* BHP has goal of net zero emissions by second half of century
* U.N. scientists said last year extreme measures needed
* Chevron, Occidental, Bill Gates also involved
By Barbara Lewis
LONDON, March 5 (Reuters) - The world's biggest coking coal producer BHP has bought a $6 million equity stake in a Canadian-based company that sucks carbon dioxide from the atmosphere, as miners' quest to become sustainable and retain ethical investors gathers pace.
U.N. scientists warned last year that temperature rises could only be kept under control if much more radical action were taken, including lifestyle changes and technologies that capture and remove CO2 would be needed.
BHP, alone among the major miners has a target of net zero emissions by the second half of the century, in line with U.N. carbon-cutting goals.
That is a huge challenge, especially if the emissions caused by selling its amounts of coking coal and iron ore for steel-making are included.
Canada's Carbon Engineering (CE) has been removing emissions from the atmosphere since 2015 at a pilot plant in British Columbia and converting it into fuel since 2017.
BHP said the direct air capture technology had the potential to deliver large-scale negative emissions.
"We hope that this investment can accelerate the development and adoption of this technology," BHP Vice President, Sustainability and Climate Change, Fiona Wild said in a statement.
CE's CEO Steve Oldham said BHP's global reach and experience of complex projects made it "an ideal partner" as CE sought to deliver affordable, carbon-neutral fuels and emissions cuts.
Oil and gas companies are also acknowledging the scale of their challenge, especially as pressure mounts on them over the downstream emissions from burning their products, not just the emissions caused by their own operations.
BHP's equity stake in CE follows the investment of an undisclosed sum announced in January from a subsidiary of Occidental Petroleum and Chevron's venture capital arm. Philanthropist Bill Gates is also a backer.
Technology to capture emissions adds to costs and has struggled to find corporate investors.
Even the relatively established technology of carbon capture and storage, which captures and buries emissions released by power generation, for instance, has struggled for years.
Financial analysts are even more sceptical about direct capture from the air, although scientists say it could help to curb global warming, blamed for causing more heatwaves, wildfires, floods and rising sea levels.
Mining companies are under particular pressure to prove their ethical and sustainable credentials after a fatal dam burst in Brazil in January has heightened investor scrutiny.
Glencore, the world's biggest producer of seaborne coal, has said it will cap coal production and last week named climate change in a revised list of the risks it faces. (Reporting by Barbara Lewis; additional reporting by Nina Chestney Editing by Susan Fenton)