Using the relationship between carbon dioxide and temperature, staying within that budget means carbon dioxide
emissions over the industrial era can not contribute more than 800 billion tonnes of carbon.
It's increasingly difficult to reconcile a high climate sensitivity (say over 4C) with the observational evidence for the planetary energy
balance over the industrial era.
«The anthropogenic contribution to the actual CO2 concentration is found to be 4.3 %, its fraction to the CO2
increase over the Industrial Era is 15 %» — Harde (2017) «Scrutinizing the carbon cycle and CO2 residence time in the atmosphere»
Human emissions only contribute 15 % to the CO2 increase
over the Industrial Era.
``... The observed increase in global mean surface temperature (GMST)
over the industrial era is less than 40 % of that expected from observed increases in long - lived greenhouse gases...»