A newly developed model provides first insights into the underestimated consequences of the 90-day tariff pause and the previous tariff shock in the US-China trade war
Rebound effect looming: recovery could destabilize the global ocean freight traffic more than the previous tariff shock
Container traffic in US ports is expected to increase by up to 150 percent, depending on when the rebound occurs: without countermeasures, supply problems will be similar to those experienced during the Covid-19 pandemic
Tariff shock caused the biggest disruptions on US-China shipping route since the Covid-19 pandemic: around 10 percent were “blank sailings,” according to recent data
Around 90 percent of global trade takes place by sea, so disruptions have a correspondingly large impact on global supply chains
The surprisingly announced 90-day tariff pause in the trade war between the US and China could destabilize global maritime trade more than the tariff increases imposed so far. While the tariff shock almost completely paralyzed trade between the world’s two largest economies—with a drop in trade volumes at US ports of up to around 60 percent—there is now a threat of a “rebound effect”, an abrupt increase in demand up to 150 percent. The expected consequences are price increases, logistical bottlenecks, congestion, and delays in maritime transportation—especially on the US West Coast—similar to what was seen during the Covid-19 pandemic.
These are the key findings of a recent study by the Complexity Science Hub (CSH), Supply Chain Intelligence Institute Austria (ASCII), and Delft University of Technology. Using a simulation model, the study now shows how severely the trade conflicts of recent months have affected global shipping and how necessary it is that the global economy prepares for the recovery phase that is now beginning. The authors of the study warn of a destabilization of global trade—with particularly drastic consequences for maritime transport. As around 90 percent of global trade is transported by sea, shifts in capacity and rising freight costs could put a strain on supply chains worldwide—with noticeable consequences for European companies too.
“While the abrupt tariff increases were drastic but calculable, the current recovery is being met with unresolved structural bottlenecks and a lack of preparation. The now sudden threat of an increase in US-China trade could drive up global shipping costs as capacity is shifted to clear backlogs. This in turn could lead to higher export and import costs for European companies. The next weeks will be a litmus test for the resilience of global maritime trade and could be accompanied by bottlenecks like during the Covid-19 crisis,” explains CSH researcher and ASCII Director Peter Klimek.
Rebound Effect Looming: Tariff Pause Could Lead to Massive Congestion
According to the study, the suspension of tariffs could have a more drastic impact on global shipping than the recent tariff shock. The tariff pause that has now begun could lead to US companies wanting to replenish their stocks at record speed and reorder backlogged supplies on a large scale—a catch-up effect that could lead to a drastic increase in shipping traffic and overload entire ports. Conversely, if companies are waiting to restock due to uncertainty over whether they will be able to close deals within the 90-day pause, the subsequent rebound could be even larger. The authors of the study anticipate a 150 percent increase in deliveries to the USA. The number of ship arrivals in Long Beach-Los Angeles could increase by 73 percent—the equivalent of around 19 additional ships per day. An increase of 61 percent is expected in Oakland and 56 percent in Tacoma. Overall, US container traffic could increase by almost 19 percent. This increase will be offset by small declines in almost all other regions of the world, in particular Japan, Korea and the EU. This is likely to increase the cost of shipping along these routes.
“The expected resurgence in trade—especially towards the USA—could lead to logistical bottlenecks and port congestion, as was the case during the Covid-19 pandemic – with corresponding risks of delays and congestion. Back then, some ships had to wait more than 20 days to be unloaded off the US west coast. There is a similar risk of congestion now if no countermeasures are taken. The congestion of ports and logistics networks could massively disrupt supply chains and lead to significant price increases,” explains Klimek.
Trade War Caused Massive Cancellations: Around 10 Percent “Blank Sailings”
The trade war between the USA and China has caused noticeable disruption to maritime traffic worldwide. According to the study, around 500 container ships were traveling on routes between the two countries before the tariff increases—this corresponds to around 6 percent of all container ships worldwide that were potentially affected by the trade war and the tariff measures. Many of these ships were transporting goods that were ordered before the tariff measures but were no longer in demand due to the increased tariffs. As a result, containers had to be reloaded, rerouted or temporarily stored, which led to delivery bottlenecks, orphaned containers in transit and longer handling times. These disruptions led to a noticeable global decline in the movement of goods and so-called “blank sailings”: according to the World Container Index, around 10 percent of all ship journeys were canceled in April and May 2025. By way of comparison: during the pandemic, the rate of downtime was up to around 20 percent.
Trade War Rerouted Global Shipping: Europe and South America Benefited
According to the model-based simulation, US West Coast ports have experienced a sharp decline in container traffic due to the near-total collapse of the US-China trade, whereas ports in Europe and South America have benefited from the diversion of global shipping routes. The model suggests that in Long Beach-Los Angeles, one of the country’s most important ports, the number of container ships could theoretically have fallen by more than 63 percent, equivalent to roughly 17 fewer ships per day. In China, by contrast, the most affected port, Ningbo, could have experienced a much smaller decline of around 4 percent, due to greater diversification of trade flows. The model also suggests that the redundant shipping capacity is likely to have been shifted to the South American and European routes, which in the simulation showed increases in shipping of 5 percent and 2 percent, respectively.
“We assume that many Chinese exports were redirected quickly to other markets such as Europe and South America. As a result, ships are now lacking on the China–US route – which could lead to bottlenecks if demand rises again, putting even more strain on an already overloaded system,” says Mitja Devetak, research associate at ASCII and PhD candidate at CSH.
Political Uncertainties Jeopardize Global Trade and Supply Chains
The authors of the study emphasize that the ongoing political uncertainties are increasingly jeopardizing international trade, especially in the maritime sector. In order to overcome the associated challenges, port authorities and political decision-makers need to take coordinated and forward-looking political measures and invest in infrastructure. Companies should make their supply chains more resilient and minimize risks through strategic warehousing and alternative procurement sources. The authors warn that short-term fluctuations in demand in particular—triggered by customs measures—could destabilize global supply chains within a matter of weeks.
“The trade conflict is a wake-up call for our economy. It shows how quickly political decisions can translate into very real bottlenecks at ports and in supply chains. The ongoing uncertainty in trade illustrates how important it is to shape trade agreements and tariffs carefully in order to avoid destabilizing global supply chains again,” concludes Klimek.
About the study
The current study by the Complexity Science Hub (CSH), Supply Chain Intelligence Institute Austria (ASCII), and TU Delft, analyzes the effects of the US-China trade war on global maritime trade for the first time using its simulation model TIDES. The TIDES model takes into account 1,315 container ports worldwide and simulates maritime container trade as a network transport process based on a detailed maritime transport network with 10,000 container ships. The study has been published as a preprint.
