Climate change scenarios are used to provide policy makers with a range of uncertainty, not to serve as crystal balls. Until now, model-based scenarios have used a step-by-step, sequential process between loosely connected disciplines. The disciplinary disconnect has led to inconsistent use of scenarios in policy-relevant assessment reports like those by the Intergovernmental Panel on Climate Change.
With nearly a decade of new economic data, emerging technologies and updated environmental observations, there is now a shift in focus towards a 'parallel' approach to developing scenarios. Central to this process are four new 'representative concentration pathways', which will provide a framework for modelling, increased collaboration and timely incorporation into climate research. These pathways span the range of radiative forcing scenarios, consisting of one rising scenario, two which stabilize, and one which peaks and later declines.
This new integrated approach will provide valuable insights into the interaction of natural and human-induced climate processes, and the potential costs and benefits of different mixes of adaptation and mitigation policy.
Contact: Richard Moss (University of Maryland, College Park, MA, USA), T: +1 301 314 6711; E-mail: rhm@pnl.gov

Prof. Nakicenovic's abstract

Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth’s climate system and its likely response to human and natural influences. The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in future forcings of and responses to climate change, necessitating the use of ‘scenarios’ of the future to explore the potential consequences of different response options. To date, these scenarios have not adequately examined crucial possibilities, such as climate mitigation and adaptation, and have relied on processes that limited the exchange of information among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the international community.