The “personal carbon footprint” concept was popularised by an oil company advertising campaign to divert attention away from their own climate-unfriendly practices.

The concept of a carbon footprint is a very clever one: distil all of the variables that contribute to the climate crisis and express them in a single number. For any industry, consumer product, or person, you can calculate the equivalent amount of CO2 that industry / product / person puts into the atmosphere. The higher the number, the worse for us all. It’s simple, transparent, and useful.
Climate change is complex. People have very reasonable anxiety about their future. Given this, reducing your carbon footprint represents direct and immediate action. So I was surprised to discover that the concept of a personal carbon footprint was not popularised by climate scientists or political activists. No, this one came from BP, and it was not altruistic.
In 2005, BP employed the advertising agency Ogilvy to create a marketing campaign. Evaluate your own carbon footprint, and take steps to reduce it. Take personal responsibility for your impact on the climate! Do the right thing.
Why did BP do this? Well, they were and are one of the world’s largest harvesters of fossil fuels. So they were very keen to shift attention away from what they had done, and towards what everyone should do. Take a global problem and make it personal. Get people to make individual changes rather than pushing for systemic ones.
I don’t want to denigrate anyone’s attempts to solve the climate crisis. We need to do a lot, and we need to do it now. But personal changes have limited effectiveness compared to the other levers: legislation, technological change, international cooperation. After all, the Covid-19 pandemic meant a huge drop in commercial air travel, one of the most polluting industries in the world, and that had only a modest impact on global emissions.
[Thanks to Ryan Orbuch]