The United States, United Kingdom and Australia have announced a joint initiative to deploy fleets of autonomous underwater drones for defence purposes. This tripartite agreement, framed under the AUKUS pact, aims to develop and operate unmanned maritime systems capable of surveillance, mine detection and potentially offensive operations in the world's oceans.
As a climate scientist, I must note that this technological leap occurs against a backdrop of rapidly changing marine environments. The oceans have absorbed more than 90 per cent of the excess heat from global warming, and the volume of water is expanding. Sea surface temperatures are rising, and we are witnessing mass die-offs of coral reefs, shifts in fish populations and a decline in oxygen levels. These physical changes directly affect the performance of underwater drones: sound propagation, corrosion, buoyancy and battery efficiency all depend on water temperature, salinity and density.
Data from the Intergovernmental Panel on Climate Change indicates that the top 2,000 metres of the ocean have warmed at a rate of 0.4 Watts per square metre since the 1990s. This means the thermocline, the sharp temperature gradient that submarines use to hide from sonar, is shifting. The Arctic Ocean, in particular, is becoming noisier as ice melts and human activity increases. Autonomous systems will have to adapt to these new conditions.
The Energy Transition Agency recently reported that the military sector accounts for roughly 5 per cent of global greenhouse gas emissions. While the move to drones may reduce the carbon footprint of naval operations, the construction of these vehicles involves rare earth minerals and advanced composites, which have their own environmental costs. Moreover, the lithium-ion batteries that power many underwater drones are sensitive to temperature extremes: colder waters reduce capacity, while warmer waters accelerate degradation.
We must also consider the biosphere. The ocean is a noisy place naturally, but the addition of dozens, perhaps hundreds, of drones will create a new layer of acoustic pollution. Marine mammals rely on sound for communication, navigation and hunting. The US Navy’s own environmental impact statements have acknowledged that sonar can cause strandings and behavioural changes in whales. Autonomous drones, while possibly quieter than manned vessels, still emit pings and propulsion noises.
I am not suggesting we halt defence innovation. Security is a legitimate concern, especially as climate change exacerbates geopolitical tensions over resources and shipping lanes. But we must proceed with eyes open. The same ocean that hosts these drones is undergoing a fundamental shift. Its chemistry, temperature and biology are all in flux. We cannot treat the underwater domain as a static environment.
What gives me calm urgency is the belief that we can design these systems to be part of a solution. The drones themselves could be equipped with sensors to monitor ocean acidification, salinity and temperature. They could help track illegal fishing, a major driver of ecosystem collapse. They could even assist in carbon sequestration verification. The technology is dual-use by nature.
The AUKUS partners have a track record of innovation. If they integrate climate monitoring into their defence platforms, they will set a global standard. If they ignore it, they risk building weapons for an ocean that no longer exists.
In the end, the revolution under the waves is not just about drones. It is about how we understand, use and protect the last great wilderness on Earth. The data we gather from these machines could be as valuable for science as for security. The choice is ours.
