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ÒUnequivocalÓ warming of the climate system
l
lThe oceans and land surface have warmed
lThe troposphere has warmed
lAtmospheric water vapor has increased
lSea level has risen
lGlaciers have retreated over most of the globe
lSnow and sea-ice extent have decreased in the Northern Hemisphere
lIndividually, these changes are consistent with our scientific understanding of how the climate system should be responding to human influences
 Detecting ÒsignificantÓ climate change means showing that a given change in climate is unusual relative to some yardstick that you have of ÒnormalÓ behavior.
 If you feel hot, and measure a body temperature of 102oF, then youÕve ÒdetectedÓ a fever - you know that that this elevated temperature is outside the limits of ÒnormalÓ body temperature.
 But this measurement doesnÕt give you the cause of the fever.
 To deduce the cause, youÕll probably need to undergo some more sophisticated tests - perhaps urine and blood analyses, maybe even x-rays or CAT scans.
 Once you have the results from these tests, itÕs much easier to narrow down the potential causes of the fever.
 This is attribution - the process of establishing cause and effect.