Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozoic eon

Atmospheric carbon dioxide concentrations are believed to drive climate cha nges from glacial to interglacial modes', although geological(1-3) and astr onomical(4-6) mechanisms have been invoked as ultimate causes. Additionally , it is unclear(7,8) whether the changes between cold and warm modes should be regarded as a global phenomenon, affecting tropical and high-latitude t emperatures alike(9-13), or if they are better described as an expansion an d contraction of the latitudinal climate zones, keeping equatorial temperat ures approximately constant(14-16). Here we present a reconstruction of tro pical sea surface temperatures throughout the phanerozoic eon (the past sim ilar to 550 Myr) from our database(17) of oxygen isotopes in calcite and ar agonite shells. The data indicate large oscillations of tropical sea surfac e temperatures in phase with the cold-warm cycles, thus favouring the idea of climate variability as a global phenomenon. But our data conflict with a temperature reconstruction using an energy balance model that is forced by reconstructed atmospheric carbon dioxide concentrations(18). The results c an be reconciled if atmospheric carbon dioxide concentrations were not the principal driver of climate variability on geological timescales for at lea st one-third of the Phanerozoic eon, or if the reconstructed carbon dioxide concentrations are not reliable.