Research has shown climate change in the American West since 11,000 years ago

People often say that Phoenix is ​​dry; Seattle has always been wet; and San Francisco was always foggy. But “always” is a strong word.

A study from the University of California, Davis, combined the climate in the Western United States during the short period of Earth’s history – the Holocene Era, which extends from today to 11,000 years ago. This look at the true Old West shows that the hallmarks of California’s climate – the misty beaches that gave rise to the giant redwoods, the rising seas that led to fishing, the hot summers and cold winters – started around the age of 4,000 ago.

It also describes when the Pacific Northwest is warm and dry and the Southwest is warm and wet.

The uneducated age: the present

It was published in Old weather, the study provides a basis from which the modern climate change in the region can be considered. It also sheds light on a small geological study—currently, the Holocene.

“We kept looking for this paper, and it didn’t exist,” said lead author Hannah Palmer, who recently received her Ph.D. from the UC Davis Department of Earth Sciences. “There are many records of past conditions for the same place, but no one has put them all together to understand the big picture. So we decided to write it.”

The authors analyzed more than 40 published studies, examining the interaction between soil and temperature, hydroclimate and fire activity in three 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 oceans, a warm and dry Pacific Northwest, a warm and wet Southwest and less firework.
• By the Middle Holocene (8,200-4,200 years ago), this pattern reversed: The oceans cooled, the Pacific Northwest became cooler and wetter, and the Southwest became drier.
• The Late Holocene (4,200 years ago-present) was the period of greatest climate change. It shows when the “modern” conditions and temperatures are established. The study noted a significant interval of fire activity over the past two centuries that was linked to human activity.

An unprecedented gap

The study also considers the impact of humans on environmental changes during that time, noting that the colonial era (1850-present) represents an unprecedented environmental gap in the climate record.

“People have been living here throughout the Holocene,” Palmer said. “They were influenced by the environment, and they influenced the environment, especially in the past centuries. This paper shows how push and pull has changed over the last 11,000 years.”

Different responses

“Sometimes people point to recent rain or cold weather as evidence of climate change,” said study author Veronica Padilla Vriesman, a Ph.D. who graduated from UC Davis Department of Earth and Planetary Sciences. “This study illustrates how different regions have responded differently to global climate change. This long-term perspective helps us better understand the historical landscape of the American West and how it may respond moving forward.”

The research is the result of a seminar on the Holocene period led by Tessa Hill, a professor in the Department of Earth and Earth Sciences and Assistant Vice President for Social and Interdisciplinary Studies. Additional co-authors include Caitlin Livsey and Carina Fish. All authors are part of Hill’s Ocean Climate Lab at the UC Davis Bodega Marine Laboratory in the Department of Earth and Planetary Sciences.

“Climate records from the Holocene provide an excellent window into the context of human-induced climate change,” Hill said. “They allow us to understand areas that may be more or less likely to change in the future.”