We live in a town with three beaches. There are two parks less than 10 minutes' walk from home where neighbourhood children gather to play. However, what my children want to do after school is pick up a screen — any screen — and stare at it for hours. They are not alone. Today's children spend an average of four and a half hours a day looking at screens, split between watching television and using the Internet.

In the past few years, an increasing number of people and organisations have begun coming up with plans to counter this trend. A couple of years ago, film-maker David Bond realised that his children, then aged five and three, were attached to screens to the point where he was able to say "chocolate" into his three-year-old son's ear without getting a response. He realised that something needed to change, and, being a London media type, appointed himself "marketing director for Nature". He documented his journey as he set about treating nature as a brand to be marketed to young people. The result was Project Wild Thing, a film which charts the birth of the Wild Network a group of organisations with the common goal of getting children out into nature.

"Just five more minutes outdoors can make a difference," David Bond says. "There is a lot of really interesting evidence which seems to be suggesting that if children are inspired up to the age of seven, then being outdoors will be a habit for life." His own children have got into the habit of playing outside now: "We just send them out into the garden and tell them not to come back in for a while."

Summer is upon us. There is an amazing world out there, and it needs our children as much as they need it. Let us get them out and let them play.

"What would the world be if there were no hunger?" It's a question that Professor Crystal would ask her students. They found it hard to answer, she wrote later, because imagining something that isn't part of real life—and learning how to make it real—is a rare skill. It is taught to artists and engineers, but much less often to scientists. Crystal set out to change that, and helped to create a global movement. The result一an approach known as systems thinking—is now seen as essential in meeting global challenges.

Systems thinking is crucial to achieving targets such as zero hunger and better nutrition because it requires considering the way in which food is produced, processed, delivered and consumed, and looking at how those things intersect (交叉) with human health, the environment, economics and society. According to systems thinking, changing the food system—or any other network- requires three things to happen. First, researchers need to identify all the players in that system, second, they must work out how they relate to each other, and third, they need to understand and quantify the impact of those relationships on each other and on those outside the system.

Take nutrition. In the latest UN report on global food security, the number of undernourished (营养不良) people in the world has been rising, despite great advances in nutrition science. Tracking of 150 biochemicals in food has been important in revealing the relationships between calories, sugar, fat and the occurrence of common diseases. But using machine learning and artificial intelligence, some scientists propose that human diets consist of at least 26,000 biochemicals—and that the vast majority are not known. This shows that we have some way to travel before achieving the first objective of systems t hinking - which,in this example, is to identify more constituent parts of the nutrition system.

A systems approach to creating change is also built on the assumption that everyone in the system has equal power. But as some researchers find, the food system is not an equal one. A good way to redress (修正) such power imbalance is for more universities to do what Crystal did and teach students how to think using a systems approach.

More researchers, policymakers and representatives from the food industry must learn to look beyond their direct lines of responsibility and adopt a systems approach. Crystal knew that visions alone don't produce results, but concluded that "we'll never produce results that we can't envision".

When almost everyone has a mobile phone, why are more than half of Australian homes still paying for a landline (座机)

These days you'd be hard pressed to find anyone in Australia over the age of 15 who doesn't own a mobile phone. In fact plenty of younger kids have one in their pocket. Practically everyone can make and receive calls anywhere, anytime.

Still, 55 percent of Australians have a landline phone at home and only just over a quarter （29%） rely only on their smartphones, according to a survey （调查）.Of those Australians who still have a landline, a third concede that it's not really necessary and they're keeping it as a security blanket —19 percent say they never use it while a further 13 percent keep it in case of emergencies. I think my home falls into that category.

More than half of Australian homes are still choosing to stick with their home phone. Age is naturally a factor （因素）-only 58 percent of Generation Ys still use landlines now and then, compared to 84 percent of Baby Boomers who've perhaps had the same home number for 50 years. Age isn't the only factor; I'd say it's also to do with the makeup of your household.

Generation Xers with young families, like my wife and I, can still find it convenient to have a home phone rather than providing a mobile phone for every family member. That said, to be honest the only people who ever ring our home phone are our Baby Boomers parents, to the point where we play a game and guess who is calling before we pick up the phone （using Caller ID would take the fun out of it）.

How attached are you to your landline? How long until they go the way of gas street lamps and morning milk deliveries?