Greenhouse gases have dominated climate change since about 1850. Members of the Past Global Changes (PAGES) project have reconstructed the global record of average surface temperatures over the past 2,000 years. Based on this work, the experts were able to identify the primary drivers of climate change for each of the last 200 decades.
The research suggests that the Earth is currently warming at the highest rate ever observed as a result of greenhouse gases. The study also shows that brief periods of global cooling prior to the Industrial Revolution were mainly driven by airborne particles associated with volcanic activity.
The temperature reconstruction largely corroborates climate model simulations of the same time period. This indicates that climate models accurately represent the contributions of various influences on climate change and are reliable predictors of future warming.
PAGES co-chair Professor Michael Evans is a geologist at the University of Maryland.
“Our reconstructions look like the ‘hockey stick’ diagram of global temperature change that was first reconstructed more than two decades ago,” said Professor Evans. “Thanks to the work of the PAGES community, we have much more data now. The results were consistent regardless of how we created the reconstructions or which randomly chosen subset of input data we used.”
The PAGES researchers compiled the most detailed database of its kind for the temperature reconstruction, including nearly 700 records of climate indicators from across the globe such as old trees, reef-building corals, ice cores, and marine and lake sediments.
Based on seven different statistical methods, the experts found that volcanic activity was responsible for climate variations up until about 1850. After that, greenhouse gases became the dominant influence on the global climate.
By removing these influences, the study authors pinpointed the magnitude of climate fluctuations that cannot be traced to a specific cause. Their estimates of these random changes strongly correspond with climate model calculations.
“This makes us more confident that our reconstructions are realistic and, in turn, that the climate models are simulating past and future climate warming faithfully,” said Professor Evans. He pointed out that the global temperature change over the next few decades will rely heavily on the choices that humans make, which is very difficult to predict.
“The uncertainty in the influence of human activities is not so large when looking forward only a few decades. But in the longer term, the choices we make for our energy sources and how much carbon these sources emit really matter.”
The study is published in the journal Nature Geoscience.
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Image Credit: Anupma Gupta/Michael Evans