2200 BC

4.2-kiloyear event

The debated 4.2-kiloyear climate interval

A 2024 synthesis of 109 studies found the supposed global megadrought neither globally coherent nor exceptional against the rest of Holocene variability.

Why there is no day, and barely a year

Approximately 2200 BCE is the best representative anchor for this entry, and even that is a convenience: nothing is recorded as having happened in any particular year. The listing's 2150 BCE is one point inside a broad, debated interval, and the formal stratigraphic marker tied to that interval is a different number again — 4,250 years before 2000 CE, or approximately 2250 BCE. Neither figure is a demonstrated onset year.

That marker is a stable-isotope shift 7.45 millimetres deep in speleothem KM-A from Mawmluh Cave in Meghalaya, India, ratified by the International Commission on Stratigraphy in 2018 as the base of the Meghalayan Stage.

A boundary fixed in a stalagmite is a chronostratigraphic convention, not proof that every region experienced the same climate anomaly.

An interval that starts at 4.6 ka in some records and ends at 3.4 ka in others

There is no agreed onset. Published records labelled 4.2 ka begin as early as 4.6 ka and end as late as 3.4 ka, and a recent review in PLOS Climate works with a broad window of 4.26–3.97 thousand years BP.

No single forcing has been agreed either. Current syntheses favour a mixture of regional circulation changes, internal variability, feedbacks and longer-term trends rather than one demonstrated global trigger.

A 2024 Nature Communications synthesis assessed 109 articles and found the reported excursions averaged 325 ± 170 years. It identified no coherent global-scale excursion and no unusually significant regional one.

Drying here, wetter there, and one abandoned Mesopotamian quarter

The regional records disagree in direction as well as in timing. Individual palaeoclimate archives show drought, wetter conditions, or no clear anomaly at roughly this time, varying in onset, duration, direction and location.

The concrete case is Tell Leilan in northern Mesopotamia, where an urban and administrative quarter was abandoned around 2200 BCE. The original influential study of the site argued that an abrupt change at that date caused the abandonment, wider regional desertion, and the collapse of the Akkadian Empire.

That argument remains a causal interpretation rather than a demonstrated result, and the contribution of climate to Akkadian political change is still actively disputed.

Sources

Researched 23 Aug 2026 8 sources 2 audit passes, 1 issue open Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~-2200.

What the sources leave uncertain

The listed 2150 BCE date is not an independently supported onset date; it is at most a representative point inside a broad interval.
The ICS boundary is a formal chronostratigraphic convention, not proof that a synchronous global climate event began in that year.
Published records labeled 4.2 ka begin as early as 4.6 ka and end as late as 3.4 ka, indicating substantial chronological heterogeneity.
The causal contribution of climate to Akkadian, Egyptian, Harappan, and Chinese political changes remains actively disputed.