Science journalism fail?
Original article (sub req):
At the accepted equilibrium climate sensitivities of 1.5–4.5 °C warming per doubling of CO2 (ref. 1), our calculated 1.7-fold increase in CO2 would at most have caused approx3.5 °C warming during the PETM main phase (Fig. 4). This constitutes an enigma because proxy records globally indicate surface warming by 5–9 °C (refs 5, 6, 7, 8, 9). If the temperature reconstructions are correct, then feedbacks and/or forcings other than atmospheric CO2 caused a major portion of the PETM warming. The origin of this additional warming is unknown at present. Possible causes of the excess warming include increased production and levels of trace greenhouse gases as a consequence of the climatic warming (such as CH4; ref. 28). Regardless, this mismatch poses a challenge for our understanding of past episodes of strong and rapid global warming. Undoubtedly, the climatic boundary conditions before the PETM were different from today's—including different continental configuration, absence of continental ice and a different base climate, which limits the PETM's suitability as the perfect future analogue. Nevertheless, our results imply a fundamental gap in our understanding of the amplitude of global warming associated with large and abrupt climate perturbations. This gap needs to be filled to confidently predict future climate change.In other words, during a previous warming period, only about half to 1/3 of the warming can be explained by rising carbon levels. This rise presumably caused a cascade of other (as yet unknown) events to occur which led to the full extent of the warming. Hence, a small amount of carbon increase could be really really bad, depending on whether these feedback mechanisms are still in place now.
Could the best climate models -- the ones used to predict global warming -- all be wrong?
Science shows global warming is a hoax!