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

This briefing by the Stockholm Environment Institute assesses three global mitigation pathways—the 1.5°C marker, the 2°C marker, and the G8 marker—against the carbon budgets provided in the IPCC Fifth Assessment Report (2013). The analysis concludes that only the highly ambitious 1.5°C pathway has a high probability of limiting global warming to below 2°C, while the 2°C and G8 pathways carry significantly higher risks of exceeding that threshold than previously estimated.

• The 1.5°C marker pathway is characterized as an "emergency mobilization" approach that is the most challenging yet technoeconomically achievable pathway. It requires emissions to peak in 2014 and decline by up to 7.1% annually for all gases, with a total cumulative budget of 1,720 Gt CO2e for 2000–2100. This pathway has a probability significantly greater than 66% of keeping global warming below 2°C.
• The 2°C marker pathway, based on the Climate Action Tracker and UNEP emissions gap reports, peaks in 2014 with a maximum annual decline of 3.4% for all gases and a cumulative budget of 2,380 Gt CO2e for 2000–2100. Contrary to previous estimates that it had a "likely" (greater than 67%) chance of limiting warming to 2°C, this analysis suggests it actually has a less than 50% chance of doing so.
• The G8 marker pathway, derived from the 2009 L’Aquila summit declaration, is found to be insufficient for meeting the 2°C objective. It peaks in 2021 with a maximum annual decline of 4.5% for all gases and a cumulative budget of 2,860 Gt CO2e. The probability of this pathway keeping warming below 2°C is far less than 33%.
• The document argues that deferring mitigation (back-loading) is a "false economy" that increases total costs and climate risks. It warns that relying on future negative emissions technologies to offset current emissions is risky, as it may lead decision-makers to defer necessary near-term action while the 2°C target drifts out of reach.
• The analysis highlights that the 2°C threshold is now viewed by climate scientists as the transition point from "dangerous" to "extremely dangerous" climate change, potentially leading to unmanageable warming and catastrophic impacts such as several meters of sea-level rise.

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} }