Why 80% by 2050?

The agreed GHG reduction target for developed nations is supported by evidence from science.

You may have noticed in an earlier post that developed nations are targeting an 80% reduction in greenhouse gases (GHGs) by 2050 relative to 1990 levels. Where did this number come from? It turns out to be a generally agreed policy that is supported by evidence from science.

The IPCC’s 2007 AR41 and 2013 AR52 reports indicated that atmospheric CO2 must not exceed 450 ppm (and possibly lower) if global warming is to be limited to 2°C. The 2°C threshold is associated with dangerous climate change. IPCC projections show that global CO2 emissions will need to be cut to about half of 1990 levels by 2050.3

But who should make the cuts? It isn’t reasonable to ask developing and developed nations to carry the same burden. The 1992 United Nations Framework Convention on Climate Change (UNFCC) acknowledges this in Article 3:

“The Parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. Accordingly, the developed country Parties should take the lead in combating climate change and the adverse effects thereof.”

A literature developed around the problem of how the cuts should be partitioned. The IPCC summarized the research in AR4, suggesting that developed countries should reduce their emissions 80% to 95% by 2050.4

Per capita GHG emissions for mostly developed (Annex I) and developing nations consistent with the goal of reducing worldwide emissions by half in 2050. Source: UN.
Per capita GHG emissions for mostly developed (Annex I) and developing nations consistent with the goal of reducing worldwide emissions by half in 2050. Source: UN.

A guiding principle for partitioning the cuts is that developed and developing nations should ultimately have the same emissions per capita. The figure, from a 2008 UN report, gives per capita emissions curves consistent with a 50% worldwide reduction by 2050. Annex I (mostly developed) nations reduce their emissions by 80% by 2050, but have much higher per capita emissions than developing nations until then. Notice that action by developing nations is delayed.

The G8 adopted the 80% by 2050 target at their meeting in 2009:

“We reaffirm the importance of the work of the Intergovernmental Panel on Climate Change (IPCC) and notably of its Fourth Assessment Report, which constitutes the most comprehensive assessment of the science. We recognise the broad scientific view that the increase in global average temperature above pre-industrial levels ought not to exceed 2°C. Because this global challenge can only be met by a global response, we reiterate our willingness to share with all countries the goal of achieving at least a 50% reduction of global emissions by 2050, recognising that this implies that global emissions need to peak as soon as possible and decline thereafter. As part of this, we also support a goal of developed countries reducing emissions of greenhouse gases in aggregate by 80% or more by 2050 compared to 1990 or more recent years.”

(emphasis mine).

Unfortunately, the Canadian federal government has since backed away from this commitment. They worked behind the scenes to “water down” targets at the 2015 G7 meeting. Canada’s emissions are projected to rise through 20205, and our proposal for the upcoming talks in Paris lags far behind the US and EU. We needs to do more if we are to do our share.

  1. AR4/WGI, Chapter 10, pg. 791: “Stabilising atmospheric CO2 at 450 ppm, which will likely result in a global equilibrium warming of 1.4°C to 3.1°C, with a best guess of about 2.1°C”.

  2. AR5/WGI: “Temperature change above 2°C under RCP2.6 is unlikely but is assessed only with medium confidence as some CMIP5 ensemble members do produce a global mean temperature change above 2°C” (pg. 1055). Table 12.3 (pg 1055) indicates the temperature change for RCP2.6 is 1.6 ± 0.4°C above the 1850-1900 mean. From Box 1.1, Figure 2 (pg 148) we can see the maximum CO2 concentration for the 21st century for RCPC2.6 is 450 ppm.

  3. See a) AR5/WG1, pg. 94, Fig. TS.19 (RCP2.6); and b) AR4/WGI, pg. 791, Fig. 10.21c (SP450).

  4. See AR4/WGIII, Box 13.7, Chapter 13, pg. 776.

  5. The projected emissions might change in light of the drop in the price of oil and consequences for oilsands development.