Are things looking brighter? Not according to folks on “Nova” (7 p.m., PBS, check local listings). The documentary “Dimming Sun” looks at evidence that airborne pollution is actually reducing the amount of heat and light reaching the Earth’s surface.

So while greenhouse gasses have been aiding and abetting the symptoms of global warming, a phenomenon now called “global dimming” has pulled the Earth’s thermostat in the opposite direction.

But it also might explain some dramatic climate changes, including long-term droughts that have affected millions in Africa and could play havoc with the monsoons that bring needed water to areas that are home to billions of Asians. Chilling stuff, to be sure.

¢ On a similar theme, Matt Damon narrates “Journey to the Planet Earth: The State of the Planet’s Wildlife” (8 p.m., PBS, check local listings).

¢ It’s a little odd when a sitcom most of us gave up for dead returns to the schedule, but that’s the case with “Less Than Perfect” (8:30 p.m., ABC). For those who don’t remember, “Perfect” stars Sara Rue as Claude Casey, a lowly temp at a TV news organization who became the assistant to a vain anchor (Eric Roberts) and who baffled his hapless yuppie staff with her pluck and can-do nature.

But as “Perfect” returns, Claude discovers that her boss has quit, to be replaced by an even more clueless egotist played by Patrick Warburton (“Seinfeld”), who has made a career out of playing dim bulbs.

There aren’t a lot of laughs here, but there is plenty of room for Andy Dick (who plays the naive Owen) to improvise. And you wonder why this show was left for dead?

Tonight’s other highlights

¢ A spy’s suicide seems suspicious on “NCIS” (7 p.m., CBS).

¢ Patti LaBelle, Ashley Parker Angel and Gabrielle Reece compete on tonight’s “Celebrity Cooking Showdown” (7 p.m., NBC).

¢ The seven remaining singers perform great American standards under the tutelage of Rod Stewart on “American Idol” (7 p.m., Fox).

¢ Bachelors and bachelorettes share a party on “Gilmore Girls” (7 p.m., WB).

¢ A patient with a mysterious ailment needs a new liver on “House” (8 p.m., Fox).

¢ Shirley and her ex (Tom Selleck) reunite on “Boston Legal” (9 p.m., ABC).

Late night

Jane Fonda and Shooter Jennings appear on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno hosts Kim Basinger and Sen. John McCain, R-Ariz., on “The Tonight Show” (10:35 p.m., NBC) … Cheryl Hines and Landon Donovan appear on “Jimmy Kimmel Live” (11:05 p.m., ABC) … Jennifer Aniston, 50 Cent and Dan Naturman chat on “Late Night with Conan O’Brien” (11:35 a.m., NBC).