“An Inconvenient Truth” started off marching bigger than the penguins, but now it’s looking more like “Bowling for Columbine.” Paramount Vantage’s global-warming doc bowed Memorial Day weekend to a boffo $367,311 at just four theaters, giving it a three-day average of $70,333 per play, the highest ever for a documentary. But after expanding, doc has slowed down significantly as it opened in smaller cities and suburban markets. Pic was helped in its early days by a huge round of promotion by Al Gore. The former VP stirred significant media attention, which generated discussion about global warming and attention for the film. That buzz died down as the pic went into its fourth and fifth weekends.