Historical global land surface air apparent temperature and its future changes based on CMIP6 projections

Area of Science:

• Climate Science
• Earth System Science
• Environmental Science

Background:

• Global surface air temperature (SAT) and apparent temperature (APT) trends are crucial for understanding climate change impacts.
• Projecting future warming requires analyzing different socioeconomic pathways (SSPs) and global warming thresholds.
• Comparing climate model outputs with observational data is essential for validating climate projections.

Purpose of the Study:

• To systematically analyze the warming magnitudes and spatial distribution of global land surface air apparent temperature (APT) under various Shared Socioeconomic Pathways (SSPs).
• To project future APT warming by the mid and late 21st century, considering 1.5°C and 2.0°C global warming thresholds.
• To compare the warming trends of APT and SAT and assess the vulnerability of populations to enhanced warming.

Main Methods:

• Systematic analysis of warming magnitudes and spatial distribution of global land surface air apparent temperature (APT).
• Comparison of in-situ observations, extended reanalysis, and Coupled Model Intercomparison Project Phase 6 (CMIP6) model outputs.
• Projection of APT warming under different Shared Socioeconomic Pathways (SSPs) and global warming thresholds (1.5°C and 2.0°C).

Main Results:

• CMIP6 multi-model ensemble mean (MME) shows good agreement with observed climatological mean and temporal variations for SAT and APT over the past 100 years.
• Global surface APT warming over land is significantly larger than SAT warming, with similar spatial gradients under SSP2-4.5 and SSP5-8.5.
• Under 1.5°C and 2.0°C global warming thresholds, global mean APT is projected to be 1.9°C and 2.7°C, respectively. By the end of the 21st century, APT is projected to increase by 3.9°C under SSP2-4.5 and 6.7°C under SSP5-8.5 relative to pre-industrial levels.

Conclusions:

• The warming trend of global surface APT over land is significantly larger than that of SAT, making populations in low latitudes more vulnerable to enhanced warming.
• Under SSP5-8.5, the probability and intensity of extreme warm events for both land SAT and APT are projected to be remarkably higher than under SSP2-4.5.
• Urgent regulation of greenhouse gas emissions is implied to reduce future thermal discomfort and mitigate extreme heat events.