Several articles are in the media discussing UN meetings in progress to move the climate change goal posts from preventing 2C of warming to a goal of 1.5C additional warming. The US have questioned the plausibility of such an ambition, and this post goes into some of the reasons why. At the bottom I shall raise several skeptical points about this whole enterprise, but first we should look at the data UN uses as a trampoline for leaps of faith.
Data on Annual CO2 Concentrations
The annual average concentrations of atmospheric CO2 are reported from Mauna Loa in a dataset accessed from NOAA here. The graph below shows the record.
Note that in 1959 there was 316 ppm of CO2 according to this dataset, and in 2017 the annual average CO2 was 407 ppm. So the rise of 91 ppm over 59 years is a rate of 1.53 ppm per year. Of course the actual interannual differences vary from that average rate, and as we shall see, many recent years have exceeded 2 ppm per year additional CO2. The table below shows all years in the record that added more than 2 ppm of CO2.
Note that as warming increased so also did CO2 in ppm. You can pick out El Nino years in the list, suggesting that ocean outgassing has a large impact on atmospheric CO2.
The larger point is that, for whatever reasons, the annual addition of CO2 has increased this century to a rate of 2.14 over the last 20 years.
UN Aspirational Goalposts
UN insiders have been making a simple case for some years preceding the Paris 2015 accord. IPCC has claimed that in their judgement keeping atmospheric CO2 less than 450 ppm ensures future warming will not exceed 2C. I don’t buy it, but that has been sold to Paris signatories. Now comes increasing the ambition to limit warming to 1.5C, and the same authorities translate that into a limit of 430 ppm of CO2.
These numbers and their logic can be seen in a document from Climate Analytics: Timetables for Zero emissions and 2050 emissions reductions Excerpts in italics with my bolds.
This briefing note outlines suggested time frames for reaching zero global CO2 and total greenhouse gas emissions for the ‘below 2 °C’ and ‘below 1.5 °C by 2100’ limits based on the findings of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) and the 2014 UNEP Emissions Gap Report.
Emissions scenarios leading to GHG concentrations in 2100 of about 450 ppm CO2eq or lower are likely to maintain warming below 2 °C over the 21st century relative to pre-industrial levels. These scenarios are characterized by 40% to 70% global anthropogenic GHG emissions reductions by 2050 compared to 2010, and emissions levels near zero or below in 2100.” (IPCC AR5 SYR) Information in Table SPM.1 of the IPCC AR5 SYR
“A limited number of studies provide scenarios that are more likely than not to limit warming to 1.5 °C by 2100; these scenarios are characterized by concentrations below 430 ppm CO2eq by 2100 and 2050 emission reduction between 70% and 95% below 2010.” (IPCC AR5 SYR)
UN Goals Stretch Beyond Credibility
So let’s look at these two scenarios in relation to observed CO2 in the atmosphere.
The blue line is CO2 in ppm observed at Mauna Loa. The linear regression line shows the continuation of the 1.53 ppm per year rate projected to the end of this century. As noted above the blue line is already exceeding the earlier rate. The orange line shows CO2 hitting 430 ppm in 2032 at the 1.53 rate, or earlier if more recent rates continue. For example, if the 2.14 ppm per year rate continues, 430 ppm is reached by 2028. The red 450 scenario is reached in 2045. Both scenarios presume zero additional CO2 after those dates.
UN Piles Supposition on Top of Supposition
Previous posts here have taken issue with UN IPCC assertions that rising CO2 causes temperatures to rise and that human fossil fuel emissions cause CO2 to rise.