Southern Hemisphere leads global temperature changes during the last Glacial Cycle

Glacial inceptions and terminations are driven by orbital forcing and non-linear responses of the carbon cycle and ice sheets. Traditional theory primarily points to peak summer insolation at 65°N to explain changes in Northern Hemisphere ice sheet extent, a process amplified by atmospheric CO2 concentration. In the meantime, several studies of the last deglaciation find that Southern Hemisphere temperatures and atmospheric CO2 concentration increase earlier than temperatures in the Northern Hemisphere. Hence, Northern Hemisphere ice sheets may be more strongly coupled to surface temperature in the Southern Hemisphere than in the Northern Hemisphere. We expand this analysis for the entire last glacial cycle, with regional reconstructions of Sea Surface Temperatures. We find that the Southern Hemisphere leads the Northern Hemisphere by 3kyr for timescales above 10kyr. In addition, variations in the Southern Hemisphere show significantly larger amplitudes and correlate with peak summer insolation at 65°N. We test a range of mechanisms using CLIMBER-X and LOVECLIM simulations, including direct effects of orbital forcing and AMOC variability, to explain these results. These findings bring a new understanding of the role of the bipolar seesaw and the orbital forcing to explain temperature variability on timescales above 10kyr. Finally, our study provides new insights into the triggers of glacial inception and termination.