Multi-timescale interactions between the tropical and polar climate systems

<sec><p indent="0mm">The tropical and polar climate systems are the primary source and sink of the Earth’s energy budget and are inextricably linked through complex atmospheric and oceanic processes. Their interactions play a pivotal role in regulating the global cycle of energy and matter, thereby shaping climate variability across multiple spatiotemporal scales. However, global warming is leading to a fundamental reconfiguration of this coupled system. Observed shifts—including the expansion of the Hadley cell, poleward shifts in jet streams, and persistent sea-ice loss—are exacerbating global risks, ranging from extreme weather and sea-level rise to ecosystem degradation. The Arctic is experiencing “Arctic Amplification”, with warming rates far exceeding the global average, which has begun to impact tropical monsoon systems via atmospheric circulation. Significant regional warming and ice sheet thinning in Antarctica also exhibits close dynamic links to tropical–polar teleconnections. This review synthesizes current understanding of the physical mechanisms governing tropical–polar interactions, from orbital to interannual timescales, and identifies critical challenges for future research. </sec><sec> On orbital to millennial timescales, paleoclimate records show that the interaction between high-latitude ice sheet–albedo feedbacks and the low-latitude hydrological cycle drives glacial–interglacial cycles. The Atlantic Meridional Overturning Circulation (AMOC) is a central connector in this system. During the Last Glacial Period, Dansgaard–Oeschger and Heinrich events highlighted the bipolar seesaw mechanism: freshwater perturbations in the North Atlantic weakened the AMOC, disrupting interhemispheric heat transport. This triggered abrupt cooling in the Northern Hemisphere and forced a southward shift of the Intertropical Convergence Zone (ITCZ), inducing warming in Antarctica and demonstrating the profound influence of high-latitude oceanic processes on the tropical hydroclimate. </sec><sec> In the modern climate, atmospheric teleconnections and oceanic circulation remain the dominant pathways for tropical–polar climate system interactions. The influence of the tropics on the poles is primarily mediated by atmospheric dynamics. Tropical convection anomalies associated with the El Niño–Southern Oscillation excite Rossby wave trains that propagate poleward, altering polar temperature, precipitation, and circulation patterns. Furthermore, stratosphere–troposphere coupling serves as a vertical pathway, whereby tropical variability modulates the polar vortex. Conversely, polar feedbacks to the tropics are increasingly significant. Arctic Amplification and sea-ice loss weaken the meridional temperature gradient, modifying mid-latitude jet streams and triggering Rossby waves that can influence tropical sea surface temperatures. Recent studies also highlight that Antarctic meltwater and Southern Ocean cooling can propagate signals to the tropics via ocean–atmosphere coupling, potentially driving the tropical Pacific toward a La Niña-like mean state. </sec><sec> Despite significant progress, projections of these interactions remain subject to substantial uncertainty. We found that current state-of-the-art climate models exhibit systematic biases in simulating polar sea ice and AMOC stability. A critical limitation is the widespread omission of dynamic ice-sheet meltwater inputs in standard projection scenarios. Omitting this process could underestimate AMOC weakening and its subsequent impacts on the ITCZ and global monsoon systems. Additionally, the scarcity of long-term, high-resolution observations in the Southern Ocean and deep ocean limits our ability to validate model physics. </sec><sec> To reduce uncertainties in climate projections, it is imperative to improve the representation of physical processes in climate models, particularly regarding ice–ocean–atmosphere interactions and freshwater forcing. We advocate enhanced multi-model intercomparison projects specifically designed to isolate tropical–polar coupling mechanisms. Furthermore, sustaining and expanding comprehensive observation networks in key polar and deep-ocean regions is essential. Deepening the mechanistic understanding of how these two critical zones interact is fundamental to improving the predictability of the Earth’s climate system under continued anthropogenic forcing. </sec>