Earth Day is a good time to think about the human footprint revealed by NASA satellite images of cities at night.

My Earth Day guilt trip through the Ecological Footprint quiz, and out the other side.

The National Research Council says that, unless man-made carbon dioxide (CO2) emissions are substantially curbed or controlled, Earth's oceans will continue to become more and more acidic.

Many unique Hawaiian plants and animals are in trouble. A major reason is invasive species that have no natural predators. Read more on Hawaiian endangered species.

The U.S. census it a great resource to look at population change," said Mather, "not only at the national level, but the regional level, state level, and to see what's happening in local communities all the way down to the city block level."

"The Hubble Space Telescope has literally changed our view of the universe," said NASA astrophysicist Ed Weiler. April 2010 marks its 20th anniversary.

This event on the sun can knock out satellites and interfere with earthly communications. It can result in magnificent auroras - the famous northern or southern lights. Be alert in the coming days ...

A break in the weather, and we are back in the air monitoring sea ice. The ice cap is starting to thin. Read more about the ICESat mission here.

"Some people don't believe global warming will happen in this century. And now we have this incident ... " Read more about the Andes tsunami here.

In October, 2010, NOAA will form a new federal office devoted solely to climate, called the NOAA Climate Service. We spoke with interim director Thomas Karl.