IPCC AR5 Synthesis Report Presentation Miscalculated the Emissions for 2C of Warming

In a previous post I mistakenly claimed that the Ladybird Book on Climate Change (lead author HRH The Prince of Wales) had incorrectly interpreted the AR5 IPCC Synthesis Report in its egg-timer. It is the IPCC that is at fault.
In 2014 the IPCC produced a simplified presentation of 35 slides to summarize the AR5 Synthesis Report Summary for policy makers. A quick summary of a summary of the synthesis report.

Slide 30 on Limiting Temperature Increase to 2C, clearly states that it is global reductions in greenhouse gas emissions that are needed.


The Ladybird egg-timer is adapted from slide 33 of 35.

As a (slightly manic) beancounter I like to reconcile the figures. How are the 1900 GtCO2 and the 1000 GtCO2 arrived at? It could be that it is GtCO2e, like the throughout the synthesis report, where other greenhouse gases are recast in terms of CO2, which accounts for well over half of the warming from trace gases.

Some assumptions for my quick calculations.

1. A doubling of CO2 will lead to a warming of 3C. This was the central estimate of the Charney Report 1979 (pdf), along with all five of the UNIPCC assessment reports.
2. If the pre-industrial level of CO2 was 280ppm, the dangerous 2C of warming will be reached at 445ppm. Rounded this is 450ppm.
3. In 2011 the Mauna Loa CO2 level was 391.63 ppm.
4. Using the CDIAC World CO2 emission figures, gives the following figures for billions of tonnes of CO2 to achieve a 1ppm rise in CO2 levelsin the graph below. In the five years to 2011 on average it took 17.02 billion tonnes of CO2 to raise CO2 levels by 1 ppm. Lets round it to 17.

Now some quick calculations.
Start with 280ppm
Add 111.76 (=1900/17) gives 391.76. Pretty close to the CO2 level in 2011 of 391.63ppm
Add 58.82 (=1000/17) gives 450.58. Given rounding, this pretty close to 450ppm.

There are problems with these calculations.

  • The estimate of 17 GtCO2e is on the high side. The World CO2 emissions from the CDIAC National Emissions spreadsheet gives a sum of 1069.68 GtCO2 from 1960 to 2011, against a rise in CO2 of 74.72 ppm. That is 14.3 GtCO2e over the whole period. Since 2011 there has been a drop towards this long-term average.
  • The Ladybird Book, like the UNFCCC at COP21 Paris December 2015 talks about restraining emissions to 1.5C. If a doubling of CO2 leads to 3.000C of warming then going from 280ppm to 401ppm (the average level in 2015) will eventually 1.555C of warming. This is a tacit admission that climate sensitivity is vastly overstated.
  • But the biggest error of all is that CO2 is only the major greenhouse gas (if you forget about water vapour). It might be the majority of the warming impact and two-thirds of emissions, but it is not all the warming impact according to theory. That alone would indicate that climate sensitivity was 2 instead of 3. But actual warming from 1780 to 2011 was less than 1C, against the 1C from CO2 alone if CS=2. That indicates that CS ≈ 1.3. But not all of the warming in the last 230 years has been due to changes in GHG levels. There was also recovery from the Little Ice Age. Worst of all for climate alarmism is the divergence problem. In this century the rate of warming should have increased as the rate of CO2 levels increased, in turn due to an increase in the rate of rise in CO2 emissions. But warming stopped. Even with the impact of a strong El Nino, the rate of warming slowed dramatically.

 

Conclusion

The IPCC calculated their figures for 1000 billion tonnes of CO2 emissions for 2C of warming based on CO2 being the only greenhouse gas and a doubling of CO2 levels producing 3C of warming. On that basis 401ppm CO2 level should produce >1.5C of warming. Add in other greenhouse gases and we are in for 2C of warming without any more greenhouse gas emissions. It is only if climate sensitivity is much lower is it theoretically possible to prevent 2C of warming by drastically reducing global CO2 emissions. The IPCC, have concocted figures knowing that they do not reconcile back to their assumptions.

The questions arise are (a) where do the cumulative emissions figures come from? and (b) whether the UNIPCCC has copied these blatant errors in the COP processes?

This is an extended version of a comment made a Paul Homewoods’ notalotofpeopleknowthat blog.

Kevin Marshall