Decline in the Volume of World Trade

Graph by Barry Eichengreen and Kevin H. O’Rourke, displayed as Figure 3 in their article at Vox. The entire article is worth reading.

I've been wondering, since my Smoot-Hawley posts (Smoot 1 and Smoot 2), if the tariff was really important in reducing international trade, and thus contributing to the depth and duration of the Depression of the 30's, or if the trade decline was a direct result of the unfolding depression, and the tariff was relatively unimportant.

Here is a comparison, on a month by month basis, of the decline in world trade from the peak months listed for The Great Depression and Now. I haven't heard much noise about increasing tariffs yet, this time around, and don't know if any have been implemented.

The graph offers Nothing definitive as an answer to my question, but is at least consistent with the idea that trade was falling on its own, and Smoot-Hawley might not have mattered much.

This article, co-authored by Eichengreen, goes into some related detail, and explicitly assumes that Smoot-Hawley was a bad thing. But, it does not demonstrate that trade declines were caused by tariffs.