The researchers next pointed out that the IPCC’s Fifth Assessment Report, from 2013, estimated that cumulative carbon dioxide emissions since 1870 would have to remain less than 2,260 gigatons of carbon dioxide to stay below the 1.5 C threshold. But as of 2014, cumulative emissions stood at just over 2,000 gigatons of carbon dioxide. Since humanity is currently emitting about 36 gigatons of carbon dioxide annually, that implies that humanity would blow through the remaining IPCC carbon budget around 2021.
Here’s where it gets interesting. The average global temperature now stands at about 0.9 C above the pre-industrial baseline, which implies that global temperature would have to increase by 0.6 C between now and 2021 if the IPCC carbon budget calculations were right. This is highly implausible since such an increase would be about 10 times faster than than what has actually heretofore been observed.
But why reuse the models that have already been shown to be off by 30 percent in their projections? Again, the difference between 0.9 C above the preindustrial baseline and the 1.5 C threshold is 0.6 C. According to the National Oceanic and Atmospheric Administration, global average temperature is rising at 0.17 C per decade, suggesting that the 1.5 C temperature threshold might not be passed for 30 years. The satellite temperature measurements find that the globe is warming at the rate of 0.13 C per decade, implying that the 1.5 C threshold might not be passed for 45 years or so.
These rough temperature increase calculations imply an even larger carbon budget. That might mean that humanity could burn significantly more carbon dioxide-emitting fossil fuels without necessarily crossing the 2 C above preindustrial average temperature threshold set out in the Paris Agreement.