A: Sensitivity and Variability in the Climate System

Leaders: Johanna Baehr (UHH), Lars Kutzbach (UHH), Jochem Marotzke (MPI-M).

Theme A is working on key questions of physical and biogeochemical climate research that are essential for assessing possible and plausible climate futures:

• Where does the anthropogenic carbon go?
• How does the weather change with climate?
• To what extent are key regions particularly variable in their climate or particularly sensitive to climate change – and why?

A critical connection exists with Themes B and C in that Theme A passes on information about irreducible (aleatoric) uncertainty due to internal climate variability, as well as regional predictions and information about climate and carbon cycle variability including the probability of extreme events.

List of projects:

• A1 Carbon Dynamics in the Arctic – crucial because the Arctic warms faster than the rest of the globe and because the Arctic hosts large carbon reservoirs
  Chairs: V. Brovkin (MPI-M), L. Kutzbach (UHH), D. Notz (UHH)
• A2 Clouds and Tropical Circulation – crucial for global climate sensitivity and inextricably linked to weather changes
  Chairs: S. A. Buehler (UHH), B. Stevens (MPI-M)
• A3 Canopies in the Earth System – crucial for all interactions and feedbacks between the land surface and both weather and climate
  Chairs: F. Ament (UHH), J. Behrens (UHH), B. Leitl (UHH)
• A4 African and Asian Monsoon Margins – where over a billion people rely on the supply of freshwater through the monsoons, and where future habitability may be threatened 
  Chairs: J. Böhner (UHH), G. Schmiedl (UHH)
• A5 Land-Ocean Transition Zone – crucial for both the carbon cycle and the ecological health and hence habitability in the densely populated coastal regions
  Chairs: J. Hartmann (UHH), P. Korn (MPI-M), C. Schrum (Helmholtz-Zentrum Hereon)
• A6 Earth System Variability and Predictability in a Changing Climate – crucial for an improved understanding of the processes leading to internal climate variability and extreme events as well as for the development of sustainable adaptation and mitigation strategies of societies in response to ongoing climate change  
  Chairs: J. Baehr (UHH), Eleanor Frajka-Williams (UHH), T. Ilyina (UHH), J.-S. von Storch (MPI-M), E. Zorita (Helmholtz-Zentrum Hereon)

Accomplishments and Prospects

In the first years of CLICCS, major progress regarding the development of ICON ESM-based Earth system models as well as the implementation of previously neglected key physical and biogeochemical processes – have been made. High-quality results have been produced that led to better understanding of the dynamics of important components of the climate system on cascading spatial and temporal scales. Major upcoming questions are:

• How is the probability of extremes events influenced by the on-going climate change and what are their impacts beyond meteorological variables to other components of the climate system as well as society?
• How do climate change-induced changes in key regions affect the global climate system as a whole?
• Which physical and biogeochemical processes constrain or enable the achievement of the Paris agreement temperature targets? This question will be one of the leading questions of the next Hamburg Climate Futures Outlook 2022, which is in preparation.