The production of heat is responsible for about half the UK’s total CO2 emissions and the announcement of the details of the Renewable Heat Incentive (RHI) is a welcome step forward. Many significant issues remain unaddressed – most importantly whether the active encouragement of the use of biomass (primarily, wood) is likely to increase pressures on land use. Put simply, are the targets for renewable heat announced today compatible with commitments not to increase deforestation around the world? Also, will the RHI mean land is converted from agricultural use to wood production, in the UK or elsewhere? The calculations in this note suggest that to achieve the 2020 targets from domestically grown wood about a third of the UK’s total land area would have to be given over to new forest. The preamble to the RHI says that the government wants to see about 12% of the UK’s heating provided by renewable sources by 2020. Since about half of all energy use in the UK is employed to provide heat, this implies that just under 6% of total national energy consumption will be provided from renewable sources. Not all of this will be wood. The government’s plans mention biomass from the municipal waste stream and biomethane from the digestion of agricultural wastes. But it is almost inevitable that wood will be used to provide a large majority of the total power sources. There just isn’t much energy in domestic waste and agricultural residues.

I have done a series of quick calculations that demonstrate how much wood is needed to provide about 6% of UK energy demand. (For fans of incomprehensible energy numbers, this is about 100 terawatt hours.) This could be provided by about 24 million tonnes of dry wood, burnt in very efficient boilers. Fresh-cut wood is about 40% moisture, meaning that about 40 million tonnes needs to be cut down and then dried.

For comparison purposes, it may be helpful to note that the UK currently produces about 9 million tonnes of forest products a year – somewhat less than 25% of what we will need for wood for energy.

I think that well-managed UK woodlands and land given over to energy crops such as elephant grass (Miscanthus) can produce about 3 dry tonnes a hectare a year, averaged over soil and climate types. So to produce enough wood domestically, we need to use about 8 million hectares. The UK’s total land area is about 25 million hectares. So to get 12% of our heating needs from wood, we would need to set additionally aside about one third of the surface of the country for forestry and energy crop production. The figure today is about 12%.

Of course this won’t happen. We will import the vast bulk of the wood we need. The Forestry Commission publishes estimates of the UK’s likely output of wood well beyond 2020 – after all, this is now planted - and the most we can hope for is an extra 3m or so tonnes, less than a tenth of what we will need.

Other countries have far more woodland than the UK does. We could meet the UK’s targets for renewable heat in 2020 by giving over less than one quarter of one percent of world forest land to meet the 12% commitment. The problem is that the world needs to decrease the pressure to log slow-growing hardwood forests not add, however marginally, to the demands for wood as fuel. And the UK’s policies towards renewable heat will probably be copied by other countries, adding to the pressure on world timber stocks. The uncomfortable fact is that we need the world’s land to produce more food, more ethanol and biodiesel for vehicle and aircraft fuels and more biomass for heat. Although we can use our land more productively, for example re-establishing forests on the UK’s upland grasslands, the RHI will inevitably add more pressure to food prices – and to the price of wood itself.