For us living (ecologicallay) sustainable means to live in a way that if everyone would live that way the earth would stay a place that is worth to live in forever. That's why we try not to produce any permanent waste (neither plastic bags nor CO_2 emission), save energy and utilize our resources so that they can self-regenerate. This requires a very concious way of consumption.
Many people try in their daily lives at home to save resources and minimize their harming effects on the environment. But when it comes to travelling only very few people think of sustainability and pretection of the environment. But that's where the rabbit sits in the pepper and the dog lies buried. (That's a german saying, meaning "that's the key point".)
According to http://www.co2-emissionen-vergleichen.de the CO_2 emission of an airplane is about twice as much per person pero kilometer than that of a car. But why do many people feel guilty when they drive 2 km to the next bakery by car but not when they fly to Hawaii for new years? That's 24 000 km!
For us this became clear when I (Philip) calculated my ecological footprint [e.g. http://www.footprint-deutschland.de/]. When I did this I forgot to indicate my airmiles and after correcting this the result was suddenly miserable. A huge part of my environmental impacts was due to
Another key experience was our trip to India in spring 2013. We went there also for travelling but most of our time we actually spent working at a reforestation project. Sustainability was very important in that community: the food was completely vegan, electricity was generated with soalar panles, and for showering and washing clothes you would pump water in some bucktes with muscle force. The soap and even toothpaste was organic. And on top you would seperate solids and liquids when going to the toilet in order to ensure optimal reusage.
A big part of that community was actullay formed by vlounteers like us taht would only live and work there for a couple of weeks - and most of them travelled there by airplane. Slowly we realized that the efforts we made during the projecta are neglectable compared to the ecological impact that arose due to our flight form germany to India. And more: the same is true for many of our daily efforts we make at home.
So, what can one do to live sustainable - and travel nevertheless?