Yeah, there's a modest increase in the 1850s, but nothing near enough to bring it up to previous historical norms. Calling that a 50% increase is misleading through cherry-picking data; it's true if you cherry-pick 1851 (7.4), but why not pick 1850 (11.7) or 1856(12.4)? So what's your source's agenda is cherry-picking data?
Thanks for posting a most interesting chart.
I think it helps confirm what I quoted above.
As I read that chart, you have a string of low-price years in the 1840s, ending about 1850 after which prices doubled -- ie., from 5.8 in 1849 to 11.7 in 1852.
Sure cotton prices were occasionally higher earlier in the century, but not often, and those years were before wide-spread use of cotton gins, when production was orders-of-magnitude lower.
Further more, those earlier prices were irrelevant in the 1850s, because what mattered then was all the cotton plantations which survived the low-priced 1840s were positioned to prosper mightily in the higher-priced 1850s.
And that's the whole point being made here: during the 1850s, with greatly expanded land under cultivation (1/3 more) and higher cotton prices (nearly doubled), total US cotton production rose from $74 million in the 1840s to over $207 million (tripled) in 1860.
Meanwhile, inflation rose just 33% during the 1850s.
The result of this unprecedented prosperity was average slave prices rising from $925 in 1850 to $1,658 in 1860 (79% increase).
So, it seems to me this picture of Southern prosperity is consistent and long-term, during the 1850s.
What exactly is your problem with it?