Artist Chin Chih Yang will unveil an icy new installation on global warming in Union Square this weekend. On Saturday, the public will be invited to gather around “Burning Ice,” his construction from 21,000 pounds of frozen water. Warmed by the crowd and summer sun, the sculpture’s melting will trigger increasingly alarming lights, sirens and video projections from within the ice–“a forceful visual representation of how human activity is hastening the melting of the world’s great ice deposits.” The public is invited to cool out with the work from 11 to 7 PM, or until it all disappears.