Decadal attribution of historic temperature and ocean heat content change to anthropogenic emissions

TL;DR

This paper introduces a novel method to attribute historical temperature and ocean heat content changes to human activities, providing insights into the roles of greenhouse gases and aerosols over the past century.

Contribution

It develops an alternative radiative forcing estimation method using observed data and kernels, enabling independent assessment of aerosol effects and decadal contributions to climate change.

Findings

Aerosols had a cooling effect in the early 20th century.

Recent temperature rise is mainly due to emissions in the last two decades.

Ocean heat content is influenced more by earlier decades.

Abstract

We present an alternative method of calculating the historical effective radiative forcing using the observed temperature record and a kernel based on the CMIP5 temperature response. This estimate is the effective radiative forcing time series that the average climate model would need to simulate the observed global mean surface temperature anomalies. We further infer the anthropogenic aerosols radiative forcing as a residual using the better-known greenhouse gas radiative forcing. This allows an independent estimate of anthropogenic aerosol radiative forcing, which suggests a cooling influence due to aerosols in the early part of the 20th century. The temporal kernels are also used to calculate decadal contributions from the dominant forcing agents to present day temperature, ocean heat content, and thermosteric sea level rise. The current global mean temperature anomaly is dominated by emissions in the past two decades, while current ocean heat content is more strongly affected by earlier decades.