Driving cars with petrol or diesel directly burns fossil fuels, so contributing to climate change.
If you have to drive a car, there are a number of actions which can reduce your climate impact.
Electric cars, hybrid, and bio fuelled cars, are just some of the innovations on the market.
Your old car can be made more fuel efficient.
And you can learn smarter driving habits:

http://www.dft.gov.uk/ActOnCO2/

Flying also burns fossil fuels. The impacts on the climate are also understood to be worse due to the height that they are emitted.

If you wish to try lower carbon emitting ways of travelling, this is a useful journey planner.
It shows you the options of taking a journey and how they compare in time and carbon.
You can compare between flight, car, coach and train:

http://www.transportdirect.info/

This is also a useful website for exploring train journeys as an alternative to flying. This can also be a more enjoyable and interesting way to take a holiday.

http://www.seat61.org