Investigating state and timescale-dependency of climate variability using an isotope-enabled coupled general circulation model
Oceanography
Final Report Abstract
It is still largely unclear whether global and regional climate variability will increase or decrease along with global mean temperature rise. Variability changes are crucial to understand, as they entail changes in the frequency of extreme events. In light of this, the aim of this project was to understand and quantify links between mean changes and variability in temperature. For centennial to millennial timescales, palaeoclimate data are the only source of information. The focus period of this project was the last Glacial Maximum state (LGM, approximately 27000 to 19000 years ago) and the Holocene (10700 years ago to present day). From the LGM to the Holocene state global mean temperature rose by 3-8 degrees C, similar to the increase projected for the next centuries. For variability-oriented climate model-data comparison, long model integrations are required, which should also test the role of natural (solar and volcanic) forcing in fostering longer term variability in different Earth system states. Furthermore, using isotopeenabled climate models allows to test not only climate responses, but also potential changes in the relationship between the proxy data (e.g., ice-core d18O) to the climate variable of interest. Here, relationships between global mean temperature changes and changes in the variability of temperatures (the width of the temperature distribution) were investigated using a proxy data synthesis of published proxy records for temperature, published climate model output, and using new millennial simulations with an isotope-enabled general circulation model. The proxy synthesis evaluation focused on global patterns of variability change from the LGM to the Holocene. On centennial-to-millennial timescale temperature variability in the Holocene, on a global scale, was found to have decreased to roughly a quarter of the LGM value. The change in variability was found to have been smallest in the Tropics, larger in the mid-latitudes, and largest in Greenland. A significant correlation between the estimated change in temperature variability, and the estimated change in the temperature gradient, could point at reduced temperature variability in warmer-than-present worlds on long timescales. The planned model experiments with and without variable natural forcing, and in the different Glacial/Interglacial Earth states, were successfully performed with only minor modifications to the prior experimental plan. An ensemble of model simulations are now available and allow to investigate changes in global temperature, atmospheric and oceanic dynamics, and the role of sea-ice in polar oxygen isotope variability in future work.
Publications
- (2017). “Climatic and in-cave influences on δ18O and δ13C in a stalagmite from northeastern India through the last deglaciation”. In: Quaternary Research 88 (03), pp. 458–471
Lechleitner, F. A. et al.
(See online at https://doi.org/10.1017/qua.2017.72) - (2017). “Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw”. In: Scientific Reports 7 (1), p. 45809
Lechleitner, F. A. et al.
(See online at https://doi.org/10.1038/srep45809) - (2018). “Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene”. In: Nature 554 (7692), pp. 356–359
Rehfeld, K., T. Münch, S. L. Ho, and T. Laepple
(See online at https://doi.org/10.1038/nature25454) - (2018). “Holocene fire activity during low-natural flammability periods reveals scale-dependent cultural human-fire relationships in Europe”. In: Quaternary Science Reviews 201, pp. 44–56
Dietze, E. et al.
(See online at https://doi.org/10.1016/j.quascirev.2018.10.005)
