The Greenpeace ship Rainbow Warrior visits the United Kingdom as part of the "Quit Coal" tour in the North Sea. The expedition takes place in the run-up to crucial UN climate negotiations in Poznan, Poland, in December. The aim of the tour is to promote renewable energy and encourage the countries to quit the use of coal. Coal is the most polluting of all fossil fuels and the largest single source of CO2 in the world. Currently, one-third of all carbon dioxide emissions come from burning coal.