Page 344 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

308 part II The Water, Weather, and Climate Systems
Everything we have learned in Geosystems up changes in the global climate over recent decades are hap-
to this point sets the stage for our exploration of
climate change science—the interdisciplinary study of the causes and consequences of changing climate for all Earth systems and the sustainability of human so- cieties. Climate change is one of the most critical issues facing humankind in the 21st century, and is today an integral part of physical geography and Earth systems science. Three key elements of climate change science are the study of past climates, the measurement of cur- rent climatic changes, and the modelling and projection of future climate scenarios—all of which are discussed in the chapter ahead. We revisit some of the principles of the scientific method as we explore global climate change, and by doing so address some of the confusion that com- plicates the public discussion of this topic.
The physical evidence for global climate change is ex- tensive and is observable by scientists and nonscientists alike—record-breaking global average temperatures for air, land surfaces, lakes, and oceans; ice losses from mountain glaciers and from the Greenland and Antarctic ice sheets; declining soil-moisture conditions and resultant effects on crop yields; changing distributions of plants and animals; increasing intensity of precipitation events; and the perva- sive impact of global sea-level rise, which threatens coastal populations and development worldwide (Figure 11.1). These are only a few of the many complex and far-reaching issues that climate change science must address to under- stand and mitigate the environmental changes ahead.
Although climate has fluctuated naturally over Earth’s long history, most scientists now agree that pres- ent climate change is resulting from human activities that produce greenhouse gases. The consensus is overwhelm- ing and includes the vast majority of professional scien- tific societies, associations, and councils in Canada and throughout the world. Scientists agree that natural cli- mate variability, which we discuss in the chapter ahead, cannot explain the present warming trend. The observed
▲Figure 11.1 Sea-level rise along the world’s coastlines. From 1993 to 2010, sea-level rise occurred at a rate of 3.2 mm ⋅ yr−1, caus- ing high tides and storm waves to encroach on developed areas and hastening coastal erosion processes (discussed in this chapter and in Chapter 16). Pictured here is a road adjacent to the shoreline at Cow Bay, nova Scotia, during a storm in December, 2010. [andrew Vaughan/ The Canadian Press.]
pening at a pace much faster than seen in the historical climate records or in the climate reconstructions that now extend millions of years into the past. According to NASA and its Goddard Institute for Space Studies, 2014 broke all records for the warmest year in the record, surpassing 2005 and 2010 record years. A scientific consensus assigns human cause for these temperature milestones.
In this chapter: We examine techniques used to study past climates, including oxygen isotope analysis of sediment cores extracted from ocean-floor and ice cores, carbon isotope analysis, and dating methods using tree rings, speleothems, and corals. We examine long-term cli- mate trends and discuss mechanisms of natural climate fluctuation, including Milankovitch cycles, solar vari- ability, tectonics, and atmospheric factors. We survey the evidence of accelerating climate change now underway as measured by record-high ocean, land, and atmospheric temperatures; increasing acidity of the oceans; declin- ing glacial ice and ice-sheet losses worldwide and record losses of Arctic sea ice; accelerating rates of sea-level rise; and the occurrence of severe weather events. We then examine the human causes of contemporary climate change, and the climate models that provide evidence and scenarios for future trends. The chapter concludes with a look at the path ahead and the actions that people can take now, on an individual, national, and global level.
Population Growth and
Fossil Fuels—The Setting
for Climate Change
As discussed in earlier chapters, carbon dioxide (CO2) pro- duced from human activities is amplifying Earth’s natural greenhouse effect. It is released into the atmosphere natu- rally from outgassing (discussed in Chapter 9) and from microbial and plant respiration and decomposition on land and in the world’s oceans (discussed in Chapter 19). These natural sources have contributed to atmospheric CO2 for over a billion years, unaffected by the presence of humans. In recent times, however, the growing human population on Earth has produced significant quantities of atmospheric CO2. The primary anthropogenic source is the burning of fossil fuels (coal, oil, and natural gas), which has increased dramatically in the last two centuries and added to greenhouse gas concentrations. To illustrate the increase, Figure 11.2 shows carbon dioxide (CO2) levels for the last 800000 years, including the steadily rising CO2 trend since the Industrial Revolution began in the 1800s.
During the 20th century, population increased from about 1.6 billion people to about 6.1 billion people (please review Chapter 1, Figure 1.5, and see Figure 11.3). At the same time, CO2 emissions increased by a factor of 10 or more. The burning of fossil fuels as an energy source has contributed to most of this increase, with secondary effects from the clearing and burning of land for development and agriculture. Notice in Figure 11.3 that the majority of population growth is now occurring in the less-developed countries (LDCs). It is especially rapid in China and India.