Thomas Piketty has a new book coming out and Paul Krugman isn't sure why

Thomas Piketty - the French economist who took the economics world by storm last year with his landmark tome "Capital in the Twenty-First Century" - has a new book out.

And Nobel Laureate Paul Krugman isn't sure why.

Writing in Sunday's New York Times, Krugman says the book - "The Economics of Inequality" - is basically a re-hash of a paper published by Piketty in 2001 that established the then-30-year-old Piketty as a major player in modern economics.

As Krugman writes, that paper, titled "Income inequality in the United States, 1913-1998," was a "landmark piece of research that has had a major impact, not just on economics, but on political science too."

But things have changed.

Namely, Piketty himself has built on that work and published "Capital," a 700-page book about income inequality that was sold out on Amazon in the spring of 2014.

Additionally, the trend towards increasing inequality has seemed to accelerate since that paper first emerged while research in this area of economics has flourished.

This leads Krugman to write that the book leaves readers with, "a lucid statement of our understanding of inequality as it stood almost two decades ago, with hardly any allowance for the subsequent research and real-world developments that have changed that understanding."

And if the point of publishing a book is, well, to add something new to a conversation, then in Krugman's view Piketty's latest offering falls very short.

"I'm sorry to be so negative about a book by such an important figure in our economic thinking," Krugman writes. "But releasing this youthful effort as if it were a new contribution does a disservice to readers, and I'd argue to the author himself."

Brutal.

Piketty's latest book will be released on August 3. It is already Amazon's #1-ranked book in the theory of economics.