Actress Li Bingbing poses with a leopard. [Photo/Official Weibo account of Our Street Style]

Listening to birdsong makes us smarter and more relaxed. A walk through a forest improves our short-term memory and wards off the blues. Woodlands reduce our blood pressure and lower our stress levels. It may sound far-fetched but the science is increasingly clear: simply being close to nature is good for our mental and physical health. I am sure almost everyone can recall a time when we just felt better after a few minutes in nature.

What science is only just starting to prove in the lab, humans have known intuitively for thousands of years. Ancient Chinese philosophers wrote often about the need to live in harmony with nature. Their thinking inspired some of the world's most beautiful gardens. These were places in which to relax, to stretch one's thoughts out, to find solace from the hustle and bustle of city living.

That scientists today need to prove that spending more time in nature is beneficial to our health tells us so much about where the modern world has taken us as a species. More people now live in cities than in rural areas. By 2050, another 2.5 billion people will follow. I have always found it sad that humans - a species evolved for life in the world's forests and savannahs - have found themselves living in ever greater numbers among high rise buildings made from concrete, shut off from nature and the profound benefits it brings.

This move to the city - and away from nature - is having a major impact on our health. Every year, three million people die from outdoor air pollution worldwide- more than ever before. Many more suffer severe respiratory problems because of the dirty air they breathe. Our increasingly sedentary lifestyles have also triggered other health epidemics like obesity. It is not a coincidence that studies in America have found that the average adult spends more time inside a vehicle than outdoors. We need nature in our lives more than ever and yet, sadly, we are more removed from it than ever before.

Our growing detachment from nature is disastrous for the environment. The further we drift from the natural world, the less likely we are to appreciate it. Our failure to grasp the importance of the environment has triggered some of the gravest catastrophes of our time. We have hacked down forests, polluted rivers, dumped plastic in our oceans and driven species to extinction in pursuit of short-term economic gains. We belch vast amounts of carbon dioxide and other greenhouse gases into the atmosphere despite the damage this does to our climate and the danger it poses to our way of life. In failing to understand how the environment supports us, and how the dots are connected, we are rapidly overwhelming nature's ability to sustain life as we know it.

As a UN Environment Goodwill Ambassador, I have been a frontline witness to the harm humans have done to the environment. I have travelled to Kenya where I witnessed the bliss of watching wild elephant herds and the devastation of poaching to supply an illegal trade in ivory, which has led to the slaughter of hundreds of thousands of these magnificent creatures. In my own country, China's haze problem arises on a scale as sweeping and epic as the vast nation itself. The haze has affected people's daily lives and it is also the result of human activities.

Yet I have cause for hope. I am repeatedly amazed at the giant leaps that my country is making to address the environmental challenges it faces. Some of China's cities are among the most polluted on earth and they suffer debilitating air pollution. Bad air causes massive health problems and makes people's lives inconvenient. Sometimes the Education Ministry even has to order a shutdown of schools due to the haze.

But there is another side to the story. China has installed the largest air-quality monitoring systems in the world. It is designing better, more energy efficient cities and investing in cleaner forms of transport. Last year, it invested $88 billion in renewable energy, the highest in the world. Its emissions fell by 1 per cent in 2016 while its economy expanded by 6.7 per cent, proving that it is possible for countries to grow economically while reducing the damage done to the environment.