe, N.M., was seated while eating a breakfast of organic yogurt and buckwheat pancakes. She is a member of the Great March for Climate Action, a cross-country walk to raise awareness for alternative and sustainable energy practices.

“We hope the heart and mind of the people will be awakened,” she said. “Coal is not the way to go.”

The march was expected to tie up traffic across a broad area of Manhattan, from the Upper West Side through Midtown. In a traffic advisory, the police braced the public for the closing of dozens of streets along the route. A lane for emergency vehicles, however, was kept open.

Nearly 500 buses have been bringing marchers from South Carolina, Kansas, Minnesota and Canada, while a “climate train” transported participants from California.

Marchers assembled before 11:30 a.m. north of Columbus Circle, specifically along Central Park West between 65th and 86th Streets, which the police planned to use as a staging area. A number of pre-march events were planned in the vicinity of Columbus Circle, including a labor event on Broadway, an interfaith religious service on West 58th Street and a rally by scientists outside the Hayden Planetarium on West 81st Street.

At 12:58 p.m., a moment of silence will be followed by a blare of noise — a symbolic sounding of the alarm on climate change — from horns, whistles and cellphone alarms. More than 20 marching bands and tolling church bells will contribute to the cacophony.

There will be no speeches, but the march will end with a block party on 11th Avenue between 34th and 38th Streets. There, participants can get a closer look at many of the floats and other artwork created for the march, including a 30-foot inflatable life preserver, 100 sunflowers and a model of the New York City skyline with bicyclists powering its lights.

New York’s political establishment was set to come out in force. On Friday, Mayor de Blasio announced on Twitter his intention to join the protest. “Proud to walk in #PeoplesClimate March on Sunday,” he wrote. “It’s everyone’s responsibility to leave a livable planet for the next generation.”

At least 17 council members planned to march. In a nod to the event, the Council announced a related package of bills on Friday aimed at reducing the city’s carbon footprint by connecting unemployed New Yorkers to green jobs, making buildings more energy-efficient and promoting low-carbon transportation. The legislation seeks an 80 percent reduction in the city’s greenhouse gas emissions by 2050.

With its bands and colorful floats, the march offers a festive atmosphere, but organizers said that the underlying message was somber. “We are trying to celebrate our lives and this planet in order to show that this is what we are fighting for,” said Leslie Cagan, the logistics coordinator for People’s Climate March. “It’s the human spirit — and everything else on this planet — that is in danger.”

The march was organized by a dozen environmental, labor and social justice groups, including the Sierra Club, Avaaz, New York City Environmental Justice Alliance, 350.org, the Transport Workers Union Local 100 and 1199 S.E.I.U. In addition, more than 1,570 “partner organizations” have signed on to march.

Organizers were hoping that the warm weather forecast for the day would yield a large turnout.

“Our biggest problem is the financial power of the fossil fuel industry,” said Bill McKibben, co-founder of 350.org and author of “The End of Nature.”

“We can’t match that money,” he said. “So we have to work in the currency of movements — passion, spirit, creativity and bodies — and it will all be on display on Sunday.” More

 

ON SEPTEMBER 23rd 120-odd presidents and prime ministers will gather in New York for a UN meeting on climate change. It is the first time the subject has brought so many leaders together since the ill-fated Copenhagen summit of 2009.

Now, as then, they will assert that reining in global warming is a political priority. Some may commit their governments to policies aimed at reducing greenhouse-gas emissions. What few will say is how many tonnes of carbon dioxide these will save—because they almost never do.

According to scientists, cutting carbon-dioxide emissions is an essential part of reducing catastrophic risks from climate change. Yet governments are persistently averse to providing estimates of how much carbon a policy saves. That may be because, in countries where climate change is controversial, it makes more sense to talk about the other benefits a scheme offers rather than its effect on carbon. Or it may be that, in countries which are enthusiastic about renewable energy, pointing out that it may not save that much carbon is seen as unhelpful. Or perhaps governments think climate change is so serious that all measures must be taken, regardless of cost (though their overall lacklustre record suggests this is not the case).

Whatever the reason, the end result is that while the world’s governments have hundreds of policies for tackling climate change, some of them very expensive—China, America and the European Union spend $140 billion a year on subsidising renewable energy—it is hard to say which policies are having the greatest effect.

So The Economist has made a stab at a global comparison of carbon-mitigation efforts. Chart 1 is the result. It ranks 20 policies and courses of action according to how much they have done to reduce the atmosphere’s stock of greenhouse gases. We have used figures from governments, the EU and UN agencies. As far as we know, this exercise has not been carried out before.

Apples, meet oranges

First, a health warning: the policies and actions on our list are not strictly comparable. Some are global, some regional and some national. Some are long-standing; some new. A couple are not policies at all, such as the collapse of the Soviet Union, which led to the closure of polluting factories and to inefficient state farms reverting to grassland, locking up carbon.

And the numbers almost all come with caveats. It is fairly easy to estimate how much carbon a new field full of solar cells or a nuclear-power plant saves by looking at the amount of electricity it produces in a year and how much carbon would have been emitted if fossil fuels had been used instead, based on the local mix of coal, gas and oil. But as Paul Joskow of the Massachusetts Institute of Technology has pointed out, the standard “levelised” calculations, which divide the total amount of power a plant will produce over its lifetime by its total lifetime cost, are a poor way to compare fossil fuels and renewable energy.

Other measures have problems, too. Take the effects of fuel-efficiency standards. Would companies have curtailed their cars’ emissions anyway to sell more of them to cost- and mileage-conscious drivers? And how much has better fuel efficiency encouraged drivers to drive farther?

A further complication is that many policies have benefits beyond—or indeed closer to hand than—those they offer in terms of climate. Burning less coal saves lives in the near future as well as reducing climate risks in decades to come. Saving forests preserves wildlife, not just carbon.

So our table should be treated with caution. It is only safe to say that one policy is better than another in climate terms if it beats it by a wide margin.

As it happens, though, there are some very wide margins to be found. One policy stands head and shoulders above all others. And it is one that few people other than climate-policy specialists will have thought of in this context: the Montreal protocol, a 1987 agreement to phase out substances such as chlorofluorocarbons (CFCs) used in air conditioners, refrigerators and so on. It was enacted to limit the damage such substances were doing to the ozone layer, a goal which it has achieved.

Like carbon dioxide and many other gases emitted by industry and agriculture—methane and nitrous oxide, for example—CFCs are greenhouse gases. And they are extremely potent ones, causing thousands of times more warming per molecule than carbon dioxide does. That means stopping CFC production, which was in the range of millions of tonnes a year, delivered a climate benefit equivalent to cutting carbon-dioxide emissions by billions of tonnes.

Collateral benefits

Guus Velders of the Dutch National Institute for Public Health and the Environment has compared the warming effect that would have come about if the emissions of such chemicals had continued to grow at the rate they were growing before the protocol with what has come about thanks to their banning. The net effect is equivalent to that of a whopping 135 billion tonnes of carbon dioxide. That is more than twice today’s total annual greenhouse-gas emissions, which are equivalent to about 50 billion tonnes of carbon dioxide (carbon dioxide itself makes up about three-quarters of that, with methane, nitrous oxide and some gases used in industry making up the rest). Durwood Zaelke of the Institute for Governance and Sustainable Development, a think-tank, says that if CFCs were uncontrolled the annual figure would be 8 billion tonnes higher. The Montreal protocol has had nearly as big an effect as all the rest of our list put together.

Trailing some way behind the Montreal protocol is a small group of measures—not really climate policies—that have been responsible for avoiding between 4% and 7% of greenhouse-gas emissions. According to the International Atomic Energy Agency, nuclear power avoided the production of 2.2 billion tonnes of carbon dioxide in 2010—that is, emissions would have been 2.2 billion tonnes higher if the same amount of electricity had been produced by non-nuclear plants. Energy from dams and other hydroelectric sources avoided 2.8 billion tonnes (though emissions of methane from the reservoirs behind some of those dams mean the net effects were less than that). Between them they generated 6,000 terawatt-hours of electricity in 2011, compared with 450TWhrs for wind and less than 60TWhrs for solar. The high rate at which new wind and solar capacity is being built will eat into this lead, but it will take some time to overturn it.

The other item in this group is something of a cheat. In 2007 Su Wei of China’s foreign ministry said that his country’s one-child policy, by reducing the number of births between the late 1970s and the mid-2000s by 300m, had reduced carbon emissions by 1.3 billion tonnes in 2005 (because there were fewer people to consume goods which generated greenhouse gases in their production). Taking this argument further, one could say that the fall in global fertility since 1960 cut emissions even more. That is not exactly a climate policy. But it is a reminder that greenhouse gases are powerfully influenced by factors far beyond the scope of climate-change policies.

Three other lessons emerge. First, policies to slow or reverse deforestation are more important than one might expect. Trees absorb carbon as they grow and release it when they are cut down. According to a recent study in Science, declining deforestation in Brazil meant that the country produced 3.2 billion tonnes less atmospheric carbon dioxide between 2005 and 2013 than it would have if the tree-felling had continued unabated. That is 400m tonnes a year. The slowdown in deforestation in tropical countries is one of the reasons that the conversion of forests to farmland now accounts for only 11% of greenhouse-gas emissions globally, much less than 20 years ago.

The other reason for deforestation’s dramatically reduced share of total emissions, though, is that industrial emissions of carbon dioxide have continued to grow rapidly. The rise is not as fast as it might have been. Rules that make vehicles more efficient and improve the energy efficiency of buildings and appliances have done more than might be expected. America has been setting standards for vehicle greenhouse-gas emissions and fuel efficiency since the mid 1970s; the current rules are forecast to reduce carbon-dioxide emissions by 6 billion tonnes in 2012-25, meaning by about 460m tonnes a year. America’s Department of Transportation reckons that overall such rules have reduced carbon-dioxide emissions by a cumulative 14 billion tonnes. Europe’s equivalent regulations for passenger cars and light trucks do less (European vehicles were more efficient to start with) but are still respectable; being adopted by overseas manufacturers who want to sell cars in Europe gives them an unquantified extra clout. More