Atmospheric rivers around Antarctica are behind daily global temperature spikes and dips

The global mean surface temperature is the primary metric used to track how the climate is changing. While variability and change in global mean temperatures on interannual scales has been studied extensively, there has been limited analysis of daily global temperature variability. This is despite record-setting daily global average temperature events, such as in July 2024, generating widespread media interest.

Here, we explore the characteristics of spikes and dips in daily global average temperatures using the ERA5 reanalysis. We find that daily global temperature spikes are typically associated with Antarctic heatwaves while dips are related to Antarctic cold spells. For other parts of the world, the relationship between local and global average temperatures is much weaker. As Antarctic heatwaves are often preceded by atmospheric rivers, we examine poleward integrated water vapour transport and atmospheric river coverage in the days prior to daily global temperature spikes and dips. We find a strong signal of heightened poleward moisture transport 3-6 days prior to spikes in daily global mean temperature and the opposite pattern ahead of global temperature dips. We then examine to see if atmospheric river activity around Antarctica can help explain annual global mean temperature anomalies and find some effect, albeit weaker relative to daily scales.

This work highlights the importance of Southern Ocean atmospheric rivers in explaining variability in global mean temperatures across scales. Further study of modelling and prediction of global average temperatures based on atmospheric river activity is envisaged.