Developed and developing world responsibilities for historical climate change and CO2 mitigation.

Area of Science:

• Climate Science
• Earth System Science
• Environmental Policy

Background:

• The 2010 Cancun Agreement aimed to limit global temperature rise to 2°C above preindustrial levels.
• Global temperature rise is primarily driven by cumulative anthropogenic greenhouse gas emissions.
• International negotiations on emission reductions face challenges due to differing views on historical responsibility.

Purpose of the Study:

• To quantify the historical contribution of developed and developing countries to global temperature rise.
• To assess the impact of Cancun pledges on future temperature rise.
• To identify the mitigation gap required to meet the 2°C target.

Main Methods:

• Utilized two Earth system models: NCAR Community Earth System Model (CESM) and Beijing Normal University Earth System Model (BNU-ESM).
• Simulated historical contributions to global temperature rise, upper ocean warming, and sea-ice reduction up to 2005.
• Modeled future temperature trajectories based on Cancun pledges extended to 2100.

Main Results:

• By 2005, developed countries contributed 60-80% and developing countries 20-40% to global temperature rise, ocean warming, and sea-ice reduction.
• Implementing Cancun pledges reduces projected temperature rise compared to a business-as-usual scenario.
• Under Cancun pledges, developed countries contribute 33-67% (CESM) and 35-65% (BNU-ESM) of the warming, with developing countries contributing the remainder.

Conclusions:

• Historical emissions from developed nations have disproportionately contributed to current global warming.
• Cancun pledges alone are insufficient to meet the 2°C target.
• Substantial additional mitigation efforts are necessary from all countries to prevent exceeding the 2°C global temperature limit by 2100.