1. Examining the Evidence
Climate Change -
Examining the Evidence

2. Changes in Greenhouse Gases
Recall that the natural greenhouse effect occurs because of the water vapour in the atmosphere.
Water vapour traps most of the thermal energy in the atmosphere!
Professor
Frink sez:
Human activity has had a large effect on the three other greenhouse gases, causing the enhanced greenhouse effect.

3. Global Warming Potential
Gas
Global Warming Potential
Persistence (y)
carbon dioxide 1
50-200
methane 23 10
nitrous oxide (N2O)
296
120
Global warming potential (GWP) is a measure of the relative ability to trap thermal energy in the atmosphere.
Carbon dioxide is used as the reference to which the other greenhouse gases are then compared.
Persistence is how many years each gas will remain in the atmosphere.

4. Analysis of ice core samples (to give us an idea about the distant past) and atmospheric conditions have shown the levels of all three greenhouse gases in Earth’s atmosphere are increasing.

7. Greenhouse Gases and Human Activity
Since the Industrial Revolution in the late 18th century, the level of carbon dioxide in the atmosphere has been increasing.
Any process that releases carbon into the atmosphere is called a carbon source.

8. Fossil fuels are formed from the remains of living organic material, so they contain a lot of carbon, and when burned, they release carbon dioxide and nitrous oxide (N2O) into the atmosphere.

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Modern agriculture also contributes to the level of greenhouse gases.

10. Forests are called carbon sinks, because photosynthesis removes carbon dioxide from the atmosphere.
The size of Earth’s carbon sinks have been steadily decreasing because of human’s need for fuel and land for agriculture and industrialization.

11. The combination of increased use of fossil fuels and the decrease in available carbon sinks, the level of atmospheric carbon dioxide has increased by about 32% over the last 200 years.

12. Halocarbons are another class of man-made chemicals that can trap thermal energy in the atmosphere.
They have a global warming potential of about !

13. Many scientists believe that human activity since the industrial revolution has led to global warming, the observed overall increase in Earth’s average temperature.

14. Besides the increase in average global temperatures, other possible pieces of evidence of global warming may include:
1) Flowers in the northern hemisphere have begun to bloom earlier and earlier over the past century.
2) The incidence of extreme weather events such as ice storms and floods has been on the rise.

15. 3) Snow cover in some polar regions has decreased.
4) The average level and temperature of the Earth’s oceans have been increasing.

16. Most scientists agree that global warming is occurring, the causes of global warming and their relative effects on the biosphere are not clear.
Climate change is a relatively new field and the confidence in the predictions by man-made models is up for debate.

17. Homework: read pages 410 – 418 D3.1 Check and Reflect