California Academy of Sciences in San Francisco

RENZO PIANO DESIGN: The 2-plus-acre roof is grassy, and the San Francisco buildingÂ’s bulbous forms push their way up. Different sections of the landscape will bloom throughout the year. (Tim Griffith / California Academy of Sciences)

RENZO PIANO'S original concept for the new California Academy of Sciences building in Golden Gate Park was elegantly simple: Slice out a huge, rectangular section of the park landscape, lift it 36 feet into the air and slide a new piece of architecture underneath. The floor of the park would become a green roof atop the facility -- a feature Piano dubbed "the flying carpet."

The completed academy, which opens to the public today, is neither perfectly elegant nor perfectly simple. The building's marriage of well-behaved classical proportion and shape-shifting organic form is sometimes strained. Its precise, transparent facade sits rather uncomfortably atop a long fragment of the academy's old neoclassical building, the rest of which was demolished four years ago after suffering damage in the 1989 Loma Prieta earthquake. Inside, blindingly white re-creations of some of the old facility's most beloved architectural spaces -- including the arched, coffered ceiling above the African dioramas and the colonnaded entrance to the aquarium -- offer a sugary counterpoint to Piano's glass walls.

But these seeming contradictions wind up producing an unusually rich, thoughtful and evocative building. It is precisely Piano's attempt to bring together the very different priorities of cutting-edge and green design -- to bring together art and nature, to put it another way -- that makes the $488-million, 410,000-square-foot academy such a breakthrough in the short history of sustainable architecture in this country. Never before has a public building in the U.S. so persuasively made the case for reconciling the architecture profession's high-design wing with its ecological true believers.

In the end, Piano proves self-assured enough to let the academy, which squeezes a natural history museum, an aquarium and a planetarium into a single facility, look a little ungainly in places. (There are many talented architects who would have refused to include the replica of the aquarium entrance, for instance, simply on aesthetic grounds.) The entire structure, in fact, operates as a sizable and moving essay on the difficulty, and the necessity, of compromise. Science, meet intuition. Fixed, meet flux.

Seen from the entrance, where it looks out over Herzog & de Meuron's 2005 De Young Museum, the academy resembles a pavilion in the Mies van der Rohe mold: tall and imposingly wide, with perfect posture. But once you walk inside you see that a number of less rectilinear shapes -- in particular, a pair of huge domes, one holding a new version of the Morrison Planetarium, the other a stunning rain forest with live trees, birds and butterflies -- are pushing to break free of or through the hangar-like Miesian box. Below ground awaits another jaw-dropping space: the reconfigured Steinhart Aquarium, with snaking, almost liquid-looking wall panels by the New York firm Thinc Design. The fish tanks are filled with saltwater piped in from the Pacific.

Once you make your way, via elevator or staircase, to the green roof, which covers 2 1/2 acres and wraps around a large viewing platform, you see not only the tops of the two main domes but other bulbous architectural forms pushing their way up against the structure. Rather than cage the natural world, the box is deformed and perhaps liberated by it. Looked at another way, the curving forms are like bubbles in some primordial muck.

Academy officials and Arup, the engineering firm that worked with Piano and a local firm, Stantec, to realize the building, have called the roof one of the museum's primary exhibits. Containing nine species of native plants, it will filter storm runoff and keep the building cool in summer and warm in winter. It is also ringed by photovoltaic panels that will produce somewhere between 5% and 10% of the building's energy needs. Although that's not a particularly impressive number, most green roofs have no energy-generating power.

Different sections of the roof's landscape will bloom throughout the year, which means that the building itself will have a seasonal character, its personality changing dramatically from month to month. How's that for a concept that strict Modernists -- or strict classicists, for that matter -- would find unsettling?

In a more self-consciously subversive way, the Dutch architect Rem Koolhaas and his firm Office for Metropolitan Architecture toyed with some of the same "Mies is dead, long live Mies" themes in a 2003 student center at the Illinois Institute of Technology. There, a train tunnel runs across and squashes the roof of an otherwise perfectly boxy Miesian building. But at the institute, where Mies taught and designed several buildings, the shadow of the master's work on the campus is literal. In San Francisco, Piano uses the Miesian pavilion as a stand-in for certain architectural standards that are either threatened or made obsolete, depending on your point of view, by the idea that energy efficiency and harmony with nature should be the priorities in any new building.

Many contemporary architects who are captivated by formal innovation -- or perhaps hamstrung by their own egos -- are unwilling to acknowledge those new priorities. Quite a few came to realize at some point during the 1990s that pursuing sustainability in good faith could put a serious dent in their aesthetic standards. That caused many to reject green architecture outright. Others have come around only reluctantly.

Among certain critics, meanwhile, it has become fashionable to say that sustainable design should be invisible. These critics wait for the day that every building will be green as a matter of course -- that we will expect eco-efficiency from our buildings the same way we expect basic structural engineering. This point of view resembles the argument from well-meaning Americans that too many minorities in this country keep making an issue of their race, instead of simply pushing for an entirely colorblind society.

But just as race continues to matter in this culture, there is still a need for green design to operate as much on a rhetorical level as a purely practical one. In the interest of progress -- and in winning hearts and minds, even in a city as progressive as San Francisco -- the opportunities and challenges inherent in green design still need to be made conspicuous. The academy is a necessary step toward the ultimate goal of invisible green architecture, not a premature declaration of it.

Piano's early sketches of the design, of course, hinted at all of these themes. The very act of lifting the park up was a way of making architecture literally subordinate to nature. But as you walk through the building, you realize that a search -- and sometimes a struggle -- for balance suffuses practically every corner. Throughout, the basic layout insists on rationality, symmetry, transparency and a kind of timelessness. But those values are everywhere forced to yield to messier notions: decay and rebirth, hunger and waste, the murkiness of the ocean and the universe, the cycles of the seasons.

The fact that Piano figures out a way for those typically stiff architectural ideals to bend without breaking makes the academy a supremely optimistic piece of architecture. In a moment of collective worry about the environment and the global economy that is edging into panic, Piano, ever the even-keeled humanist, makes a reassuring case that we can figure it all out.

Even more provocatively, he suggests we can do it under one roof, under the collective embrace of universal ideals, without breaking off into factions or tribes. I'm not sure if I believe him. But the building makes me want to.

christopher.hawthorne @latimes.com