Political tensions, new tariffs, shifting trading patterns and reconfigured shipping lanes are reshaping the geography of maritime trade, the United Nations' trade and development agency, UNCTAD, said in a fresh report.

"Not since the closure of the Suez Canal in 1967 have we witnessed such sustained disruption to the arteries of global commerce," UNCTAD chief Rebeca Grynspan said in the report.

"Ships that once transited the Red Sea in days now sail for weeks around the Cape of Good Hope. Freight rates that were relatively stable for years now swing wildly from month to month. Supply chains we thought were resilient have proven fragile," she pointed out.

Amid such disruptions, Wednesday's report said that "growth is forecast to slow in 2025".

After global maritime trade volumes swelled by 2.2 percent in 2024, they are estimated to inch up just 0.5 percent this year, it said.

Over the medium term, between 2026 and 2030, UNCTAD projected total maritime trade volumes would grow at an average annual rate of 2 percent.

The slowdown was coming amid ongoing technological, environmental and geoeconomic transitions, which Grynspan said were "converging at a speed that demands fundamentally rethinking how maritime transport operates".

UNCTAD said the impact on maritime trade of new US policy measures, including steep new tariffs and port fees, were not yet fully understood.

But the agency said the result would surely be "more rerouting, skipped port calls, longer journeys and ultimately increased costs".

It also highlighted that deeper shifts were reshaping the sector, including efforts to decarbonise shipping.

There is still a long way to go.

Greenhouse gas emissions from shipping rose by five percent last year, and only eight percent of the world's fleet's tonnage was equipped to use alternative fuels, the report said.

But at the same time, it pointed out that the order books show that the shift is underway, with alternative fuels now representing more than half of the ship tonnage of new orders.

UNCTAD has warned that decarbonising maritime transport will entail steep costs, including for fleet renewal, port adaption and alternative fuel infrastructure.

Fast advancing automation and digitalisation of the sector would also incur significant costs, it said.

The agency called on governments to send "clear regulatory signals" and make greater investment to drive the transition.

"The transitions ahead - to zero carbon, to digital systems, to new trade routes - must be just transitions," Grynspan said.

"They must empower, not exclude. They must build resilience, not deepen vulnerability."