Describing the COVID-19 pandemicas the biggest threat in the history of human civilisation, West Bengal Chief Minister Mamata Banerjee on Wednesday cautioned the people that the bigger threat of climate change is looming large.On Earth Day, Banerjee urged the people to come together and fight the challenges of climate change to protect the planet.Today is #EarthDay. Our planet is going through one of the biggest crisis in human history - the #CoronaPandemic. But a bigger threat is staring at us - climate change. We must all act together to fight these challenges and preserve our beautiful planet, she tweeted.To demonstrate support for environmental protection, Earth Day is celebrated annually around the globe on April 22.