An important new paper published today in Global Biogeochemical Cycles finds that "In contrast to recent claims, trends in the airborne fraction of anthropogenic carbon [dioxide] cannot be detected when accounting for the decadal-scale influence of explosive volcanism and related uncertainties." In other words, after accounting for the large effect of volcanic eruptions, ENSO, and other uncertainties upon natural CO2 sinks, trends in the man-made fraction of atmospheric CO2 "cannot be detected." Thus, despite an exponential increase in man-made CO2 emissions, there is no statistically significant trend in the man-made fraction of CO2 in the atmosphere. This further suggests that man is not the primary cause of the increase of CO2 in the atmosphere, that temperature is responsible for the increase in CO2 levels due to out-gassing. According to the authors, "Our results highlight the importance of considering the role of natural variability in the carbon cycle for interpretation of observations and for data-model intercomparison."
Note man-made emissions are only about 4% of the total CO2 emissions in the atmosphere, and CO2 only represents about 0.04% of the entire atmosphere.
Thomas Lukas Frölicher et al
Abstract: Tropical explosive volcanism is one of the most important natural factors that significantly impact the climate system and the carbon cycle on annual to multi-decadal time scales. The three largest explosive eruptions in the last 50 years - Agung, El Chichón, and Pinatubo - occurred in spring/summer in conjunction with El Niño events and left distinct negative signals in the observational temperature and CO2 records. However, confounding factors such as seasonal variability and El Niño-Southern Oscillation (ENSO) may obscure the forcing-response relationship. We determine for the first time the extent to which initial conditions, i.e. season and phase of the ENSO, and internal variability influence the coupled climate and carbon cycle response to volcanic forcing and how this affects estimates of the terrestrial and oceanic carbon sinks. Ensemble simulations with the Earth System Model CSM1.4-carbon predict that the atmospheric CO2 response is ~60% larger when a volcanic eruption occurs during El Niño and in winter than during La Niña conditions. Our simulations suggest that the Pinatubo eruption contributed 11 ± 6% to the 25 Pg terrestrial carbon sink inferred over the decade 1990-1999 and -2 ± 1% to the 22 Pg oceanic carbon sink. In contrast to recent claims, trends in the airborne fraction of anthropogenic carbon cannot be detected when accounting for the decadal-scale influence of explosive volcanism and related uncertainties. Our results highlight the importance of considering the role of natural variability in the carbon cycle for interpretation of observations and for data-model intercomparison.