Earlier this summer, the Armed Forces of the Philippines spotted dozens of Chinese fishing vessels in—or very near to—the Philippines’ exclusive economic zone. This influx occurred just weeks after the US National Oceanic and Atmospheric Administration announced, “El Niño is here.”

Armed spats over fisheries in the East and South China Seas are nothing new, but the specific timing of this incident reflects broader trends with potentially explosive implications as climate change strengthens the El Niño cycle. Recent research we have published in Marine Policy found that among the many worrisome effects of El Niño is that it significantly increases the risk of militarized fisheries disputes in the East and South China Seas.

These waters are among the ocean regions already most-marked by fisheries conflict and broader geopolitical tensions. Our new evidence suggests this relationship is getting stronger over time.

El Niño and What It Means for Fisheries

At a recent Wilson Center event, experts noted that the El Niño Southern Oscillation (ENSO) is a pattern of alternating warming and cooling in the waters of the east-central Pacific Ocean; this pattern is the single most important driver of year-to-year variation in global climate.

ENSO oscillates between cool (La Niña) and warm (El Niño) phases at intervals averaging five-to-seven years. The currently forming El Niño comes on the heels of a rare “triple dip” La Niña, lasting nearly three years (34 months), which is the longest observed over the last 50 years. Via planet-spanning teleconnections, ENSO affects weather patterns and food production, economic growth, and civil conflict around the world, even as far away as Sub-Saharan Africa.

Closer to “home,” El Niño effects for fisheries in the Western Pacific are strong and negative. El Niño events are linked to marked declines in fish catch in the East and South China Seas, as well as for highly migratory and lucrative fisheries like tuna.

These negative effects occur against a baseline of historical overfishing and tense, contested relations between countries in the region—including China, Indonesia, Japan, Malaysia, the Philippines, South Korea, Taiwan, and Vietnam—over their maritime borders. These tensions are so high that Vietnam banned box office juggernaut Barbie over the inclusion of the nine-dash line, which depicts China’s contested territorial claims in the South China Sea, on a comically inaccurate world map.

Our research analyzed 60 years of data (1950–2010) on militarized fisheries disputes between pairs of East and South China Sea-adjacent countries (i.e., China and Japan; Taiwan and the Philippines; etcetera.). These incidents ranged in intensity from non-fatal interactions such as ramming, firing warning shots, vessel seizures, and arrests to skirmishes between naval and coast guard vessels, attacks on fishing boats, and the sinking of crewed vessels. While most were non-fatal, deaths occurred in 7.4% of these incidents, totaling hundreds of lives lost during our study period.

Our statistical analysis yielded striking results: relative to La Niña conditions, these militarized fishing disputes were more than three times as likely to occur during El Niño conditions. And while our work was heavily quantitative and statistical, the relationship was clear from even a casual perusal of the raw data (Figure 1).

Over the 60 years we studied, La Niña/El Niño conditions were split nearly 50/50, but 77% of the fisheries disputes occurred during El Niños. For Vietnam, Japan, and Indonesia, these disputes occurred more frequently during El Niño episodes by a margin of more than four to one.

Figure 1: Occurrence of Fisheries Disputes and El Niño Episodes, East and South China Sea-Adjacent Country Pairs

Source: Hendrix, C. S., Glaser, S. M., Lambert, J. E., & Roberts, P. M. (2022). Global climate, El Nino, and militarized fisheries disputes in the East and South China Seas. Marine Policy, 143, 105137.

Our data also show these disputes are occurring much more frequently over time. From the mid-1950s to mid-1980s, these disputes were relatively infrequent (Figure 2). But since the early 90s—a period marked by the end of the Cold War and the early years of China’s economic boom—the trendline has been consistently upward. By the late 2000s, the annualized risk of conflict outbreak during an El Niño had increased nearly five-fold. Data constraints prevent us from saying whether this acceleration has continued in the past decade.

Figure 2. Locally Weighted Scatterplot Smoothing Estimates of Annualized Probability of Militarized Fishing Dispute Onset, 1950-2010. Source: authors’ calculations based on data in Hendrix et al. (2022).

Reasons for Conflict—and Possible Remedies

While our analysis can be interpreted causally—the fisheries disputes did not cause the warming/cooling cycle in the Pacific—we did not test causal mechanisms, or the tissue that connects causes and effects. But we can speculate.

The most plausible mechanism is scarcity: El Niño events reduce fisheries productivity, drive down fishers’ incomes, and increase competitive pressures. These circumstances encourage fishing fleets to follow migrating stocks into the high seas or into other countries’ exclusive economic zones (or EEZs).

A second hypothesis is that El Niños create greater uncertainty about fish abundance and location. As fishing boats react to changing conditions, they cross may cross literal (but invisible) EEZ lines, come into contact with other fishing vessels and coast guards, and generally disrupt established practices.

In either scenario, violent competition over these resources becomes more likely—especially in regions where maritime borders are already hotly disputed. The East and South China Seas are ringed by two of the world’s three largest economies (China and Japan), two of the four most populous countries (China and Indonesia), and the top two fishing countries (China and Indonesia, based on total fish landings). It is also one of the ocean regions where the impacts of climate change on fisheries are forecast to be the most uniformly negative.

The confluence of large economies and militaries, growing populations, and anticipated sharp declines in fisheries productivity are likely to result in increasing—and increasingly militarized—competition for remaining fisheries resources. Our research indicates the risk is particularly acute during El Niños, which are forecast to increase in their severity under climate change.

So, what can be done? On the high seas, frameworks established by the UN Convention on the Law of the Sea and various regional fisheries management organizations could help to manage fisheries resource conflicts and prevent them from turning violent (and risking escalation). Those frameworks should be applied specifically to conflict mediation between nations to develop concrete standard operating procedures to follow in the immediate unfolding of conflict events.

But the East and South China Seas are not part of the high seas, and they include hotly contested EEZs that are themselves the source of much geopolitical friction between regional parties. Establishing an RFMO with jurisdiction over the waters of the South and East China Seas—all areas within national jurisdictions—would be unprecedented. No RFMO currently exists, and establishing one with any teeth – real enforcement/dispute adjudication power – would be very challenging.

Absent a dedicated RFMO, a maritime information fusion center within the East and South China Seas, or even across the Indo-Pacific region more broadly, would support conflict prevention and resolution through shared maritime domain awareness, more uniform knowledge sharing, and fewer military-fishing vessel surprise encounters. The most frequent party to these disputes – China – is a rising economic and military power with clear designs on establishing regional hegemony. Something more akin to a stabilizing balance-of-power may develop as the United States and Australia increase their cooperation with and security commitments to regional partners like the Philippines.

Like many security challenges related to climate change, this may be a problem set without easy answers. In the long term, the world must grapple with the fact that our consumption of seafood and marine natural resources is unsustainable. Reducing waste and by-catch in the seafood sector, adhering to strict catch limits based on scientific assessments of fish stocks, and ensuring equitable access to shared fish stocks around the world is an absolute pre-requisite for a peaceful and sustainable ocean.