The skies opened Saturday over New York, but not even rain and lightning stopped the street fair at the World Science Festival. Where else could you see a band called “The Mathematicians” playing songs with titles like “Input, Output” lyrics about the x axis and the y axis? I’m afraid I can’t fully explain the significance of the axes — the lyrics were a little hard to understand — but I liked the music, and I loved the fair. It was great seeing Washington Square filled with kids dissecting owl pellets, oohing at rocket launches and talking to Lucky, Disney’s animatronic dinoasaur.

My colleague Patricia Cohen has a report at ArtsBeat on the Disney Imagineering demonstration Saturday. I can report that my 9-year-old son, Luke, gave it a rave. He also enjoyed the show by the “mathemagician” Arthur Benjamin, who wowed the audience with mental math — he squared a five-digit number — and he even explained how he did it. He also revealed a very simple and quick technique to multiply 11 times any two-digit number. Can any reader tell me a trick for instantly multiplying 72 by 11? (No, you can’t use a calculator, and no, it’s not multiplying 72 by 10 and adding 72 — that’s too slow.)

My colleague Cornelia Dean attended a session of the festival ominously titled “The Sixth Extinction.” Here’s her report:

When it comes to homo sapiens, you might expect Richard Leakey to take the long view. His parents were the famed paleontologists Louis and Mary Leakey and he spent his childhood in Kenya, where they elucidated the early history and antecedents of our species. Eventually, he became a paleontologist and a conservationist there himself. But though he can see far back into the human past, Mr. Leakey holds out slim hope for our future. He hopes humanity survives at least another generation, he told his audience at Miller Theater at Columbia Friday night, because “I do want my grandchildren to exist.” Unfortunately, though, he told his audience, unless things change it would be unwise to bet on the long term survival of our species. A mass extinction of plants and other animals – the sixth seen on earth — is well under way, he said, with 60 percent or more threatened with extinction within decades. Such a mass extinction would lead to an ecological collapse, he said. “The ability of our species to survive is something we should not take for granted.” In fact, he said, “I don’t think we can project our species with confidence for 100 years.” Another speaker, Bernie Krause, a musician who turned to what he calls bioacoustics, underlined Mr. Leakey’s gloomy message by playing and analyzing audio clips of birds, animals, insects and even trees he recorded in ecological niches from Borneo to Alaska. Most of these audio-files could not be duplicated today, he said, because the environments in which they were recorded have been ruined by logging and other human activity. David Thoreson, a sailor, added photos and stories about his navigation through the Northwest Passage last summer, in an Arctic unusually free of ice. And the audience saw footage provided by the oceanographer Sylvia Earle showing undersea life threatened by everything from climate related ocean acidification to overfishing. The unusual – and hopeful– thing, Mr. Leakey said, is that while earlier extinctions were the result of natural conditions or calamities, this wave of extermination is one we brought on ourselves. Human activity, including the forcing of climate change, is driving this extinction, he said, but if we change our ways, maybe we can turn things around. If not, well…. When climate change forced early humans out of Africa, he said, there were hardly any of us. Today a species of six billion and more, occupying virtually every ecological niche on the planet, cannot simply up sticks and move elsewhere in response to changing conditions. “We have to deal with climate change in a different way,” he said.

If you have any reactions to these warnings — or if you have the instant solution to 11 x 72 — feel free to post a comment.