Page 171 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 5 global Temperatures 135
Decadal Surface-Temperature Anomalies (C°)
1970s
1980s
1990s
2000s
-3.2 -1.5 -1 -.6 -.3 -.1 .1 .3 .6 1 1.5 2.3
▲Figure 5.17 Surface-temperature anomalies by decade, compared to 1951–1980 baseline. reds and oranges indicate positive temperature anomalies; blues indicate negative anomalies. The temperature-anomaly maps are based on data from 6300 stations. [giSS/naSa.]
To get an idea of the magnitude of this temperature trend, consider these statistics: In 2012, the average global temperature was 14.6°C. This is 0.6 C° warmer than the baseline temperature in the mid-1900s. It is
also 0.8 C° warmer than any other average yearly global temperature since recordkeeping began.
According to the U.S. National Research Council of the National Academy of Sciences, for each Celsius degree of global temperature increase, we can expect 5%–10% changes in precipitation in many regions; 3%–10% increases in the amount of rain falling dur- ing the heaviest precipitation events; 5%–10% changes in flows of streams and rivers (either up or down); 25% decreases in the extent of Arctic summer sea ice; 5%–15% reductions in crop yields (as currently grown); and 200%–400% increases in the area burned by wildfire in some areas of the western United States. Thus, a 1 C° change can have far-reaching effects on Earth systems.
This so-called global warming is related to com- plex changes now under way in the lower atmosphere. Scientists agree that human activities, principally the burning of fossil fuels, are increasing atmospheric greenhouse gases that absorb longwave radiation, de- laying losses of heat energy to space. The bottom line is that human actions are enhancing Earth’s natural greenhouse effect and forcing climate change.
However, “global warming” is not the same thing as global climate change, and the two terms should not be considered interchangeable. Climate change encom- passes all the effects of atmospheric warming—these effects vary with location and relate to humidity, pre- cipitation, sea-surface temperatures, severe storms, and many other Earth processes. An example already dis- cussed is the positive feedback loop created by Arctic sea-ice melting and temperature rise in Chapter 4. Other impacts will be discussed in chapters ahead—the effects of climate change link to almost all Earth systems.
The long-term climate records discussed in Chapter 11 show that climates have varied over the last 2 million years. In essence, climate is always changing. However, many of the changes occurring today are be- yond what can be explained by the natural variability of Earth’s climate patterns. The scientific consensus on human-forced climate change is now overwhelming. In 2007, the Intergovernmental Panel on Climate Change (IPCC), the leading body of climate change scientists in the world, concluded,
Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.
In 2010, the U.S. National Research Council of the National Academy of Sciences, in its report Advancing the Science of Climate Change, stated,
Climate change is occurring, is caused largely by human activities, and poses significant risks for—and in many cases is already affecting—a broad range of human and natural systems.
The Association of American Geographers, composed of geographers and related professionals working in the