The carbon intensity of the world economy - the amount of greenhouse gases emitted per dollar of gross domestic product (GDP) - fell by 2.7 percent in 2014, the steepest decline since PwC started issuing reports seven years ago, it said.
"The 2014 numbers suggest a turning point" towards making growth less dependent on fossil fuels, said PwC, a network of firms in 157 countries in assurance, advisory and tax services.
World GDP rose by 3.2 percent in 2014, while carbon emissions rose by just 0.5 percent, Reuters quoted.
Britain was best of the Group of 20 nations with a steep 10.9 percent fall in its carbon intensity last year, a shift PwC linked to strong economic growth, a warmer winter that reduced energy demand and lower use of coal.
France, Italy and Germany also had big falls in carbon intensity last year.
Almost 200 governments will meet in Paris from Nov. 30-Dec. 11 to agree a pact to curb greenhouse gas emissions, mainly from burning fossil fuels, that are blamed by a U.N. panel for causing downpours, heat waves and rising seas.
PwC said the rate of decarbonisation needed to more than double, to 6.3 percent a year, to get on track to limit rising temperatures to a U.N. target of 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times.
That would be a wrenching pace of change. Even in Germany in the 1990s, when inefficient Soviet-style factories were shut in the east after reunification, decarbonisation rates were only about 3 percent a year, the report said.
"You need revolutions in the energy sector in every country, every decade," Jonathan Grant, PwC sustainability and climate change director, told Reuters.
Since the year 2000, the report said that global carbon intensity had fallen by an average 1.3 percent a year. At that rate, PwC estimated that the amount of carbon that could be emitted before exceeding 2C would run out in 2036.