Then, in the 1730s, the annual temperature rose fairly sharply. There was a series of hot summers, warm autumns and, with the exception of 1730–31, a decade of exceptionally mild winters. The winter of 1734 was the warmest for a hundred years, and 1732 and 1736 were probably the two best years of the century overall. Suddenly, in the autumn of 1738, the weather started to degenerate. There followed 28 disastrous months in which three successive and widespread bad harvests brought the worst famine of the century.
The 1741 and 1845 famines were classic examples of the demographic disasters to which a subsistence agrarian society is peculiarly vulnerable. In 1741 the catastrophe was aggravated by a combination of circumstances. Harvests failed not only all over Ireland, but also in England and parts of western Europe. In addition it coincided with the economic dislocation created by the outbreak of a major European war, the War of Austrian Succession.
For these reasons, the impact of the 1740–41 harvest failure was magnified by the concurrent impossibility of any amelioration. The significance of this became very clear when the poor harvests of the early 1740s culminated in the harvest failure of 1744–5. In Co. Roscommon, Charles O’Conor of Belanagare considered that the autumn and winter of 1744–5 were at least as severe as those of 1739–40, but food could be redistributed and the human catastrophe was averted.
Recoveries were often as rapid as disasters, and after the 1740s disasters the population rose rapidly, with slight checks such as the poor harvests of the early 1780s, until it was just under nine million at the time of the next major demographic catastrophe, the great famine of the mid– to late 1840s. It is thought that the population rose from about two million to five and a quarter million between 1700 and 1800, increasing slowly in the first half of the century but with ever–increasing momentum in the second half.
In 1785 the Royal Irish Academy was founded as a theoretical counterpart to the Royal Dublin Society, and in 1799 the second President of the Academy was Richard Kirwan FRS, an internationally distinguished, if eccentric, scholar with a scientific interest in meteorology and a practical one in weather forecasting. Under his influence, the early volumes of the Academy’s Transactions published a considerable amount of information on Irish weather during the preceding century.