So the more recent the data, the more reliable. For example, only in the last few years has it been possible to get reliable data from the formerly centrally planned economies. It is therefore unwise to make specific comparisons of data from one decade to the next. The graph is intended rather to show the broad patterns of steel production trends over the past 100 years. Steel use strongly reflects major economic forces, as well as major political upheavals.
Economic recession meets with a dip in steel production as such investments falter.
If you were to overlay the above graph with a time sheet showing major historical events, the peaks and dips become meaningful. Note for example the peaks corresponding to the years of the two World Wars, followed each time by a dip, and soon after by strong climbs as the major economies recovered from the war and entered new periods of prosperity and growth, most notably in the '50s and'60s. The trend over the past three decades can also be seen to be in line with cyclical economic trends, with alternating periods of prosperity and recession.