We’re not the only globe in town anymore. On Thursday, the traveling exhibit “Cool Globes: Hot Ideas for a Cooler Planet” will be officially unveiled to the public, with dozens of giant globes designed by local and internationally known artists on display on Boston Common and elsewhere around the city. But the installation of the globes began Monday. The public art display features globes 5 feet in diameter that take on the theme of climate change. On Monday, onlookers got an early glimpse at a globe by artist Alexandra Overing.