Tonight, PBS will be airing “Nova: Dimming the Sun” and “Journey to Planet Earth: The State of the Planet’s Wildlife.” (Check local listings.)

Over in the television section of The New York Times you’ll find a review of these two shows, as well as HBO’s “Too Hot Not to Handle” that Dave wrote about here.

When television is such a mathematical word problem, it hurts the idle brain. But idling is exactly the problem, and three nationwide Cassandra cries dominate this week’s public-affairs programming, with urgent calls for action. “Journey to Planet Earth: The State of the Planet’s Wildlife,” being shown tonight on PBS, explains the increasingly inhospitable outlook for all earthly creatures. The “Nova” report “Dimming the Sun,” also on PBS tonight, complicates matters with the latest findings about how pollution has masked the effects of global warming. And on Saturday HBO declares the whole climate-change crisis “Too Hot Not to Handle.”

If you watch any of these, feel free to write your own review here.