There are now four major oil companies pledging to cut emissions to “net zero,” after Total followed Repsol, BP, and Shell in laying out its plans. And, yet, each one of them defines that vital goal in a different way.  The variations might seem small and technical, but they matter. Oil companies sell fossil fuels that create billions of metric tons of carbon emissions each year. How each company counts and categorizes those greenhouse gases will have a direct impact on the emissions trajectory the world follows in the decades to come.

“Every time an oil company releases a net-zero plan, it adds a layer of cloud,” says David Doherty, an oil specialist with Bloomberg NEF. Let’s clear some of those clouds by digging into the details. The different definitions of “net zero” all depend on counting different types of emissions that can be tied to a company.

Scope 1 emissions are those that companies produce on-site, such as when burning natural gas for heat. Scope 2 emissions are those that third parties produce on the company’s behalf—for example, coal burnt in a power plant. Scope 3 is all of the rest, including the emissions that customers produce when they burn the oil and gas the majors sell.

Here’s what Total announced on May 5:

  • Reach net-zero emissions on Scope 1 and 2 worldwide by 2050
  • Reach net-zero emissions on Scope 3 emissions of all European energy products by 2050 (about 60% of Total’s global Scope 3 emissions currently)
  • Cut the carbon intensity—emissions per unit energy—of any remaining energy products by 60% by 2050, with intermediate targets of 15% by 2030 and 35% by 2040.

All four oil companies with net-zero plans agree on fully cutting Scope 1 and 2 emissions. That’s the easy part, because it’s typically less than 10% of total emissions The hard part is the rest, namely Scope 3 emissions. All the oil companies have different targets:

  • BP will cut Scope 3 emissions from the oil and gas it extracts to zero, and then cut the carbon intensity of the rest by 50% by 2050.
  • Repsol will cut Scope 3 emissions from the oil and gas it extracts to zero by 2050. It does not take responsibility for Scope 3 emissions of the products it sells that come from crude that some other company has extracted.
  • Shell will cut the carbon intensity of all its Scope 3 emissions by 65% by 2050, and then vow to only sell oil and gas to those companies that have a net-zero plan in place or it will offset the emissions for the customers.

No company is really cutting emissions to zero, and definitely not without relying on some form of offsets, such as planting trees, that rarely live up to the high standard of verifiably storing away carbon. A report from Transition Pathway Initiative, a global program, found that none of Big Oil’s climate plans yet comply with meeting the goals set under the Paris climate agreement of keeping average temperature rise to well below 2 degrees Celsius.