claim: Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.
evidence: IPCC AR5 WG1 Summary for Policymakers 2013, p. 4 : Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.