When you travel or live abroad, you leave behind Australia's support systems, emergency service capabilities and medical facilities. The Australian Government will do what it can to help Australians in difficulty overseas, but there are legal and practical limits to what can be done to assist travelers in other countries. You should have realistic expectations about this and read the Consular Services Charter, before you go.
Traveling abroad puts a lot of pollution into the air, but restricting travel just leads to a less globalized community and prevents people from experiencing other cultures. Instead, focus on making being environmentally friendly part of every day life, with restrictions and priorities on saving energy, recycling and reusing items.
While it is true that passenger jets emit a considerable amount of pollution into the air, it does not follow that restrictions on travel will serve to save the envoronment. Often times, people travel to visit exotic sights and experience the wonders of different areas. Because of this desire, the people that travel have an interest in preserving the area. For example, many will never go to the rainforests, However,because there is the possibility that they might and then there are people who definitely will go at some point, those people will be willing to take action to save the rainforest. In short, knowledge and familiaritiy helps to foster a desire to protect.
I do not believe restrictions on traveling abroad would help save the environment. For an already vast amount of the population travel abroad is already out of grasp due to the high price associated with it. I believe adding restrictions would only stop a tiny fraction of the population from traveling, so it wouldn't make a big enough difference to impact the environment either way.
The majority of travel is done by everyday people going too and from work. The only way to make travel restrictions abroad save the environment would be if those restrictions were so onerous that they stopped trade. Such restrictions would be met with widespread opposition, and breakdown of civil society, until power could be wrested back, and environmental destruction could be started up again.