The grim and the grimmer

Earth Day, the annual examination of our planetary well-being, is approaching, which means that environmental documentaries with their gloomy assessments are at the ready. This year is no exception -- in fact they’re gloomier than ever, which either says something about the state of the Earth or the state of documentaries.

PBS lets loose with both barrels Tuesday: “Dimming the Sun” followed by “The State of the Planet’s Wildlife.” Neither will be made into a Broadway musical anytime soon.

Even discounting for the tendency of environmental reporting to be Cassandra-esque in tone (The leaping lizard is no longer leaping!!) and overly worshipful of certain scientists, “Wildlife” and “Dimming” are solid efforts to bring attention to major menace in our ecological, zoological, climatological midst.

The scope is wide, the photography compelling and, except for too much syrupy background music in “Wildlife,” the presentation is crisp. Take notice unless you’ve already booked passage to another galaxy.

With Matt Damon as narrator, “Wildlife,” done by Emmy Award-winners Marilyn and Hal Weiner, is a survey of threats posed to animals in Asia, Africa, America and points in-between by mankind’s need for food and room to grow.

“We’ve just kind of taken over the planet and there isn’t room for these other species,” says one scientist.

This is not altogether breaking news, but “Wildlife” shows how globalization has exacerbated the downward spiral for many species and their habitat.

The rapid industrialization and population growth in China come in for a kick in the pants, as it does also in “Dimming.” The effect of that growth can be felt thousands of miles away from China. For example, the Chinese demand for soybeans -- to feed the livestock -- means the Amazon rain forest is being cleared away for planting, often with fire.

“In search of soybeans, China is literally burning up the forests of the world,” Damon says.

There are some global bright spots: improved farming in parts of Zambia that has decreased poaching; enlightened cattlemen in Montana who want to save, not destroy, the grizzly bear population.

But mostly it’s a depressing litany of the world’s most exotic animals -- gorillas, tigers and polar bears among them -- struggling to survive. Flights out of Singapore regularly carry rare animals and birds to Europe for pets and even slaughter.

If “Wildlife” is a downer, “Dimming” is enough to make you pull the covers over your head. It’s more science-y but still accessible to the nonmajor.

This is the “Nova” series at the top of its genre: the scientific mystery story, the hunt for answers on several continents, the startling thesis that demands attention.

In this case, the proposition falls into the “no good turn goes unpunished” category. It starts with the finding that less sunlight is reaching the Earth because of air pollution. This makes clouds act as mirrors that bounce the light back into space.

The U.S. and Europe are reducing air pollution in the name of reducing respiratory distress and other ills. That should be good. Should be but isn’t, according to “Dimming.” Air pollution, by cutting sunlight, has been reducing the rate of global warming due to greenhouse gases.

If you reduce pollution -- a good -- you end up increasing the temperature of Earth -- a definite bad -- and increasing the chances that millions will drown, fry or starve -- a mega-bad.

“We’ll get a double whammy,” says one of the scientists.

Yes, two unwanted whammies. And neither one helpful for people or animals dependent on Momma Earth.

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‘Nova: Dimming the Sun’

Where: KCET

When: 8 to 9 tonight

Ratings: TV-G (suitable for all ages)

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‘Journey to Planet Earth: The State of the Planet’s Wildlife’

Where: KCET

When: 9 to 10 tonight

Ratings: TV-G (suitable for all ages)