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2009 Literature Review Archives - Policy/Mitigation

Akbari, H., S. Memon, and A. Rosenfeld, 2009. Global cooling: increasing world-wide urban albedos to offset co2. Clim. Change 94, 275-286, DOI 10.1007/s10584-008-9515-9.
By changing from dark roofs and paved surfaces in urban areas to reflective ones, world-wide albedo could be increased to offset more than the equivalent of the projected yearly co2 emissions in 2025.
A study by three U.S. scientists looks at an engineering solution to climate change. By changing black roofs and paved surfaces in urban areas to reflective surfaces, they have calculated the increased albedo would offset the equivalent of 44 Gt of co2 emissions globally. This is compared to projected world co2 emissions in 2025 of 37Gt/year. The study comes with many caveats and generalizations, which raise some doubts about the final number for the strength of the enhanced albedo; however, it does demonstrate that there might be reasonable engineering solutions that could make a difference in reducing the effects of climate change.

Allen, M.R., Frame, D.J., Huntingford, C., Jones, C.D., Lowe, J.A., Meinshausen, M. and Meinshausen, N. 2009. Warming caused by cumulative carbgon emissions towards the trillionth tonne. Nature 458:1163-1166; Meinshausen, M., Meinshausen, N., Hare, W., aper, S.C.B., Freiler, K, Knutti, R., Frame, D.J. and Allen, M.R. 2009. Greenhouse-gas emission targets for limiting global warming to 2°C. Nature 458:1158-1162; Editor. 2009. Time to act. Nature 458:1077-1078.
New research studies indicate that, to avoid dangerous global warming, governments around the world should focus on limiting the total cumulative global CO2 emissions between now and 2050, rather than on targeting total greenhouse gas emission levels at specific time milestones. Authors also note the urgency in undertaking serious mitigative actions now.
More than 100 countries around the world have now accepted the threshold of a 2°C global warming, relative to pre-industrial temperatures, as a guiding principle for mitigative action to avoid dangerous human interference with the climate system. Discussions amongst policy makers on how to limit peak global warming to this level have to date largely focused on actions to eventually stabilize atmospheric concentrations, but are faced with large uncertainties in both climate sensitivities to rising CO2 concentrations and to carbon cycle-climate feedbacks. Two new papers recently published in the journal Nature have tried to address this dilemma by examining the risks of excessive warming against cumulative CO2 emissions over time. Using climate-carbon cycle models and probability analyses, the researchers involved find that limiting cumulative emissions from pre-industrial times to 2050 to 3.7 trillion tonnes of carbon dioxide (or 1 trillion tones of carbon) would likely achieve the 2°C peak warming goal, although uncertainties still suggest the resulting warm peak might be as much as 3.9°C. Half of this emission total has already been released through past human activities. If the recent G-8 target of halving global greenhouse gas emissions by 2050, relative to 1990 levels, is achieved, there remains a 12-45% probability of exceeding the 2°C threshold. This rises to a 53-87% probability if emissions in 2020 are still more than 25% above 2000 levels. An accompanying editorial notes that this indicates there is still time to act, but barely. While there are hypothetical geo-engineering strategies that might be pursued to cool off the planet should we get too hot, these are poorly understand and also have large risks of danger associated with them. Hence they should not be an alternative to aggressive mitigative action. However, the editorial notes that serious mitigative action aimed at achieving the above goal are unlikely to happen without commitment at the highest political levels of government.

Burton, I., T. Dickinson and Y. Howard, 2008. Upscaling adaptation studies to inform policy at the global level, IAJ, 8 (2), 25-37.
A recent Canadian study re-emphasizes the importance of considering climate change as an issue for which adaptation measures are necessary, even with aggressive efforts to reduce greenhouse gas emissions.
A Canadian research team, including two Environment Canada scientists, have looked at how difficult it is to modify the conventional view that anthropogenic climate change is an environmental pollution issue. The authors contend that such a view results in a distorting effect on policy and dominates the international negotiations on climate change. It also explains why mitigation and the reduction of greenhouse gas (GHG) emissions have always been at the heart of the political agenda, while adaptation, finally considered today as an important part of that agenda, is still receiving much less attention and support. The authors argue that climate change must also be considered as a development issue and an equity issue, an argument that already has considerable support from other sources. To support their view, the authors identify and briefly explore four approaches that might help to bring about this transformation in the way in which the climate change issue is framed. The four approaches are: 1) the qualitative accumulation of case study evidence, 2) meta-analysis, 3) adaptation modelling, and 4) the integration of adaptation with mitigation in case studies and in models. They consider that these approaches are not mutually exclusive and might be combined in various ways. In their analysis, the authors note that science has made it clear that aggressive efforts to reduce GHG emissions will have little effect in reducing climate change for decades and that mean surface temperatures will continue to rise even under the most optimistic scenario. Considering this, adaptation measures are not only necessary, but become imperative and complementary to efforts to reduce GHG emissions.

Chakravarty, S. A. Chikkatur, H. de Coninck et al., 2009. Sharing global CO2 emission reductions among one billion high emitters, PNAS, 106 (29), 11884-11888.
A framework is proposed for allocating fossil-fuel CO2 emission reduction targets among nations based on their proportion of high CO2- emitting individuals. Thus the principle of 'common but differentiated responsibilities' is applied to individuals not nations.
The problem of how to divvy up the required carbon emission reductions between industrialized and developing countries, under the principle of 'common but differentiated responsibilities', is challenging and remains controversial. Chakravarty and colleagues propose to divide the burden of reduction not between countries but among individuals who are the highest greenhouse gas emitters, regardless of where they live. Their approach is restricted to future fossil-fuel CO2 emissions and focuses on the next two decades, and is based on an assumed tight linkage between income, economy-wide carbon intensities and CO2 emissions. The authors produce a global cumulative distribution of annual individual emissions that sum to a business-as-usual emission total in the year 2030 of 43 GtCO2. A universal individual emissions cap is then proposed such that eliminating all emissions above the cap achieves the target. For example, a global fossil-fuels-CO2 emission target of 30GtCO2 in 2030 would require a 30% global cut in emissions and results in an individual emission cap of 10.8 tCO2 which would apply to 1.13 billion high-emitters globally. Country level emission targets can then be developed that reflect the number of 'high emitter' individuals in that country and their aggregate emissions. Interestingly, the approach can be modified to allow for increased emissions from the poorest segment of the global population by imposing a 'floor' to individual annual emissions of, for example, 1 tCO2/yr per person (which in this case is consistent with the Millennium Development Goals but above the projected emissions for about one-third of the world population in 2030). With this modified approach, the universal cap is lowered to accommodate increased emissions from the lowest emitters. The authors assert that this universal emission cap approach could achieve equity and fairness between countries, as countries with more high emitters do more and countries with similar emission profiles have similar commitments. The modified approach also allows climate change mitigation to be decoupled from efforts to meet the basic energy needs of the poor.

House, J., C. Huntingford, W. Knorr et al. 2008. What do recent advances in quantifying climate and carbon cycle uncertainties mean for climate policy? Environ. Res. Lett. 3 (2008) 044002.
A study that accounts for the large range of uncertainty in both climate sensitivity and climate-carbon cycle feedbacks shows that an 80% reduction in global emissions by the end of this century, while not achieving stabilization of atmospheric CO2 concentrations, will approach it. Still, the projected range in global temperature increase by 2100 is large.
Climate-carbon cycle feedbacks are a source of uncertainty for estimating the total amount of "allowable emissions" to meet a given concentration or temperature target. Currently, the evidence from studies of such feedbacks is that they are primarily positive. That is, for any given emission scenario, the resulting atmospheric concentration and global temperature increase become higher than they would be without such feedbacks. In this paper by House et al., the implications of climate-carbon cycle feedbacks for two specific emission targets are explored - the G8 and Stern emission targets. For the G8 scenario, a 50% reduction in global emissions by 2050 was simulated (relative to 2007 emissions) after which emissions were held constant (which allowed atmospheric concentrations to continue to grow). The Stern scenario cut emissions by 25% by 2050 (relative to 2007 emissions), with progressive cuts thereafter, down to 80%. Simulations were performed using a simple coupled climate-carbon cycle model (HadSCCM1) that was calibrated to capture the range of carbon cycle responses and climate sensitivity of 11 fully coupled climate-carbon cycle models. The main difference between the two scenarios was that CO2 concentrations and global temperature increases after 2100 were only slight in the Stern scenario, following the 80% reduction in global emissions, whereas both continued to grow significantly in the G8 scenario. Atmospheric CO2 concentrations were 480-620 ppm in 2100 with the Stern scenario, with an associated 1.4-3.4°C global temperature increase by that time. These results highlight the need for sustained deep cuts in global emissions of at least 80%, relative to current emissions, sometime this century, in order to approach stabilization of atmospheric CO2 and global temperature. This conclusion is robust even allowing for the large range in the climate-carbon cycle feedback.

Matthews, H.D., N. Gillett, P.A. Stott and K. Zickfeld. 2009. The proportionality of global warming to cumulative carbon emissions. Nature Vol 459, June 11, 2009, pp 829-833.
A study by Canadian and British scientists adds further support to the notion that it is the total 'slug of carbon' (the cumulative emissions total) that matters most to global temperature change over timescales of decades to centuries. A method is proposed for estimating the global climate response to accumulated carbon emissions.
Projecting the global temperature response to increases in atmospheric co2 relies on metrics such as the equilibrium climate sensitivity or the transient climate response, which have been difficult to constrain and which do not account for feedbacks in the carbon cycle that will affect how much emitted co2 remains airborne. This study by a team of authors that includes two from Environment Canada's climate modeling centre proposes a new metric for relating the global climate response to anthropogenic carbon dioxide emissions. The 'carbon-climate response' (CCR) is defined as the ratio of temperature change to cumulative carbon emissions and therefore encapsulates both 'carbon sensitivity' (the increase in atmospheric co2 in response to emissions) and 'climate sensitivity' (the temperature response to increased atmospheric co2). The CCR is found to be almost independent of emissions scenario and constant in time, and is estimated to be in the range of 1.0-2.1°C per trillion tonnes of carbon (TtC) emitted (5th to 95th percentiles). The proposed metric is similar to one proposed by a different team of authors recently in an April issue of the same journal (Allen et al.), the 'cumulative warming commitment', defined as the peak warming response to a given total amount of emitted co2, however the range calculated here is somewhat lower. (See ASAI climate science review of May 1, 2009).

Pollard, R.T, I. Salter, R.J. Sanders et al. 2008. Southern Ocean deep-water carbon export enhanced by natural iron fertilization. Nature, 457, doi:10.1038/nature07716, 5 pages.
A recent study shows that carbon sequestration from artificial iron-enrichment of the oceans is much lower than in areas of natural iron enrichment. Therefore, this geo-engineering approach may not be a viable option for mitigating CO2 emissions.
Adding iron into the oceans, to induce a phytoplankton bloom that will take up atmospheric CO2, is one of the many proposed geo-engineering solutions to slow down climate change. Some perspective on such an approach is provided by research conducted by an international team of scientists in a region of the southern ocean where there is a natural source of iron enrichment. Specifically, the scientists tested the hypothesis that the observed north-south gradient in phytoplankton concentrations is induced by natural iron fertilization (in which iron-rich dust blowing off the Crozet Islands settles on the waters) and that the areas of higher concentration have enhanced organic carbon flux into the deep ocean. Their observations indicate that natural iron fertilization does enhance new phytoplankton production and does lead to higher export of carbon into the ocean. At 100 metres depth, there was a two- to threefold increase in carbon export compared to an adjacent high nutrient, low-chlorophyll area not fertilized by iron. Moreover, the carbon fluxes at 3000 metres were similarly two to three times higher beneath the iron fertilized region. These results support an earlier hypothesis that increased iron supply to the glacial sub-Antarctic enhances carbon sequestration into the deep ocean. However, comparing their results with previous experimental studies, they found that carbon sequestration efficiency was 18 times greater than that of a phytoplankton bloom induced artificially by adding iron. The authors note that the large losses of iron during artificial iron enrichment experiments can explain the lower efficiency of the induced bloom. These results have significant implications for proposals to mitigate the effects of climate change through purposeful addition of iron to the ocean since they indicate that such approaches may not be very efficient.

Zickfeld, K., M. Eby, H.D. Mattews and A. Weaver. 2009. Setting cumulative emissions targets to reduce the risk of dangerous climate change. PNAS Vol 106 No 38 pp 16129-16134. September 22, 2009. See also Commentary by England, M.H., A. Sen Gupta and A.J. Pitman. Constraining future greenhouse gas emissions by a cumulative target. PNAS Vol 106 No 38 pp 16539 - 16540.
Canadian scientists provide estimates of the probability that different cumulative emission limits for carbon dioxide will exceed specified long-term global mean temperature targets.
A group of Canadian scientists, including one who is now with Environment Canada's climate modeling centre, have just published the results of their research on allowable CO2 emissions limits compatible with different temperature stabilization targets. What distinguishes this work from other similar studies is the use of a state-of-the-art coupled climate carbon-cycle model (UVic ESCM version 2.8), and an inverse approach that enabled them to diagnose CO2 emissions compatible with evolving temperature trajectories towards stabilization. They performed climate simulations out to the year 2500, and applied a probabilistic approach to incorporate uncertainties due to both climate sensitivity and climate-carbon cycle feedbacks into the analysis. First, their results show that the cumulative emissions budget compatible with a given global mean temperature target is independent of the pathway to stabilization, consistent with earlier published results (i.e. what matters is the 'total slug' of CO2 rather than the timing of emissions). Secondly, for all temperature targets considered (2, 3 and 4°C), long-term temperature stabilization requires near-constant cumulative emissions, which means that once the emissions budget is used up, annual emissions must become ~zero. Third, the results regarding cumulative emissions limits to meet a stabilization target of 2°C are sobering. To keep the risk of exceeding this target to 'unlikely' in IPCC parlance (i.e. below a probability of 0.33), then allowable emissions from year 2001 on should be kept to about 590 PgC (median estimate, with a range of 200 to 950 PgC when uncertainties due to climate sensitivity and climate-carbon cycle feedbacks are taken into account). If the acceptable probability of exceeding this target is reduced to 10% (0.1; (very unlikely in IPCC parlance) then allowable emissions must be kept to about 170 PgC (median estimate, with a range of -220 to 700 PgC). Allowable emissions are higher with low climate sensitivity and a weaker carbon cycle feedback. By the year 2010, net carbon emissions will have reached about 100 PgC (see commentary by England et al.) which means a sizeable chunk of the allowable emissions limit has already been used up.

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