Abstract
Part of the stated rationale for this work is a homage to, and a modern update of, the book Klima-Schwankungen seit 1700 written by the great German climatologist and geographer Eduard Brückner. This seminal work was published in 1890 while he was a Professor at the University of Bern, the same institution where Brönnimann now works. While this is an interesting idea as a basis for this book, it is by no means the central focus of the work. However, it does give some interesting insights into the history of climate change research, placing the research discussed and presented in its historical context. Footnotes giving brief biographies of notable figures in climate change research are presented throughout the book. I was especially interested in the importance of the International Geophysical Year (IGY) 1957–1958, an abbreviation which until recently I had been more familiar with from Donald Fagan (The Nightfly, 1982).
The references to Brückner and the other historical aspects of this book form only a minor part of the work, and in truth, for most readers, the book would function perfectly well were these parts omitted. Personally, I feel it is important and useful to position science in its historical context: if only to remind us that in 100 years our research may, at best, be viewed as an interesting footnote in history – and more likely totally forgotten. This slightly humbling thought should not, however, discourage us. It certainly does not discourage Brönnimann from trying to further our understanding of the Earth’s climate system. Brückner’s book is, no doubt, a work very much of its time (I have never seen a copy). Despite this, as Brönnimann points out, in a number of places, some of his findings still appear consistent with modern research.
It is, however, mostly climate change since Brückner wrote his book, which forms the background to Brönnimann’s impressive work. The focus of the book – as the title would suggest – is climate since AD 1700, and while this may not seem especially exciting and interesting to those more interested in long-term climate change, it is a highly important and well-chosen period, as it is probably the furthest back in time that we can hope to understand the climate system in any semblance of a holistic manner, as this period is approaching the extent of early instrumental climate records. It is also a period for which we have a wealth of excellent historical climate records (in Europe at least) and the period over which many of our proxy records – especially tree rings – are strongest and perform most coherently.
The book is divided into five chapters, the first three acting, to some extent, as a backdrop for the main act of Chapter 4, which is the major, research-driven part of the book. Brönnimann points out in the preface that the first three chapters are for less advanced readers and start at rather a basic level, although I initially failed to understand the third figure in the book (Fig. 1.3). Much of what is presented in the book is cutting-edge research, and some of it is quite complex. However, everything is generally well presented and explained and at no point does the level of detail become overwhelming. Each of the main chapters (Chapters 2–4) stands alone, to a large extent, with a brief introduction and individual conclusion. The structure of the book is as follows, excluding the preface.
Chapter 1 introduces in seven pages the key concepts and some of the data sets used in the book, although climate – which is the central focus of the book – is not defined. Chapter 2, ‘The basis: Past climate observations and methods’, is an excellent introduction to past climate observations, proxy evidence, climate models and important topics such as errors. This chapter contains a great deal of useful information for people at almost any level of academic study, dealt with using an appropriate level of detail and plenty of suitable references for those interested in deeper study. Chapter 3, ‘The machinery: Mechanisms behind climate change’, is another very interesting and well-written chapter, again covering the key issues of this large topic in just under 100 pages. It includes sections on climate physics and modes of atmospheric circulation such as ENSO and the NAO. The sections on forced climate change are a very good summary of the current understanding of major climate forcing mechanisms over the past few hundred years, including volcanism, solar variability and well-mixed greenhouse gases. The idea that the largest volcanic eruption may not be the most important for climate change was an interesting idea that I had not come across before. Finally, the section on feedbacks within the climate system is a very useful and thorough summary of the topic, although there was no mention of recent research (e.g. Lozier, 2012) that has cast some doubt upon the classic model of density-driven ocean circulation (Section 3.1.4.2), which is something of an oversight.
Chapter 4, ‘Climate changes since 1700’, is the central focus of the book and the longest, at just over 150 pages. It deals with changes in climate in a semi-chronological manner, starting with a brief overview of climate change of the past millennium. The chapter attempts to deal with climate as holistically as possible, including temperature (including sea surface temperatures), precipitation and, where possible, measures of atmospheric circulation. It also looks at changes geographically both in terms of regions and scales. Many of the results shown are model simulations produced by Brönnimann and his colleagues, which in many cases are compared – especially when dealing with the earlier of the period – with proxy-based reconstructions. The individual sections of this chapter deal with discrete temporal windows from c. AD 1700 to present roughly divided up into thematic periods of climate or climatic change, such as the end of the ‘Little Ice Age’ (‘LIA’) (AD 1700–1890) and the most recent period of warming (since AD 1985). Much of the data and discussion surround work by Brönnimann and his research group. This is therefore a highly research-driven chapter, which makes it extremely relevant, up-to-date and interesting. In dealing with climate change, it not only describes events but attempts to understand – in some depth, with varying degrees of success – the reasons and mechanisms behind these changes. For example, much discussion surrounds the possible reasons behind the stepped nature of global temperature increase over the past century or so, including the recent, much debated, hiatus in warming. Chapter 5 concludes the book by briefly summarising the advances and challenges in climate science since the time of Brückner.
In general, I found this to be a rewarding and very interesting book. The timescale it addresses is an interesting one: a period long enough to cover many interesting and important changes and events in climate history – the end of the ‘LIA’ to recent warming and discrete events such as AD 1816 and ENSOs. It is also the longest window for which we have any semblance of instrumental climate data, which combined with probably the highest quality proxy data available means that we should have some confidence in estimates of climate for this period. The book attempts to deal with climate change globally, but is rather biased to Europe and especially Central Europe. Partly this is because of proxy data availability, but also partly because of the research interests of Dr Brönnimann and his illustrious predecessor, Professor Brückner. Therefore, for example, Section 4.2, ‘The period from 1700 to 1890: The Little Ice Age’, discusses the timing of this notoriously hard-to-pin-down event, very much in terms of the European Alps, where the peak of glaciation was at c. 1850. However, as close by as Scandinavia, the peak of the ‘LIA’ was c. AD 1750, while the period after AD 1750 appears to have been rather warm. The ‘LIA’ appears to have been strongly regional in its expression, even across Europe, and this is rather overlooked in this book.
Something which this book highlighted for me is the coherence, or rather lack of coherence, between many of the proxy records which purport to reflect the same climatic variable, even over such a relatively short period as back to AD 1700. This is especially acute in tropical regions (e.g. Fig. 4.7), but even in the Central Europe and the European Alps (Fig. 4.8) the scatter in the reconstructions is quite considerable. Anyone viewing the recent spate of multi-millennial reconstructions of temperature and precipitation should consider the lack of consensus over the past 400 years in – for example – Alpine temperatures, an area with many supposedly excellent temperature-driven proxy records.
In summary, this is an excellent and informative book, well-written and presented. I would strongly recommend it for anyone studying, researching or merely interested in climate and climate changes over the past millennium or so. It also attempts to place climate research into a historical perspective, which is both useful and interesting.