Policy Brief #14, November 2016. Two temperatures feature prominently in the Paris Climate Agreement: 1.5°C and 2°C. New studies from IIASA reveal substantially different climate impacts under these two targets and provide a clearer understanding of the challenges and benefits of aiming low on global warming goals.


The Paris Agreement of November 2015 commits signatories to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels.” The agreement also states that in order to achieve this goal, greenhouse gas emissions need to peak as soon as possible then decline rapidly, becoming net-zero in the second half of the century by achieving a balance between emissions and removals.

Effectively, this leaves the world committing to at least a stringent 2°C goal but also continually shooting for an even more stringent 1.5°C goal. Many countries, including those most vulnerable to climate change, consider the lower level a much safer bet than the higher one. In this policy brief we discuss the substantial benefits of hitting the lower goal and the need to set near-term benchmarks on emissions in order to achieve it. Tapping into recent research, we also explore the differences and characteristics of the pathways to both goals while remaining focused on 1.5°C as the lowest risk option.  

  • The difference a half degree makes. Limiting global temperature rise to 1.5°C by 2100 is technically achievable and will mean fewer and shorter heat waves in the tropics, greater crop yields, and a reduction in sea level rises compared to a 2°C world. The risks of just half a degree higher warming are clarified by new studies providing essential information on the likely different outcomes under the two warming levels. 
  • Where are we now? Despite recent efforts, global greenhouse gas emissions are still increasing and are projected to continue to do so until 2030 under the current pledges. Although there have been some positive signs showing stalling global emissions in recent years, it is still too early to say if this will become a long-term trend. This lack of progress means carbon budgets are burning up quickly, placing a tighter constraint on future emissions. 
  • What are the key elements to achieving the 1.5°C goal? A rapid, near-term decarbonization of energy supply; greater mitigation efforts to reduce energy demand; and acceptance that mitigation costs will be greater in the next two decades than for a 2°C goal. Energy efficiency improvements will also be crucial and comprehensive emissions reductions must be achieved in the coming decade.

IIASA Policy Briefs present the latest research for policymakers from
IIASA—an international, interdisciplinary research institute with National
Member Organizations (NMOs)
 in 24 countries in Africa, the Americas,
Asia, Europe, and Oceania. The views expressed herein are those of the
researchers and not necessarily those of IIASA or its NMOs.