Over the last decade considerable progress has been made in understanding and defining climate sensitivity, a quantity that is extensively used to quantify the impact of increasing atmospheric CO2-concentrations on the global mean temperature. Nevertheless, the uncertainty in climate sensitivity remains high. The climate system, however, shows variability on many time scales, is subject to non-stationary forcing and is mostly out of equilibrium with the changes in radiative forcing, which makes it a real challenge to quantify and predict the future evolution climate. Currently, an assessment of climate sensitivity is ongoing within the World Climate Research Programme (WCRP) aiming at combining as many lines of evidence as possible to constrain the uncertainty in climate sensitivity.
We welcome contributions that investigate specific feedbacks and their impact on climate sensitivity in all components of the climate system; processes on intermediate to long time scales that are generally difficult quantify such as ocean heat uptake are particularly encouraged.
Moreover, we welcome constraints on climate sensitivity from different lines of evidence, such as present day observations and modelling, historical and palaeoclimate records. From palaeoclimate and historical studies we also encourage contributions investigating new proxies or climate information other than only global mean temperature and greenhouse gases; for example (local) changes in seasonality and/or climate variability under different greenhouse gas concentrations may be easier to detect in data than the global mean long-time average.
We also encourage studies that combine different types of (independent) information to potentially further constrain the width of the distribution of possible climate sensitivity values. Moreover, we welcome contributions studying the state dependence of climate sensitivity, including (those focusing on) the potential proximity of tipping points.
More general approaches to quantifying the climate response to non-stationary forcing in the climate system are encouraged.
Maria Rugenstein (ETH Zurich)
Martin Rypdal (UiT/ The Arctic University of Norway)