▁We ather ▁is ▁also ▁influenced ▁by ▁the ▁seasons , ▁which ▁result ▁from ▁the ▁Earth ' s ▁axis ▁being ▁t ilt ed ▁relative ▁to ▁its ▁orb ital ▁plane . ▁Thus , ▁at ▁any ▁given ▁time ▁during ▁the ▁summer ▁or ▁winter , ▁one ▁part ▁of ▁the ▁Earth ▁is ▁more ▁directly ▁exposed ▁to ▁the ▁ray s ▁of ▁the ▁sun . ▁This ▁expos ure ▁altern ates ▁as ▁the ▁Earth ▁revol ves ▁in ▁its ▁orbit . ▁At ▁any ▁given ▁time , ▁regardless ▁of ▁season , ▁the ▁northern ▁and ▁southern ▁hem is pher es ▁experience ▁opposite ▁seasons . ▁ ▁We ather ▁is ▁a ▁cha otic ▁system ▁that ▁is ▁readily ▁modified ▁by ▁small ▁changes ▁to ▁the ▁environment , ▁so ▁accurate ▁weather ▁forec ast ing ▁is ▁limited ▁to ▁only ▁a ▁few ▁days . ▁Over all , ▁two ▁things ▁are ▁happening ▁world wide : ▁( 1 ) ▁temperature ▁is ▁increasing ▁on ▁the ▁average ; ▁and ▁( 2 ) ▁regional ▁clim ates ▁have ▁been ▁under going ▁notice able ▁changes . ▁ ▁Water ▁on ▁Earth ▁ ▁Water ▁is ▁a ▁chemical ▁subst ance ▁that ▁is ▁composed ▁of ▁hydro gen ▁and ▁o xygen ▁( H 2 O ) ▁and ▁is ▁vital ▁for ▁all ▁known ▁forms ▁of ▁life . ▁In ▁typical ▁usage , ▁water ▁refers ▁only ▁to ▁its ▁liquid ▁form ▁or ▁state , ▁but ▁the ▁subst ance ▁also ▁has ▁a ▁solid ▁state , ▁ice , ▁and ▁a ▁g ase ous ▁state , ▁water ▁v apor , ▁or ▁steam . ▁Water ▁covers ▁ 7 1 % ▁of ▁the ▁Earth ' s ▁surface . ▁On ▁Earth , ▁it ▁is