From Badvertising: Polluting our minds and fueling climate chaos:

The only provably legitimate offset [for carbon emissions from a flight] would be an engineered solution that removed a measurable amount of carbon directly from the atmosphere on roughly the same timeframe as the plane exhaust put it there, and indeed this option is now available for purchase from a company called Climeworks - at a price of around $1,000 per ton. This is approximately 100 times the price of an equivalent offset from a low-cost carrier like Ryanair; readers can no doubt draw their own conclusions.

Climeworks “is the first direct air capture company worldwide to achieve certification of its carbon dioxide removal activities…”.

From what I’ve read, it is the real deal. It's not just for businesses, but for individuals too. Use them to do your own offsetting.