The British oil giant BP set the most ambitious climate change goal of any major oil company on Wednesday, saying that it aimed to eliminate or offset by 2050 all of the planet-warming emissions from its operations — as well as the emissions caused by the burning of the oil and gas it pumps out of the ground.

The company provided few details on how, exactly, it would achieve that difficult feat. But the pledge is another sign that major companies, including fossil-fuel producers, are facing growing pressure from investors and activists to show they are taking global warming seriously.

“We are aiming to earn back the trust of society,” said Bernard Looney, BP’s chief executive, at a news conference in London. “We have got to change, and change profoundly.”

Rising concerns about climate change pose an existential threat for oil and gas companies, since scientists have said that preventing dangerous temperature increases will require steep reductions in the use of fossil fuels. In recent years, shareholders have pressed oil companies to prepare for a future in which countries shift to electric vehicles or enact new regulations to limit carbon dioxide emissions.

Other European oil companies — including Royal Dutch Shell, Total and Equinor — have already adopted targets to curb their emissions. But BP is going further, pledging to also zero out the emissions associated with the oil and gas it pumps out of the ground and sells.

That last step is both the hardest and most significant, since it is where oil companies have an outsize climate impact. BP said that the company emits about 55 million tons of greenhouse gases each year directly from its extraction operations and refineries. But an additional 360 million tons each year are emitted when the oil and gas that BP extracts is sold and eventually burned to fuel vehicles or heat homes.

To put that in context, the entire state of California produced 424 million tons of greenhouse gas emissions in 2017.

To shrink the emissions that come from the use of its products, BP may have to reduce the amount of oil and gas that it extracts, develop lower-carbon fuels such as those made from algae or plants, or offset its fuel emissions through steps like planting trees or investing in still-nascent technology to suck carbon dioxide out of the air.

Mr. Looney said in a statement that BP would begin laying out a more detailed strategy in September.

The announcement came with a caveat: BP isn’t currently planning to zero out emissions from oil and gas extracted by other companies and then processed by BP and resold. The burning of those fuels creates an additional 77 million tons or so of emissions each year, the company said. Instead, BP will aim to cut the carbon intensity — the amount of emissions per unit of energy — from these products in half by 2050.

That falls slightly short of the target set by the Spanish oil company Repsol, which in December set a net zero goal for all of the products it produces and sells. But Repsol is a much smaller oil company than BP.

Some environmental groups offered cautious praise for BP’s pledge, though they said they would need to see more details and concrete actions. But other green groups said they would not consider BP serious about climate change until it made a commitment to stop expanding its extraction of fossil fuels.

“Unless BP commits clearly to stop searching for more oil and gas, and to keep their existing reserves in the ground, we shouldn’t take a word of their P.R. spin seriously,” said Ellen Gibson, a campaigner for fossil-fuel divestment with the environmental group 350.org in Britain.

At the news conference, Mr. Looney said he expected BP would still be producing oil and gas by 2050, though he added that he expected oil production to “decline over time.”

Mr. Looney also said BP planned to push governments to enact stricter climate policies, such as a tax on the carbon dioxide emitted by companies. But it remains to be seen how aggressively BP will pursue this strategy. In 2018, under its previous leadership, BP spent $13 million lobbying against a ballot initiative in Washington State that would have imposed a statewide carbon tax, saying that the policy would set a “bad precedent.”

Mr. Looney, who took over as BP’s chief executive in February, signaled he wanted to take the company in a new direction. He vowed to end a corporate advertising campaign that critics called greenwashing and said the company would review its membership in trade associations that opposed stricter climate policies.