It's quite easy to for instance remove global warming from the game. The file GlobalDefines.xml which exists for every version of the game (vanilla, Warlords and BTS) holds many parameters that effect the game. One of them is:
Code:
<Define>
<DefineName>GLOBAL_WARMING_PROB</DefineName>
<iDefineIntVal>20</iDefineIntVal>
</Define>
Changing the 20 to 0 removes global warming from the game.
The file is located in:
...\Civilization 4\Assets\XML
...\Civilization 4\Warlords\Assets\XML
...\Civilization 4\Beyond the Sword\Assets\XML
depending on the version of the game that you wish to change. It's preferable to create a tiny mod out of it than changing the original file(s). If you do change the original files, then make a backup of the file first so that you can revert back to the original files.