This book is about biology and human ecology as they relate to climate change. Let's take it as read that climate change is one of the most urgent and fascinating science-related issues of our time and that you are interested in the subject: for if you were not you would not be reading this now. Indeed, there are many books on climate change but nearly all, other than the voluminous UN Intergovernmental Panel on Climate Change (IPCC) reports, tend to focus on a specialist aspect of climate, be it weather, palaeoclimatology, modelling and so forth. Even books relating to biological dimensions of climate change tend to be specialist, with a focus that may relate to agriculture, health or palaeoecology. These are, by and large, excellent value provided that they cover the specialist ground that readers seek. However, the biology of climate change is so broad that the average life sciences student, or specialist seeking a broader context in which to view their own field, has difficulty finding a wide-ranging review of the biology and human ecology of climate change. Non-bioscience specialists with an interest in climate change (geologists, geographers and atmospheric chemists, for example) face a similar problem. This also applies to policy-makers and policy analysts, or those in the energy industries, getting to grips with the relevance of climate change to our own species and its social and economic activities.

In addition, specialist texts refer mainly to specialist journals. Very few libraries in universities or research institutes carry the full range. Fortunately the high-impact-factor and multi-disciplinary journals such as Science and Nature do publish specialist climate papers (especially those relating to major breakthroughs) and virtually all academic libraries, at least in the Anglophone world, carry these publications. It is therefore possible to obtain a grounding in the biology (in the broadest sense) of climate change science from these journals provided that one is prepared to wade through several years’ worth of copies.

Having an understanding of climate change is one thing, but relating it to real-world development is another. In the latter half of the 20th century it became apparent to politicians that human impacts on the environment were sufficiently detrimental that they undermined the sustainability of human well-being, and hence environmental quality. ‘Human well-being’ is a catch-all term relating to material and cultural standards as well as quality of life.

Many of these terms, while having a clear meaning to Western politicians and policy-makers, have no strict definition or individual basis of quantitative indexing in the strict scientific sense, although in some instances attempts have been made. Other terms have been used so much by the media that they are often used in policy-making, although human ecologists are often more precise. For example, ‘carbon footprint’ is misleading as it generally does not include biofuels (which are carbon-based) and it also seemingly relates to the spatial concept of ecological footprint as opposed to a quantitative dimension of carbon mass. Academic comment on misleading terms and usage has reached the highest impact-factor journals (for example, see Hammond, 2007). A better term is fossil carbon burden, or fossil burden for short. Indeed some terms (such as medieval climatic optimum, climate tipping point and fertility that were discussed in earlier chapters, and zero carbon, which will be mentioned in section 8.5.1) are not only misleading but mean different things to different people. In 2009, with regards to the term ‘carbon neutral’ the UK government's Department of Energy and Climate Change even held a formal consultation on the term's usage (Department of Energy and Climate Change, 2009).

With this book's first edition (2007) Cambridge University Press kindly afforded a couple of pages as Appendix 4 to allow a brief summary of the IPCC's 2007 assessment (AR4) at the book's final page-proof stage: that assessment literally came out a couple of months before this book's first edition was published. This time the IPCC's 2013 assessment (AR5) will come out several months after this edition sees light of day and so I now use this appendix in a different way.

In the course of lectures and encounters following this book's first edition I have invariably been asked a number of questions as to my personal thoughts, as opposed to recounting the climate science and policy developments. Other than commenting on likely prospective research and policy analysis avenues, in the main I have shied away from answering, especially as most people have expected me to be predictive: what will happen to such and such in coming decades? And of course nobody can predict the future. Having said that, I do have some personal thoughts on climate science and policy. Given that there has been interest in my own take beyond that of appraising the literature, I now make a couple of points in this short appendix, quite separate from the main body of the text: I do not wish to contaminate my earlier (hopefully) sober review of the science and policy with wilder personal musings.

Post-industrial global warming is not the Earth's first major climate change event. If we are to appreciate the significance and relevance to biology of current climate change, it is important to be aware of past climate events, at least the significant ones. This chapter summarises some of the major episodes between the Earth's formation and the beginning of the current, Quaternary, ice age. When reading this chapter you may also want to refer to Appendix 2.

Early biology and climate of the Hadean and Archaean eons (4.6–2.5 bya)

The Pre-Biotic Earth (4.6–3.8 bya)

The Earth and the Solar System formed some 4.6 billion years ago (bya), give or take a few hundred million years. The Earth formed with the Solar System (containing ‘Sol’, our sun) accreting out of a dust and gas cloud. The dust, ice (composed of not just water but various volatile compounds) and rocks were not all small and particulate but themselves had accreted into small and large asteroid-sized bodies that ranged in size up to, and including, small planets. One of these, a Mars-sized planetoid (Thea) is thought to have had a glancing blow with the proto-Earth, exchanged material, and formed the Moon (Luna) 4.5 bya. This is not irrelevant to the nature of the Earth's climate. The lunar/Earth ratio of mass of 1:81.3 is much greater than any satellite/planet mass ratio for any other planet in the Solar System. Taking the Copernican principle, that there is nothing cosmologically special about the Earth as a life-bearing planet, this begs the question as to whether our large moon is a necessary factor facilitating a biosphere, or at least a biosphere with longevity. There is a suggestion that the Earth–lunar system is one that confers some axial stability to the Earth (affecting the variation in its angle of tilt), and hence climate stability, so enabling complex ecosystems to form. Indeed, in Chapter 1 we discussed axial tilt as a dimension of Milankovitch forcing of climate, but planets without large moons are prone to larger axial tilting and this means that good portions of such worlds spend half the year in sunlight and half the year in darkness. On Earth this only takes place within the polar circles, which form a minor proportion of the planet.

Recent climate change

The Latter Half of the Little Ice Age

The 17th century was not just the time of the Little Ice Age, it is also noted (and for some better noted) for the Renaissance, which saw the gathering of scientific understanding that in turn was to drive the Industrial Revolution of the 18th and 19th centuries. In Britain in the 1640s and 1650s scientists sought what they termed ‘a great insaturation’, which drew on the philosophies exposed by the likes of Francis Bacon. Among these, Bacon's principles of exact observation, measurement and inductive reasoning provided the intellectual tools for scientific advance. These advances had yet to percolate through to day-to-day application in technology, so life, society and its economy were still largely powered by humans and animals together with the burning of wood. Major global impacts from human activity were not yet manifest (although, of course, trace global signatures such as metals in Greenland ice cores can be found dating to thousands of years earlier).

In terms of climate and weather, 1659 – within the Little Ice Age – is an important date. Before that date we rely solely on the proxy indicators (see Chapter 2) for climatic information. After 1659 there began a source of new information: direct meteorological measurement. The first significant series of measurements began in 1659 and (much later) were compiled into a monthly series of temperature readings for rural sites in central England by Gordon Manley (1974). This is the longest homogeneous record and is still kept up to date by the UK Meteorological Office. The earlier measurements were varied but increasingly included, and were soon dominated by, instrumental measurements. The Central England Temperature (CET) records were soon accompanied by others to ultimately be built into a series such as those for De Bilt in The Netherlands from 1705. Such records are fundamentally important. As we have seen, although we can use a variety of proxies to build up, piece by piece, quite a good picture of past climate, deep-time climatic proxy indicators simply are either not sensitive or representative enough to tell us what was going on. This is especially true with regard to finer changes. For example, ice-core isotopic records are very fine for charting regional glacial and interglacial transitions of a few degrees but are less useful for discerning trends in changes of fractions of a degree within our current interglacial.

We are currently in the middle of an ice age! This ice age is known as the Quaternary ice age, and it began roughly 2 million years ago (mya) (I say ‘roughly’ because how much ice do you need on the planet to say that it is an ice age?). We might not think we are in an ice age and this is because we are in a warm part, called an interglacial. As we shall see, there have been a number of glacials and interglacials in our Quaternary ice age. However, this ice age did not just start by itself but arose out of a number of factors that became relevant earlier, in the Oligocene (34–23 mya) and Miocene (23–5.3 mya) epochs, well before the beginning of our ice age and the Pliocene and Pleistocene glaciations (Zachos et al., 2001). These glaciations actually had their beginnings some 5.3 mya. To understand how our Quaternary ice age came about we will need to briefly re-cap part of the previous chapter and note some other material to provide a more biological perspective while leaving out the extinction events.

The Oligocene (33.9–23.03 mya)

Between 35 and 15 mya the Earth's temperature was roughly 3–4°C warmer than today and atmospheric carbon dioxide concentrations were twice as high. However, climate forcing factors were coming into play that were to cool the planet. Carbon dioxide levels were falling and, as noted in the previous chapter, this fall could only have been furthered by the new C4 plants (even though their period of major expansion was not to take place until 8 mya: see below).

In most places on this planet's terrestrial surface there are the signs of life. Even in places where there is not much life today, there are frequently signs of past life, be it fossils, coal or chalk. Further, it is almost a rule of thumb that if you do discover signs of past life, either tens of thousands or millions of years ago, then such signs will most likely point to different species than those found there today. Why? There are a number of answers, not least of which is evolution. Yet a key feature of why broad types of species (be they broad-leaved tree species as opposed to ones with narrow, needle-type leaves) live in one place and not another has to do with climate. Climate has a fundamental influence on biology. Consequently, a key factor (among others) as to why different species existed in a particular place 5000, 50000, 500000 or even 5000000 years ago (to take some arbitrary snapshots in time) is because different climatic regimens existed at that place at those times.

It is also possible to turn this truism on its head and use biology to understand the climate. Biological remains are an aspect of past climates (which we will come to in Chapter 2). Furthermore, biology can influence climate: for example, an expanse of rainforest transpires such a quantity of water, and influences the flow of water through a catchment area, that it can modify the climate from what it otherwise would have been in the absence of living species. Climate and biology are interrelated.

The foundations of the quantum theory of radiation were laid by the work of Planck, Einstein, Dirac, Bose, Wigner, and many others. Historically Planck's [1] work on black body radiation is the foundation of any work on the quantum theory of radiation. Einstein's [2] work on the photoelectric effect established the particle nature of the radiation field. These particles were named as photons by Lewis [3]. Einstein [4] also introduced the A and B coefficients to describe the interaction of radiation and matter. He characterized stimulated emission using the B coefficient. Using thermodynamic arguments, he could also extract the A coefficient describing spontaneous emission which is at the heart of the origin of all spectral lines. This was quite a remarkable achievement. Dirac [5] implemented the quantization of the electromagnetic field and showed how Einstein's A coefficient emerges naturally from the quantization of the radiation field. It should be remembered that stimulated emission is the key to the working of any laser system. Following Dirac's quantization of the radiation field, Weisskopf and Wigner [6] were able explain in a very fundamental way the decay of the excited states of a system and hence derive the remarkable law of exponential decay. Bose [7] discovered a quantitative explanation for Planck's law. He introduced a new way of counting statistics relevant to quantum particles with zero mass. This was the beginning of quantum statistics. Bose's work was followed by Einstein [8] who produced a counting statistics for particles with finite mass (now known as Bosons).

In Chapter 13 we saw how the optical properties of a two-level system can be modified by the application of an additional strong coherent field. For example, the absorption of light by a two-level system depends on the strength and frequency of the driving field. Figure 13.5 showed that in certain frequency regions we can amplify a probe beam. We assumed in Chapter 13 that the coherent light beam was acting on the same optical transition as the weak probe beam. However, the atomic/molecular systems have many energy levels and we can take advantage of this to produce a variety of ways of controlling the optical properties. This would offer much more flexibility as different optical transitions would have different frequencies and hence one could use a variety of sources. In this chapter we present results for the optical properties of a multilevel system. We show that coherent control can make an opaque medium transparent. We also show that the dispersive properties, which are important for the linear and nonlinear propagation of light, can be manipulated by light fields [1–3].