MAL4b

Records of past climate trends, variability, and extremes hold key insights into Earth’s changing climate, yet their full potential will remain untapped without a concerted effort to surmount several critical challenges, some time-sensitive.  In a century defined by accelerating climate change and human disturbance, the climate archive itself is at grave risk given that i) many paleoclimate records end in the late 20^th century, with no concerted effort to extend them to the present-day, and ii) many paleoclimate archives are disappearing under pressure from climate change and/or human disturbance. Second, many paleoclimate records are comprised of oxygen isotopes, yet the coordinated, multi-scale observational and modeling infrastructures required to unravel the mechanisms governing water isotope variability are as yet underdeveloped. This dramatic oversight exists despite development of technologies that avoid costly analysis via mass spectrometers, and despite the fact that water isotopes may very well be one of the most powerful diagnostic tracers of a changing global water cycle. Lastly, in part owing to the aforementioned deficiencies, paleoclimate data assimilation efforts remain fraught with large uncertainties, despite their promise in constraining many of the most uncertain aspects of future climate impacts, including the evolution of extreme events and hydrological trends and variability. Climate science for the 21^st century requires deep investments in the full integration of paleoclimate data and approaches into frameworks for climate risk and hazard assessments. In this sense, it is not surprising that paleoclimate scientists have played a key role in the communication of climate change science to decision-makers and the general public alike. Their understanding of the Earth system also equips them to contribute valuable insights to teams comprised of researchers, practitioners, and  decision-makers charged with leveraging science to inform solutions, in service to society. It’s time to recognize that all climate scientists study climate of the past, and all paleoclimate scientists have insights that are relevant to our climate future.

How to cite: Cobb, K. M.: (Paleo)climate science for the 21st century, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16571, https://doi.org/10.5194/egusphere-egu21-16571, 2021.

We live on land and are daily affected by land climate variations, but early climate pioneers often focused on ocean-climate interactions and ice-covered regions. With good reasons, since oceans cover two third of the Earth and are thus critical for the global climate, and because ice sheets have strongly varied over millennia and include key indices on past climate. However, recent research has increasingly shown that land climate, where we live, displays specific climate characteristics, which cannot be simply inferred from global climate responses. This is particularly the case for climate extremes, such as heatwaves and droughts. I will present recent evidence for these properties and some avenues for future research.

Land-climate interactions, which are modulated by vegetation, play a key role for climate variability on continents. This implies a fascinating interface between biological processes and climate physics. The limitation of water on continents, and the role of vegetation in the land water input to the atmosphere, implies very different water-cycle responses compared to what is seen on oceans: For instance, dry regions do not necessarily get drier, nor wet regions wetter under increasing greenhouse gas forcing. In addition, land climate can strongly deviate from global climate in other ways: During the so-called “hiatus period” in the early 2000s, changes in temperature extremes on land actually showed an amplified increase. Furthermore, key land processes are still insufficiently captured in state-of-the art Earth System Models (ESMs), such as land water effects on the global carbon cycle, and climate response to irrigation or land management.

Land processes are playing an increasingly central role in the development of pathways for climate mitigation consistent with the aims of the Paris Agreement, for instance related to afforestation or the development of bioenergy use in combination with carbon capture and storage. However, these scenarios often overlook biological and physical constraints for these land cover and land use changes, such as risks from climate extremes, including fire, in a warming world. ESM emulators for grid-cell responses may help to proof such scenarios in the needed rapid and safe transition to a net-zero CO₂ world.

How to cite: Seneviratne, S.: Understanding and predicting climate extremes on land: The new frontier, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15772, https://doi.org/10.5194/egusphere-egu21-15772, 2021.

Terrestrial ecosystems are intimately linked with the global climate system, but their response to ongoing and future anthropogenic climate change remains poorly understood. Reconstructing the response of terrestrial ecosystem processes over past periods of rapid and substantial climate change can serve as a tool to better constrain the sensitivity in the ecosystem-climate response.

In this talk, we will present a new reconstruction of soil respiration in the temperate region of Western Europe based on speleothem carbon isotopes (δ¹³C). Soil respiration remains poorly constrained over past climatic transitions, but is critical for understanding the global carbon cycle and its response to ongoing anthropogenic warming. Our study builds upon two decades of speleothem research in Western Europe, which has shown clear correlation between δ¹³C and regional temperature reconstructions during the last glacial and the deglaciation, with exceptional regional coherency in timing, amplitude, and absolute δ¹³C variation. By combining innovative multi-proxy geochemical analysis (δ¹³C, Ca isotopes, and radiocarbon) on three speleothems from Northern Spain, and quantitative forward modelling of processes in soil, karst, and cave, we show how deglacial variability in speleothem δ¹³C is best explained by increasing soil respiration. Our study is the first to quantify and remove the effects of prior calcite precipitation (PCP, using Ca isotopes) and bedrock dissolution (open vs closed system, using the radiocarbon reservoir effect) from the speleothem δ¹³C signal to derive changes in respired δ¹³C over time. Our approach allows us to estimate the temperature sensitivity of soil respiration (Q₁₀), which is higher than current measurements, suggesting that part of the speleothem signal may be related to a change in the composition of the soil respired δ¹³C. This is likely related to changing substrate through increasing contribution from vegetation biomass with the onset of the Holocene.

These results highlight the exciting possibilities speleothems offer as a coupled archive for quantitative proxy-based reconstructions of climate and ecosystem conditions.

How to cite: Lechleitner, F., Day, C. C., Kost, O., Wilhelm, M., Haghipour, N., Henderson, G. M., and Stoll, H. M.: A coupled multi-proxy and process modelling approach for extraction of quantitative terrestrial ecosystem information from speleothems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4761, https://doi.org/10.5194/egusphere-egu21-4761, 2021.