There used to be a puzzle as to how early humans migrated north across the Sahara. Caves were discovered with paintings depicting wildlife and vegetation. The evidence showed periods of water.
https://en.wikipedia.org/wiki/Orbital_effects_on_climate
Climate in general is an extremely complex system, dealing with temperature and weather conditions over an extended period of time. There are many things which influence Earth's climate. Among these many things, are various solar effects. Earth’s climate is affected by a number of factors dealing with the Earth as a whole, in relation to its position in the space relative to the sun. These factors include the angle of Earth’s axial tilt (also known as Earth’s obliquity), the eccentricity of Earth’s orbit (how circular/elliptical Earth’s orbit is), and Earth’s position in time in the precession of the solstices and equinoxes (with different Earth-Sun distances during any given season).[2]
Although these are the primary three factors in shaping Earths climate, there are other, external, factors that can help shape Earth’s climate. These external factors usually affect Earth climate on a very different time scale than the other three, and include factors such as meteors striking Earth and geomagnetic storms.[3] These external forces usually contribute to climate change on a time scale, as meteorites strike the earth, on average, every 50 to 100 million years, where as geomagnetic storms occur periodically through the sun’s eleven-year activity cycle. With all of these factors affecting climate in their own way, it becomes easy to see that Earth’s climate is in fact, largely dependent on various solar effects/circumstances.
Vulcanism has caused short term climate change. Watrched a show on this one.
https://en.wikipedia.org/wiki/Year_Without_a_Summer
The year 1816 is known as the Year Without a Summer (also the Poverty Year and Eighteen Hundred and Froze To Death)[1] because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.7–1.3 °F).[2] This resulted in major food shortages across the Northern Hemisphere.[3]
Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in the Dutch East Indies (the largest eruption in at least 1,300 years after the extreme weather events of 535–536), perhaps exacerbated by the 1814 eruption of Mayon in the Philippines....
As a result of the series of volcanic eruptions, crops in the aforementioned areas had been poor for several years; the final blow came in 1815 with the eruption of Tambora. Europe, still recuperating from the Napoleonic Wars, suffered from food shortages. Food riots broke out in the United Kingdom and France, and grain warehouses were looted. The violence was worst in landlocked Switzerland, where famine caused the government to declare a national emergency. Huge storms and abnormal rainfall with flooding of Europe's major rivers (including the Rhine) are attributed to the event, as is the August frost. A major typhus epidemic occurred in Ireland between 1816 and 1819, precipitated by the famine caused by the Year Without a Summer. An estimated 100,000 Irish perished during this period. A BBC documentary, using figures compiled in Switzerland, estimated that the fatality rates in 1816 were twice that of average years, giving an approximate European fatality total of 200,000 deaths.
New England also experienced major consequences from the eruption of Tambora. The corn crop in New England failed. Corn was reported to have ripened so poorly that no more than a quarter of it was usable for food. The crop failures in New England, Canada, and parts of Europe also caused the price of wheat, grains, meat, vegetables, butter, milk, and flour to rise sharply.
The eruption of Tambora caused Hungary to experience brown snow. Italy's northern and north-central region experienced something similar, with red snow falling throughout the year. The cause of this is believed to have been volcanic ash in the atmosphere.
In China, unusually low temperatures in summer and fall devastated rice production in Yunnan, resulting in widespread famine. Fort Shuangcheng, now in Heilongjiang, reported fields disrupted by frost and conscripts deserting as a result. Summer snowfall or otherwise mixed precipitation was reported in various locations in Jiangxi and Anhui, located at around 30°N. In Taiwan, which has a tropical climate, snow was reported in Hsinchu and Miaoli, and frost was reported in Changhua.[28]
