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Naturally we in the Cidade Maravilhosa are delighted to have beaten out the Windy City and snatched the 2016 Olympics from under the nose of the not-quite-glamorous-enough first couple of the United States: even Obama can’t compete with Copacabana when it comes to wowing Olympic committees.

But now that the cheering has died down along with the hangovers, a sober consideration of what the Olympics will mean for the world’s most interesting and biodiverse urban environment is in order.

You don’t normally associate biodiversity and conservation with cities, but Rio de Janeiro is an exception. Its extraordinary topography means steep hill slopes and mountainsides are still forested: not the least of the issues associated with the growth of favelas, Rio’s hillside slums, is that their expansion corrodes this green mantle.

Rio’s forests are a remnant of the Atlantic Forest that once covered most of coastal Brazil and stretched as far inland as Paraguay. Only 7 percent is left, making it much more threatened than the Amazon and even more biodiverse, since the surviving fragments act as refuge areas for species that once had much wider ranges. This makes what survives of the Atlantic Forest extraordinarily important. One of Latin America’s oldest national parks, Tijuca National Forest, sits entirely within the city’s boundaries, a natural treasure greater than any of its beaches. What does the Olympics mean to all this? In short, a mixed bag.

There will be big environmental benefits. The thing that first strikes visitors arriving at Rio’s international airport, after the dilapidation of the airport itself, is the stench when you step outside the terminal. This toxic olfactory cocktail comes from the chemical plants and oil refineries that line Guanabara Bay, together with the sewage produced by the 5 million inhabitants of the Zona Norte, where tourists never go but half of Rio’s population lives. Gagging on your way into town is an appropriate introduction to the contradictions produced by our glamorous international profile.

With the eyes — and, more to the point, the noses — of the world upon us, something will finally be done: serious sewage treatment and pollution control is coming. Maybe by 2016, for the first time in generations, it will even be possible to swim in the bay. One shudders to think what will happen to the yachting crews otherwise.

But beyond the bay, things are more ambiguous. The coming construction boom will provide alternative employment to the young men in the favelas who would otherwise move into our biggest growth industry after oil: narcotráfico. This boom will tamp down violence from criminals and the police (there’s a big overlap between the two). The easy headlines about the risks posed by violence in Rio are misleading: nobody, from the drug lords down, has any interest in choking off the multidimensional bonanza the Olympics promises to be.

And therein lies a problem: after having been stable for 20 years, the city’s population is likely to jump again as the boom attracts migrants from all over Brazil, which means expanding favelas and more human pressure on that precious Atlantic Forest.

This will be most acute in the southern beachside neighborhoods of Barra, Recreio and Vargem Grande, which were booming for years even before the Olympics. Many of the new sporting facilities in Rio’s bid, including the Olympic village, will be built here. As recently as the 1970s this area was still largely undeveloped, the stupendous beach of Barra fringing an unspoiled expanse of mangroves, coves and headlands ending in Barra da Sepetiba, a scalloped and shifting promontory of dunes and beaches pointing 12 miles into the Atlantic and the glorious (now rapidly overdeveloping) coastline south of Rio.

This oasis of nature so close to a megacity couldn’t last. From the late 1970s, a gigantic real estate boom saw Barra transformed into a depressingly Americanized complex of malls, highways, condominiums and apartment blocks. As the only reasonably flat area with land available anywhere in the city, it was inevitable this area would be earmarked for Olympic development, but the key issue is what impact this will have on the coast’s surprisingly strong zoning and development controls.

Rio’s governments, appalling as they often are, occasionally get some things spectacularly right — the 40 percent drop in driving deaths since a well-enforced ban on alcohol and driving began last year is a current example. In the late 1990s, in the nick of time, a municipal park called Prainha put the coast immediately south of the real estate boom off limits to developers, preserving the two stunning beaches of Prainha and Grumarí and linking them up to the still pristine coastline around and including Barra da Sepetiba, long preserved by the Brazilian Navy, to whom the promontory belongs. Ironically, a few months before the success of the Olympic bid, the developers had managed to get the zoning laws in Prainha relaxed. Now, with blood already in the water, the level of development is about to spiral. It could well spiral out of control — and if it does, the last piece of properly preserved coastline within the city’s boundaries will go.

Those of us who know and love Rio feel torn. On the one hand, there’s no denying this is a great city with a great talent for spectacle, and it has all the potential to stage a great world event like the Olympics, perhaps more memorably than has ever been done before. But Rio is a memorable place in other, less positive ways. Many local politicians would shock even Tony Soprano, and their corruption and incompetence has mismanaged the city into the ground. Many of its well-known problems are directly traceable to the city’s dreadful politics. With Brazil’s international image on the line, the federal government may have to step in.

The stakes for Rio’s environment are even higher. An image taking a hit is, in the final analysis, a trivial thing — but once a coast or a forest goes, it almost never comes back. Fingers crossed.

-- Text by David Cleary, Cool Green Science Blog

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