What Levels of Warming Are Projected What Are the Uncertainties

A credible base case, or business as usual (BAU), scenario must be established if we are to estimate warming with any confidence between now and the year 2100. IPCC [1], IEA [6, 7], and Hawksworth [8] have all postulated such scenarios that

Factors Influencing CO2 Growth Rate; 2000 to 2004

Factors Influencing CO2 Growth Rate; 2000 to 2004

India China FSU

USA EU Japan World

Population Energy Use/GDP GDP/Population v CO2 annual growth CO2 emissions/Energy Use

India China FSU

USA EU Japan World

Population Energy Use/GDP GDP/Population v CO2 annual growth CO2 emissions/Energy Use

Fig. 1.4 Factors influencing CO2 emission growth rate for selected countries for 2000-2004

allow such estimates. The IEA base scenario was selected as the basis for this analysis, because it does not assume major technology changes over time. Since it was limited to 2050, the projection was extended to 2100 by assuming reduced emission growth rates between 2050 and 2100. This scenario assumes the following CO2 growth rates in the specified time intervals: 2000-2030, 1.6%; 2030-2050, 2.2% (from IEA); 2050-2075, 1.2%; and 2075-2100, 0.7%. Note that the reduced 2050-2100 growth rate assumption was based on projected declines in global population growth rates, but relatively stable GDP, carbon intensity and energy intensity growth rates.

Figures 1.5 and 1.6 present model-generated graphics of both CO2 concentrations and warming from pre-industrial times projected to 2100, assuming this emission scenario. The Model for the Assessment of Greenhouse-Induced Climate Change, MAGICC (version 5.3) [9], was used to generate these projections. An earlier version of this model was used by the IPCC in its Third Assessment Report to evaluate impact of various emission scenarios. MAGICC is a set of coupled gas-cycle, climate, and ice-melt models that allows the determination of the estimated global-mean temperature resulting from user-specified emissions scenarios, which the author generated. Note that in both figures, which were generated directly by the model, the uncertainty range is included, as calculated by the model. As can be seen, warming uncertainties are much higher than for concentration projections. The main uncertainty factor for warming projections is the extent to which the earth is sensitive to permanent increase of CO2 concentration (i.e., how much does the global equilibrium temperature change as a function of elevated CO2 concentrations).

Courbe Granulom Trique Sable

For a doubling of CO2 levels from pre-industrial levels, also known as equilibrium climate sensitivity, IPCC [1], Wigley [9], and others state that this is quite uncertain, and their estimates range from 1.5°C to 6.0°C. This is the default range assumed by MAGICC when calculating warming ranges. The model assumes a default value of 3.0°C for the most likely atmospheric sensitivity.

Warming is projected to continue after 2100. When one accounts for continued warming projected into the next century, the equilibrium, or eventual warming, is projected to range from 2.3°C to 10.1°C with the best guess at 4.8°C above 1990 levels; this assumes an ultimate steady state 850 ppm CO2 concentration.

As mentioned earlier, new data indicates that the recent annual global CO2 emission growth rate is 3.25% in the 2000-2008 time frame. However, model calculations for Figs. 1.5 and 1.6, assumed a 2000-2030 growth rate of 1.6%, consistent with mainstream projections. Figure 1.7 illustrates the impact of assuming a 3.0% growth rate in this critical period. As can be seen, it would substantially increase the atmospheric CO2 concentrations and global warming. Equilibrium warming, which would occur during the next century, would be from 3.0°C to 12.8°C, with the best guess 6.2°C above 1990 levels.

Was this article helpful?

0 0
Waste Management And Control

Waste Management And Control

Get All The Support And Guidance You Need To Be A Success At Understanding Waste Management. This Book Is One Of The Most Valuable Resources In The World When It Comes To The Truth about Environment, Waste and Landfills.

Get My Free Ebook


Post a comment