This passage is largely about ----.

Various estimates suggest that by 2050 nearly one
third of the world's energy needs could come from
renewable sources such as solar power, wind power,
geothermal power and hydrogen fuel cells. This
leaves the other two thirds to come from conventional
fossil fuels such as oil and gas. We have to find a
balance between the need to protect people's way of
life and the environment, and the need to provide
them with affordable energy; and also between the
cost of developing new technology to get the most
from fossil fuels, and the cost of developing new
power sources.