Climate and Change 2

2.1 How and why has climate changed in the past? Title: Natural Causes of Climate Change Learning Objectives: To understand that climate has changed in the past through natural causes To understand that these timescales can range from millions to hundreds of years. Key vocabulary: Geological Time Scale The Eruption Theory – volcanic activity The Sunspot Theory – solar output The Orbital Theory – Milankovitch Cycles Stratosphere Troposphere Lithosphere

Natural Causes of Climate Change Copy out: The Earth’s atmosphere is affected by changes in the lithosphere (check old vocab.) as well as by cosmic influences such as the Sun’s activity or variations in the Earth’s orbit. These are NATURAL CAUSES of climate change. Some changes take place over a short timescale (years/decades of warming/cooling) Other changes are far more significant and can last for thousands, or even millions of years.

Are the reasons for this change natural or human….? Watch the following clip: Causes of Climate Change - BBC Class Clip 1491 http://www.bbc.co.uk/learningzone/clips/causes-of-climate-change/1491.html Duration: 04:23 Description: A look at climate change over a range of timescales. Long term changes include changes in the suns output, the orbit of the earth, the tilt of the earth's axis and wobble in the earth's axis of rotation. It ends with a look at how changes in albedo and increased urbanisation and industry have influenced global warming through increased pollution. Now watch the following clip: Volcanoes and Global Climate - BBC Class Clip 1479 (please note there is no sound) http://www.bbc.co.uk/learningzone/clips/volcanoes-and-global-climate/1479.html Duration: 02:35 This un-narrated clip starts with an animation of a volcano erupting and spewing huge amounts of dust into the upper atmosphere. This is shown capturing incoming short wave solar radiation and trapping outgoing long wave radiation from the Earth’s surface. The clip finishes by showing the impact of these on the net average temperature of the Earth over time.

Orbital Changes Changes in how the Earth moves around the Sun are believed to cause ice ages. According to Milankovitch (a Serbian physicist), every 100,000 years or so the Earth’s orbit changes from a circular to elliptical (egg-shaped) pattern. It is when the orbit is in the circular pattern that the ice ages are most likely to occur. This changes how much sunlight we receive. He also identified that the Earth’s axis moves and wobbles about, changing over 41,000 and 21,000 year cycles. This also affects how much sunlight is received. Put all of this together and the history of ice ages can be explained!

Solar Output The Sun’s output is not constant. Cycles have been detected that reduce or increase the amount of solar energy. The most well-known phenomenon is sunspot activity, when uneven temperatures develop on the Sun’s surface. These can be seen as tiny black spots on photographs of the sun taken by experts (never try this yourself). Sunspots seem to come and go following an irregular cycle that lasts about 11 years. Interestingly, temperatures are greatest when there are plenty of spots – because it means other areas of the Sun are working even harder!

The Occurrence of Sunspots since 1600

Volcanic Activity Major volcanic eruptions lead to a brief period of global cooling, due to ash and dust being ejected high into the atmosphere, blanketing the earth. The 1883 explosion of Krakatoa is believed to have reduced world temperatures by 1.2 °C for at least one year afterwards. The most recent explosion to have a similar effect was Pinatubo (1991) – link to Restless Earth work completed recently. Sunlight reaching earth was reduced by 10%. World temperatures fell by nearly half a degree in the following year.

Your Tasks Write down the names of the three orbital changes and the time each change takes. 2. a) When was the Little Ice Age? b) How many years did it last? c) How many sunspots were there during this time? d) Approximately how many sunspots have there been since 1800? e) What effect has this had on global temperatures? 3. Explain how variations in the Sun’s output can affect global temperatures. 4. Explain how big volcanic eruptions might change our climate.