A consideration of the forcings of climate change using simple physics - Grantham Discussion Paper 2

Author: Dr Arnaud Czaja
Published: April 2011

This paper aims to show how we can comprehend the size of anthropogenic forcing of our climate using simple physics.

Overview

This Discussion Paper is motivated by the recent debates about the “truth” of climate change research and the shift in public opinion about whether man made climate change is actually happening or not. It occurred to me that discussions were always centred on either instrumental records from the late 19th Century onwards, or past climate reconstructions from proxy data like tree rings, or climate models’ predictions. All these require training to be appreciated and discussed. Any measurement comes with uncertainty, any proxy data comes with a theoretical model linking it to the climate variable it is supposed to measure, and of course all climate models, however complex, come with simplifications. This state of affairs is very unfortunate because it takes away from people the freedom to understand for themselves the scientific issues when these appear to be solely understandable by experts in the field in question.

It is the goal of this Discussion Paper to show that one does not need to have a PhD degree in Statistics or Physics to grasp the problem. One does not need to go into the fine detail of the physical mechanisms or how a particular time series (e.g. for global mean temperature) is constructed to realize how large is the anthropogenic forcingof the climate. It is simply a matter of putting numbers on the size of this well understood effect using well established and straightforward physics.

The main idea of this paper is really just this: rather than focus on the projections of climate change at the end of the century resulting from combustion of fossil fuels, let us simply pause and reflect on the magnitude of the climate forcing that this causes.

What we can be sure of is that global warming—expressed, for example, through higher sea and land surface temperatures—is affecting the outcomes, increasing the incidence and severity of the droughts, floods and other extreme weather events that these drivers produce.

Contents

1. Motivation 
2. Anthropogenic forcing 
3. Cryospheric melting and sea level rise 
4. Planetary albedo and infrared radiation
5. Limitations of the previous
6. Conclusions