years. CO2 has increased from 280 parts
per million (ppm) in 1750 to the present day level of
380 ppm (most of which has occurred in the last 50
years). 380 ppm is higher than any other time in the
past 650,000 years. Concentrations of the second
most abundant greenhouse gas, methane (CH4),
have also increased since the pre-industrial era by
150%. Consequently, these increased
concentrations have trapped more heat, thereby
creating an enhanced greenhouse effect, which has
caused the earth’s surface temperature to rise.