Page 345 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 11 Climate Change 309
For 800,000 years, atmospheric CO2
has never been above this line ... until now
May 1958 (318 ppm)
May 2014 (402 ppm)
300 ppm
Industrial Revolution
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800 700
▲Figure 11.2 Carbon dioxide concentrations for the last 800 000 years. Data are from atmospheric samples contained in ice cores and direct CO2 measurements. note the rise in CO2 over the past several hundred years since the industrial revolution. [Based on data from nOaa.]
Animation
Global Warming, Climate Change
600 500
Thousands of years before present (0 = 2014)
Although more-developed countries (MDCs) currently emit the greatest share of total greenhouse gases and lead in per capita emissions, this portion is changing. Accord- ing to some projections, LDCs will contribute over 50% of global greenhouse gas emissions by 2050 (Figure 11.4).
The rate of population growth increased dramati- cally after 1950 (see Figure 11.3), and this trend correlates with a dramatic rise in atmospheric CO2 since that time. In 1953, Charles David Keeling of the Scripps Institute of Oceanography began collecting detailed measurements of atmospheric carbon dioxide (CO2) in California. In 1958, he began CO2 measurements in Hawai‘i, resulting in what is considered by many scientists to be the single most important environmental data set of the 20th century. Figure 11.5 shows the graph, known as the “Keeling Curve,” of monthly average carbon dioxide (CO2) con- centrations from 1958 to the present as recorded at the Mauna Loa Observatory in Hawai‘i.
The uneven line on the graph in Figure 11.5 shows fluctuations in CO2 that occur throughout the year, with
May and October usually being the highest and lowest months, respectively, for CO2 readings. This annual fluc- tuation between spring and fall reflects seasonal changes in vegetation cover in the higher latitudes of the northern hemisphere. Vegetation is dormant during the Northern Hemisphere winter, allowing CO2 to build up in the atmo- sphere; in spring, when plant growth resumes, vegetation takes in CO2 for photosynthesis (discussed in Chapter 19), causing a decline in atmospheric CO2. More important than these yearly fluctuations, however, is the overall trend, which is that from 1992 to 2014, atmospheric CO2 increased 16%, and in May 2013, CO2 concentrations crossed the 400-ppm threshold, and by May 2014 reached 402 ppm—a level that is unprecedented during the last 800000 years, and several studies found CO2 not over 400 ppm in the last 1.5 million years. These data match records from hundreds of other stations across the globe.
The Mauna Loa CO2 record is now one of the best- known graphs in modern science and is an iconic sym- bol of the effects of humans on Earth systems. The
▲Figure 11.4 Industrial growth and rising CO2 emissions in India. Farmers plough a field next to one of india’s many industrial plants. india’s population now makes up about 18% of earth’s total, and the country’s rapidly growing economy relies heavily on the use of fossil fuels for energy. [Tim graham/alamy.]
400 300 200 100 0
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1950 1970 1990 2010
2030 2050
Less- developed countries (LDCs)
More-developed countries (MDCs)
▲Figure 11.3 Human population growth since 1950, and projected to 2050. Since 1950, population has increased in lDCs far more than in MDCs, a trend that is expected to increase to 2050. [reprinted by permission of the Population reference Bureau from www.prb .org/Publications/Datasheets/2013/world-population-data-sheet/fact- sheet-world-population.aspx]
Population (billions)
CO2 parts per million