Aswe’rejusttwodegreesawayfromaclimatecatastrophe,we"llreachthethresholdforirreversibleenvironmentaldamagewithin40years.Butwehavethepowertopreventit.DavidAttenboroughtakesastarklookatthefactssurroundingclimatechangeintoday"sworld.Thisisthegreatestchallengewe"veeverfacedandthehumanracecanrisetoit..