【推荐1】Human activity emits far less methane(甲烷) than carbon dioxide, but methane has a bigger impact on the earth. Over the course of 20 years, a ton of the gas will warm the atmosphere about 86 times more than a ton of CO₂. As a result, methane has been responsible for 23% of the rise in temperatures since pre-industrial times. Carbon dioxide gets most of the attention, but unless methane emissions are limited, there is little hope of stabilizing the climate.

Unfortunately, methane emissions have been anything but stable. After briefly pausing in the early 2000s, atmospheric concentrations of the gas started rising again in 2007. A global inventory (清单) concluded last year, found that humans were largely to blame. Chief among the reasons for the rise are the gassy output of livestock farming, rice cultivation and the fossil-fuel industry. Agriculture and energy each make up roughly one-third of annual methane emissions.

By how much do methane emissions need to fall? Carbon dioxide lingers in the atmosphere for centuries, making it hard to reduce its atmospheric concentrations. By contrast, methane has a half-life of roughly ten years, which means that it degrades quickly. If new emissions can be cut to below the rate at which old emissions reduce, the concentration of methane lingering in the atmosphere will soon fall, slowing global warming. The Intergovernmental Panel on Climate Change estimates that, to keep temperatures between 1.5°C and 2°C above pre-industrial levels, human methane emissions must drop to 35% below where they stood in 2010 by mid-century.

Politicians and the public tend to worry about carbon-dioxide emissions but neglect the effects of cutting methane. But dealing with the gas would have a large effect rapidly and at relatively low cost. Governments are supposed to firm up their commitments to cut emissions under the Paris agreement. It should go further and include a specific target for methane.

【推荐3】XI’AN — China has introduced various emergency responses and long-term measures against air pollution in the central and eastern regions.

The air quality index (AQI)) for Xi’an reached 500 on Wednesday afternoon, at the top of the AQI scale, according to the national air quality monitoring website. Xi’an weather forecasters predict the smog will continue for the next week and air pollution may worsen.

“I have to keep buying masks for my family,” said Liu, buying masks at a pharmacy (药店) near her home in downtown Xi’an. “This is the only thing we can do to protect ourselves.”

On Wednesday, a city government emergency response plan was put into action, suspending all construction and taking at least 50 percent or government vehicles off the road. Power plants must limit their output and reduce emissions.

Nearly half the country, more than 100 cities in 20 provinces, has suffered from smog since last December. Many have taken action, including experimenting with artificial methods to reduce smog, limiting vehicle use and fining polluters.

Assessments based on GDP alone were abandoned last month and more emphasis has been put on public well-being and the environment. Whether the move will be effective or not in forcing the local governments to consider environmental issues over economic growth remains to be seen. Environmental protection professionals are doubtful about the immediacy of the effects of these measures.

Xiao Hang, an urban researcher at the Chinese Academy of Sciences, said it took London 50 years to lose the moniker (绰号) “foggy London town”, and Los Angeles still struggles to control its photochemical (光化学) smog. “We can’t ignore environmental problems during the development process and China has a long way to go,” he said.