Seeing climate change through space and time
Does the climate become more stable or more variable during warmer periods? What amplitude of climate variations should we expect to see in the future? And to what extent do these variations occur naturally versus being caused by human activity? Helping to answer these questions – and more – is the EU-funded SPACE project. “We use the space-time structure of climate change from years to millennia to test climate models and fundamentally improve our understanding of climate variability,” says Thomas Laepple, SPACE project coordinator, researcher at the Alfred Wegener Institute – Helmholtz Centre for Polar and Marine Research and professor of Earth System Diagnostics at the University of Bremen. With a focus on the palaeoclimate record, the project looked at the intrinsic link between the timescale and the associated spatial scale of climate variations. “While fast variations such as weather are regional, glacial-interglacial cycles appear to be globally coherent,” adds Laepple. By quantifying this presumed tendency of the climate system, the project aimed to constrain the often sparse, noisy and at times contradictory evidence of past climate change in favour of a more informed understanding about the amplitude, origins and mechanism of climate variability.
Temperature variability increases in colder climates
The project, which received support from the European Research Council, analysed global compilations of palaeoclimate data and instrumental data supplemented by their own measurements in both ice and sediment cores, alongside using statistical and complex climate models. Based on this work, it produced several important findings, including that temperature variability depends on the mean state of the climate. “Our results showed increased variability in colder climates, associated with stronger temperature differences between the poles and the tropics,” explains Laepple. “This is the inverse of what we expect in the future, indicating a potential decrease in temperature variability in a warmer climate.” Researchers also determined that the ocean is the main driver of slow temperature variability, even on land. Furthermore, the project concluded that global discrepancies between the variability simulated by climate models and reconstructed from palaeoclimate archives likely originate in the ocean.
Regional climate variations persist for longer timescales
By comparing the variations of the global mean temperature with regional temperature variations in proxy data and climate models, researchers also determined the spatial extent of these variations. Specifically, they demonstrated that regional climate variations persist for longer timescales than what climate models simulating past climate states can reproduce. “This suggests an underestimation of regional variability on multidecadal and longer timescales and a potential bias in climate projections and attribution studies,” notes Laepple. Researchers also showed that models can accurately simulate global-scale temperature variability, strengthening the confidence in the simulated response to anthropogenic forcing in future climate projections.
The importance of natural regional climate variations
The SPACE project succeeded at demonstrating the importance of natural regional climate variations, even on long timescales, contrasting with models that largely lack regional natural variability over such periods. “We successfully inferred how the spatial scale of temperature variations depends on the temporal scale, including how the spatial extent of temperature anomalies increases with longer timescales,” concludes Laepple. “While weather anomalies are localised, interannual variations typically span several hundred kilometres, and multidecadal to centennial variations stop growing in the proxy data but continue to expand in the models.”
Keywords
SPACE, climate change, climate variability, space-time structure, climate models, climate, palaeoclimate
