Everyone arriving at the festival, which will take place between 22 and 24 June, will be given a wristband with the I Count campaign message "We can stop climate chaos". People can sign up to the campaign on their arrival and at information points across the festival's site. The rising total will be registered at the main Pyramid music stage.
A spokesman for Greenpeace said: "We have been going to Glastonbury for years, but this year climate change is going to be emphasised like never before. It's the first time the three charities have been so on the same page."
Stop Climate Chaos is a coalition of more than 50 organisations formed to raise awareness of climate change.