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Greenhouse gas emissions, driven by population growth and an increasing demand for resource-intensive goods, foods and services, are altering the planet's climate in ways that threaten the habitability of the planet. Transparent modeling tools and recent literature are used to quantify the mitigation challenge and assess potential remedies. Model results identify mitigation actions needed to have a chance of limiting global warming to 2 C, and how difficult it will be to limit warming to 1.5 C. Since a recent study concluded that there could be "runaway," irreversible warming when global temperatures reach 2 C or higher, this would argue for the importance of limiting warming to 1.5 C, despite the difficulty in meeting such a target. Serious emission reductions must start as soon as possible, involve all countries, include emission reductions in all sectors and for all the greenhouse gases. For achieving the 1.5 C target, and probably to meet the 2 C target, Carbon Dioxide removal (CDR) technologies/practices will need to be operational at large scale. Unfortunately, given their early stage of development, and high projected costs, there is no guarantee that removing CO2 from the air will be practical at the scale needed. For the U.S., a unique model examines key impactful mitigation actions and quantifies the monumental challenge of achieving net zero emissions by 2050. Also examined are the different mitigation trajectories needed for developed versus developing countries, how different emission trajectories would affect warming this century, and a summary of the status of R, D&D needs for key technologies. The two most impactful global mitigative actions, are to implement a strong, escalating price on carbon and greatly expanding R, D&D on promising clean energy and CDR technologies. Implications: Humanity continues on its unsustainable trajectory. Greenhouse gas emissions, driven by population growth and an increasing demand for resource-intensive goods, foods and services are altering the planet's climate in ways that threaten the habitability of the planet. Transparent modeling tools and recent literature are used to quantify the mitigation challenge and assess potential remedies. Model results identify mitigation actions needed to have a chance of limiting global warming to 2 C, and how difficult it will be to limit warming to 1.5 C. Since a recent study, concluded there could be "runaway," irreversible warming when global temperatures reach 2 C or higher, this would argue for the importance limiting warming to 1.5 C, despite the difficulty in meeting such a target. Serious emission reductions must start as soon as possible, involve all countries, include emission reductions in all sectors and for all the greenhouse gases. For achieving the 1.5 C target, and probably to meet the 2 C target, Carbon Dioxide removal (CDR) technologies/practices will need to be operational at large scale. Unfortunately, given their early stage of development, and high projected costs, there is no guarantee that removing CO2 from the air will be practical at the scale needed. For the U.S., a unique model examines key impactful mitigation actions and quantifies the monumental challenge of achieving net zero emissions by 2050. Also examined are the different mitigation trajectories needed for developed versus developing countries, how different emission trajectories would affect warming this century, and a summary of the status of R, D&D needs for key technologies. It was concluded that the two most important global mitigative actions are to implement a strong, escalating price on carbon and greatly expanding R, D&D on promising clean energy and CDR technologies. [ABSTRACT FROM AUTHOR]

Population growth and the pressures spawned by increasing demands for energy and resource-intensive goods, foods, and services are driving unsustainable growth in greenhouse gas (GHG) emissions. Recent GHG emission trends are consistent with worst-case scenarios of the previous decade. Dramatic and near-term emission reductions likely will be needed to ameliorate the potential deleterious impacts of climate change. To achieve such reductions, fundamental changes are required in the way that energy is generated and used. New technologies must be developed and deployed at a rapid rate. Advances in carbon capture and storage, renewable, nuclear, and transportation technologies are particularly important; however, global research and development efforts related to these technologies currently appear to fall short relative to needs. Even with a proactive and international mitigation effort, humanity will need to adapt to climate change, but the adaptation needs and damages will be far greater if mitigation activities are not pursued in earnest. In this review, research is highlighted that indicates increasing global and regional temperatures and ties climate changes to increasing GHG emissions. GHG mitigation targets necessary for limiting future global temperature increases are discussed, including how factors such as population growth and the growing energy intensity of the developing world will make these reduction targets more challenging. Potential technological pathways for meeting emission reduction targets are examined, barriers are discussed, and global and U.S. modeling results are presented that suggest that the necessary pathways will require radically transformed electric and mobile sectors. While geoengineering options have been proposed to allow more time for serious emission reductions, these measures are at the conceptual stage with many unanswered cost, environmental, and political issues. Implications: This paper lays out the case that mitigating the potential for catastrophic climate change will be a monumental challenge, requiring the global community to transform its energy system in an aggressive, coordinated, and timely manner. If this challenge is to be met, new technologies will have to be developed and deployed at a rapid rate. Advances in carbon capture and storage, renewable, nuclear, and transportation technologies are particularly important. Even with an aggressive international mitigation effort, humanity will still need to adapt to significant climate change. [ABSTRACT FROM AUTHOR]