Because no means of transport is more harmful to the climate than air travel.
You suspect it, you know it - with air travel you undeniably boost your carbon footprint. Because no means of transport is more harmful to the climate than air travel. Since 1990, global air traffic has almost tripled and continues to grow strongly. Realise that air travel is so cheap because environmental damage is not priced in. And kerosene for air travel is not taxed, unlike energy for rail and car travel. Consider whether or how often you can do without air travel in order to live more sustainably. How about taking the train to climb the Alps instead of trekking in the Andes? Or how about less spontaneous city trips and more biking tours? If it still has to be a flight, look for ways to offset your CO2 emissions.