Skip to main content
College of Computer, Mathematical, and Natural Sciences
  • Undergraduate
  • Graduate
  • Alumni & Friends
  • Faculty & Staff
  • Support CMNS

See Also...

  • About CMNS
  • Departments
  • Research
  • News & Events
Share
News & Events
  • News
    • Coronavirus Stories
    • New Study Identifies Causes of Multidecadal Climate Changes
  • Odyssey Magazine
  • Events
  • Newsletters

Related Stories

Revising the History of Big, Climate-Altering Volcanic Eruptions
New method, co-developed at UMD, refines the 2,600-year history of large eruptions that inject planet-cooling particles into the stratosphere.
Saltier Waterways are Creating Dangerous “Chemical Cocktails”
New UMD-led research highlights the need for better regulation and pollution management strategies.
North American Waterways are Becoming Saltier and More Alkaline
New UMD-led research highlights the need for better regulation of road salt, fertilizers and other salty compounds.
  • Home
  • News & Events
  • News
  • New Study Identifies Causes of Multidecadal Climate Changes

New Study Identifies Causes of Multidecadal Climate Changes

UMD geologist contributes to analysis that suggests current climate models can accurately predict climate warming several decades into the future

A new reconstruction of global average surface temperature change over the past 2,000 years has identified the main causes for decade-scale climate changes. The analysis suggests that Earth’s current warming rate, caused by human greenhouse gas emissions, is higher than any warming rate observed previously. The researchers also found that airborne particles from volcanic eruptions were primarily responsible for several brief episodes of global cooling prior to the Industrial Revolution of the mid-19thcentury.

Global climate change threatens the continued existence of glaciers, such as the Aletsch Glacier in Switzerland, photographed in July, 2015. Image credit: Anupma Gupta/Michael Evans (Click image to download hi-res version.)The new temperature reconstruction also largely agrees with climate model simulations of the same time period. The researchers found agreement for temperature changes caused by identifiable factors, such as volcanic aerosols and greenhouse gases, as well as for random fluctuations in climate that take place on the same timescales. This suggests that current climate models accurately represent the contributions of various influences on global climate change—and are capable of correctly predicting future climate warming.

The research team—19 members of the Past Global Changes (PAGES) project, including University of Maryland Geology Professor Michael Evans—used seven different statistical methods to perform the reconstruction. The results are published online July 24, 2019, in the journal Nature Geoscience.

“Our reconstructions look like the ‘hockey stick’ diagram of global temperature change that was first reconstructed more than two decades ago,” said Evans, who is also co-chair of PAGES and has a joint appointment at UMD’s Earth System Science Interdisciplinary Center (ESSIC). “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 new 2,000-year reconstruction improves on previous efforts by using the most detailed and comprehensive database of its kind yet assembled. This dataset, painstakingly compiled by PAGES researchers, includes nearly 700 separate publicly available records from sources that contain indicators of past temperatures, such as long-lived trees, reef-building corals, ice cores, and marine and lake sediments. The data are sourced from all of Earth’s continental regions and major ocean basins.

By comparing the new reconstructions with existing climate simulations generated using the Coupled Model Intercomparison Project 5 (CMIP5) climate models, the PAGES research team was able to determine the relative contributions of several influences on global temperatures over time. These included natural influences, such as fluctuations in solar heating and the cooling effect of particles ejected by volcanic eruptions, as well as the human-caused influence of greenhouse gas emissions. 

This graph shows global mean rates of temperature change over the last 2,000 years, as determined by a new reconstruction based on climate proxy data. Red denotes temperature increases while blue denotes temperature decreases. The green line shows the maximum expected warming rate without human influence; the dashed orange line signifies the ability of climate models to simulate this natural upper limit. The black line indicates average global as determined by direct measurements since the Industrial Revolution. Image credit: University of Bern (Click image to download hi-res version.)The results suggest that volcanic activity was responsible for variations before about 1850. After that, greenhouse gases became the dominant influence on global climate. By removing these influences in their analysis, the researchers also identified the magnitude of the random changes that cannot be traced to a specific cause. The team’s data-based reconstructions also agreed with model simulations when evaluating these random changes.

“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,” Evans added.

This agreement between the researchers’ data-based reconstructions and the CMIP5 simulations suggests that existing climate models can accurately predict future global temperature change over the next few decades, according to Evans. However, these simulations depend heavily on the choices that humans make in the future, which is very difficult to predict, Evans added. 

“The uncertainty in the influence of human activities is not so large when looking forward only a few decades,” Evans said. “But in the longer term, the choices we make for our energy sources and how much carbon these sources emit really matter.”

###

The research paper, “Consistent multi-decadal variability in global temperature reconstructions and simulations over the Common Era,” the PAGES 2k Consortium (Raphael Neukom, Luis Barboza, Michael Erb, Feng Shi, Julien Emile-Geay, Michael Evans, Jörg Franke, Darrell Kaufman, Lucie Lücke, Kira Rehfeld, Andrew Schurer, Feng Zhu, Stefan Brönnimann, Gregory Hakim, Benjamin Henley, Fredrik Charpentier Ljungqvist, Nicholas McKay, Veronika Valler and Lucien von Gunten), was published in the journal Nature Geoscienceon July 24, 2019.

This work was supported by the National Science Foundation, the Swiss Academy of Sciences, the Swiss National Science Foundation (Award No. PZ00P2_154802), the German Research Foundation (Award No. RE3994-2/1), the European Union (Award No. 787574), the National Natural Science Foundation of China (Award Nos. 41877440, 41430531, and 41690114), and the UK Natural Environment Research Council (Award No. NE/P006752/1). The content of this article does not necessarily reflect the views of these organizations.

Media Relations Contacts: Matthew Wright, 301-405-9267, mewright@umd.edu 

University of Maryland
College of Computer, Mathematical, and Natural Sciences
2300 Symons Hall
College Park, MD 20742
www.cmns.umd.edu
@UMDscience

About the College of Computer, Mathematical, and Natural Sciences

The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million.

Date: 
Wednesday, July 24, 2019
Michael Evans Climate Change Climate Reconstruction
Research News Faculty Geology Earth System Science Interdisciplinary Center
  • Contact Us
  • Careers & Recruiting
  • Odyssey Magazine
  • CMNS Photo Library
  • UMD Home
  • UMD Directory
  • Privacy Notice
  • Web Accessibility
Stay Connected:
  • Facebook logo and link to CMNS Facebook account
  • Instagram logo and link to CMNS Instagram account
  • LinkedIn Logo and link to CMNS LinkedIn group
  • RSS icon and link to CMNS RSS feed
  • Twitter Logo and link to CMNS Twitter account
  • YouTube Logo and link to CMNS YouTube account

The College of Computer,
Mathematical, and Natural Sciences

2300 Symons Hall, University of Maryland
College Park, MD 20742
p 301.405.2080 • f 301.314.9949
Webmaster