Breathing dirty air can cost someone’s lifespan (寿命) months—even years, a new study finds. Worldwide, air pollution lowers average lifespans by a year. Scientists shared their new findings in Environmental Science & Technology Letters.

Air pollution (污染) has been linked to many health problems. Most earlier studies have looked at how tiny air pollutants affected rates of illness or death. But now an environmental scientist, Joshua Apte, is going even further. He works at the University of Texas, Austin. He together with his team is looking at life expectancy, hoping to make the threat easier to understand.

PM 2.5 is what scientists call tiny particles of pollution in the air. Higher levels of PM2.5 can cause health problems and cut months, if not years, from the average lifespan. This analysis shows pollution affects life expectancy in different parts of the world.

The World Health Organization (WHO) recommends limiting PM 2.5 to 10 micrograms (微克) per cubic (立方) meter of air. Apte’s group used data to try to find how this low level would help people. But meeting the WHO standard won’t get rid of health damage from dirty air. That’s because even below 10 micrograms per cubic meter pollution still causes huge risks.

Reducing air pollution could increase life expectancy. The scientists also compared how other threats shorten life spans across the globe. These risk factors included smoking and cancer.

These results show that in poor countries, cleaning up dirty air could greatly increase lifespans. It could have as big an effect as cleaning up drinking water, or curing lung cancer. However, in wealthier countries air pollution shortens life expectancy by less than half a year. All forms of cancer, in fact, shorten the average life expectancy by more than 3.5 years. “Knowing this can really help people or policymakers, decide where to spend their money.” says Kirk Smith.

We have a problem，and the strange thing is that we not only know about it, but also celebrate it. Just today, someone boasted (自夸) to me that she was so busy she’s averaged four hours of sleep a night for the last two weeks. She wasn’t complaining; she was proud of the fact. She is not alone.

Why are rational (理性的) people so irrational in their behavior? The answer is that we’re in the midst of a bubble (泡沫). I call it “The More Bubble”.

The nature of bubbles is that something is overvalued until—eventually—the bubble bursts, and we’re left wondering why we were so irrational in the first place. The thing we’re overvaluing now is the opinion of doing it all, having it all, achieving it all.

This bubble is being enabled by a combination of three powerful trends: smart phones, social media, and extreme consumerism (消费主义). The result is not just information overload, but opinion overload. We are more aware than at any time in history of what everyone else is doing and, therefore, what we should be doing. In the process, we have been sold a bill of goods: that success means being supermen and superwomen who can get it all done. Of course, we boasted about being busy—it’s code for being successful and important.

And our answer to the problem of more is always more. We need more technology to help us create more technologies. We need to move our workload to free up our own time to do yet even more.

Luckily, there is a solution to asking for more: asking for less, but better. A growing number of people are making this change. I call these people Essentialists.

These people are designing their lives around what is essential and removing everything else. These people arrange to have actual weekends (during which they are not working). They create technology-free zones in their homes. They trade time on Facebook with calling those few friends who really matter to them. Instead of running to different meetings, they put space on their plans to get important work done.

So we have two choices: We can be among the last people caught up in “The More Bubble,” or we can join the growing community of Essentialists and get more of what matters in our one precious life.

How does an ecosystem(生态系统)work？What makes the populations of different species the way they are？Why are there so many flies and so few wolves？To find an answer，scientists have built mathematical models of food webs，noting who eats whom and how much each one eats.

With such models，scientists have found out some key principles operating in food webs. Most food webs，for instance，consist of many weak links rather than a few strong ones. When a predator(掠食动物)always eats huge numbers of a single prey(猎物)，the two species are strongly linked；when a predator lives on various species，they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species，it can survive the extinction(灭绝)of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare，the switch allows the original prey to recover. The weak links may thus keep species from driving one another to extinction.

Mathematical models have also revealed that food webs may be unstable，where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s，scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species---including species they did not directly attack.

And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean，we fished for top predators such as cod on an industrial scale，while on land，we killed off large predators such as wolves. These actions have greatly affected the ecological balance.

Scientists have built an early-warning system based on mathematical models. Ideally，the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key，which scientists says because once ecosystems pass their tipping point(临界点)，it is remarkably difficult for them to return.