The year 1816 is famous from the meteorological point of view. More has been written about this year than any other. All the older books on climate and weather and many biographies and histories have something to say about it. There are many references to it in the periodical literature but the statements are often inaccurate and exaggerated.
Good observations were made in Williamstown, Mass., from 1816 to 1838. The observations for 1816 as compared with those from 1816 to 1838 and from 1901 to 1923 are discussed. The year 1816 was the seventh coldest, averaging 44.3° F. or 1.3° F. below normal. The two coldest years (1816–1838) were 1836 and 1837, each averaging 42.6° F., or lust 3° F. below normal. Thus 1816 as a whole was not record-breakingly cold. February, October, November, and December of 1816 were too warm, while the remaining months were much too cold. The year was thus exceptional because of a very cold summer. The lowest temperatures at 7 a. m. for June, July, and August, 1816, were 35° F., 43° F., and 37.5° F., respectively and these were the lowest for these months for the 23-year period. The individual cold spells during the summer months are discussed next and the observations taken at other stations during 1816 are compared with those at Williamstown
In the second art the possible reasons why 1816 was so abnormal are treated. there had been the violent volcanic eruption of Tomboro in April, 1815. A weak sun-spot maximum had also occurred during 1816.
In the third part the possible causes of the abnormality of any month or year are discussed. Volcanic eruptions, changes in the activity or condition of the sun (sun spots, solar constant), changes in the surface temperatures of the oceans, changes in the composition of the atmosphere (ozone, carbon dioxide), and accidental causes are treated in order.
Annual presidential address read before the American Meteorological Society at Washington, D. C., Dec. 31, 1924.