Former US treasury secretary Henry Paulson says his time with Chinese children is happier than when he held his government post.

Since leaving the treasury in 2009, Paulson has been working on environmental-protection campaigns, especially in China.

"You have amazingly strong kids here, and they stand in cold for a long time, and they are smiling the whole time," he said, at a water-conservation project in Beijing's Baijiazhuang Primary School in early December.

Tsinghua University economist Hu Zuliu says: "Paulson might be the former US treasury secretary who's closest to China."

Paulson met with China's Vice-Premier Wang Qishan to discuss China's modernization and urbanization during his recent Beijing trip.

"It is important to change people's behavior in protecting the environment," Paulson says.

The campaign he recently joined in Beijing calls upon people to limit showers to four minutes.

The 66-year-old shared his childhood experience with the kids at the event.

"My father only gave us two minutes for showers when we were kids," he recalls.

"If we stayed too long in the shower, my father took a glass of cold water and threw it on me.

"So, we talk about how important human behaviors are. And you can take many steps, but water resources - we will find that there won't be much left for all of us as our population continues to grow."

He says he was also impressed by the Chinese children's English proficiency. He was particularly surprised by a 9-year-old boy at Baijiazhuang Primary School, who did all the interpreting throughout the water event's opening ceremony.

"Kids (have) impressive potential," he says.

"And it is vital to let them understand about environmental protection at a very early age."

Paulson chaired and set up the Asia Pacific Council of the Nature Conservancy in 1998, establishing parks in Yunnan province.

Over the past decade, he has continuously praised China's charity sector's development.

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"Yunnan was spectacularly beautiful when I visited it - spectacular in terms of natural resources," he says.

What struck me from the first time is how much fun it was to work with Chinese people, and how charitable the Chinese people were - because I found all kinds of partners in China to work along with us with their time, efforts and their donations."

However, he points to the challenges created by the country's rapid development.

"We need sustainability," he says.

"So, I think all of us need to do more."

zhangyue@chinadaily.com.cn