If the goal was to get the world focused on sustainable development, then this definitely counts as terrible timing.

With global leaders pressured by the unending European debt saga—which most recently has engulfed Spain, the euro zone’s fourth largest economy—it’s not surprising that environmental concerns aren’t exactly at the front of their minds. Accordingly, Barack Obama, Angela Merkel, and David Cameron aren’t attending the United Nations Conference on Sustainable Development (dubbed “Rio+20”), which opens in today in Brazil’s “Marvelous City.” They’re dispatching their administrations’ next tier personages in their stead—still heavyweights (especially in Hillary Clinton’s case), but the move hardy suggests that Rio is at the top of the global agenda.

Indeed, the gloom and pessimism about this mega-environmental conference is manifest. In one sad tweet, Bill Easterly of New York University commented, “Delegates gather in Rio to commemorate 20 years of nothing happening since a UN Summit where nothing happened.” In fact, leaked negotiating text from the summit suggests we can expect a statement full of good intentions, expressing much concern, oh yes much concern about our environmental plight–but few commitments to do anything.

In other words, more of the same.

In the 20 years since the historic 1992 Earth Summit in Rio, the world has clearly failed to fulfill that event’s lofty goals. And perhaps that was too much to ever expect. Describing the ethos of that bygone era, Mikhail Gorbachev recently put it this way: “there was an overwhelming air of enthusiasm and hope for the future. It was a time of optimism and, in retrospect, innocence, as everyone celebrated the end of the Cold War.”

A case in point of such over-dreaming and under-delivering is the 1992 United Nations’ Framework Convention on Climate Change (UNFCCC), forged in Rio, in which signatory countries pledge to avoid “dangerous anthropogenic interference” with the climate system. The U.S. is a party to this treaty; and then-president George H.W. Bush attended the 1992 Earth Summit to endorse it.

And what have we done since? Nothing serious, nothing binding—while the problem gets worse, and worse, and worse. Back in 1992, carbon dioxide concentrations in the atmosphere were just over 350 parts per million. Today, they’re fast approaching 400. Climate scientists today are terrified about the world we are creating—one destabilized by more frequent extreme weather events, higher sea levels, and many other effects. And yet we do nothing.

So what should we then expect from Rio+20, other than another occasion to muse upon the inability of Earth’s dominant species to see itself in the mirror, and rise above daily concerns to address the big picture?

My honest take on all this is not mind-blowingly optimistic—just less than fatalistic.

First, let me admit that I’m as cynical as the next person about big U.N. galas. For instance, I was sorely disappointed by Copenhagen after attending in December of 2009. Notably, the event was held in a northern winter, which completely undermines the global warming message for every person who learns about Copenhagen through, you know, a television broadcast. (The same is technically true of Rio+20—it’s winter in the Southern Hemisphere—but hey, it’s Brazil.)

More generally, I’m worried by the mass chaos of these events—the epitome of how liberal do-gooders get it wrong, by being unorganized and undisciplined and kinda all over the place. In Rio right now, the impression from outside is that everybody’s battling over a very diffuse agenda, with bureaucrats producing wonky texts that are high on detail but dramatically scant on clear, uplifting messages or firm commitments.

But nevertheless, there are some reasons for at least modulated optimism. Here’s the first, and simplest: Expectations are so radically low at this point that Rio could definitely surprise us. In effect, there’s nowhere to go but up.

Here’s another positive: Environmental activists have done a stunning job of getting their message out about what should happen at Rio. They want an agreement to cut the hundreds of billions of dollars in global fossil fuel subsidies—surely, if one actually cares about sustainable development, a no-brainer. And they launched a powerful trending Twitterstorm (#endfossilfuelsubsidies) on June 18 to get across this indisputable message. That’s going to be remembered, even if the “message” of Rio’s bureaucrats isn’t.

Third: Whatever doesn’t or doesn’t happen at Rio, let’s remember that we have a lot of reasons to feel good about the big picture future of clean energy.

I spend a lot of time with scientists, including those who focus on renewables. And to compare the tone of cynicism around Rio+20 with the optimism and the vision they impart can only be called jolting. They’ll tell you the straight facts: The sun provides enough energy to the Earth, in an hour, to power our societies for a year. And you seriously tell me we can’t tap into it enough to make it our dominant energy source? We absolutely can. We’re already beginning to.

Researchers today are digging into all sorts of ingenious ways to do it, like engineering nanoparticles that will make our ability to tap solar energy more efficient. For an example, see here. And that’s just one case, at one university that Uncle Sam happens to be funding.

Indeed, whatever happens in Rio, Stephen Lacey points out that the growing global alternative energy industry has seen $ 1 trillion in investments since 2004. That’s certainly not enough, in significant part because the United States hasn’t been the leader it should have been. Plus, fossil fuel subsidies are dramatically thwarting progress—a problem that Canada is certainly not helping. But the bottom line is that this is serious. And in the long term, it will change the world.

So in sum, it’s very true that right now, we’re staring down a stupendous failure of vision and leadership, on a global scale, to address pressing problems of environmental degradation. Rio+12 is shaping up to provide an exclamation point on that—and it’s fundamentally because we’re wedded to short-term, amygdala-driven thinking. It’s myopic in the extreme: In 20 years, people aren’t going to remember what the bond yield was on a Spanish 10 year note. They’re not going to remember the stock market gyrating whenever Wall Street decides to remember the existence of Europe. No: They’re going to remember that we were about to cross 400 parts per million in the atmosphere, and we didn’t do anything about it.

Or our policymakers didn’t, anyway. But our scientists and entrepreneurs? Let’s remember they’re at work on the problem–and they’ve always been a better long term bet than politicians anyway.