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Weather Eye with |
Some of the answers to the complexities of the climate system are given in my recently published book Fifteen shades of climate... the fall of the weather dice and the butterfly effect.
The following are extracts are from pages 351-359..
Continued from last week
Coal to biomass
According to Drax, the decision to move from coal to biomass has slashed the plant's CO2 emissions by over 80% since 2012.
'In that time, we moved from being western Europe's largest polluter to being the home of the largest decarbonization project in Europe,” writes Will Gardiner, chief executive of Drax Group, on the company's website.
However, those calculated savings rest on a few key assumptions: first, that the carbon released when wood pellets are burned is recaptured instantly by new growth; second, that the biomass being burned is waste that would have released CO2 naturally when it rotted down. But are those assumptions right?
MIT's John Sterman stresses that he is not advocating a return to burning coal.
'Coal and other fossil-fuel use must fall as soon and as fast as possible to avoid the worst consequences of climate change. But there are many ways to do that, with improving energy efficiency being one of the cheapest and fastest.”
However, biomass energy advocates say that Sterman's carbon debt is a fallacy, created by assessing the forest stand by stand (referring to a group of trees planted at the same time and then harvested a few decades later) rather than viewing it at the landscape level.
'What actually happens is that one part of the forest is harvested (typically 3–4%) while the rest of it grows (typically net growth after harvesting is about 0.7 to 1% per year), supported by active forest management,” says Stevenson (Renewable Energy Association).
But Sterman argues that the opposite is actually true. 'Harvesting one part of a growing forest does not cause trees miles away to grow even faster,” he says.
'The trees harvested for bioenergy would have continued to grow, thus removing more CO2 from the atmosphere. The faster a forest is growing, the greater the future carbon storage is lost.”
It had been assumed that young trees mop up more carbon than old ones because they are fast-growing, but recent studies have revealed that ancient woodland growing in temperate regions takes up more CO2 than young plantations.
This is because in some cases, growth accelerates with age and CO2 absorption is approximately equivalent to biomass (Nature, 2014: 507,90).
'Far from plateauing in terms of carbon sequestration at a relatively young age as was long believed, older forests (for example over 200 years of age without intervention) contain a variety of habitats, typically continue to sequester additional carbon for many decades or even centuries, and sequester significantly more carbon than younger and managed stands,” researchers write in the journal Frontiers in Forests and Global Change (2018: 2,27).
But even if old trees are continuing to draw down CO2, what happens when a tree dies? Current carbon accounting assumes that all the carbon from dead wood is released back into the atmosphere again.
Removing forest thinnings and burning them to produce energy is therefore viewed as better than leaving them on the forest floor to rot. Indeed, Biomass in a Low-carbon Economy – a report produced in November 2018 by the UK Committee on Climate Change – states that 'Unharvested, the maintenance of these carbon stocks in perpetuity is essential to ensure that the sequestered carbon does not re-enter the atmosphere.”
However, Sterman argues that this fails to take account of the entire system.
'We need to consider the carbon stored in the soil too. Removing and burning ‘waste' wood lowers the source of carbon for forest soils. This allows soils to become net sources of carbon to the atmosphere as bacterial and fungal respiration continue to release soil carbon into the atmosphere,” he says.
Mary Booth, an ecosystem ecologist and director of the Partnership for Policy Integrity in Pelham, Massachusetts, shares Sterman's concerns.
In 2017 she used a model to calculate the net emissions impact – the difference between combustion emissions and decomposition emissions, divided by the combustion emissions – when forestry residues are burned for energy.
'It is the percentage of combustion emissions you should count as being ‘additional' to the CO2 the atmosphere would ‘see' if the residues were just left to decompose,” she explains.
Her calculations revealed that even if the pellets are made from forestry residues rather than whole trees, combustion produces a net emissions impact of 55– 79% after 10 years (Environ. Res. Lett. 13 035001).
Even after 40 years her model shows that net emissions are still 25–50% greater than direct emissions.
Like Sterman, Booth concludes that it takes many decades to repay the carbon debt, and she concludes that biomass energy can't be considered carbon neutral in a timeframe that is meaningful for climatechange mitigation.
A climate-friendly renewable fuel?
Booth was so concerned by what she found that she co-ordinated a lawsuit against the EU in March 2019 (eubiomasscase.org), challenging its treatment of forest biomass as a climate-friendly renewable fuel.
'Our position is that policies should count biogenic carbon emissions, and burning forest wood for fuel should not be eligible for renewable-energy subsidies,” says Booth.
On May 12, 2020, the case was denied access to the courts.
But even if biomass energy isn't 100 per cent carbon neutral, there may still be a place for it in the energy mix.
Currently around two-thirds of renewable energy in Denmark is provided by biomass, and it plays a vital role in keeping district heating systems running, particularly when the wind fails to blow.
Simon McQueen Mason, a biologist from the University of York, UK, thinks that simply burning biomass is missing a trick.
'Just using it to generate heat and electricity seems like a waste of a really good resource,” he says.
Instead, McQueen Mason is investigating ways of making gas and liquid fuel from biomass, by getting micro-organisms and bacteria to munch their way through woody material, and collecting the resulting gas and liquid produced as the bugs digest the biomass.
Pilot plants using sugar cane residue are already proving promising and could provide a solution to the vexing problem of de-carbonizing the petrochemical industry.
'We've done a good job in reducing emissions from heat and electricity, but we've barely touched our emissions from transport,” he says.
'Biofuel is probably the only way we can decarbonize the aviation industry in the next hundred years or so.”
But even if living trees can claw back these CO2 emissions relatively quickly, there is a danger in front-loading our emissions in this way.
'Regrowth is not certain,” says Sterman. 'Forest land may be converted to other uses such as pasture, agricultural land or development.
And even if it remains as forest, wild fire, insect damage, disease and other ecological stresses including climate change itself may limit or prevent regrowth, so that the carbon debt incurred by biomass energy is never repaid.”
When a country runs out of rubbish
You would have thought running out of rubbish would be a blessing rather than a curse. Yet in Norway, the lack of waste is becoming a major headache for the waste management business.
DW on their website de.com/en/first-world-problem has an interesting insight into when a country runs out of rubbish.
Since a 2009 ban on landfills, Norway has invested in modern wasteto-energy incineration plants with enormous capacity for burning waste and creating heat energy which is fed to private houses and businesses.
Peering into a giant oven burning waste at between 850 and 1000°C Jannicke Gerner Bjerkås from Oslo's waste-to-energy agency explains how the Klemetsrud incineration plant now turns people's rubbish into heat for their homes in the capital.
'The heat from the incineration is used to heat water, and the water is sent off to the district heating system in Oslo, and also we produce electricity from the steam,” she says.
”From this plant alone we provide around 60,000 households in Oslo with heat. In total there are about 340,000 households.”
The Klemetsrud plant can burn 300 tons of waste every day, and this huge capacity means it needs a lot of waste to run efficiently.
Rubbish has become a market commodity, and for plants like Klemetsrud a major headache.
'The market works like any other market, but the big difference is that we are not paying for the waste. The waste holder is actually paying to get rid of the waste,” says Bjerkås.
'What we've experienced in the past couple of years is the price is dropping, and it's basically hard to make money, because Sweden is building a lot of waste incinerators, and they're now competing in the Norwegian market.”
Paradoxically, hundreds of large trucks carrying Norwegian waste now drive straight past the Klemetsrud plant near Oslo and carry straight on to Sweden where it is cheaper to offload the cargo.
Swedish incinerator plants can offer cheaper rates because many are older than their Norwegian counterparts and debt-free.
The general cost level is also lower in Sweden.
Some campaigners now want Norway to introduce the EU's proximity principle to the waste business - which would force municipalities to take their waste to the treatment plant closest to them, not the cheapest.
'We hope that the governments both in Sweden and in Norway will see that the EU's principle of using the closest plant for municipal waste will support recycling better than exporting it to the cheapest oven,” says Torbjørn Leidal.
He is campaigning on behalf of Norway's waste management industry to keep Norwegian rubbish Norwegian. It is better for business, he argues.
'The level of recycling in Norway is diving, and we are burning too much waste that could have been recycled.”
Environmentalists say waste that should be recycled is being burned to keep the incinerators going.
So much waste is now going to Sweden that Norway has to import waste from elsewhere in Europe.
Containers arriving from Leeds and Manchester in the UK are unloaded in harbours south of Oslo, put on trucks and driven to the Klemetsrud incinerator plant.
This transport of waste across European borders worries environmentalists.
'The trade in waste is a problem, and you don't always know what the waste contains,” says Lars Haltbrekken from Friends of the Earth Norway.
'The problem in both Norway and Sweden is that we have too much capacity for burning waste. The consumers in Norway and Sweden are not producing enough waste. In our view we should not produce more waste but we should reduce the amount of waste we produce.”
The Norwegian government says it is considering various options to make sure incineration plants like Klemetsrud near Oslo have enough raw materials – including introducing the EU proximity principle which would see local waste burned locally.
Yet as long as the waste market remains open and Sweden is the cheaper place to get rid of household waste, Norwegian rubbish trucks will continue to head straight for the border.
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