Chapter 1. Introduction
The fossil fuel resources of our planetâestimated at between 4000 and 6000 gigatonnes of carbon (Gt-C)âare the product of biological and geologic processes that have occurred over hundreds of million of years and continue today. The carbon sequestered in these resources over geological time was originally a constituent of the atmosphere of a younger earthâan atmosphere that contained âŒ1500 parts per million (ppm) CO2 at the beginning of the Carboniferous age, 360 million years ago, when the evolution of earthâs first primitive forests began the slow process of biogeological sequestration.
Since the dawn of the industrial age, circa 1750, and particularly since the invention of the internal combustion engine, âŒ5% of these resource volumes have been combusted and an estimated 280Gt-C released back into the atmosphere in the form of CO2. In the same period a further âŒ150Gt-C has been released to the atmosphere from soil carbon pools as a result of changes in land use. The atmospheric, terrestrial, and oceanic carbon cycles have dispersed the greater part of these anthropogenic emissions, locking the CO2 away by dissolution in the oceans and in long-lived carbon pools in soils. During the period since 1750, the CO2 concentration in the atmosphere has increased from 280ppm to 368ppm in 2000, and âŒ388ppm in 2010, the highest level in the past 650,000 years and one that is not likely to have been exceeded in the past 20 million years, where âlikelyâ reflects the Intergovernmental Panel on Climate Change (IPCC) judgment of a 66â90% chance.
This increase in atmospheric CO2 concentration ([CO2]) influences the balance of incoming and outgoing energy in the earth-atmosphere system, CO2 being the most significant anthropogenic greenhouse gas (GHG). In its Fourth Assessment Report (AR4), published in 2007, the IPCC concluded that global average surface temperatures had increased by 0.74 ± 0.18°C over the 20th century (Figure 1.1), and that âmost of the observed increase in global average temperatures since the mid-20th century is very likely (>90% probability) due to the observed increase in anthropogenic GHG concentrations.â
Although anthropogenic CO2 emissions are relatively small compared to the natural carbon fluxesâfor example, photosynthetic and soil respiration fluxes, at âŒ60Gt-C per year, are 10 times greater than current emissions from fossil fuel combustionâthese anthropogenic releases have occurred on a time scale of hundreds rather than hundreds of millions of years. Anthropogenic change has also reduced the effectiveness of certain climate feedback mechanisms; for example, changes in land-use and land-management practices have reduced the ability of soils to build soil carbon inventory in response to higher atmospheric CO2, while ocean acidification has reduced the capacity of the oceans to take up additional CO2 from the atmosphere.
The energy consumption of modern economies continues to grow, with some scenarios predicting a doubling of global energy demand between 2010 and 2050. Fossil fuels currently satisfy 85% of global energy demand and fuel a similar proportion of global electricity generation, and their predominance in the global energy mix will continue well into the 21st century, perhaps much longer. In the absence of mitigation, the resulting emissions will lead to further increase in atmospheric [CO2], causing further warming and inducing many changes in global climate. Even if [CO2] is stabilized before 2100, the warming and other climate effects are expected to continue for centuries, due to the long time scales associated with climate processes. Climate predictions for a variety of stabilization scenarios suggest warming over a multicentury time scale in the range of 2°C to 9°C, with more recent results favoring the upper half of this range.
Although many uncertainties remain, there is little room for serious doubt that measures to reduce CO2 emissions are urgently required to minimize long-term climate change. While research and development efforts into low- or zero-carbon alternatives to the use of fossil fuels continues, the urgent need to move toward stabilization of [CO2] means that measures such as the capture and storage of carbon that would otherwise be emitted can play an important role during the period of transition to low-carbon alternatives.
Within the field of carbon capture and storage (CCS), a diverse range of technologies is currently under research and development and a growing number of demonstration projects have been started or are planned. A few technologies have already reached the deployment stage, where local conditions or project specifics have ...