Harry and wife Meghan have faced mounting criticism after reportedly taking four private jet journeys in 11 days during the summer, which is at odds with their views on supporting the environment.
The duke flew to the Netherlands on a commercial plane for the launch event in Amsterdam but faced a question on his past use of private jets.
He responded: "I spend 99% of my life travelling the world by commercial, occasionally there needs to be an opportunity based on a unique circumstance to ensure that my family are safe - it's genuinely as simple as that."
He went on to say that he balances out the impact he has on the environment and will continue to do so.
The duke added: "I've always offset my CO2, I think part of the group discussion we had earlier was 'what is off-setting CO2?'
"There are so many people out there that hear about it, don't know about it. In my mind it's the right thing to do and we need to make it cool, but it can't just be a ticking-the-box exercise."
The event in Amsterdam focused on encouraging travel firms and tourists to make sustainable decisions.
Harry has spent three years working on the initiative, called Travalyst, which he hopes will improve conservation, environmental protection and help increase the economic benefits from tourism for local communities.
The duke and the co-founders of the project – Booking.com, Ctrip, Skyscanner, TripAdvisor and Visa – hope to spark a movement of like-minded organisations to transform the future of travel.
Harry said in a speech to launch the initiative at the A’dam Tower: “What is clear across this vast landscape is that our world faces environmental challenges of unprecedented scope and scale.
"From deforestation and the loss of biodiversity, to ocean plastics and poaching, the problems can sometimes seem too big to fix."
The duke added these challenges could be solved by a "giant system shift", which is what this partnership is trying to do.
“Sometimes the scale of the conservation crisis feels overwhelming and that individual actions can’t make a difference."
He added: “And, while no-one is perfect, we are all responsible for our own individual impact; the question is what we do to balance it out.”
It is unlikely the duke or other members of the royal family will stop taking private jets as security, time constraints and safety are normally put forward by royal households for travel decisions.
But it remains to be seen if there will be any public announcements about how the Duke mitigates his impact on the environment.
In his speech at Amsterdam’s iconic A’dam Tower, the duke outlined the , made famous by the film The Beach, where its reefs have died, to Africa, where safari vehicle “traffic jams” are beginning to outnumber the wildlife.
But he stressed there were positives, adding: “Tourism can be a source of opportunity for communities that might not otherwise find it. Tourism can strengthen the local economy.
"Tourism drives improvements in the quality of life for so many. In some cases, it’s all they have.
“It accounts for 10% of global GDP and about one in ten jobs worldwide, figures that will continue to grow in the coming years. This is the scale of the opportunity.
“There are positive trends in the travel industry as well. Seven in ten travellers say they want more sustainable travel options.”
The launch comes as trips made by travellers are increasing, according to the UNWTO, the United Nation’s agency responsible for the promotion of sustainable tourism.
During 2018 it estimated that worldwide international tourist arrivals increased 6% to 1.4 billion.
Harry added: “People are speaking up. They want to see the world, but they also want to know that with all the good that they take home — souvenirs, memories, photos, that they leave just as much good behind.
“They want a paradigm shift and I believe one is coming. I believe we can -and we must -find new ways to minimise the dangers and maximise the opportunities of tourism.”