Sebastian Sonntag

Projected climate change impact on Baltic Sea cyanobacteria

Compared to other phytoplankton groups, nitrogen-fixing cyanobacteria generally prefer high water temperatures for growth and are therefore expected to benefit from global warming. We use a coupled biological-physical model with an advanced cyanobacteria life cycle model to compare the abundance of cyanobacteria in the Baltic Sea during two different time periods (1969–1998; 2069–2098). For the latter, we find prolonged growth and a more than twofold increase in the climatologically (30 years) averaged cyanobacteria biomass and nitrogen fixation. Additional sensitivity experiments indicate that the biological-physical feedback mechanism through light absorption becomes more important with global warming. In general, we find a nonlinear response of cyanobacteria to changes in the atmospheric forcing fields as a result of life-cycle related feedback mechanisms. Overall, the sensitivity of the cyanobacteria-driven system suggests that biological-physical and life-cycle related feedback mechanisms are important and must therefore be included in future projection studies.

Earth System Science Frontiers: An Early Career Perspective

AbstractThe exigencies of the global community toward Earth system science will increase in the future as the human population, economies, and the human footprint on the planet continue to grow. This growth, combined with intensifying urbanization, will inevitably exert increasing pressure on all ecosystem services. A unified interdisciplinary approach to Earth system science is required that can address this challenge, integrate technical demands and long-term visions, and reconcile user demands with scientific feasibility. Together with the research arms of the World Meteorological Organization, the Young Earth System Scientists community has gathered early-career scientists from around the world to initiate a discussion about frontiers of Earth system science. To provide optimal information for society, Earth system science has to provide a comprehensive understanding of the physical processes that drive the Earth system and anthropogenic influences. This understanding will be reflected in seamless pre...

Quantifying and Comparing Effects of Climate Engineering Methods on the Earth System

To contribute to a quantitative comparison of climate engineering (CE) methods, we assess atmosphere-, ocean-, and land-based CE measures with respect to Earth system effects consistently within one comprehensive model. We use the Max Planck Institute Earth System Model (MPI-ESM) with prognostic carbon cycle to compare solar radiation management (SRM) by stratospheric sulfur injection and two carbon dioxide removal methods: afforestation and ocean alkalinization. The CE model experiments are designed to offset the effect of fossil-fuel burning on global mean surface air temperature under the RCP8.5 scenario to follow or get closer to the RCP4.5 scenario. Our results show the importance of feedbacks in the CE effects. For example, as a response to SRM the land carbon uptake is enhanced by 92Gt by the year 2100 compared to the reference RCP8.5 scenario due to reduced soil respiration thus reducing atmospheric CO2. Furthermore, we show that normalizations allow for a better comparability of different CE methods. For example, we find that due to compensating processes such as biogeophysical effects of afforestation more carbon needs to be removed from the atmosphere by afforestation than by alkalinization to reach the same global warming reduction. Overall, we illustrate how different CE methods affect the components of the Earth system; we identify challenges arising in a CE comparison, and thereby contribute to developing a framework for a comparative assessment of CE.

ICYESS2013: Uncertainty as an example of interdisciplinary language problems

In final form 25 February 2014 ©2014 American Meteorological Society H ere we report on the first Interdisciplinary Conference of Young Earth System Scientists (ICYESS), which focused on understanding and interpreting uncertainty. Funded by a variety of German research organizations and hosted by the climate research cluster KlimaCampus of the University of Hamburg, ICYESS was organized and chaired by young Earth system scientists, partially from the graduate School of Integrated Climate System Sciences (SICSS) as well as the Young Earth System Scientists (YESS) community. The ICYESS followed upon a series of graduate conferences of the northern German excellence clusters for marine and climate research and extended the focus to more disciplines and an international audience. A big portion of the available travel money was spent to enable young scientists from Africa and Asia to join ICYESS, a move that enabled discussions on the North–South gap in climate science and politics from the inside and was highly beneficial toward the idea of a global community of young Earth system scientists. WHY DO WE NEED TO TALK ABOUT UNCERTAINTY? The motivation of the ICYESS was foremost to enable interdisciplinary capacity building in the diverse field of Earth system science and to improve the exchange between the variety of scientific disciplines that are part of it. The conference focus on uncertainties in Earth system sciences was chosen as a focal point to illustrate the problems that appear when historically and methodologically very distant sciences try to work together. There are a multitude of causes for uncertainties in different research fields and they are often multiplied in interdisciplinary research. Examples include:

Insight into nuclear body formation of phytochromes through stochastic modelling and experiment

Spatial relocalization of proteins is crucial for the correct functioning of living cells. An interesting example of spatial ordering is the light-induced clustering of plant photoreceptor proteins. Upon irradiation by white or red light, the red light-active phytochrome, phytochrome B, enters the nucleus and accumulates in large nuclear bodies (NBs). The underlying physical process of nuclear body formation remains unclear, but phytochrome B is thought to coagulate via a simple protein-protein binding process. We measure, for the first time, the distribution of the number of phytochrome B-containing NBs as well as their volume distribution. We show that the experimental data cannot be explained by a stochastic model of nuclear body formation via simple protein-protein binding processes using physically meaningful parameter values. Rather modelling suggests that the data is consistent with a two step process: a fast nucleation step leading to macroparticles followed by a subsequent slow step in which the macroparticles bind to form the nuclear body. An alternative explanation for the observed nuclear body distribution is that the phytochromes bind to a so far unknown molecular structure. We believe it is likely this result holds more generally for other nuclear body-forming plant photoreceptors and proteins.

Enhanced Rates of Regional Warming and Ocean Acidification After Termination of Large-Scale Ocean Alkalinization: AOA TERMINATION

Termination effects of large-scale artificial ocean alkalinization (AOA) have received little attention because AOA was assumed to pose low environmental risk. With the Max Planck Institute Earth system model, we use emission-driven AOA simulations following the Representative Concentration Pathway 8.5 (RCP8.5). We find that after termination of AOA warming trends in regions of the Northern Hemisphere become ∼50% higher than those in RCP8.5 with rates similar to those caused by termination of solar geoengineering over the following three decades after cessation (up to 0.15 K/year). Rates of ocean acidification after termination of AOA outpace those in RCP8.5. In warm shallow regions where vulnerable coral reefs are located, decreasing trends in surface pH double (0.01 units/year) and the drop in the carbonate saturation state (Ω) becomes up to 1 order of magnitude larger (0.2 units/year). Thus, termination of AOA poses higher risks to biological systems sensitive to fast-paced environmental changes than previously thought. Plain Language Summary Climate engineering (CE) methods are intended to alleviate the environmental perturbations caused by climate change and ocean acidification. However, these methods can also lead to environmental issues. Among all the different CE techniques, the method of artificial ocean alkalinization (AOA) is commonly discussed. AOA involves the release of processed alkaline minerals into the ocean, which enhances the uptake of atmospheric carbon by the ocean while reducing the acidification of seawater. We study the impacts caused by the termination of AOA on environmental properties that are relevant for organisms and ecosystems because they are sensitive not only to the magnitude of environmental change but also to its pace. We analyze the rate at which the environment changes after termination of this method using an Earth system model that simulates the response of our climate to CE. We found that the abrupt termination of large-scale implementation of AOA leads to regional rates of surface warming and ocean acidification, which largely exceed the pace of change that the implementation of AOA was intended to alleviate. This enhanced rate of environmental change would restrict even more the already limited adaptive capacity of vulnerable organisms and ecosystems.