Ocean's Impact: How Indian Ocean warming affects the world

Climate models indicate that the Indian Ocean will experience uneven warming, with warming hotspots in the Arabian Sea (AS) and South East Indian Ocean (SEIO).

Indian Ocean Warming

A recent study using large ensemble simulations of the Community Earth System Model 2 has shed light on the various underlying mechanisms responsible for these warming patterns.

The researchers found that changes in ocean circulation patterns amplify warming in the AS, while reduced low-cloud-cover-induced heat fluctuations lead to SEIO warming.

Climate change is a significant global concern, resulting in a substantial increase in temperatures both on land and in the oceans. However, this warming is not uniform, with some regions warming faster than others. This temperature variability has far-reaching consequences for wind and weather systems, affecting societies and ecosystems around the world.

For example, amplification patterns in the Arctic and temperature differences in the equatorial Pacific can affect regions well beyond the tropics. Similarly, changes in sea surface temperatures over the Indian Ocean (IO) can influence climate and precipitation trends in Asia, Africa and Australia.

Non-uniform warming in Indian Ocean

IO warming variations may also have implications for North Atlantic temperature patterns and the Atlantic meridional overturning circulation, an essential component of the global climate system.

Many climate projections indicate non-uniform warming in the Indian Ocean, with hotspots in the Arabian Sea (AS) and Southeast Indian Ocean (SEIO). However, little is known about the mechanisms driving these warming patterns and their potential impacts on adjacent land areas.

To bridge this knowledge gap, a team of researchers from Korea and Japan led by Professor Kyung-Ja Ha from Pusan National University (PNU), Korea, has recently investigated the IO warming patterns using large ensemble simulations.

In this study, authored by Ph.D. student Sahil Sharma from PNU and published online in Nature Communications on 30 March 2023, the researchers performed an ocean–atmosphere-based analysis using the Community Earth System Model 2 (CESM2), identifying the physical mechanisms underlying the future non-uniform IO warming.

Ocean–atmosphere interactions

“Instead of running the climate model simulation only once, we performed one hundred simulations on CESM2, which represented the different realizations of the variability in the IO climate system. This new modelling resource has been instrumental in identifying the complex ocean–atmosphere interactions responsible for modulating the IO circulation and warming patterns,” explains Sharma.

Instead of running the climate model simulation just once, the researchers ran one hundred simulations in CESM2, representing different realizations of variability in the Indian Ocean climate system. This broad modelling approach allowed them to identify complex ocean-atmosphere interactions that modulate RO circulation and warming patterns. One of the key drivers of warming in the Arabian Sea (AS) was identified as air-sea interactions in the Eastern IO (EIO), near western Indonesia.

In this region, cooler deep waters upwell to the surface, resulting in relatively cooler water in the EIO with weak regional warming. This, in turn, leads to increased pressure at sea level and strong winds blowing into the AS, significantly altering IO Walker's circulation. These changes cause warmer tropical waters to move into the AS, causing it to warm.

Additionally, this induces wetter conditions in the region, with more precipitation and less evaporation, resulting in more stable near-surface water stratification. Consequently, this prevents the upwelling of deeper, cooler waters, further intensifying AS warming.

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