Microsoft has pledged to remove "all of the carbon" from the environment that it has emitted since the company was founded in 1975. Chief executive Satya Nadella said he wanted to achieve the goal by 2050. To do so, the company aims to become "carbon negative" by 2030, removing more carbon from the environment than it emits. That goes beyond a pledge by its cloud-computing rival Amazon, which intends to go "carbon neutral" by 2040. "When it comes to carbon, neutrality is not enough," said Microsoft president Brad Smith. "The carbon in our atmosphere has created a blanket of gas that traps heat and is changing the world's climate," he added in a blog. "If we don't curb emissions, and temperatures continue to climb, science tells us that the results will be catastrophic." The company also announced it was setting up a $1bn climate innovation fund to develop carbon-tackling technologies.

Carbon neutral v carbon negative

When a business says it is carbon neutral, it aims to effectively add no carbon to the atmosphere. It can do this by:

• balancing its emissions, for example by removing a tonne of carbon from the atmosphere for every tonne it has produced
• offsetting its emissions, for example by investing in projects that reduce emissions elsewhere in the world
• not releasing greenhouse gases in the first place, for example by switching to renewable energy sources

Until now, most companies have focused on offsetting emissions to achieve neutrality. This often involves funding projects in developing economies to reduce carbon emissions there, for example building hydroelectric power plants, encouraging families to stop using wood-based stoves, and helping businesses make use of solar power. These reductions are then deducted from the main company's own output. The result of this slows carbon emissions rather than reversing them. To be carbon negative a company must actually remove more carbon from the atmosphere than it emits. Microsoft says it will do this using a range of carbon capture and storage technologies. The announcement was largely welcomed by environmentalists, who said it showed Microsoft was thinking about the bigger climate change picture and not just its own role. "It's a hat trick of sustainability leadership," said Elizabeth Sturcken from the Environmental Defence Fund. "But to really shift the needle on climate change, we need 1,000 other [companies] to follow-suit and turn rhetoric into action." However, Greenpeace warned that Microsoft still needed to address its ongoing relationship with oil and gas companies. "While there is a lot to celebrate in Microsoft's announcement, a gaping hole remains unaddressed: Microsoft's expanding efforts to help fossil fuel companies drill more oil and gas with machine-learning and other AI technologies," said senior campaigner Elizabeth Jardim. Microsoft's plan is still more aggressive than those taken by other tech firms, including Facebook, Google, Apple and Amazon, which have not made "carbon negative" commitments.

How will Microsoft achieve its goal?

Microsoft has suggested a range of ways it could remove carbon from the atmosphere, including:

• seeding new forests and expanding existing ones
• soil carbon sequestration - a process of putting carbon back into the ground. This could be achieved by adding microbes and nutrients to parched earth, which should have the added benefits of making the soil more fertile and less susceptible to erosion
• direct air capture - sucking carbon dioxide out of the atmosphere, possibly by using large fans to move air through a filter that can remove the gas
• bio-energy with carbon capture - growing crops and then capturing the CO2 they emit when, for example, they are burned to produce heat or fermented to make fuels such as bioethanol. Negative emissions become possible if the amount of CO2 stored as a result is greater than that emitted during production, transport and use

Tech companies' manufacturing and data-processing centres create large amounts of carbon dioxide. By one estimate, the sector will account for up to 3.6% of the world's greenhouse gas emissions this year, more than double the level in 2007. And it has been forecast that in a worst-case scenario, this could grow to 14% by 2040. Microsoft has said it plans to halve emissions created directly by itself and those involved in its supply chain by 2030. One way the company intends to do this is by increasing the carbon fees it charges its internal business groups. Since 2012, Microsoft has forced its divisions to set budgets that take account of the cost of emissions created through electricity use, business travel and other activities. Now that charge will incorporate indirect emissions such as those created by customers using electricity to power the divisions' products. And since Microsoft cannot avoid producing CO2 altogether, it will invest in technologies to capture and store the gas to reduce the amount in the atmosphere. Mr Smith said this would involve tech "that doesn't fully exist today". The firm added that its data centres and other facilities would use 100% renewable energy by 2025.

How do Microsoft's plans compare to rivals?

Software-maker Intuit has also pledged to be carbon negative by 2030. The Californian company has said it will reduce emissions by 50 times more than its 2018 carbon footprint. Amazon's Jeff Bezos announced in September 2019 that his company would be carbon neutral by 2040. His pledge included plans to buy 100,000 electric vehicles for the online retailer's delivery fleet. Google has launched a set of digital tools to allow cities to track and reduce emissions. The search giant also offsets its own emissions by investing in green projects.