To recap Give 2 examples of research methods that show long term historical climate change? How reliable are these? Give 2 ways of measuring medium term climate change? How reliable are these? What about short term?

Recap On your whiteboards reproduce an annotated drawing of the greenhouse effect

Learning Objectives K- Know that there are both human and physical causes for climate change U- Understand the evidence for and against the view that climate change is unprecedented S- Be able to attempt an exam style question using knowledge from previous lessons

Is climate change natural or human induced? Last lesson we focussed upon how we have the data to justify claims of climate change. We also discussed the human causes of climate change Today we are looking at the views that climate change is a natural event

The natural argument! There are 3 main ways that scientists believe are affecting the worlds climate naturally 1 Variation in the earths orbit 2 Variation in solar output 3 Volcanic eruptions and cosmic causes

1. Variations in the Earth’s Orbit Milankovitch Cycles A Serbian physicist working at the beginning of the 20 th century. He identified 3 variations in the Earth’s orbit around the Sun Milutin Milankovitch

Every 100,000 yrs the Earths orbit changes from spherical to elliptical, changing solar input100,000 yrs Earths orbit!

Tilt of the Earth The Earth’s axis is tilted at 23.5 o, this changes over a 41,000 yr cycle between 22 o & 24.5 o, affecting solar input, especially in higher latitudes.41,000 yr

Wobbly axis! The Earth’s axis wobbles, so which way the hemispheres are facing to the sun when closest to the sun varies over 21,0000 yrs. Affecting solar input. 21,0000 yrs

Until recently Milankovitch’s had no real support from past climate history. However, from measuring ice cores these now support this theory!

Milankovitch Cycles Many scientists argue that the Milankovitch cycle may have been just enough to trigger a major global climate change, but that climate feedback mechanisms are needed to sustain it. KEY WORD: Feedback effects are those that can amplify a change and make it bigger (positive) or smaller (negative). An e.g. of positive feedback is snow and ice cover. Small increase in snow and ice raises surface Albedo reflecting more solar energy back into space. Resulting in further cooling An e.g. of negative feedback s cloud cover. As GW occurs, more evaporation occurs increasing cloud cover, which in turn may reflect more solar rays back into space diminishing effects of the warming.

2. Variations in Solar Output The sun’s output is not constant is also varies. A variety of cycles have been detected, most are short term, the most obvious is due to sun Spot activity – 11yrs The effect of sunspots is to blast more solar radiation towards the earth Some scientists have suggested that around 20% of 20 th Century warming may be because of solar output variation

3. Volcanoes Major eruptions eject material into stratosphere. The sulphur dioxide forms a haze of sulphate aerosols, which reduces the amount of sunlight received at Earth’s surface The eruption of Tambora led to the year without a summer in 1816 as global temperatures dipped by degrees C

Unprecedented Global warming? What does this phrase mean?? Never been seen before! So is Global warming unprecedented? Not unprecedented as we have had changes before where periods of time have been warmer. However, the quote from the IPCC in 2007 sums up the current views on Global warming: “ The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 yrs can be explained without external forcing, and very likely that it is not due to known natural causes alone”

So anthropogenic causes seem to be confirmed! Note down some of the recent facts to emphasize this! The level of CO2 in the atmosphere is far above the ‘natural’ level and continues to rise. 11 of the 12 warmest years on record occurred between 1995 and 2006 Temperature rises have been recorded on all continents since 1970 Satellite observations since 1993 suggest an annual rise in sea level of 3.1mm, and a decline in Arctic sea ice of 2.7% per decade

Homework- Complete the exam practice questions at the bottom of your worksheet

To end…. Make 2 columns in a table -List in one column human causes of GW -In the other column natural causes for GW