According to the BP Statistical Review of World Energy 2015 it
happened because of sharp deceleration of global primary energy
consumption and strong shift of energy production growth from fossil fuels to
renewables.
Chinese consumption growth was the slowest since 1998
and energy consumption in the EU fell to its lowest level since 1985. From the supply side, low-carbon energy
sources led the race in 2014 – solar output expended by 38% and wind – by 10%. At
the same time, coal demand growth slumped from 3.6% over the decade to just
0.4% last year, and oil and gas also grew by less than 1%, far below historical
averages. Read more at http://www.carbonbrief.org/