Coal gasification as a transition plan to build lead time to develop sustainable, climate-friendly energy technologies....
Bridging the Carbon Gap: Fossil Fuel Use for the 21st Century
more forgiving limit-of between 650 and 1,000 gigatonnes in carbon emissions through the end of the 21st century. Those experts are willing to accept these higher, but manageable, levels of anthropogenic carbon emissions, as they would lead to further increases in average global surface temperatures of no more than about 2° to 2.5° C (3.6° to 4.5° F). 2, 6, 7
Of course, these predicted changes in temperature reflect median-level assumptions for various factors that can affect weather and climate. These factors include feedback effects that are due primarily to changes of water vapor concentrations in the troposphere and stratosphere, and of cloud height and reflectivity resulting from the additional warming.
Yet this measured approach appears prudent. The predicted increase in average global surface temperature over the next 100 years still would fall within the range of natural temperature fluctuations that have occurred during the current 10,000-year-old interglacial period, known as the Holocene Age. 9
Nevertheless, by 2100 we would need a truly sustainable and essentially carbon-emission-free global energy system. And that need will force private industry and government policymakers to address two basic questions:
- Bridge Technologies. First, what fuels, options, or strategies are available, and which offer the greatest opportunity for success, to sustain the level of human economic and social progress made possible today by fossil fuels, 10 yet also manage carbon emissions and global warming during the century-long transition to more sustainable energy technologies?
- Sustainable Technologies. Second, which fuels, resources, or processes will offer the best hope for developing commercially sustainable energy technologies that can achieve the desired equilibrium by year 2100?
From the data presented in the Second and Third Scientific Assessment Reports (SAR and TAR) issued by the Intergovernmental Panel on Climate Change (IGCC), 6, 7 it appears that it should certainly be possible to stay within the 1,000 gigatonnes constraint while pursuing an orderly transition to a sustainable energy system. That conclusion assumes that anthropogenic carbon emissions fall sharply to a level that is sequestered naturally by the global ecosystem, after peaking at about 12 gigatonnes annually between 2030 and 2040.
This level of natural sequestration is currently about four gigatonnes annually, of which two gigatonnes of carbon are sequestered by the oceans and 2 gigatonnes by increases in biomass, primarily through afforestation in the Northern Hemisphere.
By contrast, the more stringent constraint of 650 gigatonnes would permit a peak in annual emissions of only 10 gigatonnes, around 2025, followed by a sharp decline.
In a broader sense, however, the question turns into a choice of sustainable energy sources that will have the lowest cost impact after they have been fully developed and commercialized.
For instance, we might choose to bridge this century-long Carbon Gap and to rely for the task on "high-tech" but inherently intermittent renewable sources of energy, such as wind, solar thermal, and photovoltaic power.
Or we might fall back on traditional fossil fuels-augmented by new technologies that minimize carbon emissions.
The potential use of nuclear breeder reactors will also be examined. Yet the outlook seems poor for using biomass or "energy crops"