My expertise is on intrinsic climate variability and how it will change under global warming.
My research covers diverse topics such as
- developing new statistical approaches to estimate changes of intrinsic climate variability for a changing human-made greenhouse gas forcing,
- quantifying future changes in internal temperature variability,
- quantifying the possible drivers of Arctic sea-ice variability,
- understanding the evolution of sea surface temperature patterns to constrain temperature projections,
- attributing the origin-dependent severity of climate extreme events under global warming.
I complement my research activity with science communication by giving talks, demonstrating small physical experiments, and developing a strategy board game.
Projected emergence of temperature variability from the natural range
I show that human-caused changes in internal year-to-year temperature variability are expected to emerge from the unforced range by the end of the 21st century. This emergence is shown based on climate model initial-condition large ensembles forced with strong global warming scenarios. I reveal that different simulated changes in globally averaged temperature variability between models can be explained by a trade-off between strong increases in variability on tropical land and substantial decreases in high latitudes. This latitudinal pattern of temperature variability change is consistent with the observed and projected loss of sea ice in high latitudes and changes in vegetation cover in the tropics. Instrumental records support this emerging pattern, but have data gaps in key regions. Comparison of the model output with paleoclimate proxy reconstructions supports the simulated magnitude and distribution of temperature variability. The findings strengthen the need for urgent mitigation to avoid unprecedented changes in temperature variability.
Reference: Olonscheck et al. (2021), Large-scale emergence of regional changes in year-to-year temperature variability by the end of the 21st century, Nature Communications, featured as Editors’ Highlights (Climate Change Impacts).
Consistency of observed and simulated sea surface temperature patterns
I here show that observed and simulated trends in sea surface temperature (SST) patterns are globally consistent when accounting for internal variability. Some individual ensemble members of single-model initial-condition large ensembles simulate trends in large-scale SST patterns that closely resemble the observed ones. Observed regional trends that lie at the edge of the simulated distribution of internal variability - such as for the tropical Pacific east-to-west SST gradient - are hard to interpret. The observed trends could be an unusual realization of the Earth's possible behavior and/or the models are systematically biased but large internal variability leads to good matches with the observations.
Drivers of Arctic sea-ice variability
I systematically quantify the possible drivers of the sea-ice variability in the Arctic. By isolating the impact of the individual drivers in an Earth system model, I show that the internal variability of the Arctic sea-ice area is primarily caused directly by atmospheric temperature fluctuations. In contrast to the wide-spread belief that feedbacks related to surface albedo, clouds and water vapour, or the forcing by poleward ocean heat transport are crucial, I find that these processes are only of minor relevance for driving sea-ice variability.
Internal climate variability and global warming
I investigate how internal climate variability changes under global warming. To do so, I develop a new method that relates the preindustrial internal variability to the internal variability for a changing forcing. The estimate for the forced time period is derived from the ensemble spread of single-model ensembles of a multi-model ensemble. This practically applies the quasi-ergodic assumption, and allows one to assess whether the range of internal variability of any climate variable is projected to change.
Climate extremes and global warming
Climate extremes often have substantial impacts on society. However, it is unclear, how and why they will change in the future. Using an empirical threshold approach, I quantitatively attribute the future probability of changes in daily temperature, wind and precipitation extremes to anthropogenic global warming and associated changes in internal variability. I show that this different origin of future changes in climate extremes is important, because their origin determines the frequency and intensity of extremes. This is because climate extremes are, on average, much more severe when caused by an increased variability than when caused by a mere shift in the mean climate.
Science communication and outreach
I communicate my research, and our knowledge on the polar climate and climate variability by giving talks in schools and by demonstrating small physical experiments at public events. Together with colleagues, I also developed the strategy board game "Cold Cooperation" that highlights the challenge of international cooperation to both satisfy partial interests of individual countries and to avoid the most dramatic consequences of global warming. The game can be downloaded here: owncloud.gwdg.de/index.php/s/n8tghGRSGg74Hn0