The Climate Modelling Primer

Kendal McGuffie, Ann Henderson-Sellers

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118747186
• Edition: 4
• Topic: Physical Sciences
• Subtopic: Meteorology & Climatology

As a consequence of recent increased awareness of the social and political dimensions of climate, many non-specialists discover a need for information about the variety of available climate models. A Climate Modelling Primer, Fourth Edition is designed to explain the basis and mechanisms of all types of current physically-based climate models.

A thoroughly revised and updated edition, this book will assist the reader in understanding the complexities and applicabilities of today's wide range of climate models. Topics covered include the latest techniques for modelling the coupled biosphere-ocean-atmosphere system, information on current practical aspects of climate modelling and ways to evaluate and exploit the results, discussion of Earth System Models of Intermediate Complexity (EMICs), and interactive exercises based on Energy Balance Model (EBM) and the Daisyworld model. Source codes and results from a range of model types allows readers to make their own climate simulations and to view the results of the latest high resolution models. Now in full colour throughout and with the addition of cartoons to enhance student understanding the new edition of this successful textbook enables the student to tackle the difficult subject of climate modeling.

1

Why Model Climate?

‘All models are wrong, but some are useful.’ (Box and Draper 1987, p4)

‘The strongest arguments prove nothing so long as the conclusions are not verified by experience. Experimental science is the queen of sciences and the goal of all speculation.’ (Roger Bacon ca. 1214–1294)

LEARNING OBJECTIVES

After completing this chapter, you will be able to:

• recognise the many reasons for having models
• track the history of climate theory becoming fact
• list the factors affecting planetary scale climate
• explain the concept of climate feedback and give examples
• recognise the mechanisms whereby persistent and widespread life affects climate.

1.1 Introduction

This book is entitled The Climate Modelling Primer, a title that presupposes modelling to be a useful exercise, and that readers are familiar with the idea of models and the reasons for participating in modelling. We assume you are interested in building or testing models or in exploiting their results. This foundation chapter tests these assumptions by examining the important question, ‘Why model climate?’. We try to answer this question in three ways: first by looking at reasons for modelling in general; by applying a selection of these reasons to climate modelling; and then by taking a very different view of Earth’s climate, from a distant galaxy, and using this metaphorical alien climate scoping to investigate some of the fundamental ingredients of planetary climates and thus of climate models. In this opening chapter we cover a wide variety of topics quite quickly to give a sense of the wonderful breadth of climate models and their achievements. In doing this we do not define or explain in much detail because these explanations constitute the rest of this book. If you come across a concept you wish to understand better, you can locate a further description of it using the index or checking the summary of boxed material at the end of the Preface.

The characteristics of climate and hence those that climate models must try to reproduce can be thought of as a primer – or perhaps an A, B, C – as outlined in Table 1.1.

• A is for astronomy: any planet or moon with a climate is constrained by fundamental astrophysical conditions.
• B is for boundary and for biology: climate becomes interesting to model most often when it relates to living systems and where it touches boundaries.
• C is for comprehension: the reasons for constructing, operating and analysing climate models are ultimately to try to understand climate change and variability.

To encourage personal learning, we are employing an old technique that may be unexpected in this context. It is a ‘collector’s chest’. In the 18th and 19th centuries, such collector’s chests were built to hold and attractively display novel collections of scientific specimens. Many voyages of discovery included natural scientists who would have carried their rare and curious samples home in such sturdy wooden chests. Our example (Figure 1.1), the Macquarie collector’s chest, was almost certainly intended as a special presentation piece to celebrate the colony of New South Wales once the Governor, to whom it was given, arrived back in the UK. If you are not keen on stuffed birds and old seaweed, another type of treasure collection still to be found in some homes is the heritage quilt, and a still more modern version is scrapbooking.

Table 1.1 A primer, or ‘A, B, C’, of climate modelling

A, B, C	Aspects of climate modelling
A: Astronomy	Astrophysical attributes – orbit, atmosphere, radiative budget, existence/prevalence of water …
B: Biology and boundaries	Life and climate, surface conditions, volcanic activity …
C: Comprehension	Prediction, testing theories, raising questions, bracketing outcomes, directing data collection, disciplining policy …

Figure 1.1 The Macquarie collector’s chest. Collections like these were for display and specifically designed as attractive and persuasive depictions of unusual places.

Source: Mitchell Library. State Library of NSW – XR 69.

Table 1.2 The Primer authors’ climate modelling treasures, following the items in the old collector’s chest shown in Figure 1.1

Type	Old chest	Authors’ treasure collection
Visual	Paintings	The cartoon by Cathy Wilcox illustrating the CMP authors’ research on Amazonian deforestation that was published on the front page of our local newspaper
Personal experience	Butterflies, beetles, etc.	Results from the Model Evaluation Consortium for Climate Assessment intercomparisons created in 1992. These were probably the first global climate model intercomparisons (e.g. videos on CD in CMP2)
Oceans	Algae and seaweeds	Movie featuring the ocean near where we live – ‘Finding Nemo’ (2003 and in 3D in 2012), especially for its depiction of the East Australian Current – the one that carries the turtles
Change behaviour	Exotic stuffed birds	Photos from visits to the melting Mont Blanc glacier when the authors lived in Geneva
Pretty things	Arrangements of sea-shells	Art work on the cover of The Future of the World’s Climate, a book the CMP authors edited in 2011–12. Both the art itself and the quotation it contains
How it works	Artefacts	An antiquarian water band spectroscope that KMcG bought for AH-S’s birthday that shows water vapour absorption bands (an in-your-hand greenhouse demonstrator)

Climate Modelling Primer (CMP) readers are welcome to use whichever analogy they prefer: collector’s chest, heirloom or heritage quilt or digital scrapbook. The goal is that, as you read the Primer, you collect climate-modelling treasures: a small set of illustrations that you find persuasive, pretty and memorable. These can be real objects such as diagrams, papers, cartoons, printouts, etc. or virtual links as in our example at the end of this chapter (see Table 1.11). The point of the collection is to assist recall of aspects of climate modelling that you may find difficult to understand or perhaps that you find challenging to explain. Each collection is, therefore, rather personal, but not private, because like Governor Lachlan Macquarie’s chest, it will contain amazing illustrations selected for explaining, remembering and sharing. To begin your great treasure collection, we offer you the tangible version of ours (the authors’) in Table 1.2 and later we introduce our e-chest version.

At the end of this chapter, we give another of our collection examples and then each Primer reader is on their own to collect the best (most interesting) items for themselves.

1.2 What is a climate model?

In the broadest sense, models are for learning about the world (in our case, the climate) and the learning takes place in the construction and the manipulation of the model, as anyone who has watched a child build idealised houses or spaceships with Lego™, or built with it themselves, will know. Climate models are, likewise, idealised representations of a complicated and complex reality through which our understanding of the climate has significantly expanded. All models involve some ignoring, distorting and approximating, but gradually they allow us to build understanding of the system being modelled. A child’s Lego construction typically contains the essential elements of the real object, improves with attention to detail, helps them understand the real world, but is never confused with the real thing.

In the past few decades, the boundaries of the climate system that we are modelling have become much less clear. This evolution, though not inhibiting in itself, is exemplified by a quick survey of the term ‘climate’ in textbooks a century apart – say 1910 and 2010. In the former, climate is viewed as constant and stable – the average weather of a place or region defined in terms of unchanging seasons, crops, habitability, etc. In the latter, climate is typically viewed as a planet-wide characteristic, undeniably variable but also subject to change; climate is a topic of huge discussion, if not outright dispute. Co...