3.4 Pollution solutions?
At the 1992 Earth Summit in Rio de Janeiro, it was agreed that the major industrialised nations would stabilise their CO2 emissions from fossil fuels at 1990 levels by the year 2000. This decision was taken primarily to relieve possible global warming caused by the greenhouse effect, but such a policy would also stabilise emissions of other major contributors to atmospheric pollution and acid rain, such as oxides of sulphur and nitrogen. Since then, the Kyoto Protocol of 1997 committed signatory countries (but not the USA, Australia, India and China, which did not sign) to reducing annual greenhouse emissions to 5% below 1990 levels by 2012. In terms of acidification and air quality, the 1999 Gothenburg Protocol for the abatement of acidification, eutrophication (water pollution caused by excessive plant nutrients, such as NOx) and ground-level ozone requires of its signatories the following reductions (relative to 1990 levels) by 2025: sulphur emissions by at least 63%; NOx emissions by 41%; volatile organic carbon emissions by 40%; and ammonia emissions by 17%.
In Section 2 and in Figure 8 (C scenarios) you saw the dramatic potential effect of replacing fossil fuels by alternative renewable and nuclear sources, with a drive towards more efficient usage of energy. You should also have noted the caveats regarding the high pace of developing and deploying suitable technologies to achieve that. An alternative view is that humanity should reduce its overall energy consumption rapidly and significantly. That means we all would have to adopt alternative ways of doing things: greater energy conservation at home and at work; less travel overall; better use of mass transport; different lifestyles and expectations, and so on.
Renewable energy sources must be developed if we are to wean ourselves off fossil fuels. Wind power is growing in the UK and in Europe — but not without some controversy over visual impact on the landscape — and solar technologies are improving in terms of efficiency and cost. Nuclear power could meet the demand for energy while these new technologies mature, without CO2 being produced.
Another approach, however, may provide part of the answer to reducing CO2 emissions from power stations — CO2 sequestration. This experimental technology seeks to remove CO2 at source, i.e. from within a power station, before it has a chance to escape into the atmosphere (Figure 16). In other words, the CO2 is directly transferred to long-term storage, rather than being added to the carbon cycle. Theoretically, such sequestration could exceed natural rates of carbon burial. Probably the simplest solution is to pump CO2 into porous but sealed-off rocks that once held oil or gas. It is possible that some CO2 could be induced to form carbonate minerals in the host rock, i.e. a solid and therefore more stable form of storage. Another possibility is exploiting the liquefaction of CO2 at high pressures and injecting liquid CO2 into deep ocean basins. Like methane, CO2 can also form a solid gas hydrate in sea-floor sediments; a further possibility for sequestration. There are of course immense technical challenges that need to be resolved. Such technological 'fixes' would also place a heavy economic burden on conventional CO2 emitting power stations, making implementation unlikely in rapidly developing regions such as China and India. Moreover, this approach does nothing to alleviate CO2 emitted outside power stations, especially from increasing road and air transport (now considerably greater than from electricity generation).
No technologies are currently envisaged that could selectively extract CO2 from air in the volumes necessary to make any appreciable difference to its overall composition. There is one simpler means, however, photosynthesis is free and efficient, but needs encouragement. Planting enough trees to cover an area the size of Australia is believed to have the potential to reduce atmospheric CO2 to levels compatible with a stable climate. Other biological methods of sequestration include 'fertilising' open oceans to encourage phytoplankton growth, whose death, sinking and burial on the ocean floor would fix carbon in long-term storage, albeit at the possible expense of upsetting ecosystems.