The Firework singer appears in the mocked up forecast for the United Nations (U.N.) children's charity UNICEF, urging world leaders to take action to stop youngsters suffering from the effects of extreme weather.

"Droughts, floods, heatwaves and other severe weather conditions are putting children at an increased risk of disease and malnutrition, as well as destroying their families' homes and livelihoods," Katy says in the video.

"Let's encourage our world leaders to take this issue seriously. Share your story on how you are helping reduce climate change with the hashtag #FightUnfair. Together we can help change the forecast for millions of children," she adds.

The release of Katy's campaign video comes as the U.N.'s summit on climate change enters its second week, with officials from 195 countries gathered in Paris, France to finalise an agreement to halt rising global temperatures.

A host of celebrities have descended on the French capital since the talks began on 30 November (15) to urge world leaders to act, including Leonardo Dicaprio, Arnold Schwarzenegger, Sean Penn and U2 frontman Bono.

The Wolf of Wall Street actor warned that inking an agreement this week (beg07Dec15) is essential because the world is "running out of time" to prevent environmental catastrophe, and Arnold Schwarzenegger highlighted the dangers of pollution.

"There are people stuck in cancer wards now, tubes sticking out of them - seven million people die a year because of pollution," The Terminator star told Britain's The Guardian newspaper.

The Paris climate summit, dubbed COP21, concludes on 11 December (15).