Recent projections of future United States carbon dioxide (CO2) emissions are considerably lower than projections made just a decade ago. A myriad of factors have contributed to lower forecasts, including reductions in end-use energy service demands, improvements in energy efficiency, and technological innovations. Policies that have encouraged these changes include renewable portfolio standards, corporate vehicle efficiency standards, smart growth initiatives, revisions to building codes, and air and climate regulations. Understanding the effects of these and other factors can be advantageous as society evaluates opportunities for achieving additional CO2 reductions. Energy system models provide a means to develop such insights. In this analysis, the MARKet ALlocation (MARKAL) model was applied to estimate the relative effects of various energy system changes that have happened since the year 2005 on CO2 projections for the year 2025. The results indicate that transformations in the transportation and buildings sectors have played major roles in lowering projections. Particularly influential changes include improved vehicle efficiencies, reductions in projected travel demand, reductions in miscellaneous commercial electricity loads, and higher efficiency lighting. Electric sector changes have also contributed significantly to the lowered forecasts, driven by demand reductions, renewable portfolio standards, and air quality regulations.

中文翻译：

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最近的能源系统变化对美国的CO2预测的影响。

美国对未来二氧化碳排放的最新预测远低于十年前的预测。众多因​​素导致了较低的预测，包括最终用途能源服务需求的减少，能源效率的提高和技术创新。鼓励这些变化的政策包括可再生能源投资组合标准，公司车辆效率标准，明智的增长计划，建筑规范的修订以及空气和气候法规。当社会评估实现更多二氧化碳减排的机会时，了解这些因素和其他因素的影响可能是有利的。能源系统模型提供了一种发展这种见解的方法。在此分析中，应用市场分配（MARKAL）模型来估算自2005年以来发生的各种能源系统变化对2025年CO2预测的相对影响。结果表明，交通和建筑行业的转型在降低投影。特别具有影响力的变化包括提高车辆效率，减少预计的出行需求，减少其他商业用电负荷以及提高照明效率。在需求减少，可再生能源组合标准和空气质量法规的推动下，电力行业的变化也极大地降低了预测。结果表明，交通和建筑行业的转型在降低预测中发挥了重要作用。特别具有影响力的变化包括提高车辆效率，减少预计的出行需求，减少其他商业用电负荷以及提高照明效率。在需求减少，可再生能源组合标准和空气质量法规的推动下，电力行业的变化也极大地降低了预测。结果表明，交通和建筑行业的转型在降低预测中发挥了重要作用。特别具有影响力的变化包括提高车辆效率，减少预计的出行需求，减少其他商业用电负荷以及提高照明效率。在需求减少，可再生能源组合标准和空气质量法规的推动下，电力行业的变化也极大地降低了预测。