<Tr> <Td> Geothermal </Td> <Td> hot dry rock </Td> <Td> 45 </Td> </Tr> <Tr> <Td> Solar PV </Td> <Td> Polycrystalline silicon </Td> <Td> 46 </Td> </Tr> <Tr> <Td> Natural gas </Td> <Td> various combined cycle turbines without scrubbing </Td> <Td> 469 </Td> </Tr> <Tr> <Td> Coal </Td> <Td> various generator types without scrubbing </Td> <Td> 1001 </Td> </Tr>

An increase in which gas in earth's atmosphere