As thousands of people prepare to convene in Brazil this month for the Rio+20 Earth Summit, scientists and environmentalists alike are sending a sharp message: The planet is in dire straits.

On Wednesday, the United Nations Environment Program issued a report showing that the world has made significant progress on only four of the 90 most important environmental objectives agreed on through the U.N. process. Gains have come in eliminating ozone-depleting substances, phasing out lead in gasoline, increasing access to water supplies and encouraging research into marine pollutants. In most other categories — including protecting plant and animal species, curbing marine pollution and conserving water supplies — humanity is falling short.

“If current trends continue, if current patterns of production and consumption of natural resources prevail and cannot be reversed and ‘decoupled,’ then governments will preside over unprecedented levels of damage and degradation,” UNEP Executive Director Achim Steiner said in a statement.

The journal Nature published a series of articles Wednesday on the precarious state of the planet, including a study that warns that the world could be approaching a tipping point at which human activities cause a “planetary-scale critical transition” to a different environment.

Twenty years ago, the Rio Earth Summit produced three major treaties intended to head off these kinds of dire outcomes, including the U.N. Framework Convention on Climate Change and the U.N. Convention on Biodiversity. Although the global community has failed to achieve the goals set out by those accords, the meeting was seen as a critical moment at which environmental concerns took center stage in global policymaking.

But even the most prominent proponents of the U.N. Conference on Sustainable Development, which will take place June 20-22 in Rio de Janeiro, do not expect this gathering to produce a significant global agreement.

“As things currently stand, we are facing two likely scenarios — an agreement so weak it is meaningless, or complete collapse,” Jim Leape, director general of the World Wildlife Fund, said in a statement Tuesday. “Neither of these options would give the world what it needs.”

“When they gather in Rio, governments must restrain the flow of weasel words that is threatening to emasculate any agreement,” Leape added.

“We do need these moments to sit back and reflect on where we are, and where we’re going,” said Frances Beinecke, president of the Natural Resources Defense Council, adding that pledges by world leaders at these meetings often fail to materialize later on. “They don’t translate into action in the way that we would hope.”

‘Cloud of commitments’

The global economic crisis has made this year’s summit especially difficult. “The fact that we have an economic recession [in Europe] and economic problems everywhere is not helping very much,” said Jos Delbeke, the European Commission’s director general for climate action, adding that “the exact nature of what is going to be agreed to [in Rio] is hard to tell.”

At this point, many of the groups most invested in environmental action are working on what Beinecke refers to as “a cloud of commitments” — concrete pledges by businesses, governments and civil society groups that could help shift the environmental trajectory, and can be monitored in real time on the Internet.

Last month, for example, 10 African leaders vowed at a summit organized by Conservation International in Botswana to pursue a more sustainable path of development that would preserve what they called “natural capital,” the environmental resources their countries possess.

On Tuesday, the World Bank issued a report outlining how it will work to foster economic development that conserves natural resources and limits pollution even as it provides transportation, energy and food to a growing population. U.N. Secretary General Ban Ki-moon has unveiled an initiative called “Sustainable Energy for All,” which is likely to become a focus of discussions at Rio along with a push to eliminate fossil-fuel subsidies. Ban’s proposal aims to double energy efficiency and double renewable sources in the global energy mix by 2030 while providing reliable lighting and heating to the more than 1.3 billion who still lack it.

“I think everyone will know where we need to go coming out of Rio. Our job is to show, ‘Here’s one way to do it,’ ” said Rachel Kyte, World Bank vice president for sustainable development. “We don’t have to have global agreements. It would be nice. . . . It would be a whole lot easier if we had them, but we can move forward without them.”

Many are looking to the business community to take the lead at this point, by integrating environmental concerns into their everyday operations. Ceres, a group of investors, companies and nonprofit groups, recently conducted a survey of 600 major U.S. companies and found that just a quarter of them had incorporated sustainability into the way their firms were governed, and only a third had targets with a specific date for reducing their greenhouse gas emissions. At the same time, it noted that Coca-Cola was on track to improve its water efficiency this year by 20 percent compared with 2004, and Intel has cut its greenhouse gas emissions 8 percent two years after tying employee and executive compensation to meeting the firm’s environmental targets.

“Companies are getting it, that climate, water depletion and natural resource scarcity are business risks, not off-balance-sheet risks,” said Ceres President Mindy Lubber. Still, she added, “we’ve got an awfully long way to go.”

In the meantime, however, researchers continue to publish sobering findings. The UNEP report noted that indoor air pollution from fine particles — emitted from cookstoves and other sources — causes nearly 2 million premature deaths a year, including 900,000 deaths in children younger than 5.

The world missed its U.N. target for achieving a significant cut in the loss of species by 2010, it added.

In some ways, global connectivity and rising incomes are helping fuel these problems. One paper Nature published Wednesday, authored by six researchers from Australia, Japan and Italy, found that 30 percent of the threats facing species worldwide stem from international trade, whether it is palm oil production or mining.

The most daunting assessment may have come from a team of 22 scientists from five nations that warned that humans have radically changed 43 percent of the Earth’s surface from its natural state, far outpacing the 30 percent change that helped trigger the last planetary-scale environmental shift roughly 11,000 years ago, when glaciers advanced and then retreated.

The paper’s lead author, Anthony Barnosky, a professor of integrative biology at the University of California at Berkeley, said that although it is impossible to predict an exact moment when this change could occur, “what we’re trying to convey is that these planetary tipping points actually do happen.”

If development keeps up at its current pace, he added, humans will have transformed 50 percent of the world’s land by 2025, and the consequences could be dramatic.

“People don’t do so well with rapid change because we base our whole economic system and food production and way of life expecting what is natural now is going to be natural going into the future,” he said, adding that many policymakers have not grasped how interconnected their communities now are. “People tend to think on a very local scale, and that’s what we actually need to get away from, both scientifically and politically. We have to realize in some sense, there is no local scale anymore.”