I had lunch with Gabriel Zucman today, co-author of the startling new paper (pdf) showing that the concentration of wealth at the very top — the 0.1% — is fully back to Gilded Age levels.And he pointed me to another paper that flew under my, and I suspect other peoples’, radar: his demonstration that a lot of wealth at the top is held in offshore tax havens (pdf).

You might have suspected that already, but it’s one thing to rely on anecdotal evidence, another thing to find the clear footprint of underground money in official statistics. What Zucman points out is that we have international data on investment positions, with each country reporting its assets abroad and foreign-owned assets at home. But the numbers don’t add up: globally, liabilities are substantially larger than assets. That’s mathematically impossible, but Zucman shows that it’s what will appear in the statistics if a lot of money is run through offshore havens, so that the ownership doesn’t show up in anyone’s national statistics. And he uses other data and information to show that this is by far the most compelling explanation.

I think this is telling us something important about how the world really works. There was a flurry of interest in the offshore haven issue when Mitt Romney’s Cayman Islands accounts; a bit more interest when Cyprus hit the wall, and the question of what it was doing arose. But the issue keeps receding, I think due to a sense that it’s somehow trivial, a matter of a few Russians and maybe a handful of our own wealthy.

In reality, however, it’s almost surely a much bigger deal than that. At the commanding heights of the US economy, hiding a lot of one’s wealth offshore is probably the norm, not the exception.