This document discusses climate change across different timescales and possible causes. It notes that climate has varied over geological eras, with ice ages occurring in cycles of around 100,000 years. Historical records show temperature fluctuations, with a cold period from 1400-1850 AD and a warm period from 800-1400 AD. Recent climate data from 1850-2008 shows global temperatures increased by around 0.5°C since the late 1970s, corresponding to an era of global warming. The enhanced greenhouse effect, caused by gases released from burning fossil fuels, has likely contributed to increased warming by trapping more solar radiation. Transportation, industry, electricity, and heating account for over half of all greenhouse gas emissions, with carbon dioxide being the most

1. World at riskClimate change and its causes AS Geography

3. Short-term (recent) climate change is on a timescale of decades, e.g. global warming.

4. The medium-term (historical) timescale covers changes over the last few thousand years.

7. Ice ages and interglacial's (warmer periods) seem to occur on a cycle of about 100,000 years.

9. During the Little Ice Age (1400–1850) the climate was around 1C colder than it was in the twentieth century.

12. Since the late 1970s there has been a marked warming of around 0.5C.

13. This corresponds to the ‘era of global warming’.

14. Accurate instrumental measurements of air and ocean temperatures as well as ice cover testify to this record of global warming.

18. This has a net warming effect.

19. The level of carbon dioxide in the atmosphere has risen steadily since accurate recording began in the 1950s.Carbon dioxide concentrations, Hawaii, 1959–2005

21. Carbon dioxide is the most important greenhouse gas by volume.

22. Methane is a more powerful greenhouse gas per molecule.Global greenhouse gas emissions by economic sector, 2000

24. This confirms that global warming is a problem created largely by the developed world. Greenhouse gas emissions per person (tonnes of carbon dioxide equivalent, 2005)

26. The decades from 1980–2000 were the hottest for at least 400 years.

27. Measured warming in the Arctic is twice that for the rest of the world.

28. Arctic sea ice in 2007 was at its lowest recorded extent.

29. Carbon dioxide levels, at 380 ppm in 2007, are over 100 ppm higher than pre-industrial ‘natural’ levels.