At https://en.wikipedia.org/wiki/Milutin_Milankovitch … there is some surprising information about the man a lot of catastrophists regard as an arch villain of unifomitarianism, infamous for his exercise in mathematics that worked out the three cycles in the orbital history of the Ice Ages. In fact, keying in his name into your search engine reveals him to be an altogether interesting fellow that deserves a closer look.
He began his working life as a civil engineer and reinforcing concrete was what he specialised in – in order to give it strength in construction projects, such as bridges and buildings etc. Later, he was appointed Chair of Applied Mathematics at the University of Belgrade which is where he developed his theories on climate – using maths. One problem he sought to solve – what caused the Ice Ages?
One of his early works involved the Sun and how radiation drove climate on the surface of the Earth – which appears to pre-empt the role of solar wind as we now understand it. He then set out to calculate the intensity of solar insolation and developed a mathematical based theory describing Earth's climate zones. He even went so far as to attempt to expand the study to the other planets in the solar system. However, when seeking to bind his theory to geology he was confronted by a distinct problem – the Ice Ages. He read up on James Croll and various others and tried to take their ideas a stage further – using mathematical calculations, his speciality. Out of this he developed his theory of orbital cycles. In effect what he did was to tilt the Earth – but instead of near instantly as in a catastrophist model his model was designed to cosy up to uniformitarianism, and the tilt of the Earth (and therefore climate change) took an inordinately long time. His orbital cycles were eventually adopted into the Gradualist consensus theory – but some ten years after he died. Cosying up had not been all that successful, it would seem – unless there was another reason why mainstream was reluctant to endorse anything Milankovitch.
Apart from his mathematical masterpiece on orbital cycles Milankovitch was surprisingly open to the idea of polar wander. No wonder the mainstream tried to ignore his work – and they still ignore a large part of it. He became a friend of Alfred Wegener in the 1920s and they discussed various ideas. They were both intrigued by the Svalbad Islands, in the far north, and how it came about they had coal seams (which require lots of buried and compressed vegetation). Wegener had presented his theory of continental drift but mainstream did not like it as it smacked of catastrophism – the movement of continental blocks around the globe. Although they eventually adopted a bastardised version of continental drift within Plate Tectonics, the latter was mainly about the continents moving apart (at the Mid Atlantic ridge for example) and this occurred over inordinately long periods of time. Milankovitch proposed that the continents floated on a viscuous sub surface. Continental blocks sank into this semi liquid material and were able to slide around which is reminiscent of Charles Hapgood's ideas in his book, 'Path of the Poles' – and yet Milankovitch is not mentioned in the index of that book even though he was writing on the subject many years before Hapgood. When Wegener died (on an expedition in Greenland) he wrote a book in his memory. He also wrote chapters for Gutenberg's 'Handbook of Geophysics' with chapter titles such as 'rotational movement of the earth' and 'secular shifts of the poles' as well as 'the earth's position and movement in space' etc. Milankovitch remained loyal to Wegener and continental drift until the day he died. No wonder mainstream did not embrace his orbital model until he was out of the way.
There are three Milankovitch cycles. The 100,000 year cycles concerns eccentrictiy, the shape of the earth's orbit around the Sun. This is constantly fluctuating from more elliptical to less elliptical. This changes the distances, slightly, and affected the amount of solar insolation reaching the earth (see www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch-cycles-and-g…
The 41,000 year cycle involves the Earth's axis in relation to its place of orbit around the Sun – axial tilt (oscillation in the degree of axial tilt). The third cylce is earth's precession (its wobble as it spins on its axis). This has a periodicity of 23,000 years. We may assume the 41,000 and 23,000 year cycles have the greatest effect, and the 100,000 year cycle the least – yet Ice Ages are said to come in blocks of 100,000 years. Is this really what Milankovitch intended?