International Airlines Group (IAG) announced the pledge on Thursday, saying it would replace older aircraft, invest in sustainable jet fuel and develop technology that removes CO2 from the atmosphere.

Its flagship carrier, British Airways, will also offset all carbon emissions produced by its domestic flights starting next year by investing in solar energy products and planting trees in South America, Africa and Asia.

Airlines are under increasing pressure to take urgent action as rising global awareness about the climate crisis poses ever greater risks to their business.

Greta Thunberg, the teenage climate activist, helped popularize a social media hashtag in her native Sweden that translates to "flight shame."

When Thunberg traveled last year to Davos, Switzerland, to confront CEOs and global leaders, she went by train. Her recent trip to the United Nations, in New York, was made via sailing ship.

According to industry group IATA, air transport accounts for 2% of global man-made CO2 emissions. In 2017, that translated to 859 million tonnes (947 tons) of CO2.

Environmental activists argue that global aviation emissions are rising fast, and if the industry were a country, it would rank among the top 10 emitters. In addition to CO2, aircraft emit nitrogen oxides, which contribute to global warming.

An activist delayed a flight from London's City Airport Thursday by delivering a lecture on the climate crisis just before departure, as part of a protest by the group Extinction Rebellion.

The focus on aviation has helped spur the industry to action.

Seven aircraft manufacturers including Boeing (BA) and Airbus (EADSF) announced in June that their chief technology officers would collaborate at an "unprecedented level" to help the industry control emissions.

European airlines have been at the vanguard. Dutch airline KLM (AFLYY) has even encouraged customers to take trains or do video calls instead of flying, when possible.

IAG (ICAGY) said Thursday it would reach its carbon goals by investing $400 million over the next two decades in sustainable aviation fuel. One project in Britain aims to convert household trash to jet fuel starting in 2024.

The company has also committed to replacing older planes over the next five years with 142 new aircraft costing $27 billion at list prices. The new planes will be up to 25% more efficient than the models they replace.

It will also partner with an American company called Mosaic Materials, which has created an absorbent material to remove CO2 directly from the atmosphere.