From the passage note down the years when global recession happened. List the results in comma separated format.

The International Monetary Fund defines a global recession as "a decline in annual per‑capita real World GDP (purchasing power parity weighted), backed up by a decline or worsening for one or more of the seven other global macroeconomic indicators: Industrial production, trade, capital flows, oil consumption, unemployment rate, per‑capita investment, and per‑capita consumption".[1][2]According to this definition, since World War II there were only four global recessions (in 1975, 1982, 1991 and 2009), all of them only lasting a year (although the 1991 recession would have lasted until 1993 if the IMF had used normal exchange rate weighted per‑capita real World GDP rather than the purchasing power parity weighted per‑capita real World GDP).[1][2] The 2009 global recession, also known as the Great Recession, was by far the worst of the four postwar recessions, both in terms of the number of countries affected and the decline in real World GDP per capita.[1][2]

1975, 1982, 1991, 2009