* Fossils seen supplying 85 pct of energy demand in 2050
* Financial, human and biodiversity costs all huge
* CO2 cut, global CO2 mkt delays make 2 degree limit harder
LONDON, March 15 (Reuters) - Global greenhouse gas emissions could rise 50 percent by 2050 without more ambitious climate policies, as fossil fuels continue to dominate the energy mix, the Organisation for Economic Cooperation and Development (OECD) said on Thursday.
"Unless the global energy mix changes, fossil fuels will supply about 85 percent of energy demand in 2050, implying a 50 percent increase in greenhouse gas emissions and worsening urban air pollution," the OECD said in its environment outlook to 2050.
The global economy in 2050 will be four times larger than today and the world will use around 80 percent more energy.
But the global energy mix is not predicted to be very different from that of today, the report said.
Fossil fuels such as oil, coal and gas will make up 85 percent of energy sources. Renewables, including biofuels, are forecast to make up 10 percent and nuclear the rest.
Due to such dependence on fossils, carbon dioxide emissions from energy use are expected to grow by 70 percent, the OECD said, which will help drive up the global average temperature by 3 to 6 degrees Celsius by 2100 - exceeding the internationally agreed warming limit of within 2 degrees.
Global carbon dioxide emissions from energy reached an all-time high of 30.6 gigatonnes in 2010, despite the economic downturn which reduced industrial production.
COST OF INACTION
The financial cost of taking no further climate action could result in up to a 14 percent loss in world per capita consumption by 2050, according to some estimates.
Human costs would also be high as premature deaths from pollution exposure could double to 3.6 million a year, the OECD said.
Demand for water could rise by 55 percent, increasing competition for supplies and resulting in 40 percent of the global population living in water-stressed areas, while plant and animal species could decline by a further 10 percent.
To prevent the worst effects of global warming, international climate action should start in 2013, a global carbon market be set up, the energy sector transformed to low carbon and all low-cost advanced technologies should be explored such as biomass energy and carbon capture.
However, a new international climate deal might not come into force until 2020 and carbon markets not linked until then, making it harder to achieve the 2 degree limit and requiring very rapid rates of emissions cuts after 2020 to catch up.
Current international emissions cut pledges fall short of what is required to limit temperature rises to safe levels so decisive action at the national level is needed, the OECD said.
Putting a clear and long-term price on carbon emissions through market-based mechanisms such as emissions trading schemes or carbon taxes will drive low-carbon investments.
The cheapest policy response to climate change would be to set a global carbon price, which would require linking various national and regional emissions trading schemes.
Scrapping inefficient fossil fuel subsidies would also encourage energy efficiency and renewables growth - increasing global real income by 0.3 percent in 2050, the report said.
The full report is available at www.oecd.org (Editing by Keiron Henderson)