Increasing desiccation of the Sahara. End of the Saharan Pluvial period.
Associated with Pollen Zone VI Atlantic, oak-elm woodlands, warmer and maritime climate. Modern wild fauna plus, increasingly, human introductions, associated with the spread of the Neolithic farming technologies.
Rising sea levels from glacial retreat flood what will become the Irish Sea, separating the island of Ireland from the British Isles and Continental Europe.
According to the Black Sea deluge theory, the Black Sea floods with salt water. Some 3000 cubic miles (12,500 km³) of salt water is added, significantly expanding it and transforming it from a fresh-water landlocked lake into a salt water sea.
c. 5500 BC
Beginning of the desertification of north Africa, which ultimately leads to the formation of the Sahara desert from land that was previously savannah, though it remains wetter than today. It's possible this process pushed people in the area into migrating to the region of the Nile in the east, thereby laying the groundwork for the rise of Egyptian civilization.
Suggested date for an asteroid or comet impact occurring between Africa and Antarctica, around the time of a solar eclipse on May 10, based on an analysis of flood stories. Possibly causing the Burckle crater and Fenambosy Chevron.
Sahara becomes fully desiccated, and conditions become largely identical to those of today. Desiccation had been proceeding from 7500 to 6000 BC, as a result of the shift in the West African tropical monsoon belt southwards from the Sahel, and intensified by the 5.9 kiloyear event. Subsequent rates of evaporation in the region led to a drying of the Sahara, as shown by the drop in water levels in Lake Chad. Tehenu of the Sahara attempt to enter into Egypt, and there is evidence of a Nile drought in the pyramid of Unas.
Continued mountain formation in the Himalayas contributes to the drying up of the Sarasvati River and the desertification of the Thar Region. This contributes to the decline of the Harappan civilization.
Minoan civilization in the Mediterranean declines, but scholars are divided on the cause. Possibly a volcanic eruption was the source of the catastrophe (see Minoan eruption). On the other hand, gradual deforestation may have led to materials shortages in manufacturing and shipping. Loss of timber and subsequent deterioration of its land was probably a factor in the decline of Minoan power in the late Bronze Age, according to John Perlin in A Forest Journey.
Evidence of major droughts in the Eastern Mediterranean. Hittite and Ugarit records show requests for grain were sent to Egypt, probably during the reign of Pharaoh Merenptah. Carpenter has suggested that droughts of equal severity to those of the 1950s in Greece, would have been sufficient to cause the Late Bronze Age collapse. The cause may have been a temporary diversion of winter storms north of the Pyrenees and Alps. Central Europe experienced generally wetter conditions, while those in the Eastern Mediterranean were substantially drier. There seems to have been a general abandonment of peasant subsistence agriculture in favour of nomadic pastoralism in Central Anatolia, Syria and northern Mesopotamia, Palestine, the Sinai and NW Arabia.
The Eastern Zhou period of China is characterized by the formation of larger and more powerful political systems, whose ability to transform their environment is much greater than earlier states. They establish parks to protect wildlife for hunting purposes. 
The Qin dynasty founds China's first empire period of China, conquers large areas of the East Asian mainland, and soon collapses, but is soon rebuilt by the Han dynasty, whose population and environmental impact is similar to that of the Roman Empire. Qin established some of the world's first environmental protection laws. 
c. 225 BC
The Sub-Atlantic period began about 225 BC (estimated on the basis of radiocarbon dating) and has been characterized by increased rainfall, cooler and more humid climates, and the dominance of beech forests. The fauna of the Sub-Atlantic is essentially modern although severely depleted by human activities. The Sub-Atlantic is correlated with pollen zone IX; sea levels have been generally regressive during this time interval, though North America is an exception.
Great Lisbon earthquake occurred in the Kingdom of Portugal on Saturday, 1 November, the holiday of All Saints' Day, at around 09:40 local time; subsequent fires and a tsunami almost totally destroyed Lisbon and adjoining areas, accentuating political tensions in the kingdom and profoundly disrupting Portugal's colonial ambitions.
The volcano Laki erupts, emitting sufficient sulfur dioxide gas and sulphate particles to kill a majority of Iceland's livestock and cause an unusually cold winter in Europe and Western Asia.
A recent study of El Niño patterns suggests that the French Revolution was caused in part by the poor crop yields of 1788–89 in Europe, resulting from an unusually strong El-Niño effect between 1789 and 1793.
Eruption of Krakatoa in Indonesia. The sound of the explosion is heard as far as Australia and China, the altered air waves causes strange colours on the sky and the volcanic gases reduce global temperatures during the following years. A disputed but vivid sunset was captured in Edvard Munch's The Scream.
^Kerry A. Odell and Marc D. Weidenmier, Real Shock, Monetary Aftershock: The 1906 San Francisco Earthquake and the Panic of 1907, The Journal of Economic History, 2005, vol. 64, issue 04, p. 1002-1027.