Non-CO2 substances cause half of current warming
About half of current warming is caused by substances other than CO2, including methane (CH4), ozone (O3) and black carbon (BC).
Reducing this 50% of warming is vitally important. We cannot meet the Paris Agreement to keep the global temperature risk well below 2 degrees without tackling these pollutants. This was shown by a team of 50 scientists from the UN Environment Program and the World Meteorological Organization (UNEP/WMO).
The UNEP recommended “a range of compelling, and in
many cases highly cost-effective options for fast action on BC, CH4
and tropospheric ozone.”
Three experts - a Nobel prizewinner, a renowned climate scientist and sustainability guru warn about a nightmare scenario in which “feedback mechanisms” cause uncontrollable impacts. Shrinking Arctic sea ice has added an extra 25% more warming since 1979 than that from carbon dioxide emissions. As the Arctic heats up (at twice the global average rate), permafrost melts and releases methane that causes still more warming. In 2015/16, rising temperatures also contributed to Alaska’s near-record forest fires, which melt the insulating layer above the permafrost, adding still more methane to the atmosphere, on top of the CO2, BC and methane from the fires themselves.
Another research study into feedback mechanisms concluded that for every 1C of warming, the Earth’s plants and soils will release carbon dioxide to the atmosphere to the tune of about 20 parts per million.
Defusing the ‘Ticking Time
NASA’s website explains: “methane is 22 times more potent as a greenhouse gas than carbon dioxide on a 100-year timescale, and 105 times more potent on a 20-year timescale. If just one percent of the permafrost carbon released over a short time period is methane, it will have the same greenhouse impact as the 99 percent that is released as carbon.”
Prof Carlos Duarte, Director of the University of WA’s Oceans Institute also warned about the devastating consequences if current warming causes substantial quantities of methane to be released from the Arctic: “The amount of greenhouse gas stored in methane hydrates in the Arctic is several times the total CO₂ release since the industrial revolution” see Methane hydrates: a volatile time bomb inthe Arctic.
When the Kyoto protocol was developed in the 1990s, much
less was known about potential tipping points in the climate, so an arbitrary
period of 100 years was used to compare the effects of emissions. We also need to consider the Climate Tipping Potential of our emissions
The UNEP/WMO graph shows the 2 degree limit is likely to be exceeded by about 2040. Our best chance of meeting the target is to keep the temperature increase between now and 2040 as low as possible. This will minimize the risk of higher temperatures speeding up the melting of glaciers and icecaps and speeding up the release of methane from permafrost/undersea ice, and therefore creating yet more warming, more melting and more methane released in an increasing feedback look that will take us past the 2 degree limit.
Minimizing the temperature increase in the next 20 years buys us time to develop and implement clean power and transport. Within 2 decades, wind, solar PV (with improved battery or pumped hydro storage) and solar-thermal with molten salt storage will likely be cheaper than the cost of digging coal out of the ground and transporting it to a power station. Improvements in battery technology and/or fuel cells should also allow electric cars (fuelled by non-polluting solar electricity) to replace petrol.
The UNEP/WMO’s recommended a package of 16 measures to address the half of warming from SLCP, including clean cookstoves, reducing methane emissions from mining, gas extraction, pipelines and rubbish tips, avoiding diesel pollution and phasing out log-burning wood heaters in developed countries. These measures were noted to have dual benefits of reducing global warming and improving health.
How to minimize your climate impact
The table below shows the impact, over the next 20 years, of individual action to reduce gas or electricity use, bicycling instead of driving, or burning less wood. Some actions save money, e.g. cycling is healthy and costs less than driving. Installing basic home insulation and draft-proofing reduces energy bills and greenhouse gas emissions for minimal or zero net cost over time. Correctly-positioned solar cells on an unshaded roof also reduce electricity bills; the savings can be substantial savings for households that use a fair amount of daytime electricity.
Solar water heaters can also reduce
greenhouse gas emissions and fuel bills, but it may take several years to
recover the cost of replacing an electric water heater on the overnight
(controlled load 1) tariff. Moreover, reductions
in electricity demand are not guaranteed to result in reduced emissions. With the abolition of the Australian carbon tax, electricity
companies may find to cheaper to operate coal-fired power stations continuously
(even if some the electricity is wasted) than run more expensive
‘peaking’ gas plants. Purchasing ‘green
electricity’ is one way to reduce personal contributions to
global warming and indicates to electricity companies that global
warming is considered an important issue.
Why wood stoves increase the risk of dangerous climate change
Many households in colder areas burn 4 tonnes of wood per year. In the 20 years after emission, this will cause as much global warming as 50-75 tonnes of CO2 - more global warming than heating 50 similar houses with an efficient electric heat pump. Slow combustion wood heaters limit airflow, creating CH4, CO and BC as well as CO2 emissions. Individuals with wood heating (10% of all Australian households) can dramatically reduce their impact over the next 20 years by replacing the wood heater with an efficient heat pump.
Modern, efficient heat pumps have superseded wood stoves and natural gas as the most cost-effective heating. They can deliver 5 or 6 times as much heat to the home as they use in electric power and are effective at low temperatures. They are affordable (cheaper than buying a wood stove), cause less global warming (zero in households that use green power) and have lower running costs than buying firewood.CO) and methane (CH4) emissions for burning softwood are averages of all tests for generally well-operated AS4103 wood stove in John Gras’ comprehensive study . PM2.5 and CH4 emissions of 12.5 and 18.7 g/kg for hardwood are from a peer-reviewed paper published in Atmospheric Pollution Research . Estimated BC emissions for hardwood use the California Air Resources Board methodology that BC represents about 2.5% of PM2.5 emissions  . CO emissions from burning hardwood are based on the real-life emissions study showing 15% of carbon emitted as CO .
Global Warming Potentials (GWP). The IPCC 5th Assessment report shows that over 20 years, 1 kg of methane (CH4) causes as much warming as 86 kg CO2 (including direct and indirect aerosol effects; including the CO2 produced when methane is oxidized gives a slightly higher GWP of 88); 1 kg CO causes as much warming as 18.6 kg of CO2 (see Tables 8.7 and A.8.4 of Chapter 8, AR5 WG1).
The 20-year GWP for BC from the California Air Resources Board .
The estimate of CO emissions from burning hardwood is probably also an under-estimate, because it is based on measurements in Launceston , where considerable effort was spent on wood heater education. The volunteers in the study were keen to operate their heaters carefully; many refuelled their heaters in the middle of the night, rather than allowing them to smoulder overnight. PM2.5 emissions averaged 9.4 grams per kg firewood. PM2.5 are too small to be seen by the naked eye (except by the way they scatter light), and emissions of 7 g/kg are described as ‘faint smoke’, so this level of smoke would not be considered excessive. Measurements showed that 15% of carbon was emitted as CO, rather than CO2, suggesting that the heaters were used mainly on low burn, i.e. conditions conducive to CH4 production.
In other cities, much less has been spent on wood heater education than Launceston. Heaters are often operated carelessly, resulting in much higher levels of pollutants, e.g. the tragic deaths of an elderly couple from carbon monoxide poisoning from a poorly-maintained wood heater.
As discussed in the peer-reviewed paper , real-life emissions in other cities are likely to be higher than in Launceston, so 12.5 g/kg was considered the most plausible estimate of real-life PM2.5 emissions and 18.7 g/kg for CH4. The latter was based the observed relationship between CH4 and PM2.5 emissions for burning hardwood in AS4013 heaters.
Similar levels of methane and carbon monoxide emissions are reported in studies of American wood heaters (e.g 14 to 25 grams CH4 and 80-370 grams CO per kg firewood. A review discussing older style heaters in in 2008 reported estimates of 32 g/kg of CH4 and 78 g/kg CO . Real-life emissions from US-EPA phase II heaters were 9.2 g/kg (non catalyst) and (catalyst), an overall average of 9.7 g/kg . The disappointingly low 28% reduction in woodsmoke pollution levels, and continued totally unacceptable in woodsmoke pollution in Libby, Montana (pop 2,600) when 1130 old stoves were replaced with new EPA-certified ones demonstrates that real-life EPA-certified stoves are nowhere near as clean as people would like to believe.
US pellet heaters are estimated to emit 27 lbs (11.2 kg) of PM2.5 per year, i.e. health cost (at $263 per kg) of over $2,000 per heater per year. Until new models are developed with much lower emissions, US pellet heaters are not suitable for urban areas.
Heat pumps - affordable, efficient, low running costs & climate friendly
Given the very high SLCP emissions from wood heating, the best long-term solution is to transition to a modern, efficient heat pump. In 2011, Matthew Wright (as Executive Director of Beyond Zero Emissions) argued that heat pumps should qualify for Renewable Energy Certificates. Small systems cost less to buy and install than a wood stove, are remarkably efficient, with up to 6 times as much heat delivered to the home as they use in electricity. They also have lower running costs than buying firewood and avoid the considerable health costs of wood heating, estimated at thousand of dollars per heater per year. NSW Chief Medical Officer Kerry Chant says wood heaters are so detrimental to the health she supports banning and phasing out the heaters in built-up urban areas as an option to control wood smoke.
A major problem with wood heating is the lack of thermostatic control. A typical wood heater in Sydney burns about 2 tonnes of wood and generates more heat in a single room than needed to centrally heat an entire house. An efficient reverse cycle air-conditioner has lower running costs than buying firewood, will cause a lot less global warming over the next 20 years (zero for green electricity users) and saves thousands of dollars per year in health costs – a win-win-win situation!
Some people argue that if firewood is left in the forest it will eventually decompose and produce similar emissions to burning it. This however, can take much longer than the critical 20 year period. Soil scientist Glen Ayers stated that “Forest debris left in the woods will produce very minor amounts of methane, if any,unless it is squashed into a swamp or buried in a stump dump.” Another important concerns is that a considerable proportion of firewood is not from sustainable sources (e.g. 80–90% of Canberra’s firewood is said to be sourced from dead standing paddock trees up to 400 km away) and that firewood extraction is threatening biodiversity and depriving native species,including threatened wildlife, of hollow logs for homes. Far from being sustainable, firewood supplies in the Riverina are said to be running out. People have burned old railway sleepers (hardwood can survive for decades without rotting) and experienced health problems.
Although bushfires produce some CH4 (about 5 to 7 g per kg fuel) and CO (about 100 g)per kg fuel), this is only a tingy fraction of the global warming of burning the wood in the average domestic wood heater. If sustainable extraction of wood is needed to help reduce bushfire risk, there are many other competing uses (e.g. wood products, co-firing in power stations) that act as carbon stores or help avoid fossil fuel use without the substantial climate-damaging CH4 and CO and BC emite by burning wood in an enclosed wood heaters.
Professor Piers Forster from the University of Leeds, Coordinating lead author of the IPCC AR4 report chapter ‘Changes in Atmospheric Constituents and in Radiative Forcing’ and contributing author to the IPCC AR5 Chapter ‘Anthropogenic and Natural Radiative Forcing’ (both of which review the scientific evidence on the changes in the atmosphere that cause global warming) advised: "Reducing emissions from diesel engines and domestic wood and coal fires is a no-brainer as there are tandem health and climate benefits."
The information provided here will help people achieve the greatest benefits relative to their own personal effort and cost. Wood heater users can achieve the largest climate benefits by replacing wood heaters with an efficient heat pump. Others might try to persuading a friend or acquaintance to do so. The benefits from avoided CH4 and CO2 emissions are believed to be additional to the benefits of reduced BC emissions that led to the UNEP/WMO recommendation to phase out log-burning wood heaters in developed countries to reduce climate change and improve health.
Replacing them will pellet heaters is one possibility, although with health costs of PM2.5 emissions now estimated at $263 per kg in capital cities such as Sydney and Melbourne, the relatively high purchase price and PM2.5 emissions of pellet heaters (1 to 2 kg PM2.5 per year), and limited availability of sustainably-produced pellets, suggests this might not be the best possible choice. The lower purchase and running costs of efficient heat pumps together with very low greenhouse gas emissions and no PM2.5 pollution suggest they could represent the best option for both the environment and public health.
Other actions such as installing solar cells, improving energy efficiency, replacing electric hot water systems or cycling instead of driving also benefit the climate and some even save money.
References and Additional Information
1. UNEP/WMO, Integrated Assessment of Black Carbon and Tropospheric Ozone. Summary for Decision Makers. UN Environment Program & World Meteorological Organization. http://www.unep.org/dewa/Portals/67/pdf/Black_Carbon.pdf (accessed 13 March 2012). 2011.
2. UNEP, Near-term Climate Protection and Clean Air Benefits: Actions for Controlling Short-Lived Climate Forcers, 2011, United Nations Environment Programme (UNEP), Nairobi, Kenya, 78pp . http://www.unep.org/publications/ebooks/slcf/ (accessed 18 March 2012).
3. Gras, J., Emissions from Domestic Solid Fuel Burning Appliances., 2002, Environment Australia Technical Report No. 5, March 2002. Available at: http://www.environment.gov.au/atmosphere/airquality/publications/report5/index.html.
5. Meyer, C.P., et al., Measurement of real-world PM10 emission factors and emission profiles from woodheaters by in situ source monitoring and atmospheric verification methods, 2008, CSIRO Marine and Atmospheric Research (CMAR), (available at: http://www.environment.gov.au/atmosphere/airquality/publications/emission-factor.html ).
10. NEPCSC, National Environment Protection Council Service Corporation, Consultation regulation impact statement (CRIS) for reducing emissions from wood heaters. , in Available at http://www.scew.gov.au/strategic-priorities/clean-air-plan/woodheaters/index.html2013.
12. Revised Proposed Short-Lived Climate Pollutant Reduction Strategy, California Air Resources Board, November 2016. Available at: www.arb.ca.gov/cc/shortlived/shortlived.htm
13. Houck, J., Pitzman, L., Tiegs, P., 2008. Emission Factors for Aged Uncertified Residential Cordwood Heaters. Inventory Evolution– Portal to
Improved Air Quality, US Environmental Protection Agency.