Pacola and Socolow have shown that there are several established ways by which we can hold CO2 emissions at a constant level. Wind, solar, nuclear, carbon capture and storage, and fuel savings in transport are all methods that could make a significant difference soon. However, these all require a determination by governments and a realization by the public to curb our CO2 emissions immediately. The Kyoto Protocol is a step in the right direction but needs all nations to be involved, and the rate of CO2 abatement needs to be speeded up.
If the world carries on as it has been there is the real threat of dangerous climate changes within 100 years. It would be unwise to rely on the lower predictions being correct for global temperatures rises. We might just be fortunate but the consequences if we are not are too serious to risk. People need to understand and support a significant shift in their energy supply and use. Limits on CO2 emissions are already agreed among nations and quotas are being introduced on a smaller scale. Carbon taxes would bring home the seriousness of the situation to individuals. Unless there is a significant improvement we may even need to consider rationing carbon-emitting energy such as gasoline.
Hopefully, voluntary changes in use will avoid the necessity for such extreme measures. It will require a diverse approach and strong leadership. Fusion and breeder reactors could enable us to reduce our emissions after 2055 and it is important that research in these as well as in more established areas is strongly supported. We have seen in this book that there are a number of technologies that can significantly reduce our carbon emissions. By employing them we will be able to limit carbon emissions, which is vital for the well-being of future generations.
® There is strong evidence that anthropogenic emissions of CO2 have caused a significant global temperature rise of about 0.5°C over the last 50 years. The IPPC have predicted a rise of 1.4~5.8°C by 2100, with a risk of catastrophic climate change.
® Measures to limit the anthropogenic contribution to global warming have been endorsed by the vast majority of nations (but not, by 2005, the United States) in the Kyoto Protocol.
® Economics is the key factor in limiting the uptake of more carbon-free energy. To address this, carbon emissions trading, carbon taxes, and renewable obligations have been introduced.
0 Cost-benefit analysis and probabilistic risk assessment of projects together with public involvement are important in developing energy strategies.
0 To reduce the risk of dangerous climate change will require limiting the CO2 level in the
atmosphere to about 500 ppm. This will require holding carbon emissions constant for 50 years and then significantly reducing them.
® Many different carbon mitigation strategies are required in parallel to hold the level of CO2 to 500 ppm. Wind, solar, nuclear, carbon capture and storage, and fuel savings in transport are all methods that could make a significant difference soon.
Estimate the Reynolds number for: (a) treacle flowing over a plate (v = 1CT! m2 s’"1, и ~ 10""2 ms"!, L = 0.1 m); (b) air flowing around a jet aircraft (if = 1,5 x lO^ur s*"1, w = 3 x 102 m s~L = 10 m).
The Reynolds numbers in each case are: (a) Re = ~~ «s -!0………………………. ‘■ << 1; (b) Re = ~ ^
 |qence jn case fjow is predominantly laminar but in case (b) the flow
contains regions of turbulence.