Page - 10 - in options, Volume winter 2021

We need climate scenarios because the future is uncertain and complex. We cannot know what will happen to populations, international relations, societies, economies, ecosystems, and technologies. Much of the uncertainty comes from today’s choices, which can only be explored by posing “what-if” questions. So climate scientists have become storytellers, crafting consistent plotlines that span a range of futures and compare policy outcomes. Some of these scenarios have grisly ends; others are hopeful but risky; and some of the latest are telling a new kind of mitigation story, which turns out to benefit both climate and economy, and might be more feasible too. The world’s a stage The storytelling tradition goes back several decades… but let’s skip the prologue. In 2000, the Intergovernmental Panel on Climate Change (IPCC) published its landmark Special Report on Emissions Scenarios (SRES), led by then IIASA Transitions to New Technologies Program Director, Nebojsa Nakicenovic. This laid out shared scenarios, which would allow research teams to base their studies on well-established plot outlines, and compare results more easily. It started with four broad storylines. The A1 world sees rapid economic growth, technological progress, and internationalism, with regional incomes converging. B1 adds a shift to cleaner technologies and service economies. A2 tells of stronger regional differences, with higher population growth. B2 imagines more focus on local solutions to sustainability. Each storyline yields some detail on climate drivers such as GDP and energy efficiency. These numbers were fed into various integrated assessment models (IAMs), which combine economics, demographics, energy systems, and climate, to generate full scenarios – projecting how the global system of systems might evolve. The conclusion was grim. The IPCC’s third assessment report in 2001 revealed that an A2 world was heading for catastrophe, probably warming by more than 4°C relative to preindustrial levels. Even in the most climate-friendly storyline, B1, scenarios clustered around warming of roughly 2.5°C – still a sorry scene for the planet. Enter the matrix In the 2010s, researchers created a more sophisticated set of stories, based on a matrix framework with one axis for emissions, and another for socioeconomic possibilities. Plotting the future Scenarios are essential for exploring climate change. These stories of future Earth help to reveal how we might prevent global tragedy. By Stephen Battersby 10 Options www.iiasa.ac.atWinter 2021