In today's 80.000h newsletter, there is a short overview of MacAskill's new book about longtermism. It explains that Will makes the case that is some few particular people (Quakers) started the antislavery movement. If they would have died at the wrong time, maybe the antislavery movement would not have happened. And part of the basis for this assertion is that "it's estimated that abolition cost Britain 2% of its GDP for 50 years".
Some time ago I've read that a very big factor (probably the crucial factor) for why slavery was abolished is because of energy: we learned how to use the energy in coal, which made a huge amount of work types extremely cheap if you could afford to buy a steam engine. It made work so cheap that it was cheaper than slaves, which need to be fed and sheltered, and only work for so many hours/day, so they were not that needed anyway.
These two narratives do not seem to fit together. Of course, steam engines cannot do all kinds of work, so slaves could have still come handy in many aspects. Is it this "loss" what this 2% accounts for?
I would hope that there is a citation/reference/source listed in the book! Alas, I don't have the book myself. I too am curious about this question. 2% of GDP is quite a lot.
I wonder what % of Royal Navy resources were devoted to it. In some ways that's a more impressive metric than GDP, because governments make stupid decisions that cost huge fractions of GDP all the time, so just because a government made a decision that cost a fraction of GDP doesn't mean they knowingly accepted the sacrifice.
Also the economy was much less developed at that time, and governments much less able to direct it. Prior to 1900 or so total tax revenue was only around 10% of GDP.
Wikipedia quotes someone disparaging the antislavery efforts saying they used less than 5% of Royal Navy ships, which I interpret as meaning they probably used between 4% and 5%.
This article says: "At its peak in the 1840s and 1850s, British operations off the West African coast involved up to 36 vessels and more than 4,000 men, costing an estimated half of all naval spending – amounting to between 1% and 2% of British government expenditure."
Big discrepancy between "half of all naval spending" and "less than 5%." Maybe the peak was half and the min was 4%?
Either way, I'm pretty impressed. I wonder what fraction of typical Great Power military budgets go to humanitarian efforts.