Poor practice can wipe out carbon savings, the report says
Biomass power - such as burning wood for energy - could do more harm than good in the battle to reduce greenhouse gases, the Environment Agency warns.
Ploughing up pasture to plant energy crops could produce more CO2 by 2030 than burning fossil fuels, if not done in a sustainable way, it said.
Its study found waste wood and MDF produced the lowest emissions, unlike willow, poplar and oil seed rape.
The EA wants biomass companies to report all greenhouse gas emissions.
The agency is calling on the government to introduce mandatory reporting of greenhouse gas emissions from publicly-subsidised biomass facilities, to help work out if minimum standards need to be introduced.
Wood-burning stoves, boilers and even power stations are seen by many as critical to Britain's renewable energy targets.
Biomass is considered low carbon as long as what is burnt is replaced by new growth, and harvesting and transport do not use too much fuel.
'Role to play'
The EA's report reiterated the belief that biomass had the potential to play a "major role" in producing low carbon, renewable energy to help meet future energy needs and help cut greenhouse gas emissions.
But the report Biomass: Carbon Sink or Carbon Sinner also found that the greenhouse gas emission savings from such fuels were currently highly variable.
At its best, biomass could produce as little as 27kg of CO2 (equivalent) per megawatt hour - 98% less than coal, saving around two million tonnes of CO2 every year.
However, the study also found that in some cases overall emissions could be higher than those of fossil fuels.
This was particularly true where energy crops were planted on permanent grassland, it said.
Tony Grayling, head of climate change and sustainable development at the Environment Agency, said biomass could play a role in helping the UK meet its renewable energy targets.
But he argued the credibility of biomass rested on tough sustainability criteria and called on biomass projects to combine heat and power production.
"Biomass is a limited resource, and we must make sure it is not wasted on inefficient generators that do not take advantage of the emissions savings to be made from combined heat and power," he said.
"By 2030, biomass fuels will need to be produced using good practice simply to keep up with the average carbon intensity of the electricity grid."
He added: "The government should ensure that good practice is rewarded and that biomass production and use that does more harm than good to the environment does not benefit from public support."