CHAPTER 1

A Brief Overview of Recent ClimateChange and Its Ecological Context

This chapter summarizes the most prominent abiotic components of recent climatechange to establish the environmental context from which the discussionin the rest of the book proceeds. As will become clear in subsequent chapters,the rapid pace and broad geographic extent of abiotic changes reviewed herecannot be viewed in isolation for, as important as they are as drivers of ecologicaldynamics, in many if not most cases the ecological responses resultingfrom them owe to an alteration of biotic interactions. As an example we mayconsider the recent mass abandonment of retreating ice floes by Pacific walrusalong the coast of Alaska in 2007 and 2010, which coincided with the lowestand third-lowest arctic sea ice extent recorded to date (Post and Brodie 2012).Walrus are benthic feeders: they consume mussels on the seafloor in shallowwater during dives from the ice edge, which they also rest on between foragingbouts (Oliver et al. 1985; Ray et al. 2006). As the ice melts and the edge movesfarther away from shore and the shallow-water environments that harbor themussels walrus eat, it becomes energetically unprofitable for these large marinemammals to try to remain in proximity to the ice edge, for they wouldhave to travel progressively longer distances to reach the shallow-water sea-beds(Ray et al. 2010). The rate of annual sea ice loss over the Arctic has beenon the order of 56,000 km² each year since 1979 (figure 1.1). As suggested laterin this chapter, loss of sea ice does not represent simply an abiotic response torecent warming; it also represents the loss of critical habitat necessary for thesurvival and reproduction of many species, and it should probably be consideredthe high-latitude equivalent, in terms of negative impacts on faunal species,of deforestation in the Tropics (Post and Brodie 2012).

Before I summarize the most prominent abiotic features of recent climatechange, two points of clarification are necessary. First, what is meant by recent?In the context of this book, recent refers to climatic changes that were set inmotion by the onset of the Industrial Revolution but have become most clearlymanifest, in terms of global abiotic changes, since approximately the middleof the twentieth century (Mann et al. 1998, 1999). Second, what is meant byrapid? It is perhaps more difficult to identify the parameters of this characteristicof recent climate change, but at the same time the notion of rapid changeis probably more intuitive to ecologists than is the notion of recent change. Forthe purposes of this book, and in keeping with most of the examples adducedherein, rapid refers to changes occurring on annual to decadal timescales. Itwill no doubt be tempting to argue that decadal-scale climatic variation is mostcertainly not rapid in the ecology of soil microorganisms, whose populationand community dynamics are important drivers of nutrient flow rates, primaryproductivity, and even biosphere-atmosphere exchange of trace gases, but constraintsmust be established, and these are two of the clearest used throughoutthis book. Rapid environmental change most certainly presents challenges tosome species, in terms of individuals' ability to survive and reproduce, even asit presents distinct advantages to others, and no apparent benefit or disadvantageto yet others. Hence, the dynamics explored in this book include, in somecases, responses to climate change, and in other cases a lack of such response.But before we begin an accounting of these responses, from individual-levellife history responses through population-level dynamics, to community-scalechanges, to ecosystem dynamics, we must take a close look at climate changeand the abiotic dynamics it encompasses.

CLIMATE CHANGE VERSUS GLOBAL WARMING

It is tempting to use the term climate change to refer to increases in Earth'stemperatures or, similarly, to conflate the terms climate change and globalwarming. The term global warming is an oversimplification of the currentchanges in abiotic conditions on Earth because it implies that only changesin temperature are occurring, and that these temperature changes are unidirectional.Furthermore, the term has been applied most recently to connotesolely human-driven temperature increases, which has promoted dismissal ofthe entire notion of climate change by those unconvinced by the evidence ofa role for human beings in recent climate change. To draw an analogy thatillustrates the importance of avoiding conflation of the terms climate changeand global warming, we may recognize that evolution, like climate change, isa fact, whereas natural selection, like anthropogenic emissions of greenhousegases, is the accepted theory explaining how this factual process occurs.

From an ecological perspective, climate change is most meaningfully consideredas the suite of abiotic changes occurring across Earth coincident withthe onset of the Industrial Revolution and progressing over the past 150 years,including rising temperatures, temperature variability, changes in precipitationand snow cover, and diminishing sea and land ice. All these changes can belinked to ecological dynamics, though it is probably fair to state that mostresearch to date on the ecological consequences of climate change has focusedon temperature changes.

TEMPERATURE CHANGES

The Earth's surface has warmed by approximately 0.4°C since 1850 (Brohan etal. 2006; Trenberth et al. 2007), and by approximately 0.2°C per decade overthe most recent three decades (Hansen et al. 2006) (figure 1.2), largely as a resultof increases in atmospheric CO₂ concentrations driven by the human use offossil fuels (Hansen, Sato, et al. 2008). This increase hardly seems remarkable,and indeed, it would be...