The World Trade Organization warned Tuesday that the global economy could suffer a significant loss of activity by the middle of this century if trade splinters into geopolitical blocs or regional groupings. WTO economists estimate global GDP would be 5.1% lower and exports 18.6% lower by 2050 if the world divided into competing geopolitical blocs. In a more severe breakdown, where multilateral cooperation gives way to a patchwork of free-trade agreements, GDP would fall 6.9% and exports nearly 27%. Stronger multilateral cooperation could instead raise GDP 2.9% and exports almost 18%, with least-developed countries facing the largest potential gains and losses. The warning comes as the United States sharply increased tariffs on imports from around the world last year and continued imposing new duties on some countries, although those measures have not yet triggered widespread retaliation or higher tariffs on non-U.S. imports. The WTO has been pursuing reforms after members failed to reach agreement in March, with renewed talks covering decision-making, dispute settlement, subsidies and state intervention.