Study shows Earth warming at much faster rate
It’s not just humans who track long-term trends in the weather. The history of our planet’s climate is recorded by nature herself — written in tree rings and Arctic ices, corals and deep ocean sediments.
Each of these records tell only a small piece of Earth’s climate story, but together they form a sprawling and complex novel of the past, helping scientists better understand how and why certain trends emerge, and foreshadowing what we might expect Earth’s climate to look like in the future.
In 2017, an international consortium known as PAGES (Past Global Changes) published its largest database yet of climate temperature records, stretching from the present day back 2,000 years, by the start of the Common Era.
The data points were recorded by trees, ice, lake and ocean sediment, and mineral deposits in caves, as well as by humans. They come from 648 locations around the globe, including all the continents and major ocean basins.
Scientists have only just begun to mine the PAGES data for insights into trends of the past, but already they have made some intriguing discoveries.
After analyzing 2,000 years of detailed records kept by both nature and humans, researchers have discovered that the average surface temperature of Earth has warmed faster in the past few decades than it did in the previous 1,900 years, proving once again that the current warming the planet is experiencing is unprecedented in the past two millenniums. The data also suggests that the warming in the most recent decades has been uniform across all regions of the planet, a phenomenon that scientists say has not been seen in the past 2,000 years.
A third study based on the same data shows that for most of the Common Era, volcanic events have been the primary driver of global temperature change. Today, greenhouse gases in the atmosphere play a more dominant role in driving global temperature, the authors said.
Raphael Neukom, a paleoclimatologist at the University of Bern in Switzerland, who led two of the three studies, said the trio of papers all suggest the same thing: “Climate variability in the preindustrial period is totally different from what we observe today.”
Some of the findings contradict, or at least complicate, previously held truths.
For example, in the Nature paper, Neukom and his colleagues use the PAGES data to poke holes in the widely accepted theory that periods of cooling and warming over the past 2,000 years affected the globe uniformly. Perhaps the most well-known of these epochs is what scientists call the Little Ice Age — a cool period that persisted from the 16th century to the 19th century. Similarly, the Medieval Climate Anomaly is known as a warm, dry period that lasted from AD 950 to 1250.
“The traditional understanding was that climates over these periods were globally coherent,” said Nathan Steiger, a paleoclimatologist at Columbia University who worked on the paper. “When we looked at the PAGES data, we found they are not as coherent as we thought.”
After analyzing the data using multiple statistical methods, the authors found that what were previously assumed to be global trends in temperature were actually regional trends for all known climate epochs except the one we find ourselves in today.
For example, though the Little Ice Age did represent a global cooling, some parts of the planet were coldest during the mid19th century, while others had their coldest weather several centuries earlier.
But when the authors ran the same analysis for our current climatic epoch, known as the Contemporary Warm Period, they found that peak temperatures have been seen across all regions of the globe except Antarctica within the past 51 years.
This uniformity in peak temperatures was unprecedented in the past 2,000 years.
The authors did not look into what might be causing this unique phenomenon, because, as Steiger said, it wasn’t necessary.
“There is a lot of evidence that the Contemporary Warming Period is human caused,” he said. “We don’t need the paleolithic climate data to address that.”