The Three Salient Global Mitigation Pathways Assessed in Light of the IPCC Carbon Budgets

The document evaluates three prominent global emissions pathways against IPCC AR5 carbon budgets to determine their probability of limiting global warming to 2°C. It finds that only the highly ambitious 1.5°C marker pathway has a high probability of achieving this goal, while the 2°C marker pathway carries higher risks than previously believed, and the G8 marker pathway is insufficient to be considered a 2°C-compliant pathway.

• The 1.5°C marker pathway, characterized as an "emergency mobilization" pathway, is the only one of the three assessed with a high probability of keeping global warming below 2°C, with a likelihood significantly greater than 66%.
• The 2°C marker pathway, which is based on the Climate Action Tracker and UNEP emissions gap reports, carries a higher risk of exceeding 2°C than previously estimated, with a probability of staying below that threshold of less than 50%.
• The G8 marker pathway, based on the 2009 L’Aquila summit declaration, has a less than 33% chance of limiting warming to 2°C and cannot be plausibly classified as a 2°C pathway.
• The 1.5°C marker pathway is defined by aggressive front-loading of mitigation, a non-CO2 emissions floor of 5 Gt CO2e annually for agriculture, and the absence of negative emissions, with total cumulative greenhouse gas emissions for 2000–2100 at 1,720 Gt CO2e.
• The 2°C marker pathway peaks in 2014 with a maximum all-gas decline rate of 3.4% per year and total cumulative emissions for 2000–2100 of 2,380 Gt CO2e.
• The G8 marker pathway is interpreted as peaking after 2020 with a 2005 base year for its 50% reduction goal by 2050, resulting in a cumulative budget of 2,860 Gt CO2e for 2000–2100.
• Deferring mitigation (back-loading) is described as a "false economy" that increases total costs over time and raises the risk of catastrophic impacts, such as several meters of sea-level rise, by increasing reliance on unproven negative emission technologies.

APA

Baer, P., Athanasiou, T., & Kartha, S. (2013). The Three Salient Global Mitigation Pathways Assessed in Light of the IPCC Carbon Budgets. Stockholm Environment Institute. https://www.sei.org/mediamanager/documents/Publications/Climate/SEI-DB-2013-Climate-risk-emission-reduction-pathways.pdf

Chicago

Baer, Paul, Tom Athanasiou, and Sivan Kartha. The Three Salient Global Mitigation Pathways Assessed in Light of the IPCC Carbon Budgets. Stockholm Environment Institute, 2013. https://www.sei.org/mediamanager/documents/Publications/Climate/SEI-DB-2013-Climate-risk-emission-reduction-pathways.pdf.

Wikipedia

{{cite report |last1=Baer |first1=Paul |last2=Athanasiou |first2=Tom |last3=Kartha |first3=Sivan |title=The Three Salient Global Mitigation Pathways Assessed in Light of the IPCC Carbon Budgets |publisher=Stockholm Environment Institute |date=2013 |url=https://www.sei.org/mediamanager/documents/Publications/Climate/SEI-DB-2013-Climate-risk-emission-reduction-pathways.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{baer2013three, author = {Baer, Paul and Athanasiou, Tom and Kartha, Sivan}, title = {{The Three Salient Global Mitigation Pathways Assessed in Light of the IPCC Carbon Budgets}}, institution = {Stockholm Environment Institute}, year = {2013}, url = {https://www.sei.org/mediamanager/documents/Publications/Climate/SEI-DB-2013-Climate-risk-emission-reduction-pathways.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }