Bristol International Airport produces the same amount of CO2 from flying each year as the African nation of Malawi, an anti-poverty group said.
The airport has plans to expand
The World Development Movement claimed the overall UK-wide growth in aviation was undermining efforts to control climate change.
A spokesman for the airport said: "Passenger numbers are up, but aircraft numbers have gone down.
"The industry is forecast to grow, but also to become greener and cleaner."
The airport is planning to expand, with passenger numbers expected to rise from nearly six million this year, to nine million by 2015.
It wants to double the size of its terminal, allow parking for 5,000 cars and have 17 flights an hour.
The World Development Movement also called for a target of an 80% reduction in CO2 emissions by 2050 and 40% by 2020.