Now the bad news: The Lima conference is expected to have the biggest carbon footprint of any UN climate meeting measured to date.
At more than 50,000 metric tons of carbon dioxide, the negotiations' burden on global warming will be about 1 1/2 times the norm, said Jorge Alvarez, project coordinator for the UN Development Program.
The venue is one big reason. It had to be built.
Eleven football fields of temporary structures arose for the 13-day negotiations from what three months ago was an empty field behind Peru's army's headquarters. Concrete was laid, plumbing installed, components flown in from as far as France and Brazil.
Standing in the midday sun here can get downright uncomfortable, but the Lima sun is not reliable. That's one reason solar panels were not used.
For electricity, the talks are relying exclusively on diesel generators.
Organizers had planned to draw power from Peru's grid, which is about 52 percent fed by non-polluting hydroelectric power. "We worked to upgrade transformers and generators but for some reason it didn't work," said Alvarez.
Peru's hydroelectric power could be in danger by mid-century, anyway. Much of that water comes from glaciers that are melting at an accelerated pace. Peru is hardly on a green trajectory. Though it emits in a year the greenhouse gases that China spews in three days, it has doubled its carbon output in the past decade.
Nor is there a guarantee that the 580 square miles of forest, whose conservation Alvarez said would offset the talks' carbon pollution, won't someday be gone. The Houston, Texas-sized area — in four different forest preserves — must lie unperturbed for a half century in order to neutralize carbon emitted at the conference, Alvarez said.
Environmental economist John M. Reilly of the Massachusetts Institute of Technology called that accounting peculiar.
"If this forest is cut down in 50 or 100 years, all of the saved carbon will end up back in the atmosphere," he said.
Reilly called the "wasted efforts" to build makeshift quarters disturbing — unless the talks "were actually successful in halting future emissions." This is the 20th round of talks and so far there is little sign of serious progress.
Alvarez itemized the talks' carbon footprint:
— Construction, nearly 20 percent of the footprint.
— Jet fuel burned by the estimated 11,000 delegates and observers who flew in from abroad, about 30 percent.
— Local transportation. Organizers hired more than 300 buses since there are no public transit services to the venue. All burn fossil fuels. About 15-20 percent.
— Electricity, solid waste treatment, water, paper, food, disposable plates and cups, keeping 40,000 police on high alert, for the balance.
The 50,000 tons the conference emits is what China as a country emits in three minutes, the US does in five minutes and Peru does in six hours and 40 minutes. It is more than eight times as much carbon as the 2009 Copenhagen talks and twice that of the 2010 conference in Cancun, Mexico, according to the UN.
A more accurate carbon footprint will be published after the conference and certified by the Spanish company Aenor, organizers say. UN volunteers have been polling delegates on their air travel in search of precision.
The conference's green components are meager.
Peruvian Environment Minister Manuel Pulgar-Vidal asked for a bicycle parking lot. He got it, but only about 40 people use it daily. Most delegates spend about an hour in traffic traveling less than 6 miles from their hotels.
Blame that, in part, on the army. It initially balked on letting in bikes even though only the credentialed can enter the base known as "El Pentagonito."
"It took them three days to sort it out," said Andrew Marquard, an adviser to South Africa delegation and an avid cyclist who was interviewed after arriving at the talks on two wheels, skin shiny with sweat.
Blame the dearth of bikes also on Lima, one of the world's least friendly cities for cyclists. The city's few cyclists so fear drivers that they tend to prefer to compete with pedestrians for sidewalk space.
"There are quiet (leafy) areas around the convention center for riding bikes," said Alvarez. "But getting here is a problem."
No hybrid or electric vehicles have been seen at the event. Japan donated 121 electric and hybrid vehicles, chiefly for dignitaries.
"Unfortunately, most didn't arrive," Alvarez said. He blamed shipping bureaucracy.
Some energy savings were applied inside the white temporary structures where delegates wrangle, journalists toil and testy closed-door sessions take place.
"We did not put in strong air conditioning. It is (designed) only to fight the heat in the structures," said Maxime Rosenwald of GL Events, the Lyon, France-based company that built and runs the physical plant.
The air conditioning is often losing that fight as the sun regularly burns away Lima's low coastal clouds, the Southern Hemisphere summer being nigh.
On Monday, UN organizers announced that "in view of the high temperatures expected to continue and intensify," delegates were invited to adjust "by wearing business casual attire" to most events.
Associated Press Science Writer Seth Borenstein in Washington contributed to this report.