Points clés :

• We estimate the elasticities of exports to tariffs and to the real exchange rate within the same specification, allowing for a direct comparison
• We find that tariffs have significantly more impact on exports than the real exchange rate, invalidating the symmetry assumption often made in macroeconomic models
• From the point of view of short-term stabilization, tariffs and monetary policy can be considered as partly substitutes
• Monetary policy is more stabilizing due to its internal transmission channels; at the zero lower bound, though, there is an incentive to use tariffs for macroeconomic stabilization
• In normal times, a governement will more likely react to a trade "agression" through monetary rather than through trade retaliation

 Résumé :
The debate on trade wars and currency wars has re-emerged since the Great recession of 2009. We study the two forms of non-cooperative policies within a single framework. First, we compare the elasticity of trade flows to import tariffs and to the real exchange rate, based on product level data for 110 countries over the 1989-2013 period. We find that a 1 percent depreciation of the importer's currency reduces imports by around 0.5 percent in current dollar, whereas an increase in import tariffs by 1 percentage point reduces imports by around 1.4 percent. Hence the two instruments are not equivalent. Second, we build a stylized short-term macroeconomic model where the government aims at internal and external balance. We find that, in this setting, monetary policy is more stabilizing for the economy than trade policy, except when the internal transmission channel of monetary policy is muted (at the zero-lower bound). One implication is that, in normal times, a country will more likely react to a trade "aggression" through monetary easing rather than through a tariff increase. The result is reversed at the ZLB.

 Mots-clés : tariffs | exchange rates | trade elasticities | protectionism

 JEL : F13, F14, F31, F60