Delta Air Lines plans to become carbon neutral over the next decade. But that doesn't mean it will stop emitting carbon. In fact, it can't."We will continue to use jet fuel for as far as the eye can see," said Delta CEO Ed Bastian in an interview Friday on CNBC. "We'll be investing in technologies to reduce the impact of jet fuel. But I don't ever see a future where we eliminating jet fuel from our footprint."Delta will need to use carbon offsets to become carbon neutral, either buying them in the market or investing in projects to reduce carbon in the atmosphere such as tree planting programs.Air travel creates a significant amount of carbon emissions. Delta reports that in 2018, the most recent year for which data is available, its carbon dioxide emissions came to 37.7 million metric tons, with 98% of that coming from aircraft emissions.Flying is one of the worst ways to travel from a carbon emissions standpoint, said Peter Miller, a scientist at the Natural Resources Defense Council."If you're going between D.C. and New York, and you have the option for how to travel, flying that short-haul flight is the worst of the three options," he said. "Driving is not as bad, especially if you have a fuel-efficient car. The train will generally be the best."Delta says it will spend a total of about $1 billion over the next 10 years to meet its carbon neutral target over the next 10 years. It said that target includes all of its businesses, including a Pennsylvania oil refinery that it owns.While that's a significant amount of money, it's unlikely to be a major hit to the company's bottom line. Spending an additional $100 million a year would have reduced its 2019 profit by only about 2%.At this point, Delta can't say how much of its carbon neutral goal can be accomplished through reducing its actual emissions versus offsets.Delta says it is the first global airline to make such a pledge. JetBlue recently made a similar pledge, saying it would offset carbon dioxide emissions from jet fuel for all domestic JetBlue flights beginning in July.Airlines are concerned that environmentally conscious consumers might avoid air travel because of its carbon footprint. That is a larger issue in Europe, which has rail systems that provide competition to flying. The German term "flugscham" or flight shaming, has become the center of a movement there. Efforts to reduce energy consumption make good business sense. Fuel is the second largest cost at every major airline, behind only labor costs. Delta spent $8.5 billion on fuel last year."There's not a lot of opportunity for airlines to become more efficient," said the NRDC's Miller. "If there were technologies that were available to be more fuel efficient, airlines would have adopted them already."Still, Miller said Delta's pledge is admirable, although he will remain skeptical until the details are known."It's like someone saying, 'I'm going to lose 50 pounds,' or, 'I'm going to get an A in that class.' Great, that's an admirable goal. But what are you going to do to get there?" he said."I wouldn't criticize them for setting an ambitious goal without knowing all the details," he said. "But I want to see how they meet the goal."