Per IPCC AR5 Figure 6.1 prior to year 1750 CO2 represented about 1.26% of the total biospheric carbon balance (589/46,713). After mankind’s contributions, 67 % fossil fuel and cement – 33% land use changes, atmospheric CO2 increased to about 1.77% of the total biosphere carbon balance (829/46,713). This represents a shift of 0.51% from all the collected stores, ocean outgassing, carbonates, carbohydrates, etc. not just mankind, to the atmosphere. A 0.51% rearrangement of 46,713 Gt of stores and 100s of Gt annual fluxes doesn’t impress me as measurable let alone actionable, attributable, or significant.
And in some other words.
Earth’s carbon cycle contains 46,713 Gt (E15 gr) +/- 850 Gt (+/- 1.8%) of stores and reservoirs with a couple hundred fluxes Gt/y (+/- ??) flowing among those reservoirs. Mankind’s gross contribution over 260 years was 555 Gt or 1.2%. (IPCC AR5 Fig 6.1) Mankind’s net contribution, 240 Gt or 0.53%, (dry labbed by IPCC to make the numbers work) to this bubbling, churning caldron of carbon/carbon dioxide is 4 Gt/y +/- 96%. (IPCC AR5 Table 6.1) Seems relatively trivial to me. IPCC et. al. says natural variations can’t explain the increase in CO2. With these tiny percentages and high levels of uncertainty how would anybody even know? BTW fossil fuel between 1750 and 2011 represented 0.34% of the biospheric carbon cycle.
555 ----- = 1.2% 46713