Croll, feedback mechanisms, climate change and the future.

Our climate future depends on the delicate, fine balance of earth processes first elaborated on by James Croll, born 200 years ago in 1821. A childhood victim of the Scottish clearances, Croll, after following various indifferent occupations, managed to remove to the then rapidly industrialising city of Glasgow and eventually to Scotland's capital, Edinburgh. He blossomed as a most original, outside-the-box, thinker of great intellectual strength and modesty. He carried out scores of studies across a broad range of research topics, many related to the physical causes of climate change. He is well known for his astronomical theory of the ice ages, but should be much better regarded for his incisive physical insights into the central importance of feedbacks in the Earth system. Although humble, Croll was an ardent controversialist who strongly, perhaps over-strongly, always defended his corner. As well as his many accomplishments as a man of science, Croll was committed to exploring philosophical questions of theism and determinism, topics which occupied his earliest and last publications. A 'top ten' selection out of the varied subject areas that Croll tackled are explored herein, along with a brisk survey of their legacy to contemporary modelling studies and to Earth's climate future: (1) causes of climate change (1864); (2) ice-cap melt and sea-level rise (1865); (3) predicting future climates using eccentricity (1866); (4) combining orbital precession, eccentricity and obliquity (1867); (5) geological time and the date of the glacial epochs (1868); (6) geological time and denudation rates (1868); (7) ocean currents and the hemispherical temperature difference (1869); (8) feedbacks – a remarkable circumstance which led to changes of climate (1875); (9) temperature of space and its bearing on terrestrial physics (1880); (10) the causes of mild polar climates (1884). [ABSTRACT FROM AUTHOR]