A 6-year cycle in the climate system

The natural climate variability is responsible for large fluctuations in the climate system over a broad range of time and space scales. The characterization of such oscillations (accelerations, trends, seasonal signals) is critical to understand the causes of change in the climate system and improve future climate scenarios. In this study, we report an oscillation with a pseudo-periodicity around 6 years in many climate variables, including the surface mass anomalies retrieved from GRACE and GRACE Follow-On missions. Changes in terrestrial water storage are shown to exhibit a 6-year oscillation at tropical latitudes in the Southern hemisphere (North of South America, tropical Africa, North of Australia). Similar oscillations have been detected in the precipitation, but were found to be underestimated by global hydrological models such as ISBA-CTRIP or WGHM. These discoveries echo the recent detection of a 6-year cycle in the global mean sea level and the ice mass balance of the Greenland ice-sheet and continental glaciers, as well as in regional climate indices (Atlantic Multidecennal Oscillation, North Atlantic Oscillation, Pacific Decadal Oscillations) by Moreira et al., (2021). The causes for such short-term oscillations in the climate system are still unexplained but we note that a 6-year cycle has also been reported in the length of day (LOD) and robustly attributed to liquid core dynamics. While the 6-year cycle in LOD, geomagnetic field and core dynamics may be unrelated to the 6-year oscillation detected in several climate parameters, we briefly discuss potential mechanisms that could link deep Earth and surface processes.

 

Moreira, L., Cazenave, A., & Palanisamy, H. (2021). Influence of interannual variability in estimating the rate and acceleration of present-day global mean sea level. Global and Planetary Change, 199, 103450.