Atmospheric circulation as a source of uncertainty in climate change projections

Abstract

As the evidence for anthropogenic climate change continues to strengthen and 5 concerns about severe weather events increase, scientific interest is rapidly 6 shifting from detection and attribution of global climate change to prediction 7 of its impacts at the regional scale. However, pretty much everything we have 8 any confidence in when it comes to climate change is related to global patterns 9 of surface temperature, which are primarily controlled by thermodynamics. In 10 contrast, we have much less confidence in circulation aspects of climate 11 change, which are primarily controlled by dynamics and which exert a strong 12 control on regional climate. Model projections of circulation-related fields 13 (including precipitation) show a wide range of possible outcomes, even on 14 centennial timescales. Sources of uncertainty include low-frequency chaotic 15 variability and the sensitivity to model error of the circulation response to 16 climate forcing. Because the circulation response to external forcing appears 17 to project strongly onto the patterns of variability, knowledge of errors in the 18 dynamics of variability may provide constraints on the model projections. 19 Nevertheless, because of these uncertainties, higher scientific confidence in 20 circulation-related aspects of climate change will be difficult to obtain and for 21 effective decision-making it is necessary to move to a more explicitly 22 probabilistic, risk-based approach.

Extremes and Recurrence in Dynamical Systems

“…This is a further motivation to extend these techniques to geophysical extremes. Interestingly, the high sensitivity of extremes in the vicinity of tipping points suggests that observing unusual return times for extreme weather events may provide a flag signalling at an an early stage qualitative changes of atmospheric circulation, which could hardly be predicted by looking at the bulk of the statistics; see also [319]. …”

The dynamics of temperature extremes

“…The authors then partitioned observed changes in temperature extremes into those associated with changes in the occurrence of circulation regimes (dynamic changes) and those that have no such association (thermodynamic changes). This kind of partitioning is a growing theme in climate science 8 . Horton and colleagues find that most regions have experienced a clear increase in summertime high temperature extremes since 1979.…”

Towards predictive understanding of regional climate change

“…To the extent this internal variability is unpredictable, the resultant uncertainty is irreducible. This "single realization effect" is large enough to mask the forced regional response, presenting a major challenge for understanding and communication of regional climate change 45,82 .…”