Modelling studies on the probability and predictability of future climate change

• Main Author: Knutti, Reto
• Other Authors: Stocker, T. F.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2002
• Subjects: 530 Physics; Sea ice
• Online Access: https://boris.unibe.ch/192481/1/knutti02phd.pdf; https://boris.unibe.ch/192481/

There is strong evidence that the Earth’s climate has changed significantly over the last century. Direct observations of near-surface atmospheric temperature and sub-surface ocean temperature as well as numerous indirect observations of sea ice extent, snow cover and glacier retreats all point to a warming world. The topic of climate change has thus attracted worldwide attention and alarmed the public as well as the scientific community seeking for explanations. The recent Third Assessment Report of the Intergovernmental Panel on Climate Change [IPCC, 2001] has further strengthened our confidence in the widely accepted view of a strong anthropogenic influence on the climate system during the last century. Human activities affect the climate system primarily through the emission of greenhouse gases and aerosols that change the radiation balance of the atmosphere. Greenhouse gas concentrations are projected to increase further over the next century due to anthropogenic emissions, and will thus cause an acceleration of the rates of surface warming and sea level rise, probably accompanied by widespread changes in the hydrological cycle and in the frequency of extreme events. Although some aspects of anthropogenic climate change are well understood, many uncertainties remain. For the evolution of future climate, they are mainly associated with our limited understanding of the physical climate system, the limited representations of processes and feedbacks in climate models, but also with large uncertainties related to the economical, technical and social development of the World population. Of special concern is the fact that many uncertainties of key numbers in climate change are not rigorously quantified, e.g., the uncertainties of surface warming projections are generally based on expert judgement rather than on clear quantitative statistical methods. Therefore, there is a need for a quantitative assessment of the risk of climate change, and this requires probabilities that can be assigned to different scenarios ...