High Carbon dioxide Levels Linked to Warmer Tropical Oceans During Pliocene

A new study shows that tropics are affected by greenhouse gas-driven global warming. The research was based on reconstruction of climate during Pliocene epoch.

Past temperature records suggest that tropical regions experience stable temperatures and that carbon dioxide-driven warming affects Polar and mid-to-high latitudes.

The new study by researchers at the University of Bristol's Cabot Institute and their colleagues said that tropical areas have seen a rise in temperature during ancient times.

According to the study team, tropical sea surface temperatures were warmer during the early-to-mid Pliocene, which lasted around 5 to 3 million years ago.

CO2 concentrations during the Pliocene were around 400 parts per million, which was the highest level of carbon dioxide during the last five million years.

Researchers found that the hottest parts of the tropical oceans were around two or three degree Celsius warmer during the early-to-mid Pliocene than it is today.

"These results confirm what climate models have long predicted - that although greenhouse gases cause greater warming at the poles they also cause warming in the tropics.  Such findings indicate that few places on Earth will be immune to global warming and that the tropics will likely experience associated climate impacts, such as increased tropical storm intensity," said Professor Richard Pancost Project leader and Director of the Cabot Institute.

For the study, researchers focused on the temperature records of South China Sea, which is at the edge of the West Pacific Warm Pool (WPWP). The team used geochemical data to estimate the temperature of the region in the past.

According to the researchers, certain tools used to reconstructing past climate might not be accurate and need to be re-evaluated.

"It's challenging to reconstruct the temperatures of the ocean many millions of years ago, and each of the tools we use has its own set of limitations.  That is why we have used a combination of approaches in this investigation.  We have shown that two different approaches agree - but a third approach agrees only if we make some assumptions about how the magnesium and calcium content of seawater has changed over the past 5 million years.  That is an assumption that now needs to be tested," Charlotte O'Brien, said in a news release.

The current study supports earlier research that has suggested that any variation in global temperatures due to rising greenhouse gases will affect tropics long before the poles.

The study is published in the journal Nature Geoscience and is funded by UK's Natural Environment Research Council.