Michael Pidwirny
LABORATORY 7: CLIMATE CHANGE – PART 2
LEARNING GOALS
In this laboratory, we will examine the nature of past and future predicted climate change on the Earth.
Upon completion of this laboratory you will be able to:
- Describe trends in historical climate data as they relate to human-caused global warming.
- Examine and interpret the output from climate simulation models.
- Understand the possible climate change outcomes in the future under the best-case and worst-case greenhouse gas emission scenarios.
In North America, South America, Europe, Asia, and Africa annual temperatures at most meteorological stations were appreciably colder at the beginning of the 20th century. From the 1920s to the 1950s temperatures became warmer. Colder temperatures returned once again in the 1960s, and continued until the mid-seventies. A warming trend followed these cooler years, and has continued ever since with some of the warmest years in the 20th and 21st century being recorded in just the 30 years. Interestingly, these patterns mirror trends found in the annual mean global temperature record (Figure 7.2).
Figure 7.1. Historical trend in annual mean surface temperatures over the period 1901 to 2019 (119 years). Areas in grey have insufficient data. Image Copyright: Michael Pidwirny. Date Source: NASA – Goddard Institute for Space Studies – Surface Temperature Analysis. Land Data from GISS Analysis, Ocean Data from Hadl/Reyn_v2: SST 1880-Present.
Figure 7.2. Global mean annual temperature measurements from 1880 to 2019. Green line represents 7-year moving average. The red dashed line shows the average global mean for the period 1880-1950. Image Copyright: Michael Pidwirny, Data Source: http://data.giss.nasa.gov/gistemp/graphs_v4/.
Over longer periods of time, non-instrumental climate data also indicates that weather has been quite variable in North America and across the Earth. For example, over the past 800,000 years, there have been several great ice ages during which 30% of the continental surface of the Earth was covered by glacial ice several kilometers (miles) thick. Each glacial period lasted about 100,000 years and was followed by a warmer interglacial period persisting for roughly 10,000 to 12,500 years.
For the past 10,000 years, the Earth has been enjoying the warm temperatures of the latest interglacial period. During this period the Earth’s average global temperature fluctuated up and down by about 2°C (3.6°F) over short periods of time (less than 500 years). These moderate and relatively slow fluctuations in climate have not led to drastic changes in the Earth’s environment. Today’s annual mean global temperature is about 15°C (59°F).
HUMAN ENHANCEMENT OF THE GREENHOUSE EFFECT
The chemical nature of the atmosphere is an important factor in determining the Earth’s climate. Heat energy from the Sun is trapped in the Earth’s lower atmosphere by a natural process called the greenhouse effect. The amount of heat trapped depends primaril