The British Antarctic Survey found that during past periods of high carbon dioxide, temperatures in Antarctica were up to 6C above current levels. - This could cause a sea level rise of up six metres, threatening coastal cities like London, New York and San Francisco. - It is the latest research to warn of the consequences of increased greenhouse gases on the Earth's climate. - Yesterday a study warned that carbon dioxide produced by man is now rising at record rates putting the world on a pathway for a 6C rise in temperature.