Katowice (Poland), Dec 5 (IANS): The 15-year-old Swedish climate activist, who went on school strike at the parliament to ask politicians to act against climate change, on Wednesday asked world leaders to step up action to really make a difference.

"You are never too small to make a difference," student Greta Thunberg said at the Global Climate Action event, which is part of the ongoing UN climate negotiations, known as COP24, which saw world leaders and decision-makers getting to work on mitigating climate change in this Polish city.

"I thought that something has to be done... and I guess it had to be me," the climate activist said about the day she went on strike from school to take climate action.

"Everyone can do their part in fighting climate change. All over the world children and adults take climate action. But we have to step up action to really make a difference," Thunberg said.

Earlier, Thunberg in her speech to UN Secretary-General Antonio Guterres said: "For 25 years, countless people have stood in front of the UN climate conferences, asking our nation's leaders to stop the emissions.

"But, clearly, this has not worked since the emissions just continue to rise," she said, "so I will not ask them anything".

"Instead, I will ask the media to start treating the crisis as a crisis. Instead, I will ask the people around the world to realize that our political leaders have failed us," she said.

"Rich countries like Sweden need to start reducing emissions by at least 15 per cent every year to reach the two degree warming target," she added.

Thunberg began a climate protest by striking from school in Sweden in August.

Now students around the world have joined her. The school strikes have spread across the world, including Australia, Britain and the US.