Answer to Question 1
Hydroelectric is the largest source of renewable energy but most of the ideal locations have already been developed. Geothermal, tidal currents and biofuels are all potential renewable energy sources, but solar and wind power are technically mature and likely to see high rates of growth. Iceland is able to use hydroelectric and geothermal energy to meet 95 of its electrical power needs. Germany has invested heavily in solar energy and wind energy. Problems include the potential for power surges on particularly sunny and windy days. Most facilities must have a back up power source for times when it is not windy nor sunny. There may be considerable cost in upgrading existing power grids to handle these energy fluctuations. In addition, government subsidies for fossil fuels have traditionally made these much less expensive than renewable sources.
Answer to Question 2
Organisms fractionate carbon isotopes more strongly when atmospheric CO2 levels are high. Hence, a large difference in 13C values between organic carbon and carbonates is considered as evidence for high atmospheric CO2 ratios.
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