NTU HIGHLIGHTS

Assoc. Prof. Yen-Ting Hwang, Department of Atmospheric Sciences

As global temperatures rise, the world increasingly needs reliable forecasts of how climate change will play out in specific regions. However, producing accurate regional climate projections remains a major scientific challenge—often due to uncertainties in how models simulate atmospheric circulation. One promising key to solving this lies beneath the surface: the ocean.

The ocean acts as both a massive heat reservoir and a dynamic engine that drives global weather patterns. By absorbing, storing, and redistributing heat, it plays a decisive role in shaping atmospheric systems, including those that bring extreme weather to different parts of the world. Recent research from our Climate Dynamics and Global Change group highlights two major breakthroughs that show how the ocean's behavior influences our warming planet.

In the first study, PhD student Yong-Jhih Chen examined a wide range of global climate models and uncovered a striking result: the Southern Ocean's ability to absorb heat strongly influences the South Asian monsoon's behavior under global warming. Specifically, this heat uptake creates an energy imbalance between the hemispheres, which shifts monsoon rainfall northward (Figure 1). This pattern is one of the few aspects of monsoon dynamics that climate models agree on, and it aligns with long-standing theoretical frameworks.

The second finding addresses a long-standing mystery: why parts of the southeast and equatorial Pacific have continued to cool even as the rest of the planet has warmed since satellite measurements began in 1979. Global climate models have struggled to reproduce this cooling trend. Our research points to a surprising factor behind this anomaly: air pollution. Although industrial emissions have declined since the 1980s, their lingering effects have helped trap the Pacific in a La Niña–like cooling phase (Figure 2). This happens because the ocean reacts slowly to changes—once it cools, it can take decades to recover. Moreover, cooling in northern midlatitudes has strengthened ocean currents that transport colder water toward the equator, reinforcing the overall cooling effect. These insights emphasize how even short-lived climate pollutants can leave long-lasting marks on our climate by altering the ocean's circulation. Understanding this is crucial for improving forecasts of regional climate shifts.

To deepen our understanding, I'm also participating in TROPICS—a global working group under the World Climate Research Program's CLIVAR initiative. This collaboration focuses on how patterns of warming in the tropical Pacific Ocean influence climate both regionally and globally (Figure 3; Watanabe et al., 2024). Given the Pacific's central role in Earth's climate engine, this research will be critical to preparing for the challenges of a warmer future.