Australia: The Land Where Time Began

A biography of the Australian continent 

Global Warming Hiatus – Distinct Energy Budgets for Anthropogenic and Natural Changes

According to Xie et al. it is now possible to close (IPCC climate change, 2013) the energy budget of the Earth for the last 4 decades, and it supports the forcing by anthropogenic greenhouse emissions as the cause of climate warming. The closure, however, depends on an unrealistically large increase of aerosol cooling (Murphy, 2013) during the so-called global warming hiatus since the late 1990s (Murphy et al., 2009; Church et al., 2014) that was partially due to cooling of the tropical Pacific Ocean (Meehl et al., 2011; Kosaka & Xie, 2013; England et al., 2014). Xie et al. say the assumption is that the same climate feedback applies to anthropogenic warming as well as natural cooling. In this paper Xie et al. present the results of their analysis of climate model simulations with and without increases of anthropogenic gas concentrations, which show that radiation at the top of the atmosphere and mean global surface temperature are coupled much less tightly for natural decadal variability than for response induced by greenhouse gas, which implies a distinct climate feedback between anthropogenic warming and natural variability. Also, Xie et al. identified a difference in phase between radiation at the top of the atmosphere and global mean surface temperature such that the uptake of heat by the ocean had a tendency to slow down during the surface warming hiatus. Xie et al. found that this result is broadly consistent with observations, though it deviates from existing energy theory. Xie et al. say their study highlights the importance of developing metrics that distinguish between anthropogenic change and natural variations in order to attribute climate variability and to estimate climate sensitivity of climate from observations.

Sources & Further reading

1. Xie, S.-P., Y. Kosaka and Y. M. Okumura (2016). "Distinct energy budgets for anthropogenic and natural changes during global warming hiatus." Nature Geosci 9(1): 29-33.