Most Effective Ways to Reduce Your Global Warming

Non-CO2 substances cause 50% of 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 - the graph shows  we cannot meet the Copenhagen limit of 2 degrees without tackling these pollutants, a fact shown by a team of 50 scientists from the UN Environment Program and the World Meteorological Organization (UNEP/WMO).[1]

The UNEP recommended “a range of compelling, and in many cases highly cost-effective options for fast action on BC, CH4 and tropospheric ozone.”[2] 

Defusing the ‘Ticking Time Bomb’

Reducing emissions of BC, CH4 and ozone precusors produces a rapid reduction in warming (dark blue line on the graph), because these pollutants cause substantial warming, but stay in the atmosphere for shorter periods of time than CO2.  A reduction in BC and CH4 emissions therefore produces a big reduction in current warming which prevents future warming by slowing the melting of glaciers and polar icecaps, allowing them to continue to reflect radiation back into space.  

Reducing current warming also helps keep methane locked away in permafrost and frozen undersea stores.  Charles Miller, principal investigator of NASA’s Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) warned in 2013: "Permafrost soils are warming even faster than Arctic air temperatures - as much as 2.7 to 4.5 degrees Fahrenheit (1.5 to 2.5 degrees Celsius) in just the past 30 years".

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 CO release since the industrial revolution” see Methane hydrates: a volatile time bomb inthe Arctic.

What we can do

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 graph shows the 2 degree limit is likely to be exceeded by about 2040, so perhaps the best chance of keeping global temperatures below this limit is to do our best to keep the temperature increase between now and 2040 as low as possible.  This will minimize the feedback loop of higher temperatures in the next few years causing glaciers to melt and releasing methane from permafrost and undersea hydrates and so adding to future warming and melting even more glaciers and methane stores and generating even more future warming.

Minimizing the temperature increase in the next 20 years will buy us time to develop and implement clean power and transport technology.  Within 2 decades, wind, solar PV (with improved battery storage) and solar-thermal with molten salt storage are likely to 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 50% of warming from shorter-lived pollutants, 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.

Climate Impact over the next 20 years

As well as perhaps hoping for wider benefits if governments introduce climate-friendly policies, individuals may wish to reduce their personal contribution to global warming.  The table shows the impact over the next 20 years of reducing gas or electricity use, cycling 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.  Solar cells on an unshaded roof facing the equator can also reduce electricity bills.  In sunny places the net cost over time of avoiding 3 tonnes of CO2 emissions could be close to zero 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 (off-peak 1) tariff.  Moreover, reductions in electricity demand are not guaranteed to result in reduced emissions.  Now that Australia has abolished the carbon tax, electricity companies may find to cheaper to run coal-fired power stations continuously (even if some the electricity is wasted) than operate the more expensive ‘peaking’ gas plants.  Purchasing ‘green electricity’ is an alternative way to reduce your personal contribution to global warming and indicates to electricity companies that you consider global warming to be an important issue.

Global Warming (emissions & total tonnes CO2-equiv) in the 20 years after emission, Australia

Over 20 years, 1 kg of methane (CH4) is estimated to cause as much warming as 87 kg CO2 and (including direct and indirect aerosol effects) 1 kg of carbon monoxide (CO) is estimated to cause as much warming as 18.6 kg of CO2 (see Tables 8.7 and A.8.4 of Chapter 8, AR5 WG1). Estimated reductions from using less electricity are based on the assumption that reduced demand will result into power generation, which is not necessarily true for power generated by inflexible coal-fired plants.  CO and CH4 emissions for burning softwood are the average values reported in John Gras’s comprehensive study[3].
Emissions from burning hardwood are based on the real-life emissions study showing 15% of carbon emitted as CO.
CH4 emissions of 18.7 g/kg are from a peer-reviewed paper published in Atmospheric Pollution Research

The table shows one of the best ways individuals with wood heating (10% of all Australian households) can reduce their impact over the next 20 years on the climate that is to replace the a wood heater with an efficient heat pump.  Many households in colder areas burn 4 tonnes of wood per year, which causes as much global warming in the 20 years after emission as 29-34 tonnes of CO2.  Slow combustion wood heaters limit airflow, creating CH4, CO and BC as well as CO2 emissions.

The estimates for wood heating in the table are based on emissions measurements in Launceston[5], where considerable sums were 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.  Nonetheless, 15% of carbon was emitted as CO, rather than CO2, suggesting that the heaters were used mainly on low burn, 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 such as CO, even the tragic deaths of an elderly couple from carbon monoxide poisoning from a poorly-maintained wood heater.

Burning softwood in an Australian standard compliant heater also increases emissions.  Laboratory tests showed that even under quite good operating conditions, an average of 30 grams of methane was produced per kg firewood.  Wood heater user who burn dry, seasoned softwood can therefore reduce their contribution to climate change by more than installing a solar water heater by switching to dry, seasoned hardwood.

However, 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 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.

Evaluations of wood heating often ignore the lack of thermostatic control.  A typical wood heater in Sydney burns about 2 tonnes of wood, which generates about 50% more heat than needed to centrally heat the entire house.  Replacing it with an efficient reverse cycle air-conditioner reduces running costs compare to buying firewood, reduce global warming over the next 20 years from home heating by 95% 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[6]) 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)[7], suggesting that emissions cause less than half 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 CH4 and CO generated in enclosed wood heaters that is damaging our climate.


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[1].

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.

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."

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. (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 . (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:

4.    Robinson, D.L., Australian wood heaters currently increase global warming and health costs. Atmospheric Pollution Research, 2011. 2(3): p. 267-274.

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: ).

6.    McArthur, I., Report on the sustainable re-use of timber from felled urban trees in the ACT, 2010, Farm Forestry Consulting.

7.    Andreae, M.O. and P. Merlet, Emission of trace gases and aerosols from biomass burning. Global biogeochemical cycles, 2001. 15(4): p. 955-966.

8.    Fisher, L., et al., Long-term performance of EPA-certified Phase 2 woodstoves, Klamath Falls and Portland, Oregon: 1998/1999. Prepared for the USEPA, NRMRL-RTP-195 (R3/27/00), 2000.

9.    Puget Sound Clean Air Agency. Relative Emissions of Fine Particles. Available from:

10.  NEPCSC, National Environment Protection Council Service Corporation, Consultation regulation impact statement (CRIS) for reducing emissions from wood heaters.  , in Available at

    11.  Assessment of urgent impacts of greenhouse gas emissions—the climate tipping potential (CTP)

The above was based on emissions measurements from wood heaters that met the AS/NZ 4013 standard. Studies of American wood heaters report similar levels of methane and carbon monoxide emissions (e.g 14-25 grams CH4 and 80-370 grams CO per kg firewood, with a more recent publication reporting 32 g/kg of CH4 and 78 g/kg CO) implying that the conclusions for wood heaters in other countries are likely to be similar.  Real-life emissions from USEPA phase II heaters were reported as 9.2 g/kg (non catalyst) and (catalyst), an overall average of 9.7 g/kg[8].  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[9], i.e. health cost (at $263 per kg[10]) 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.