Unless the world addresses the problem, by 2030 even two planet Earths would not be enough to sustain human activity, WWF said, launching its "Living Planet Report 2012", a biennial audit of the world's environment and biodiversity - the number of plant and animal species.
Yet governments are not on track to reach an agreement at next month's sustainable development summit in Rio de Janeiro, said Jim Leape, WWF International's director general said.
"I don't think anyone would dispute that we're nowhere near where we should be a month before the conference in terms of the progress of the negotiations and other preparations," Leape told reporters in Geneva.
"I think all of us are concerned that countries negotiating in the UN system for an outcome for Rio have not yet shown a willingness to really step up to meet these challenges. Those negotiations are clearly still tangled."
EU's Rio agenda
The European Union is pushing an agenda for Rio that includes binding targets for the expansion of sustainable energy to developing nations, a shift to a more resource-efficient economy and biodiversity protection. It also wants to strengthen the UN Environment Programme to give it more muscle to monitor and enforce treaties.
However, EU officials have recently acknowledged that they face high hurdles in achieving the EU's goals.
The Rio+20 meeting on 20-22 June is expected to attract more than 50,000 participants, with politicians under pressure from environmentalists to agree goals for sustainable development, in the spirit of the Rio Earth Summit that spawned the Kyoto Protocol 20 years ago.
Despite that pact aimed at cutting planet-warming carbon emissions, global average temperatures are on track for a "catastrophic increase" by the end of the century, WWF said.
Leape said there were many initiatives governments could take unilaterally without being "held hostage" to the wider negotiations for a binding global climate deal to replace Kyoto, which expires this year.
It said the world should move away from "perverse" subsidies on fossil fuels that amount to more than €389 billion annually and ensure global access to clean energy by 2030.
Asked why environmentalists were still struggling to win the argument that something needed to be done, Leape said: "Let's not underestimate the inertia in the system.
"We've built an economy over the last century that is built on fossil fuels and on a premise that the Earth's resources could not be exhausted. You see that conspicuously in the case of the oceans, where we've been taking fish as if there were no tomorrow, as if fish would just always be there.
"Secondly, we're doing it in the context of a marketplace that continues to send the wrong signals. So many of the costs that we're talking about are not built into the prices you see ... Markets can work well if prices are telling the truth but at the moment they don't, in hugely important ways."
Consumers were helping to turn the tide, he said, because of certification regimes that give products a seal of approval, forcing companies to abide by certain standards.
"You see a growing number of commodities in which this approach is rolling out. It's in timber, it's in fish, but it's also now in palm oil and in sugar and in cotton and so forth. I think that's part of creating market signals, to allow consumers to send signals, to show their preferences and to actually begin to build a market that's heading towards sustainability."