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Carbon Emissions exceed Worst-Case Scenarios

The earliest projections of the IPCC were at first pessimistic, but ultimately proved to be hugely optimistic

IPCC Bericht 1992
IPCC Supplementary Report 1992

In 1992, the Intergovernmental Panel on Climate Change, IPCC, submitted a supplementary report to the first IPCC Report (1990) from Working Group 1. The findings of this report helped shape the negotiations at the Rio Summit (UNCED 1992), embodied in the UNFCCC (United Nations Framework Convention on Climate Change), and were the reference for future IPCC reports. It is interesting to review their methodology and projections in the light of 25 years of subsequent climate study.

The report takes pains to emphasise that their findings are very sensitive to missing data, and a large number of unknowns, and should not be taken as a prediction. They point out that some effects have both positive and negative GWP (global warming potential), such as water vapour both blocks solar radiation from penetrating to lower levels of the troposphere and adds to the greenhouse trapping of infrared radiation from the surface. Deforestation and CFCs were two areas of considerable uncertainty discussed at length by the report.

CO2 emissions from energy, cement production and deforestation were projected till the year 2100, within a set of 7 scenarios: SA90, IS92a-f. Three of these scenarios used World Bank population projections, and three UN 'Low' and 'High' case population growths. Average World Economic Growth varied from 1.2% (IS92c) to 3.5% (IS92e). The mix of energy consumption levels and choice of supply (fossil or renewable) varied greatly, and involved projections in the price of solar power compared to fossil. The scenarios also integrated projections regarding the effect of international agreements, and degree of compliance to the then recent CFC emissions restrictions (Montreal Protocol 1987).

The report includes a graph of the range of CO2 emissions which resulted from the models applying the parameter settings for each scenario, as GtC (gigatonnes of carbon). Later reports used the unit of mass of CO2 equivalent. The ratio of molecular masses of carbon and carbon dioxide is 12 : 44, or 3.67.

Comparison of 1992 and 2014 Reports

Annual CO2 equivalent emissions from all anthropogenic sources

Year1992 report /GtCO22014 report /GtCO2
200026.6 - 31.225.0
201027.5 - 42.250.3
202030.2 - 49.552.0 - 59.0
203030.0 - 58.742.0 - 69.0

The 2014 Report assumes 4 levels of commitment to the upcoming Paris Conference agenda: 'Business as Usual', 'Weaker Pledge', 'Stronger Pledge', and '2°C Path'.

Three observations can be made: the 1992 was too pessimistic for the short-term. In 2000, the actual emissions had fallen below the predicted range. This proved to be only a short-term effect, due in large to the reduction in dirty industry and vehicle emissions as Eastern Europe opened up.

In its later projections, the 1992 report was too optimistic. Actual CO2 emissions in 2010 exceeded even their worst case scenario. Strong pledge (55 GtCO2) and 2°C (42 GtCO2) in the 2014 report both fall within the upper range for 2030 in the 1992 forecast, but business as usual and weak pledge take us well above the forecast range.

Article by Andrew Bone, Sunday, 25th September 2016