He made the remark while speaking at the Asia Pacific Energy Leaders' Summit this week in Wellington.
At the meeting, international energy sector leaders and government officials discussed the challenges and opportunities in the transition away from fossil fuels in the global energy system.
Puna noted that small countries such as the Cook Islands were doing their bit to make the transition.
But the prime minister criticised the United States administration for pulling out of the Paris Climate Agreement.
The agreement, nearly three years old, was to limit the increase in global average temperature to well below 2 °C above pre-industrial levels; and to limit the increase to 1.5 °C, in order to reduce the impacts of climate change.
After his speech, Puna told Radio NZ he was heartened by the world community's commitment to the Paris agreement.
“As you can imagine, (we're) a bit disappointed now that one or two have decided to pull out," he admitted.
“But it's good that although officially those countries have pulled out, the citizens of the country are, you know, still committed to the principals of the agreement, so there's hope."
But he said that from the Cook Islands' perspective it was best to not worry too much about what other countries did in their response to climate change.
“If you worry too much about things you can't control, what's the point? Because you're not going to make them change their minds," he said
“So for me it's important to concentrate on what we can do to show leadership on this issue. And I think we've done that.
“Hopefully by our leadership, people who don't want to listen or change can change their direction."
The Cook Islands has made significant progress with installing solar power stations in the outer islands and has now converted about 80 per cent of the country's energy generation to renewables.
And with the Cook Islands on track to meet its goal of going 100 per cent renewable energy by 2020, he said the country faced a challenge with the solar power systems with storage.
“We're looking to Australia to provide some guidance. The project is in the Snowy Mountains... a hydro-storage project, and it's one that we're looking at for Rarotonga.”
Road transport was another challenge the country would soon take on, he added.
The PM said with the small size of his country's islands, it should be easy to introduce electric vehicles.
New Zealand's Minister for Climate Change, James Shaw, told the summit that the transition away from fossil fuels was a big opportunity for productivity that could not be denied.
This was echoed by business leader, Hamish Reid of New Zealand-based dairy producer Synlait, who said his company viewed its pledge to reduce carbon emissions as a great opportunity for innovation.