Near-term Risk and Opportunities
| In May, 2011, the ECO his released third Annual Greenhouse Gas Progress Report. Click here for more information on this report, including videos and communications materials. | |||||
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Climate change is an upset in Earth’s energy balance brought about by various perturbations. These can be natural, like major volcanic eruptions, or of human origin – which has predominantly been the case in recent decades. The mechanisms of perturbation can cause Earth to become cooler (termed negative radiative forcings) or warmer (positive radiative forcings). Climate change is described as being caused by global warming because the net effect when we balance out the various radiative forcings in the fossil fuel age is strongly positive. The greatest positive forcing in the atmosphere is that caused by the propensity of water vapour to act as a GHG by absorbing infrared radiation and effectively trapping it and heating the planet. But water vapour will readily condense out of the atmosphere at 100 per cent humidity. The amount of water vapour (H2O) is determined by temperature – not the other way around – so it cannot be the primary cause of global warming, only an amplifying feedback.
The dominant GHG is carbon dioxide (CO2), a gas that traps infrared radiation and, due to human activities, has increased in concentration in the atmosphere from about 280 ppm before the industrial revolution to 392 ppm today. Unlike H2O, it can accumulate in the atmosphere and persist for a very long time. Consequently, CO2 is the greatest contributor to the global warming phenomenon. The comparative importance of other GHGs is expressed by their global warming potential (GWP). CO2 has a GWP of 1 whereas methane (CH4), by comparison, has a GWP commonly expressed as 25, meaning that methane is unit-for-unit 25 times as potent a GHG as CO2 over a 100 year period in the atmosphere. Nitrous oxide has a GWP of 298 and some hydrofluorocarbons have GWPs of almost 15,000. Fortunately, these gases are present in very small quantities in the atmosphere.
That 100-year time period, sometimes expressed as ‘by 2100’ (which, of course is now less than 90 years away) is the typical period of time over which climate change implications are discussed. While on the one hand this is a useful practice because it emphasizes the long-term effects of GHG accumulation and allows scientists to bridge some of the temporal uncertainty in their models, this long-term emphasis complicates present and near-term policy decisions.
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The Tyranny of the Near Term
The next 40 years are a critical time for the planet with respect to GHG emissions. Presently the global economy is carbon-based and the content of the atmosphere is rapidly heading toward a perhaps imminent, but unknown, tipping point. Beyond this point feedback cycles will cause the rapid release of GHG emissions from biological and geological sources. Beyond that point control is lost. GHG abatement will become futile and we will suffer the full consequences of extreme weather, serious climate zone changes, ocean acidification and catastrophic sea level rise. But this doesn’t have to happen. If the global economy be can de-carbonized, with Ontario contributing an 80 per cent reduction in GHG emissions by 2050, the present trends may well be reversed before these tipping points are reached.
That is why the next 40 years are critical. The near-term release of GHGs, or other substances with a significant GWP, presents a greater risk than releasing emissions later in the century, when our use of fossil fuels will likely have stopped. The ECO has raised this concern in our 2010 Annual Greenhouse Gas Progress Report regarding the potential carbon impacts of burning forest biomass to produce electricity. There is no argument that such biomass energy could be considered ‘carbon neutral’ over the 100-year period after the trees grow back, but in the near term, when the system is most vulnerable, all the forest carbon sequestered over the past century would be lingering in the atmosphere as CO2 waiting to be taken up by the growing trees decades later.
In a related but different context, near-term GWP has other serious policy implications. Recall that methane, the second most important GHG, has a GWP of 25 over 100 years. That statistic masks the behaviour of methane over the near term. Methane oxidizes relatively quickly in the atmosphere compared to CO2 and so its impact is greatest in the early years. The GWP of methane over 20 years is 72, almost 3 times greater than over a 100-year timeframe, and so nearterm methane releases are a far bigger threat. This has serious implications for policies related to natural gas extraction and handling as well as the management of landfill gas (see Appendix 5).
The focus on the near term does provide at least one policy opportunity with regard to climate change. Although the major GHGs are around for years, there are other atmospheric constituents that play a major role in climate change which have life expectancies measured in only days or weeks. These are aerosols, tiny particles of solids or liquids which are suspended in the atmosphere and result from human activity, natural fires or volcanic eruptions. Their lifespans
may be short, but because humans and nature continually discharge these materials there is a constant (but variable) supply suspended above us. Aerosols come in two types, reflective and black carbon. The former, which are commonly sulphate aerosols, have a negative radiative forcing because they reflect incoming solar radiation back into space. Black carbon aerosols, on the other hand, have a positive radiative forcing because they absorb solar radiation and radiate infrared back to Earth. The Intergovernmental Panel on Climate Change (IPCC) has estimated that the magnitude of each of these opposing forcings at the global scale are about equal, causing them to effectively neutralize each other in terms of global warming accounting.
Notwithstanding the reflective benefits of sulphate aerosols, we continue to limit the anthropogenic emissions of sulphates because they are a source of acid rain, smog and other health related impacts. Combustion emissions have been reduced through the use of lowsulphur fuels, but smelters and volcanoes remain significant sources worldwide.
A Black Carbon Aerosol Opportunity
Black carbon aerosols originate from the incomplete combustion of fossil fuels, biofuels and biomass. In the common vernacular, black carbon is called soot. Emissions of black carbon are controlled to a great extent in many advanced economies (much less so in the developing world) but there are still opportunities to reduce these emissions in Ontario. To the extent that emissions of black carbon aerosols are reduced, the zero sum game of aerosols would be turned to a net negative forcing (i.e., a cooling of the atmosphere) assuming the status quo for sulphates. However, more recent research indicates that aerosols may not be a zero sum game. At least one published journal article that analyzed black carbon’s distribution in the atmosphere concluded that it is much more significant and is “the second strongest contributor to global warming.”
The GWP of black carbon over the 100-year term is conservatively estimated to be about 460. However, because of its short life span its GWP expressed over 20 years is 1,600 (see Table 4). Given its powerful influence on warming, black carbon deserves attention. More significantly, reductions in black carbon emissions will show reductions in radiative forcings in the very near term, a matter of weeks, unlike CO2 which persists for many decades. This makes the reduction of black carbon one of the only abatement strategies available to reduce near-term tipping-point risks – a policy opportunity that should not be ignored.
| GWP20 | GWP100 | GWP500 | |
|---|---|---|---|
| Black carbon | 1600 | 460 | 140 |
| Methane | 72 | 25 | 7.6 |
| Nitrous oxide | 289 | 298 | 153 |
| Sulfur oxides | -140 | -40 | -12 |
| Organic carbon | -240 | -69 | -21 |
| Carbon dioxide | 1 | 1 | 1 |
| Note: The methodology used for black carbon was also used for organic carbon and sulfur oxides. Values for black carbon, organic carbon and sulfur oxides were not published by the IPCC and are not official estimates.
Source: The International Council on Clean Transportation, 2009. |
A large proportion of black carbon, especially within Ontario, originates from diesel engine emissions and technology is readily available to substantially abate this pollution. To its credit, Canada has fairly advanced emission control requirements for new diesel trucks, but these standards do not apply to older vehicles still on the road. Neither do they apply to off-road diesel equipment used in construction, stand-by diesel generators or provincially operated rail locomotives. Other opportunities for abatement include petrochemical flares and non-essential open burning of agricultural residues and other organic materials.
There are also important collateral benefits to reducing black carbon emissions. When black carbon particles precipitate from the atmosphere onto snow or ice they reduce the albe do (light reflectivity) of the white surface and promote melting. This promotes heat absorption in glacial and arctic regions and thus exacerbates global warming. But most importantly, black carbon forms a major part of the fine particulate matter in street level air pollution that carries toxins and carcinogens deep into our lungs. Significant reductions in these emissions can be justified solely on the basis of public and environmental health.
Soil Carbon Opportunities
Increasing Soil Organic Carbon
Increasing soil organic carbon levels is another approach to climate change mitigation. Every tonne of CO2 captured in soil removes a tonne of CO2 from the atmosphere. Soils already hold more carbon than the atmosphere and above-ground biosphere combined, even with a historic loss of soil carbon from modern agricultural practices. The capacity for further carbon sequestration is quite high and so the ECO recommends that the Ontario government explore this mitigation opportunity.
The IPCC has conservatively estimated that improved agricultural practices could sequester anywhere from 0.18 to 2.79 tonnes of CO2e per hectare per year (t CO2e/ha/yr). A more aggressive estimate from the Rodale Institute in the U.S. reported results of an 18-year, sideby- side comparison study of conventional versus organic agriculture that found a carbonsequestration benefit of 3.6 t CO2e/ha/yr for a manure-based organic system. A recent survey of European soil studies found that the addition of compost to soil sequesters carbon at a rate of about 5 t CO2e/ha/yr for every 10 dry tonnes of compost applied. Other studies have found relatively high rates of sequestration for practices such as improved pasture management (5.5 t CO2e/ha/yr) and the growing of energy crops (6.2 t CO2e/ha/yr).
| Sector | Activity and/or Management Practice | Per cent Area Converted by 2020 | Documented Rate (tCO2e/ha/yr) | Annual Carbon Storage by 2020 (MtCO2e/yr) | Per cent of CCAP 30 Mt 2020 Gap |
|---|---|---|---|---|---|
| Cropland* | Assorted RMPs | 40 | 2 | 2.9 | 9.6 |
| Organic Farming | 10 | 3.6 | 1.3 | 4.3 | |
| Compost Application | 5 | 5 | 0.9 | 3 | |
| Pasture** | Assorted RMPs | 25 | 5.5 | 1.0 | 3.4 |
| Energy Crops | Switchgrass, Miscanthus, Poplar | 10 | 6.2 | 2.7 | 9 |
| TOTAL | 8.8 | 29.3 |
| RMP – Recommended Management Practice CCAP – Climate Change Action Plan |
Using established technologies, Ontario could promote sequestration practices on pasture land and encourage the establishment of deep-rooted perennial energy crops such as switchgrass. Using reasonable assumptions for areas turned to these practices, 8.8 Mt of annual soil-carbon sequestration might be accomplished by 2020, (about 30 per cent of the currently estimated 30 Mt CCAP gap at 2020), using a mix of measures on cropland, pasture land, and land devoted to energy crops such as switchgrass or Miscanthus (see Table 5). Given that documented sequestration rates are from temperate climates, the Ontario government would need to develop its own protocols, based on both soil-sequestration modeling and local data.
The ECO does not wish to minimize or understate the technical, political and logistical challenges involved in reaching this target. Significant unresolved issues exist in the areas of measurement and permanence, for instance. The point of these projections is simply to highlight the opportunity that soil-carbon sequestration presents as a tool for climate change mitigation.
The Special Case of Biochar
Biochar is the solid product of pyrolysis – the combustion of organic materials in the absence of oxygen. One common form of biochar is wood charcoal. Carbon in this form has the unique property of being extremely resistant to microbial degradation. Although more research is needed to confirm its stability in Ontario soils, scientific analysis has demonstrated that the bulk of biochar’s carbon will remain sequestered in the soil for decades at a minimum, and possibly for millennia. Biochar may also bring additional sequestration benefits. A recent study conducted on agricultural soils in Quebec indicated a substantial increase of mycorrhizal fungi within biochar amended plots. This suggests that biochar may work synergistically with soil microbes to create the conditions for further sequestration, additional to biochar’s own carbon.
Biochar’s potential is such that it could prove to be an excellent complement to the soil-carbonboosting measures documented on page 47 of this report. If that turns out to be the case, the sequestration projections associated with those measures could be more easily achieved, or even exceeded.
The ECO is aware that the Ontario Ministry of Agriculture and Rural Affairs is investigating biochar’s potential for Ontario soils. The ECO supports this work and has previously recommended that guidelines be developed for biochar production and use in Ontario. If even a reasonable fraction of biochar’s potential is proven to be real and practical to implement, it could make a key contribution to the province’s 2020 GHG reduction target.
