Quantifying the Occurrence of Record Hot years Through Normalized Warming Trends
We have analyzed four observational datasets and one observation-based dataset of global surface temperature to understand temperature trends, normalized trends (i.e., the original trends divided by the year-to-year variability of temperature), and their relationships with the occurrence of record-breaking hot years. We then use these results to evaluate 32 Earth system models (17 used in the previous international climate Assessment Report (CMIP5) and 15 in the current report (CMIP6)) - including the DOE model E3SM-1-0 and E3SM-1-1.
Our results enable the quantification of record hot year occurrence through normalized warming trends and provide new metrics for model evaluation and improvement. Our University released a news story, which was featured by the World Economic Forum and selected as "AMS News You Can Use" and “AGU in the News”.
Surface air temperature trends and extreme hot events are of global concern and they are related at a given location. However, it remains unknown whether this dependence is relevant to the comparison of extreme hot event occurrences over different regions. Based on observational data, 17 CMIP5 models and 15 CMIP6 models (including DOE E3SM-1-0 and E3SM-1-1), we found that: compared with the original temperature trends showing Arctic amplification, the normalized trends (i.e., the original trends divided by the year-to-year variability of temperature) show a tropical amplification over land; occurrence of record hot years in different latitudes is better correlated with normalized, rather than the original, temperature trends; Earth system models’ correlations between normalized trends and record-breaking events are as high over land as over the ocean, unlike in observations. Our results enable the quantification of record hot year occurrence through normalized warming trends and provide new metrics for model evaluation and improvement.
The University of Arizona released a news story on 6/2/2021 (https://news.arizona.edu/story/record-breaking-temperatures-more-likely-populated-tropics), which was featured on the front page of World Economic Forum (https://www.weforum.org/agenda/2021/06/tropics-record-breaking-temperatures-climate-change-environment) and was selected by the two most relevant professional/scientific societies (AGU and AMS) as "AMS News You Can Use" and “AGU in the News.”