Sunday, 25 January 2015

Week 2 - Past Climate Change


Ok so i've now progressed into the second week of this course, got 14 out of 15 in the test...get in! I have made some connections and read other peoples blog etc so progress is being made. There are some really interesting people on this course who I can definitely learn from.

Past climate change

For 4.5 billion years the Earth has been self regulating and pretty much habitable for most of that time. Throughout these years there have been some positive and negative feedback loops which have impacted the Earths climate.

The ageing sun

As the sun gets older it gets hotter and hotter but luckily enough the Earth is located in the area around the sun which is neither too hot nor cold so is called the habitable zone. Either side of us is Mercury (nearest the sun) which is so hot is can melt lead, and on the other side (further away from the sun) is Mars which is frozen.


At the birth of our solar system, blooming ages ago, the sun was a good 30% brighter than it is now which would mean that the Earth would be 20 degrees cooler meaning it would have been frozen....but it wasn't. The reason for this is because the cuddly 'blanket' around the Earth was much thicker and contained a lot more CO2 then there is now which kept the Earth nice and warm and habitable. 

 Nowadays the blanket is no longer as thick (which is pretty good as we would very toasty indeed) but the question is where has all the CO2 gone? This can be explained through chemical weathering. Chemical weathering is where carbon dioxide and rainwater forms a weak acid, carbonic acid, that dissolves silicate rocks. The carbon in the form of bicarbonate ions washes into the ocean, where it is used by many organisms to form their shells, which are then deposited on the ocean bed to form carbonate rocks.
  1. Carbonate rocks are a class of sedimentary rocks composed primarily of carbonateminerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3) and dolostone, which is composed of the mineral dolomite (CaMg(CO3)2).

So the Earth self regulated itself through negative feedback - Sun got hotter, more chemical weathering occurred and the Earth stored more carbon which then reduced the amount in the blanket.

Snowball Earth




Another thing that happened over the course of these past 4.5 billions years has been 5 times occasions where it has got pretty cold which we call the Ice Ages, during these times there were still parts of the Earth that were not completely frozen. However, there was a time when the Earth did completely freeze over which is affectionately known as Snowball Earth.

 Snowball earth describes the coldest global climate imaginable - a planet covered by glacial ice from pole to pole. The global mean temperature would be about -50°C (-74°F) because most of the Sun's (Solar) radiation would be reflected back to space by the icy surface.  The last snowball earth ended 635 million years ago (Ma), near the end of the Proterozoic Eon.  

Here is my interpretation of the Snowball Earth and the process of how it cam about. My 30 minute stab at creating something understandable with a vague artistic flare - definitely needs more work but it gives you that jist of things!






























Understanding factors which cause climate change

There are a number of natural variations which contribute to changes in the Earths climate which fall into two categories; predictable and unpredictable.

 Predictable
There are 3 predictable variations which are linked to the the way the Earth moves around the sun

  • Eccentricity - the Earth's orbit is changing from a circular one to a more elliptical
  • Obliquity - The tilt of the Earths axis varies
  • Precession - Where the Earth wobbles like a spinning top (over a period of 23,000 yrs)


Unpredictable
  • Volcanoes - eruptions cannot be planned and when they do they reduce the Earth's temperature but emitting aerosols into the atmosphere which reflect solar radiation back towards the sun
  • Solar variability - the change in the amount of radiation emitted by the Sun


Climate change records

In order to understand climate change and to reconstruct the past changes we need date. Unfortunately we have only been collecting instrumental data and making visual records in the short term (post 1600) but we need to know what happened prior to that. Current instrumental data includes weather stations, weather balloons, satellites, ocean monitoring and prior to that ships made diary entries which have been put onto databases.

 How do we find data prior to 1600? Well this lies in proxy data which are preserved physical characteristics of the environment that can stand in for direct measurements. We can obtain proxy data from tree rings, ice cores, fossil pollen, ocean sediments, corals and historical data.

 Tree rings

 In the spring time, through photosynthesis trees begin to grow. Trees generally produce one ring per year. During a good year the tree grows faster and so lays down more tissue in the year, resulting in a wider growth ring. Poor conditions mean slower growth, less tissue laid down and consequently a narrower ring. 

Tree rings are a great way of seeing what the climate conditions were on Earth going back hundreds to thousands of years...depending on the tree of course. It is important to apply the principle of cross dating, a tree may have become affected by disease or may have consumed more nutrients if a nearby neighbour has died. So a number of trees in an area can be looked at as they will depict the same patterns over time. Scientists can also over lap existing tree rings with those from fallen trees from a similar area so they can gather information even further back in time.


What effect do Volcanoes have on climate change?


When a volcano erupts it emits lots of aerosols which suspend in the stratosphere and reflect solar radiation which therefore cools the Earth. The aerosols are suspended for approximately 1-2 years and they then fall to Earth. Their impact is short term but does have a considerable cooling effect.

As well as aerosols, volcanoes emit CO2 as well as other greenhouse gases which contribute to the blanket surrounding the Earth which warm it up. These remain in the atmosphere for a longer time so after the cooling will contribute to the warming of the Earth again.


Reflection from this weeks course

  • What are the most important themes you have learned this week?
Snowball Earth, proxy data and volcanoes
  • What aspect of this week did you find difficult?
Understanding the ever changing climate changing and where we fit in to the changes today. It's pretty hard to understand that the Earth warms and cools due to lots of natural variations and then think that we will be the cause of it warming further, especially as people post youtube videos which argue against it.
  • What did you find most interesting? And why?
Snowball Earth and how the Earth completely froze over when it usually self regulates itself  through natural feedbacks/variations.
  • Was there something that you learned this week that prompted you to do your own research?
Understanding tree growth and photosynthesis as this is something I hadn't touched on for a long time also the understanding behind the snowball earth.



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