Potocnik, speaking Monday at the European Environmental Bureau's annual conference in Brussels, admitted the U.N. event fell short of expectations.
Even before the conference, EU leaders lamented the lack of clear targets in the proposed document, which they said they hoped would call for concrete goals on phasing out public subsidies for fossil fuels and providing food, water and energy security for all.
"Rio did not lead to the results we were all hoping for," Potocnik said, adding, "The truth is that the success or failure of Rio was not decided in June. It will be decided in the years to come. The success of Rio will depend on us.
"We can still make a real difference. It's only a question of will and determination. Do we have it?"
The world's nations did for the first time endorse the concept of moving toward a green economy despite reservations of developing countries that contended it may slow growth or impose restrictions on their own plans to grow out of poverty.
The call for a green economy was adopted but the final document asserts the goal should only be applied according to each country's "national conditions" and stage of development -- a bow to the concerns of China and other fossil fuel-dependent emerging economies.
That disappointed many environmentalists who were seeking binding international standards.
"From a certain perspective, one could say that Rio was weak on the green economy -- no strong statements of a global transition to a green economy were actually voiced," Potocnik said. "However, green economy as a pathway to sustainable development is now firmly rooted in the global agenda and many countries are moving forward."
One of Rio+20's chief accomplishments, he said, was the decision to develop universal sustainable development goals, applicable to all countries.
"I cannot emphasize enough how important I find the 'universal' nature of future SDGs," he said.
These goals, to be developed by 2015, are meant to establish a global framework through which every nation would be held accountable on how collectively as a group all of them moved forward to deliver sustainable development.
The debt facing Europe is hindering the efforts to transition into a green economy but the paths to both economic recovery and sustainability aren't mutually exclusive, Potocnik said.
As the European Union struggles to find its way out of the economic crisis, sustainability makes even more sense because it seeks to reduce the consumption of increasingly pricey natural resources, thus strengthening the bloc's competitiveness, he argued.
"These resources are getting more expensive and some of them will run out," he said. "After a century of declining resource prices in real terms, pressures on resource supplies have led to a steady increase of prices since 2000, and prices will inevitably continue to rise and remain volatile."
Thus, he said, the European Union remains committed to transitioning into a green economy is a means for a lasting recovery.