A United Nations report calls for fast action to reduce emissions of black carbon, ground level ozone and methane to help reduce current global warming and prevent the Earth from overheating. 
    Recommended procedures include mandatory diesel filters on vehicles, phasing out wood-burning stoves in wealthy countries, use of clean-burning biomass stoves for cooking and heating in developing nations, and a ban on the open burning of agricultural waste.
    Methane, ground-level ozone and black carbon cause about half of current global warming.  The report calls for immediate action to reduce these emissions to help limit global temperature rises over the next 20 years that could lead to catastrophic climate change from melting of glaciers and polar icecaps (that reflect radiation back into space) as well as methane permafrost and frozen sub-sea methane, which have been described as a "ticking time bombs" for our climate.  Prof Carlos Duarte, director of the Oceans Institute at the University of Western Australia, warned that the Arctic summer sea ice was melting at a rate faster than predicted by conventional climate models, and could be ice free as early as 2015.  Prof Duarte's article in 'The Conversation' explains why methane hydrates are a volatile time bomb in the Arctic  "The major risk is that the relatively modest human perturbation will unleash much greater forces."  The amount of greenhouse gas stored in the methane hydrates is several times the total CO₂ release since the industrial revolution.  NASA is investigating if a Sleeping Climate Giant is Stirring in the Arctic? the Similar sentimes are echoed by Climate Spectator: " We’ve known for a while that ‘permafrost’ was a misnomer (see Thawing permafrost feedback will turn Arctic from carbon sink to source in the 2020s). The defrosting permamelt will likely add up to 1.5 degrees Fahrenheit to total global warming by 2100."
    The immediate increase in global warming from the methane, carbon monoxide and black carbon emissions of wood heaters contribute disproportionately to current warming - in the first 20 years as much as heating 20 similar houses with gas or an electric heat pump, adding to the relatively modest perturbations that could unleash much greater forces if a tipping point is reached. 

 The graph from the latest UNEP report (November 2011) shows the effect of the measures to reduce methane (CH4) and black carbon (BC) on global temperatures.  Compared  the purple Reference line (business as usual) the dark blue line shows a rapid reduction in global temperatures of about 0.4 degrees by 2040, complementing the measures to reduce CO2 emissions.  Measures to reduce CO2 result in benefits from about 2040.  By about 2070, half the reduction is due to the reductions in methane and black carbon emissions and about half due to the reduction in CO2 emissions.      

  
   Over 100 years, methane causes at least 25 times as much warming as the same amount of CO2, but 72 to 100 times as much over the first 20 years. Fast action could help prevent frozen methane from melting and adding to the temperature increases, so that even more methane melts, leading to even greater temperature increases and so on.  This scenario of runaway climate change has been described as a point of no return, or tipping point, which cannot be reversed.   Reduce methane, black carbon and ozone will reduce losses of mountain glaciers and reduce projected warming in the Arctic over the coming decades by as much as two thirds, helping to avoid a tipping point if methane undersea and in permafrost starts to melt.
   Cutting out these pollutants now could also boost global food output and save millions of human lives lost to heart and lung disease, according to the report from the UN Environment Program (UNEP) and the World Meteorological Organization (WMO). Parallel action now on black carbon particles and ground-level ozone would buy precious time in limiting projected global temperature increases of 3.6 degrees Fahrenheit in the coming decades, the report said.

   A peer-reviewed paper in Atmospheric Pollution Research shows that, based on the latest estimates of Global Warming Potentials, over a 20 year horizon the average Australian wood heater causes more warming than heating 12 similar homes with gas (see Table 1).

  Ross Garnaut recommends credits for growing trees, taxes for chopping them down

On April 14, 2011: Professor Ross Garnaut, distinguished Australian economist and author of a review on Climate Change and Policy Response to Climate Change for the Federal, State and Territory governments of Australia, gave a lecture on Climate Change in Armidale, NSW.  When asked about how to account for biomass climate change policy, he argued that people who grow trees, should get credits for the carbon sequestered every year. But people who chop them down (and burn them) should pay tax on the carbon released into the atmosphere.

   This sensible accounting system (which relates directly to the impact on the atmosphere - sequester carbon and get credit; pay the tax when it is burned)  Methane should still be counted, as it is now, but the release of the CO2 dominates.   Under this accounting system,  a comprehensive peer-reviewed paper, published in Atmospheric Pollution Research shows that the average Australian wood heater causes more global warming than heating up to 5 similar homes with gas or a reverse cycle airconditioner. 

    The Kyoto protol used a different accounting system, in which, rather than being counted directly, CO2 emissions from wood burning were accounted for by the change in biomass in the forests and other stored carbon.  This works well for an entire country.  However, if used by individuals, it leads to wasteful and inefficient use of a valuable resource

Example: If the owner of a forest gets a credit for the amount of carbon sequestered every year, but pays a tax when the wood it burned, it may become economic to use thinnings to make wood pellets for power stations, instead of burning coal.  Without this incentive, forest owners are likely to simply burn waste wood on site, leading to much higher total greenhouse gas emissions than by using the wood as a replacement for burning coal. The same applies to domestic wood heaters.  The average Australian wood heater burns 2.7 tonnes of wood, emitting about 6.7 tonnes of CO2-equivalent, compared to 1.3 tonnes of CO2 for centrally heating an entire house with floor area of 160 square metres. 

    A Swedish study of enclosed wood burners used to heat water found that methane emissions can cause up to twice as much global warming as generating the same heat from an oil-fired burner. 

Lab tests: new Australian heaters on low burn as bad as the Swedish model causing twice as much global warming as an oil heater
        On low burn tests under a new test protocol in which the air control was turned down 2 minutes after adding more wood, two of the 4 new Australian models tested had similar emissions to the worst model in the Swedish study. This implies that, even if the wood is from a sustainabe source, under real-life operation,  the methane emissions from a new Australian wood heater used mainly on low burn will often cause much more global warming than heating the same house with gas. 

Lab results confirmed by real-life measurements 
        In Launceston, emissions from AS4013 heaters in the households of volunteers, who appeared to take condsiderable time and trouble to operate their heaters correctely, averaged 9.4 g/kg.  This is the is the best we can expect.  Most people will take a lot less time and trouble, implying that we can expect emissions of 10 to 15 g/kg.  Based on the graph (right) showing the relationship between methane and particle emissions, average amounts of wood burned, and average fuel used by households with non-polluting heating, we can conclude that, even if the wood is from a sustainable source, the average Australian woodheater will cause more global warming than gas or reverse cycle electic heating.

Even worse for global warming if climate reaches a tipping point in less than 100 years   Methane causes substantial, intense warming for some years after emission.  Over 20 years, it causes 72 as much global warming as the same amount of CO2, over 100 years this reduces to 25 times as much.  The Institute for Governance & Sustainable Development explains: “With abrupt climate change approaching faster than predicted according to scientists, fast-action mitigation strategies (reducing black carbon, methane, and tropospheric ozone) are essential in order to avoid passing the tipping points.”  See also a research paper with detailed info on Australian woodheating and global warming. 

Article in the Prince George Citizen providing a scientific explanation why burning wood produces a lot more CO2 than natural gas per unit of useful energy.  "The basic premise that wood based fuels operate under is that any carbon dioxide produced will be recycled into trees. But there is a word missing from that sentence and it is “eventually”. It takes some 80 years or so for the carbon dioxide released today to be fully captured. And with twice as much carbon dioxide being produced for the same amount of energy, that is a lot of additional greenhouse gases being introduced into the atmosphere in the short run."

Pellet heaters cause much less global warming
       

This problem can be avoided by switching to pellet heaters which emit 95% less health-hazardous PM2.5 pollution and methane per year than the average AS4013 heater.  Average emissions from pellet heaters are  less than1 g/kg, compared to 10 g/kg for the average wood heater, but because the heat is controllable, two or 3 houses can be heated for the same amount of wood burned in a single log heater.