Volcanoes lead to cooling???

Many examples show that volcanic eruptions lead to the cooling of the climate. Laki in Iceland erupted in 1783 and that winter was the coldest ever recorded in the North East of USA. Tambora in Indonesia erupted in 1815. An extremely cold spring and summer followed this eruption in 1816. Snowfalls and frosts occurred in June, July and August in Europe and North America which led to the failure of crops and therefore famine. Also, Atlantic shipping lanes were blocked by ice and alpine glaciers advanced significantly. Krakatay which is also in Indonesia erupted in 1883. This eruption was the second biggest eruption that has happened and caused the island to split. Pinatubo in the Philippines erupted in 1991 and the aerosol plume traveled around thew world in days. Global air temperatures dropped by 1 degree Celsius. This eruption demonstrated the link between sulphur (not ash) and cooling.

How does sulphur in the atmosphere lead to cooling?

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwigscrXq_DKAhXMFZoKHa4qB3gQjB0IBg&url=http%3A%2F%2Fplaza.ufl.edu%2Fairwess%2F&psig=AFQjCNEO8Dhw9I54bat6hpkY9_zSfUS8UQ&ust=1455301653689132
The volcanic eruption emits huge amounts of Sulphur dioxide into the atmosphere. This combines with water to make fine particles (aerosols) of sulphuric acid. The aerosols reflects the in coming solar radiation which means that less radiation reaches the Earth's surface and therefore leads to cooling. The extra carbon dioxide from volcanic eruptions does not have a significant impact compare to anthropogenic annual emissions.

The Evidence

Evidence from the Cyrosphere

The Artic has reduced in ice by 30% and the thickness has reduced by a half since 1980.

Greenland's land ice is moving down to the sea twice as fast as previously which has a significant effect on the sea level.

Glaciers grow and shrink in response to climate for example Solheim Glacier in Iceland.

Ice core analysis

Where they are analyzing the ice is in Greenland and Antarctica. They measure by drilling down into the ice which is thousand of years old. The layers are the winter snowfall compressed into ice which can be analysed for temperature and the trapped gases (oxygen isotopes) can be analysed for carbon dioxide. The oldest ice core is called Vostok which is 400,000 years old.

Cross dating in trees

Climate conditions influence tree growth, patterns in tree-ring widths and density.In temperate regions where there is a distinct growing season, trees generally produce one ring a year, recording the climate conditions each year. Trees can grow to be hundreds to thousands of years old and can contain annual records of climate for centuries to millennia.

Milankovitch Cycles

The theory was developed by Serbian, Milutin Milankovitch in 1924 and they are changes in the Earth's orbit and axis tilt which lead to a change in climate and therefore biome. There are variations in the amount and distribution of solar radiation received by the Earth which results in long term changes in the surface temperature of the Earth.

Impact of orbital changes on solar radiation is relatively small and would only lead to approximately 0.5 Celsius in the global temperature. Milankovitch cycles act as the trigger to major global climate change. Climate feedback mechanisms are needed to sustain change.

Orbital Eccentricity (changes in orbit)

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwim4N6qnfDKAhWH0xQKHS7XBH8QjB0IBg&url=http%3A%2F%2Fwww.ces.fau.edu%2Fnasa%2Fmodule-3%2Ftemperature-trend-changes%2Fcauses-glaciation.php&psig=AFQjCNEUkvjp58-LZbEleaceSiFAMKQkKw&ust=1455297905173325

Obliquity (changes in tilt)

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjHr_ihnvDKAhUC6xQKHY_uB5UQjB0IBg&url=http%3A%2F%2Fpics-about-space.com%2Fobliquity-of-earth-orbit%3Fp%3D1&bvm=bv.113943164,d.d24&psig=AFQjCNEf1AYvpKbWPE-poryDipbWlJCzsA&ust=1455298150388111

Precession (Axial wobble)

This happens every 22,000 years.

https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjKq8LgnfDKAhXDbxQKHebfC_wQjB0IBg&url=http%3A%2F%2Fwww.mhhe.com%2Fphyssci%2Fastronomy%2Ffix%2Fstudent%2Fchapter3%2F03f15.html&bvm=bv.113943164,d.d24&psig=AFQjCNF368IerdHMOUv52fgfdKrqhMcXVQ&ust=1455298012745229

Types of feedback

Snowball Earth and Chemical Weathering

The Earth 4 billion years ago used to be warmer than it is today. There was a thicker blanket around the Earth and the sun was 25% fainter than it is today which kept the sun warm. But where did the thick blanket or carbon dioxide go?

Chemical Weathering

This is where carbon dioxide and rainwater forms a weak acid called carbonic acid which dissolves silicate rocks. The carbon from the rocks in the form of bicarbonate ions washes into the ocean, where it is used by many organisms to form their shells and are deposited on the ocean bed to form carbonate rocks. This was where the carbon was kept and explains how our climate is self regulated. Even though the sun is getting brighter, we haven't seen a proportional increase in the Earth's temperature. This is an example of negative feedback. As the Earth's temperature began to increase, then so did the rate of chemical weathering.

Snowball Earth

2.2 billion and 700 million years ago our planet became a giant snowball. The growth of continents and the removal of carbon dioxide by weathering cools the planet, then ice cover increases which also means that reflectivity increases. This reflectivity reduces the absorption of sunlight by the Earth's surface and so increases the temperature further etc etc.... This produces positive feedback which is usually restricted. It amplifies the spread of ice cover away from the poles. If it reaches the tropics which is a tipping point where the process of amplification runs away and we get a Snowball Earth with the ice closing up the equator.

The Weathering process is stopped by the cover of ice,but volcanoes are still pumping carbon dioxide into the atmosphere which has no where to go as the carbon sink has been switched off. This creates a blanket warming the ice around the equator which causes the rest of the ice to melt. This kick starts the Weathering process once again and returning the carbon dioxide to the Earth's crust.