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Cloudy Sky, Location Unknown, 2004

Photo: Cumulus clouds

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Piles of cotton-like cumulus clouds fill the sky on a clear day. Mid-level cumulus clouds form between 6,500 feet (2,000 meters) and about 20,000 feet (6,000 meters). They form when humid air cools enough for water vapor to condense into droplets or ice crystals. A single cloud can hold billions of pounds of water, but may not always produce rain.

Earth Day, celebrated annually on April 22, marks the anniversary of the 1970 birth of the environmental movement. Scientists warn that rising temperatures worldwide could fuel extreme weather—just one of many damaging effects of global warming.

(Photo shot on assignment for, but not published in, "Signs From Earth: Heating Up, Melting Down," September 2004, National Geographic magazine)

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Photograph by Peter Essick
INSTRUCTIONS FOR DOWNLOADING WALLPAPER
For Windows 95 or Higher
  1. Determine which size is appropriate for your monitor.
  2. Click the size you wish to download. (See the top of this page.)
  3. After the image appears in your browser, click the right-hand button on your mouse.
  4. On the menu that pops up, select SET AS WALLPAPER or SET AS BACKGROUND.

For Mac OS X
  1. Determine which image size is appropriate for your monitor.
  2. Click the size you wish to download. (See the top of this page.)
  3. After it appears in your browser, drag the image onto your desktop.
  4. From the Apple menu select SYSTEM PREFERENCES.
  5. Select DESKTOP.
  6. In the pull-down menu marked "Collection," select CHOOSE FOLDER.
  7. Locate desired image file and double-click it.

INSTRUCTIONS FOR DELETING WALLPAPER
For Windows Users (Internet Explorer)
  1. From your desktop, click the "My Computer" icon.
  2. Once the window opens, click the following folders, in this order: Local Disk (usually C: drive)
    • Documents and Settings
    • Your Username
    • Application Data
    • Microsoft
    • Internet Explorer
  3. In the "Internet Explorer" folder, you will find a file called "Internet Explorer Wallpaper.bmp."
  4. To delete this file, click the file name with your mouse, then right-click and scroll down the menu to the "delete" option. Or simply hit the "delete" key on your keyboard.
  5. The wallpaper image will remain until the computer is restarted. To delete from view without restarting the computer, right-click anywhere on an open area of the desktop, scroll down and select "Properties." (This will open the "Display Properties" window.) Click on the "Desktop" tab, select a different background and click "OK." This will change your desktop background immediately.

For Mac OS X
  1. Locate the "Applications" folder in the Macintosh hard drive and choose "System Preferences."
  2. Select "Desktop & Screen Saver." This will show you what wallpaper is currently displayed on your desktop.
  3. To change the current photo, select a new photo from the drop-down menu.
  4. To remove the photo permanently from the desktop, locate the photo on the hard drive and drag it to the trash. This will delete the image.

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