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Subject: Climate change × search.filters.applied.f.series: Environmental Research Letters, Volume 10, Issue 7 ×

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    Mitigation choices impact carbon budget size compatible with low temperature goals
    (Bristol : IOP Publishing, 2015) Rogelj, Joeri; Reisinger, Andy; McCollum, David L.; Knutti, Reto; Riahi, Keywan; Meinshausen, Malte
    Global-mean temperature increase is roughly proportional to cumulative emissions of carbon-dioxide (CO2). Limiting global warming to any level thus implies a finite CO2 budget. Due to geophysical uncertainties, the size of such budgets can only be expressed in probabilistic terms and is further influenced by non-CO2 emissions. We here explore how societal choices related to energy demand and specific mitigation options influence the size of carbon budgets for meeting a given temperature objective. We find that choices that exclude specific CO2 mitigation technologies (like Carbon Capture and Storage) result in greater costs, smaller compatible CO2 budgets until 2050, but larger CO2 budgets until 2100. Vice versa, choices that lead to a larger CO2 mitigation potential result in CO2 budgets until 2100 that are smaller but can be met at lower costs. In most cases, these budget variations can be explained by the amount of non-CO2 mitigation that is carried out in conjunction with CO2, and associated global carbon prices that also drive mitigation of non-CO2 gases. Budget variations are of the order of 10% around their central value. In all cases, limiting warming to below 2 °C thus still implies that CO2 emissions need to be reduced rapidly in the coming decades.
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    Impact of short-lived non-CO2 mitigation on carbon budgets for stabilizing global warming
    (Bristol : IOP Publishing, 2015) Rogelj, Joeri; Meinshausen, Malte; Schaeffer, Michiel; Knutti, Reto; Riahi, Keywan
    Limiting global warming to any level requires limiting the total amount of CO2 emissions, or staying within a CO2 budget. Here we assess how emissions from short-lived non-CO2 species like methane, hydrofluorocarbons (HFCs), black-carbon, and sulphates influence these CO2 budgets. Our default case, which assumes mitigation in all sectors and of all gases, results in a CO2 budget between 2011–2100 of 340 PgC for a >66% chance of staying below 2°C, consistent with the assessment of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Extreme variations of air-pollutant emissions from black-carbon and sulphates influence this budget by about ±5%. In the hypothetical case of no methane or HFCs mitigation—which is unlikely when CO2 is stringently reduced—the budgets would be much smaller (40% or up to 60%, respectively). However, assuming very stringent CH4 mitigation as a sensitivity case, CO2 budgets could be 25% higher. A limit on cumulative CO2 emissions remains critical for temperature targets. Even a 25% higher CO2 budget still means peaking global emissions in the next two decades, and achieving net zero CO2 emissions during the third quarter of the 21st century. The leverage we have to affect the CO2 budget by targeting non-CO2 diminishes strongly along with CO2 mitigation, because these are partly linked through economic and technological factors.