You may not believe that humans could change the planet抯 climate,but the basic science is well understood.Each year,billions of tons of greenhouse gases are released into the atmosphere because of human activity.As has been known for years,these gases holnd heat that would otherwise escape to space,wrapping the planet in an invisible (看不见的)blanket.

　　Of course,the earth’s climate has always been changing due to“natural”factors such as volcanic eruption or changes in solar,or cycles concerning the Earth’s going around the sun.According to the scientific research,however,the warming observed by now matches the pattern of warming we would expect from a build-up of greenhouse gas in the atmosphere梟ot the warming we would expect from other possible causes.t

　　Even if scientists did discover another reasonable explanation for the warming recorded so far,that would give birth to a difficult question.As Robert Henson puts it:揑f some newly discovered factor is to blame for the climate change,then why aren抰 carbonch dioxide and the other greenhouse gases producing the warming that basic physics tells us they should be??The only way to prove with 100% certainty that humans are responsible for global warming would be to run an experiment with two identical Earths梠ne chwith human influence and one without.That obviously isn抰 possible,and so most scientists are careful not to state human influence as an absolute certainty.m

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