Rising CO2 will cause rapid climate change in the tropical Andes

A new study examining ancient temperatures and rainfall patterns in the tropical Andes of South America has revealed how climate history in this region over the past 16,000 years was influenced by carbon dioxide levels and ocean currents linked to global climate events.

The study, led by researchers from Brown University, provides the first high-resolution temperature record for the tropical Andes covering the last 16,000 years. These findings could help scientists better predict and address future climate impacts in tropical regions.

“Tropical South America is a center of biodiversity and is under pressure from ongoing climate change,” wrote the researchers.

“Understanding tropical South America’s climate history can provide valuable insight into the water cycle, ecosystems, and future climate change, yet past temperature changes are not well-known.”

Tropical Andes climate and global changes

Study first author Boyang Zhao is a scientist in Brown’s Department of Earth, Environmental and Planetary Sciences.

“Usually when we study climate change in the past, we emphasize the Northern Hemisphere or Southern Hemisphere because of the outsized role they play in affecting climates all over the globe,” said Zhao. 

“One of the biggest questions we are getting at is what are the driving factors behind temperature history in this part of the tropics, so that we can begin to potentially apply that data and knowledge to other tropical regions.”

Beyond its implications for future climate studies, this research offers a distinct perspective on how different and distant regions of the world can influence temperatures and weather patterns elsewhere, underscoring the connection between regional climates and global climate changes.

“Our evidence here suggests that temperatures in this region of the world are more influenced by the Southern Hemisphere – so places like Antarctica,” Zhao said.

Temperature patterns in the tropical Andes 

The researchers focused on sediment samples from Laguna Llaviucu, a lake in Ecuador’s Cajas National Park. The temperature patterns they identified in the tropical Andes were closely linked to global climate events that caused the planet’s temperatures to rise and fall over the past 16,000 years.

The evidence indicated that the primary factor driving these temperature changes was the concentration of CO2. The experts found that temperatures in the tropical Andes tracked with those in Antarctica, where temperatures are largely controlled by carbon dioxide levels. 

The data showed that between 17,000 and 14,000 years ago, temperatures in the tropical Andes rose as carbon dioxide levels increased, and remained relatively stable around 12,000 years ago when CO2 levels plateaued.

CO2 is a key driver of temperature changes 

Zhao said that the findings support previous research identifying carbon dioxide as a key driver of global temperature changes since the last Ice Age.

The study also highlighted the influence of ocean currents that move warm water from the tropics to the North Atlantic. 

During a cooling period known as the Antarctic Cold Reversal, about 14,500 years ago, this northward current strengthened, leading to more heat being transported north and cooling sea surface temperatures in the southern hemisphere. The researchers found that this cooling effect also extended to the tropical Andes.

Chemical indicators of past temperature patterns

To piece together past climate conditions, the team analyzed lipid biomarkers and hydrogen isotopes from sediment samples collected in 2009 from Laguna Llaviucu by scientist Mark Bush of the Florida Institute of Technology. 

Lipid biomarkers are chemical indicators that reveal information about past temperatures and rainfall patterns. The high-resolution data, combined with precise dating methods, enabled the researchers to develop a detailed timeline of climate changes over the last 16,000 years.

According to the researchers, this study marks the first time organic biomarkers have been used to create a quantitative climate history for tropical South America. It has traditionally been challenging to reconstruct temperatures in tropical regions.

Future research directions

The experts also noted several regional differences in temperature patterns, such as how the tropical Andes and Southeast Asia experienced cooling during certain historical periods while other regions, like Africa, did not. 

Moreover, the research illustrates how local factors might counteract the global effects of rising CO2 levels by comparing past temperature models with the sediment data.

The experts intend to continue exploring past temperature patterns in this part of the world, which has historically lacked comprehensive climate records.

“Mountain environments are some of the most sensitive regions on Earth to climate change,” said James Russell, a professor of Earth, environmental, and planetary sciences at Brown who oversaw the new research. 

“In fact, in the near future, high tropical mountains, such as the Andes, are predicted to experience a rate of warming second only to the Arctic, which is the fastest warming part of the planet.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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