Preprints
https://doi.org/10.5194/egusphere-2024-31
https://doi.org/10.5194/egusphere-2024-31
17 Jan 2024
 | 17 Jan 2024

Elevation-dependent warming: observations, models, and energetic mechanisms

Michael P. Byrne, William R. Boos, and Shineng Hu

Abstract. Observational data and numerical models suggest that, under climate change, elevated and non-elevated land surfaces warm at different rates. Proposed drivers of this "elevation-dependent warming" (EDW) include surface albedo and water vapour feedbacks, the temperature dependence of longwave emission, and aerosols. Yet the relative importance of each proposed mechanism both regionally and at large scales is unclear, highlighting an incomplete physical understanding of EDW.

Here we use gridded observations, atmospheric reanalysis, and a range of climate model simulations to investigate EDW over the historical period across the tropics and subtropics (40° S to 40° N). Observations, reanalysis, and fully-coupled models exhibit annual-mean warming trends (1959–2014), binned by surface elevation, that are larger over elevated surfaces and broadly consistent across datasets. EDW varies by season, with stronger observed signals in boreal autumn and winter. Analysis of large ensembles of single-forcing simulations (1959–2005) suggests historical EDW is likely a forced response of the climate system rather than an artefact of internal variability, and is primarily driven by increasing greenhouse gas concentrations.

To gain quantitative insight into the mechanisms contributing to large-scale EDW, a forcing/feedback framework based on top-of-atmosphere energy balance is applied to the fully-coupled models. This framework identifies the Planck and surface albedo feedbacks as being robust drivers of EDW (i.e., enhancing warming over elevated surfaces), with energy transport by the atmospheric circulation also playing an important role. In contrast, water vapour and cloud feedbacks along with weaker radiative forcing in elevated regions oppose EDW. Implications of the results for understanding future EDW are discussed.

Michael P. Byrne, William R. Boos, and Shineng Hu

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-31', Anonymous Referee #1, 13 Feb 2024
  • RC2: 'Comment on egusphere-2024-31', Anonymous Referee #2, 13 Feb 2024
Michael P. Byrne, William R. Boos, and Shineng Hu
Michael P. Byrne, William R. Boos, and Shineng Hu

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Short summary
In this study we investigate why climate change is amplified in mountain regions, a phenomenon known as elevation-dependent warming (EDW). We examine EDW using observations and models, and assess the roles of radiative forcing vs internal variability in driving the historical signal. Using a forcing/feedback framework we also quantify for the first time the processes driving EDW on large scales. Our results have important implications for predicting future climate change in mountain regions.