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Thermometer-Based Temperature Trends
The earliest records of temperature measured by thermometers are from Western Europe beginning in the late 17th and early 18th centuries. The network of temperature collection stations increased over time and by the early 20th century, records were being collected in almost all regions, except for polar regions where collections began in the 1940s and 1950s.
Three widely recognized research programs have used this data to reconstruct global surface air temperature trends from the late 1800’s through today. They are NOAA (National Oceanographic and Atmospheric Administration), NASA/GISS (NASA/Goddard Institute for Space Studies), and CRU (Climatic Research Unit). All use the same land-based thermometer measurement records from the Global Historical Climatology Network (GHCN). All three show the same basic trends over the last 100 years. (See Figure 1, Variations of the Earth’s surface temperature.)
Figure 1. Variations of the Earth’s surface temperature for the past 140 years (Source: IPCC Climate Change 2001 Synthesis report, p 49)
During the past century, global surface temperatures have increased at a rate near 0.6oC/century, but this trend has dramatically increased to a rate approaching 2.0oC/century during the past 25 years.
1. There have been two sustained periods of warming. Identify them on the solid red curve.
a. What years were the beginning and end of the first warming period?
b. When did the second warming period begin?
2002 was the second warmest year on record.
Global temperatures in 2002 were 0.56oC above the long-term (1880-2001) average of 13.9 oC. This makes 2002 the second warmest year on record.
2. Refer to Figure 2, ‘Jan.-Dec. Global Surface Mean Temperature Variations’. Determine which was the only warmer year from the graph. This was the year when a strong El Nino contributed to higher global temperatures.
3. Describe similarities and differences you see among the three graphs in the figure.
Figure 2. January to December Global Surface Temperature Variations
Land and Ocean Temperature Change in the last 25 years
A consistent, large-scale warming of both the land and ocean surface occurred over the last quarter of the 20th century (IPCC Climate Change 2001 Summary Report p. 54). See Figure 3 below, The greatest temperature increases were over the mid- and high latitudes of North America, Europe, and Asia.
Figure 3. Annual Temperature Trends: 1976-2000
4. Where were the only regions of cooling?
Land and Ocean Temperature Change in 2002
Global temperatures were above average during 2002 throughout most land areas. The map below, Figure 3, ‘Annual Temperature Anomalies for 2002’ shows variations from the 1961-1990 average as coloured dots. This map was created using data from the Global Historical Climatology Network, a network of more than 7,000 land surface observing stations.
Figure 4. Annual Temperature Anomalies for 2002 (Source: NOAA)
5. Identify the areas of greatest warmer than average temperatures. How much warmer were these areas on average? State a range.
6. Where are the only widespread areas of cooler than average temperatures. How much cooler were these areas? State a range.
Figure 5 ‘2002 Surface Temperature Variations’, represents blended land and ocean temperatures. The Northern Hemisphere temperature averaged near record levels in 2002 at 0.63oC above the long-term average. The Southern Hemisphere was also warmer than average by 0.46oC.
Figure 5. 2002 Surface Temperature Variations (Source: NOAA)
Annual Global Trends:
Overall, global land precipitation has increased by about 5 to 10% over most mid and high latitudes of the Northern Hemisphere since the beginning of the 20th century. However subtropical land areas have experienced a 3% average decrease in rainfall.
The map shows the percent increase or decrease in precipitation over the 20th century at 2000 sites across the Earth. The size of the circles represents the percent value.
Green: increase. Brown : decrease.
1. When we discuss global trends it is helpful to refer to ranges of latitudes for comparison.
2. Describe general trends you see for each of the zones you identified in question 1.
Seasonal Global Trends:
Figure 7. Trends for the four seasons from 1900 to 1999.
Source: Climate Change 2001: Working Group 1: Section 126.96.36.199
Figure 8 , Trends for the Four Seasons, shows mostly increasing precipitation in the Northern Hemisphere, mid- and high-latitudes. The first letters of the months are in the titles. [unclear]
3. What season does each map represent for the Northern Hemisphere? For the Southern Hemisphere?
4. During which seasons is this increase in precipitation in the Northern Hemisphere most evident?
5. What has been the range of increase over Canada?
Figure 9 The annual precipitation trends for three periods within 1910 – 1999 and the full period, 1900 to 1999.
Source: Climate Change 2001: Working Group 1: Section 188.8.131.52
6. What is the trend in precipitation over northern Europe? Over southern Europe and the Mediterranean? These trends are related to strong positive values of the North Atlantic Oscillation, with more anticyclonic conditions over southern Europe and stronger westerlies over northern Europe.
7. Identify the trend:
a. for Australia
b. for Argentina
8. List areas of Africa that show a decrease in precipitation.
9. The general increase in precipitation over the United States has increased between 5 and 10% since 1900. This increase was interrupted in the 1930s. Why?
Global precipitation was below the 1961-1990 average in 2002. Much of Australia experienced severe drought, with the eastern part of the country most affected. India monsoon rainfall was much below normal. The resulting drought was the worst since 1987. The western United States and portions of the north coast of China were also affected by drought.
Parts of southeast Asia and Japan, the southeast coast of China, Taiwan, and the Philippines were hit by several typhoons. There was extensive flooding along the Mekong Delta. Seasonal flooding in Nepal, Bangladesh, and north-eastern India from June to August claimed more than 1000 lives.
Temperature Change – Activity
Earth’s atmosphere has gradually warmed and cooled over the millennia, covering large portions of Canada with glaciers several times over the last 100,000 years. In the past 30 years, scientists have come to believe that fossil fuel combustion and ecosystem disruption have triggered more rapid climate change. The 2,500 scientists of the UN Intergovernmental Panel on Climate Change (IPCC), agree: ‘There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activity.’
1. What’s the difference between climate and weather?
2. Explain the term global mean temperature.
3. Before what year is the global mean temperature cooler than the 1961-1990 average? How much cooler is the mean temperature in 1910?
4. After what year is the mean temperature warmer? How much warmer is the mean temperature in 1998?
5. Describe the trend represented by the solid line.