Amazon, Walmart, General Motors, and now FedEx.

The giant delivery company joined more than 50 other major corporations when it announced this week that it too aims to be carbon-neutral by 2040 — an effort to curb climate change. Executives say that a gathering cultural change is fueled by companies responding not only to shareholders but also to the growing urgency of climate change and the concerns of their own employees and customers.

On Wednesday, FedEx promised to be carbon-neutral by 2040, 10 years faster than the timeline laid out by the Paris climate accord. The company pledged an initial investment of $2 billion to start electrifying its massive fleet of more than 180,000 vehicles and $100 million for a new Yale Center for Natural Carbon Capture.

“We talk to our customers pretty much each and every day about these issues,” said Mitch Jackson, FedEx’s chief sustainability officer. “Sustainability is not a discretionary thing anymore. I think it’s really become central to a lot of the considerations in thinking.”

Some of the companies promising to meet that goal and inspire other firms to do the same have signed on to an initiative called the Climate Pledge, co-founded by Jeff Bezos, who owns The Washington Post. Those companies include IBM, Microsoft, Unilever, Johnson Controls, Coca-Cola, Uber and Best Buy. Acciona, a Spanish energy and infrastructure company, went carbon-neutral in 2016.

Carbon neutrality means companies must rely entirely on renewable fuels or offset the burning of fossil fuels with the capture and storage of carbon dioxide in the atmosphere.

Yet even the prodigious voluntary steps by a portion of the corporate world lack the speed, scale or scientific know-how needed to move the thermometer of the warming planet very far in the right direction without government support or broader behavioral changes in the private sector.

FedEx, for example, plans to electrify all its delivery vehicles by 2040, but only half of new purchases will be electric by 2025, and many older vehicles will remain on the road for years. Moreover, by 2040 the electrical grids where FedEx recharges its vehicles might still be relying on natural gas, meaning they would not be entirely emission-free.

The company’s website also boasts of an improvement in carbon “intensity,” but the steady growth in FedEx’s business means its greenhouse gas emissions have increased slightly in absolute terms from 2017 to 2019. And the company’s donation to Yale’s new research center is a generous acknowledgment that the current state of carbon capture and storage knowledge is still in the research and development stage.

Even if FedEx delivers on its promise of net carbon neutrality, it will remove less than 0.3 percent of U.S. greenhouse gas emissions.

FedEx Chairman Frederick W. Smith acknowledged the scope of the challenge. Companies have to deal with the problem of climate change “at a scale that just boggles the mind,” he said on a video conference call with Yale administrators.

Raj Subramaniam, FedEx’s president and chief operating officer, said on the same video call that the company’s effort to reach carbon neutrality had “far-reaching impacts for our customers, our industry and indeed our planet.” He said that “climate change is bigger than any one business.”

“There’s an arms race underway for pledges of net neutrality. It’s impressive,” said David Victor, professor of international law and regulation at the University of California at San Diego. “What we’re seeing are big visible companies making announcements. They are bigger, better-organized and more exposed in terms of brand value.”

But Victor cautioned that “these are exploratory big shifts in corporate culture and goals. Making this a reality means doing it with smaller companies and supply chains and stuff that hasn’t been worked out yet.”

Action by big utilities, refiners and concrete manufacturers are also essential if countries are going to meet their own economy-wide goals. Though many of them have already taken steps to reduce carbon emissions, these companies remain the biggest emitters of greenhouse gases.

Getting to 2040 greenhouse gas emission goals is in some ways more difficult for public companies than past emission-reduction efforts, which could be explained as money-saving energy-efficiency measures. In the future there will be more pressure to undertake steps that will cost money rather than save it.

“There is a difference between energy efficiency and this,” Victor said of climate actions. “This is looking far beyond that. Net zero does not mean efficiency; it means complete transformation, and that’s the challenge.”

One major issue for FedEx, as well as other types of air carriers, is how to deal with the fuel used in planes. There are a variety of biofuels and synthetic fuels and newer jets use lighter materials, but given current technology, shipping packages around the world requires sending a lot of carbon dioxide into the atmosphere and probably still will in 2040. Overall, the company’s operations will still generate greenhouse gases.

That’s where the money for Yale — where FedEx chief executive Smith graduated in 1966 — comes in. FedEx, like some other companies, is searching for novel ways to remove and store more carbon dioxide from the atmosphere by using nature. Yale researchers plan to look at agricultural planting techniques to increase capture in soil; developing plants with larger or faster absorption of carbon dioxide; and weathering rocks in a way that locks in carbon.

“Earth’s natural systems are ripe with opportunities,” said Ingrid C. “Indy” Burke, dean of the Yale School of the Environment. “These natural solutions must be used as part of a portfolio of methods to reduce net greenhouse gas emissions.”

“Carbon capture is one potential tool at a time when humanity urgently needs to know more about all the potential tools that we have at our disposal to address the climate crisis,” Paul Sabin, a professor of environmental history at Yale, said in an email. But he warned that “carbon capture research also should not become an excuse for doubling down on fossil fuel consumption, or delaying urgently needed policies to move away from fossil fuel consumption, including the electrification of transportation.”

Sabin also noted that carbon capture “involves ethical considerations related to the control and transformation of rural landscapes, with serious consequences for indigenous and rural communities worldwide.”

The appeal of carbon capture is that a company could balance out its remaining fuel emissions against carbon captured from the atmosphere and stored either underground or in some other form. But while there are a handful of companies that are giving cause for some optimism currently, there are very few commercial carbon-capture companies or projects because so far capturing carbon directly from the atmosphere is costly and uses more energy in the process.

So a key element of air carriers’ plans is looking to the new technologies.

Jackson, FedEx’s chief sustainability officer, said the company is hoping that Yale can help get it to the finish line and bring a big return on the donation.

“The idea for that is to have some of the smartest people in the country, in the world, working on these intractable, intractable problems,” he said. “We think it will help us. We think it will help the industry. And that’s why we made the investment.”

“You see some real live investment in carbon removal,” said University of Chicago economist Michael Greenstone, who served as chief economist for the Council of Economic Advisers in the Obama administration. “But we’re in the top of the first inning on carbon removal, so we don’t know what that’s going to deliver yet.”

Meanwhile, pledges from the corporate world continue to roll in.

“I think there’s been a breathtaking change that’s taken place,” says Robert N. Stavins, director of the Harvard Environmental Economics Program at the John F. Kennedy School of Government. But the change, he said, is a shift in the public demand for action at all levels. And companies are recognizing it.

“They seem to be thinking: ‘We probably better get on board and do something that’s going to be reasonable for us in terms of cost before we really get hit over the head.’"