Jun 1, 2016

Multi-model attribution of upper-ocean temperature changes using an isothermal approach

Evan Weller, Seung-Ki Min, Matthew D. Palmer, Donghyun Lee, Bo Young Yim, Sang-Wook Yeh
Scientific Reports
  • States that both air-sea heat exchanges and changes in ocean advection have contributed to observed upper-ocean (i.e. ~200 m) warming most evident in the late-twentieth century
  • States, however, that it is predominantly via changes in air-sea heat fluxes that human-induced climate forcings, such as increasing greenhouse gases, and other natural factors such as volcanic aerosols, have influenced global ocean heat content
  • The present study builds on previous work using two different indicators of upper-ocean temperature changes for the detection of both anthropogenic and natural external climate forcings
  • Compares mean temperatures above a fixed isotherm with the more widely adopted approach of using a fixed depth
  • Presents the first multi-model ensemble detection and attribution analysis using the fixed isotherm approach to robustly detect both anthropogenic and natural external influences on upper-ocean temperatures
  • States that although contributions from multidecadal natural variability cannot be fully removed, both the large multi-model ensemble size and properties of the isotherm analysis reduce internal variability of the ocean, resulting in better observation-model comparison of temperature changes since the 1950s
  • Shows that the high temporal resolution afforded by the isotherm analysis is required to detect natural external influences such as volcanic cooling events in the upper-ocean because the radiative effect of volcanic forcings is short-lived