Climate Change- the way the Earth has

constantly evolved and changed temperature

throughout history

Homo Sapiens

Industrialisation

The sceptic argument...

• Earth's climate has changed long before we were pouring CO2 into the atmosphere. Europe was far warmer in the Middle Ages. During the 17th and 18th century, it was much colder, prompting the ‘The Little Ice Age’, when the Thames was frozen over months at a time. Further back, there were times when the Earth was several degrees hotter than current temperatures. Warming of several degrees often took only centuries or decades.

Discuss with a partner why some people may be skeptical about climate change. Who may these people be?

Background• The 16th century is the first period for which we have a

reliable history of climate and weather. • Private diaries, ships' logs, accounts of military

campaigns, and similar sources give descriptions of wind direction, wind speed, cloud formations, and other weather indicators.

• Precisely dated annals, chronicles, audited accounts, agricultural records, tax ledgers, and other archival material provide indirect information, particularly on extreme weather events, such as droughts, floods, or unusual cold.

• Additional evidence is available from glacial moraines, lake and ocean sediments, pollen strata, deposits of insects, tree rings, coral structure, radiometric analysis of ice cores, archaeological sites, and many other sources.

• All this information can be combined to reconstruct past climates

https://www.youtube.com/watch?v=S9ob9WdbXx0

Natural causes for climate change

Solar activity

• Solar variations have been the major driver of climate change over the past 10,000 years. When sunspot activity was low during the Maunder Minimum in the 1600's or the Dalton Minimum in the 1800's, the earth went through 'Little Ice Ages'. Similarly, solar activity was higher during the Medieval Warm Period.

• However, the correlation between solar activity and global temperatures ended around 1975.

• At that point, temperatures started rising while solar activity stayed level. This led a Finnish and German scientists to conclude "during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source

• Caption for Image Four: The Sun shows signs of variability, such as its eleven-year sunspot cycle. In that time, it goes from a minimum (seen here in 1996) to a maximum (2000) period of activity that affects us everyday. When particularly active, solar storms can spew tons of radiation to Earth in the form of Coronal Mass Ejections (CMEs) that can affect power grids, spacecraft, and communication systems. SUPER: NASA / ESA

Changes in solar output

Milankovitch cycles https://www.youtube.com/watch?v=TWJyeyV92W4

• Earth's climate undergoes 120,000 year cycles of ice ages broken by short warm periods called interglacials.

• The cycle is driven by Milankovitch cycles. Long term changes in the Earth's orbit trigger an initial warming which warms the oceans and melts ice sheets - this releases CO2.

• The extra CO2 in the atmosphere causes further warming leading to interglacials ending the ice ages.

• For the past 12,000 years, we've been in an interglacial.

• The current trend of the Milankovitch cycle is a gradual cooling down towards an ice age.

Changes in earths orbit

Volcanoes

• Volcanic eruptions spew sulphate aerosols into the atmosphere which has a cooling effect on global temperatures.

• These aerosols reflect incoming sunlight, causing a 'global dimming' effect. Usually, the cooling effect lasts several years until the aerosols are washed out of the atmosphere.

• In the case of large eruptions or a succession of eruptions such as in the early 1800's, the cooling effect can last several decades. Strong volcanic activity exacerbated the Little Ice Age in the 1800's.

• Observational and modelling studies (e.g. Kelly & Sear, 1984; Sear et al., 1987) of the likely effect of recent volcanic eruptions suggest that an individual eruption may cause a global cooling of up to 0.3°C, with the effects lasting 1 to 2 years.

• Such a cooling event has been observed in the global temperature record in the aftermath of the eruption of Mount Pinatubo in June 1991. The climate forcing associated with individual eruptions is, however, relatively short-lived compared to the time needed to influence the heat storage of the oceans (Henderson-Sellers & Robinson, 1986).

• The temperature anomaly due to a single volcanic event is thus unlikely to persist or lead, through feedback effects, to significant long-term climatic changes.

Catastrophic events-e.g. volcanic eruptions

Sample question

Mark scheme