Atacama Desert Climate Change Over Millions of Years
This guide explains how the Atacama Desert’s climate has transformed over millions of years, from a relatively moist landscape to the hyper-arid expanse we see today. You’ll learn the key geological and atmospheric drivers, the timeline of major shifts, and how scientists reconstruct this history. No special equipment is needed—just a basic understanding of geology and climate.
What You’ll Need
- A basic grasp of geological time periods (e.g., Miocene, Pliocene)
- Familiarity with terms like aridity, uplift, and ocean currents
- Access to a timeline or chart of the Cenozoic Era (optional but helpful)
Step-by-Step
- Start with the present-day baseline. The Atacama is the driest non-polar desert on Earth, with some areas receiving less than 1 mm of rain per year. Its aridity is due to a combination of the cold Humboldt Current, the rain shadow of the Andes, and a persistent high-pressure system over the southeast Pacific.
- Go back to the Cretaceous–Paleogene boundary (about 66 million years ago). At this time, the region was much wetter, with evidence of river systems and lush vegetation. The Andes were still low, and the Pacific Ocean influenced the climate more directly.
- Trace the Andean uplift (starting ~25 million years ago). As the Nazca Plate subducted beneath South America, the Andes rose. This uplift progressively blocked moisture from the Atlantic, creating a rain shadow that dried the western slopes. The uplift accelerated in the late Miocene (about 10–5 million years ago), intensifying aridity.
- Consider the onset of the Humboldt Current (about 15–10 million years ago). The cold, northward-flowing current brought cooler sea-surface temperatures, which reduced evaporation and precipitation along the coast. This further dried the region and contributed to the formation of coastal fog (camanchaca).
- Look at the Miocene–Pliocene transition (about 5–3 million years ago). Global cooling and the expansion of Antarctic ice sheets led to a drop in sea levels and a shift in atmospheric circulation. The Atacama experienced a significant aridification pulse, with evidence of increased salt flat formation and decreased river flow.
- Examine the Pleistocene glacial cycles (2.6 million to 11,700 years ago). During glacial periods, the climate was cooler and slightly wetter, with increased precipitation in the high Andes, but the desert floor remained hyper-arid. Interglacials were warmer and drier, similar to today.
- Review the Holocene (last 11,700 years). The early Holocene saw a wet phase (about 9,000–4,000 years ago) with increased rainfall and lake formation in the Altiplano, but the Atacama itself remained arid. Since then, aridity has intensified, with the current hyper-arid conditions established around 2,000–1,000 years ago.
- Synthesize the timeline. The Atacama’s climate evolved from humid in the Paleogene, to semi-arid in the Miocene, to hyper-arid in the Pliocene–Pleistocene, with minor wetter pulses during glacial and early Holocene periods. The primary drivers were Andean uplift, the Humboldt Current, and global climate shifts.
Common Mistakes
- Attributing all aridity to the Andes. While the rain shadow is crucial, the Humboldt Current and high-pressure system are equally important. The desert would not be as dry without all three.
- Assuming the desert has always been dry. Fossil evidence and paleosol studies show that the Atacama was periodically wet, with forests and lakes, especially in the Eocene and early Miocene.
- Overlooking the role of global climate. The expansion of Antarctic ice and changes in ocean circulation had global effects that also impacted the Atacama, not just local tectonics.
- Confusing the timing of uplift. The Andes rose in stages, not all at once. The main aridification pulse occurred after the late Miocene uplift, not during the initial uplift.
Tips
- Use a timeline. Visualizing the Cenozoic era helps you place events in order. Many online resources offer free geological time charts.
- Look for paleoclimate proxies. Scientists use sediment cores, fossilized diatoms, and oxygen isotopes to reconstruct past climates. Understanding these proxies helps you evaluate evidence.
- Compare with other deserts. The Atacama is often compared to the Namib Desert, which also sits on a west coast with a cold current. This comparison highlights the role of ocean currents.
- Remember that climate change is gradual. The shifts occurred over millions of years, not suddenly. Look for long-term trends rather than single events.
Troubleshooting
- If you’re confused about the rain shadow effect: Visualize moist air from the Atlantic rising over the Andes, cooling, and losing moisture as rain on the eastern slopes. The descending air on the western side is dry and warm, creating a desert.
- If you can’t find data on ancient rainfall: Check scientific papers on paleoclimate reconstructions. They often use indicators like fossilized root systems or salt deposits to infer aridity.
- If you’re unsure about the timing of the Humboldt Current: Note that it formed after the opening of the Drake Passage and the development of the Antarctic Circumpolar Current, which occurred around 30–15 million years ago. The current’s full influence on the Atacama came later.
- If you’re mixing up glacial and interglacial periods: Remember that glacial periods (ice ages) were cooler and slightly wetter in the Atacama, but still arid. Interglacials (like today) are warmer and drier.
Frequently Asked Questions
How long has the Atacama been a desert?
The Atacama has been arid for at least 15 million years, but hyper-arid conditions (less than 5 mm of rain per year) developed around 5–3 million years ago. Some areas may have been hyper-arid for 10 million years.
Was the Atacama ever green?
Yes, during the Paleogene (66–23 million years ago), the region had forests and rivers. Even in the Miocene, there were wetter periods with savannas and lakes.
What caused the Atacama to dry out?
The combination of the Andes rain shadow, the cold Humboldt Current, and a stable high-pressure system. Global cooling and the expansion of Antarctic ice also contributed.
Did the Atacama ever have rain regularly?
In the early Holocene (around 9,000–4,000 years ago), there were periods of increased rainfall, but it was still arid. Regular rainfall like in a tropical climate has not occurred for millions of years.
How do scientists know the past climate?
They use sediment cores, fossilized diatoms, oxygen isotopes in carbonate deposits, and ancient soil formations. These proxies provide clues about temperature and precipitation.
Could the Atacama become wetter in the future?
Climate models suggest that global warming could increase rainfall in some parts of the Atacama due to changes in atmospheric circulation, but the overall hyper-arid core is likely to remain dry.
Related
Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.