This is an opinion piece by Erik Solheim, Executive Director of the United Nations Environment Programme.
John Muir knew a thing or two about nature. One of America's greatest explorers and environmentalists, back in the early 20th century he lived for years in a log cabin in the remote Yosemite Valley. The great pioneer used to hike with only a tin cup, a handful of tea, a loaf of bread and a copy of Ralph Waldo Emerson's essays. He relied on nature to sustain him, and even had a stream that ran right through one corner of his room so he could enjoy the sound of running water.
This experience of the great outdoors led him to write: "Everybody needs beauty as well as bread – places to play in and pray in, where nature may heal and give strength to body and soul."
Now scientists are beginning to prove with brain scans and check-ups what Muir worked out for himself with his tin cup and his hikes in the woods.
Recent studies have found that listening to birdsong makes us smarter and more relaxed, that a forest walk can ward off depression and improve short-term memory, and that time spent in woodland can boost the immune system and reduce blood pressure.
But today, trapped in our cities and lost in our modern lifestyles, we are more cut off from nature than ever. In America, the average adult spends more time inside a vehicle than in the outdoors. In the UK, children spend less time outside than prisoners.
The result of this disconnect between people and the environment has been disastrous – for us and for the planet. Worldwide, depression is now the leading cause of disability. Air pollution kills more than 12 million people every year. As medicine strides forward, we spend more time just sitting around, leading to new health epidemics, like obesity and diabetes.
Never have we needed nature more. But never have we lived further from its benefits. So this year's World Environment Day is all about rediscovering the call of the wild.
And no one needs to pull a John Muir in the process. Rather than giving up on modern technology, we're asking people to harness its power by downloading a free app called iNaturalist and joining an online army of smartphone-toting naturalists, biologists and regular people who are using it to save the world.
The app allows you to upload geotagged photos of plants and animals, and then uses AI to sort these pictures and identify different species. The app's 400,000 users have already logged 4.8 million observations of 100,000 species.
On World Environment Day, we want to boost these numbers by encouraging as many people as possible to download the app and upload their observations between June 1 and 12.
This isn't just another tech gimmick. iNaturalist has already discovered a new species of snake and frog, and rediscovered a snail that hadn't been seen for more than 100 years. As it gets smarter, it will allow scientists to map how urbanization, deforestation and climate change are affecting the number and distribution of plants and animals across the world.
The more people upload photos, the more accurate the database becomes. If enough people get on board, it can be used to track the global health of hundreds of thousands of species, helping scientists decide which parts of the world need immediate protection and monitor how well these protected areas are doing.
So why not trade your sofa for the great outdoors for World Environment Day? Go out into your backyards, your local garden or national park and explore the natural world that surrounds us even in the most urban environments. Record and document what you find and help the world's scientists protect our planet.
As John Muir put it: "Keep close to Nature's heart … break clear away, once in awhile, and climb a mountain or spend a week in the woods. Wash your spirit clean."
World Environment Day is June 5. Learn how you can help encourage worldwide awareness and action for the protection of the environment at the UN's official site.