People often say things like Phoenix has always been dry; Seattle has always been wet; and San Francisco has always been foggy. But “always” is a strong word.
from the Ƶ, Davis, synthesizes climate trends across the western U.S. during a relatively young period of Earth’s history — the Holocene Era, which stretches from the present day to the past 11,000 years. This look at the really Old West shows that the hallmarks of Ƶ’s climate — the foggy coastlines that gave rise to towering redwoods, the ocean upwelling that spawned productive fisheries, the warm summers and mild winters — began around 4,000 years ago.
It also reveals a time when the Pacific Northwest was warm and dry and the Southwest was warm and wet.
An understudied era: The current one
Published in Climate of the Past, a journal of the European Geosciences Union, the study provides a baseline against which modern climate change in the region can be considered. It also sheds light on a lesser-studied geological epoch — the current one, the Holocene.
“We kept looking for this paper, and it didn’t exist,” said lead author Hannah Palmer, who recently earned her Ph.D. from the UC Davis . “There are many records of past climate for a single location, but no one had put it all together to understand the big picture. So we decided to write it.”
The authors analyzed more than 40 published studies, examining the interplay among land and sea temperature, hydroclimate and fire activity across three distinct phases.
The study found:
- Compared to pre-Holocene conditions (the last glacial period), the Early Holocene (11,700-8,200 years ago) was a time of warm seas, a warm and dry Pacific Northwest, a warm and wet Southwest and fairly low fire activity.
- By the Middle Holocene (8,200-4,200 years ago), that pattern reversed: The ocean’s surface cooled, the Pacific Northwest became cool and wet, and the Southwest became drier.
- The Late Holocene (4,200 years ago-present) is the most climatically variable period. It marks a period when the “modern” climate and temperature patterns are established. The study noted a defined interval of fire activity over the past two centuries that is linked to human activity.
Unprecedented interval
The study also considered the impact of humans on environmental changes at the time, noting that the Era of Colonization (1850-present) represents an unprecedented environmental interval in the climate records.
“Humans have been living here throughout the entire Holocene,” Palmer said. “The climate impacted them, and they impacted the climate, especially in recent centuries. This paper shows how that push and pull has changed over the past 11,000 years.”