Improving our understanding of past changes in the mean and variability of climate variables, for example temperature and precipitation, is crucial for reliable future projections under anthropogenic warming. Model-data comparisons between general circulation models and paleoclimate archives that store indirect proxies of climate variables have long been used to test and validate our understanding of a changing climate as represented in climate model simulations. Hydrological changes in past, present, and future are, however, far less understood and more uncertain than changes in temperature.
In the first part of the talk I will sumarize best practice methods and examples from the literature to synthezise information from isotope-enabled climate models as well as paleoclimate archives. I focus on speleothem records, a terrestrial archive in the low to mid-latitudes, in which heavy oxygen isotope ratios are routinely measured as a tracer of the water cycle.
Secondly, I will highlight some of my ongoing work, where I assess the potential and limitations of paleoclimate archives and simulations to record and resolve past hydroclimate changes on regional to global and interannual to orbital scales. We show that a multi-model ensemble represents hydrological changes between the Last Glacial Maximum and Mid-Holocene more accurately than a single model alone. The comparison is hampered by limitations in both model and proxy data. Speleothem growth rates and oxygen isotope ratios can serve as proxies for precipitation amount in low- to mid-latitudes given sufficient temporal resolution and at timescales unaffected by karst damping. Spatial patterns of simulated oxygen isotope ratios show only small offsets compared to speleothem records for the last millennium. However, the analyzed models underestimate variability on multi-decadal to centennial timescales. Our study provides the basis for future research using proxy system models and additional paleoclimate records and simulations to further explore the mechanisms of simulated and archived changes of the past hydroclimate.