Go on a holiday by train, bus, or car instead of by plane, as planes are major contributors to greenhouse gas emissions (on top of that, planes produce damaging high-altitude contrails that reflect heat back to Earth!); at least, always carefully consider wether flying really makes sense; in many countries high-speed railway links – which are amazingly energy-efficient and produce no contrails – are now competing with air traffic; unfortunately they are often still more expensive than flights: make the effort and tilt the balance in favour of the railway!