S190 Global Warming - the science behind the headlines
In addition to S180 Life in the Oceans, another short science course
I've decided to do over the winter is S190 Global Warming - the science behind the headlines.
I registered for this course on the 17th September.
The course is centered around Block 2 of the OU's introductory Science course S103. The course material arrived on 8th November, and consisted of, a video, cdrom, study file, and the 'Discovering science: A Temperate Earth' Book.
Depending on previous experience and other commitments, the course can be studied over 8 or 12 weeks, each option has a separate end of course assignment(ECA). I've chosen to take this course over eight weeks, and submit the ECA by 31st January 2003.
The course has two learning outcomes which I intend to keep in sight as I study this course:
• Have an understanding of the factors that determine the earth's surface temperature
• Be able to read a popular science article on global warming and assess whether the presentation of the arguments accurately reflect current scientific thinking.
Week one started with the study file introduction and getting used to the layout of the course. The introduction covered study skills that I was already familiar with from previous OU study. I went on to work through section 2 of the 'A temperate Earth?' book.
This section introduces the mathematical concept of mean, and the historical perspective of calculating the global mean surface temperature (GMST). Historical records indicate an irregular rise in the GMST over the past 100 years.
The material seems well laid out and easy to follow, all mathematical concepts covered can be revised in the course study file where necessary. I found the section interesting and useful to get me thinking 'scientifically' again - some of it was revision, but several new concepts were introduced:
• Urban heat island effect
• trends
• gathering reliable data
• interpreting data in a scientific way
• random uncertainties (scatter around 'true' value)
• systematic uncertainties (offset from 'true' value)
• small random uncertainties = precise
• small systematic uncertainties = accurate
To practice this section we started a practical activity of measuring precipitation over a 4 week period, using two different home made rain gauges.
This section focuses on finding evidence of climate change in the distant past before written records began. Evidence is based on the link between climate, and changes in landscape, and the animal / plant life of a region.
The shape of the landscape in the form of U shape valleys, can give show that a glacier has been present in a particular region in the past. This gives an indication that the temperature was different to what it is today.
Fossilized pollen can give an indication of the climate because plants need certain climatic conditions to grow. By comparing the species of pollen found with the conditions they need to grow today, an average temperature for a region at the time the pollen was deposited can be calculated.
The Earth's GMST depends on the rate at which the Earth's surface gains and loses energy.
The sun is the ultimate source of almost all the energy gained by the Earths surface
The course uses the 'leaky tank' analogy to explain the balance of energy gains and losses.
Activity 4.1 Summarizing the leaky tank analogy
The relationship between the GMST and gain and loss of energy at the Earth's surface can be explained by considering water pouring into a tank and then leaking out. Energy gain is represented by a tap pouring water in, and energy loss by a vertical slot allowing water to leak out. The water level represents the Earth's GMST. As water pours into the empty tank the area of the slot allowing water to leak is small so the water level in the tank rises. However, as the water level rises the area of the slot increases and more water leaks out. At a certain point the water level in the tank will remain at a dynamically steady state. At this point the input / output rates are equal.
A closer look at what determines the Earth's GMST
The majority of the solar radiation reaching the Earth is in the form of light, but there is also some ultraviolet and infrared radiation. There are different forms of electro magnetic radiation, each with a different wavelength, but they all travel through space at the speed of light and transfer energy from one place to another.
The Earth's surface gains energy by absorbing a large percentage of solar radiation and also infrared radiation emitted by the atmosphere. Energy is lost by the Earth's surface through convection in the atmosphere and evaporation of water at the surface. Energy is also lost through the emission of infrared radiation.
Most of this infrared radiation emitted from the surface is absorbed by the atmosphere. This, together with convective and latent heat transfers, sustains the atmospheric temperature, and hence the rate at which the atmosphere emits infrared radiation.
When the GMST is in a steady state, the rate of energy gain by the surface equals the loss, so the GMST remains the same. The GMST is determined by the solar constant, and by various properties of the Earth's atmosphere and surface.
The GMST is considerably raised because of the greenhouse effect, which depends on atmospheric gases that absorb most of the long wave infrared radiation emitted by the Earth's surface.
Review of progress so far - Activity 5.4
I more or less built the headings in this web page around the study plan I drew up at the beginning of this course. However, I have had some set backs, I spent two weeks away with work, did little studying over the Christmas and new year period, and also had catching up to do with other courses. I'm back in the swing of things now though, and am progressing well and enjoying this course. I'm finding using web pages to keep notes is a useful technique as it reinforces my learning and is something permanent to look back on. I can also link into other resources as I look things I'm interested in up on the Internet. The most significant thing I have learnt on the course so far, is that 'global warming' and the 'green house effect' are NOT the same thing. This is explained on the Bad greenhouse site.
After looking through the ECA, I'm still hoping to stay on track and submit my ECA by the end of January.
Composition and properties of air - Activity 6.1 - what I know before studying section 6.
Composition
A ratio of various gases:
• Oxygen
• Nitrogen
• Carbon dioxide
• other gases
Properties
• Can be compressed / various pressures
• invisible
• Moves about
• can be absorbed by water, etc
Activity 6.7 - what I know after studying section 6.
Composition
• Nitrogen 78%, oxygen 21%, argon 1%, water 0.5%, carbon dioxide 0.04%
• Oxygen is reactive, and essential for life.
• Nitrogen and argon are unreactive.
Water( H2O) and carbon dioxide (CO2) are greenhouse gases - increasing the amount of these gases in the atmosphere will increase the GMST
Properties
• Has Mass
• Is essential for life
• Ground level air pressure is I bar or 14.7 psi
• Absorbs infrared radiation emitted by surface
• Reduces solar radiation reaching surface
• Collisions of particles are responsible for air pressure
• pressure decreases with altitude
• Density decreases as temperature increases
Summary of section 6.
Properties of solids, liquids and gases can be explained by a simple 'particle model of matter'.
Pressure / particles per M3 of the atmosphere decrease as altitude increases.
Evaporation and condensation helps to transfer energy through the atmosphere via latent heat, this can also be explained by the particle model.
The Earth's atmosphere is made up of different gases, both elements and compounds.
Reactions can release energy, but atoms are not created or destroyed, they just change partners.
Carbon dioxide (0.036%) and water vapour (0.5%) are the main greenhouse gases.
Parts per million(ppm) expresses values that are present in small quantities
The amount of water vapour affects the GMST because water vapour is a greenhouse gas.
Water exists in various settings around the world, in the atmosphere, in the oceans, or in ice flows around the poles, etc., each setting could be described as a reservoir. The water cycle is constantly transferring between these reservoirs through evaporation, transpiration, and changes in temperature. In the medium term the water cycle is in a steady state, so water enters and leaves these reservoirs at the same rate, so the amount of water doesn't change. However, in the longer term this state may change, and as water vapour contributes to the green house effect, this can directly influence the GMST.
rate of transfer = mass of carbon in reservoir
residence time
Activity 8.1
Reservoir
Mass of / carbon 1012kg C
major form of carbon
Mass of / carbon/% of total mass of carbon
Mean residence time/years
Rate of transfer 1012kg C y-1
Biological cycle
atmosphere
760
carbon dioxide
0.0015
3.6
210
living things
560
organic carbon (living)
0.0012
4.7
120
surface ocean
1 000
dissolved carbon
0.002
7.9
130
soil
1 500
organic carbon (dead)
0.003
25
60
Geochemical cycle
deep ocean
37 000
dissolved carbon
0.07
1 000
37
ocean sediment
3 000
carbonate carbon; organic carbon
0.01
5 000
0.6
rock
50 000 000
carbonate carbon; organic carbon
99.9
200 000 000
0.25
Activity 8.2
A diagram of the global carbon cycle. Rate of transfer - 1012kg C-1, reservoir mass - 1012kg C.
Arrow
Process
Carbon transformation
A
Photosynthesis
by photosynthesis, CO2 in the atmosphere (or dissolved in water) is converted into organic carbon in green plants
B
Respiration
respiration is the process by which organic carbon in living organic matter is converted into CO2, releasing stored energy
C
leaf fall and death
living organic carbon stored in vegetation is transferred to dead organic carbon in the soil, either directly or y consumption by animals
D
Decomposition
organic carbon in dead organic matter is converted into CO2in the atmosphere (or dissolved in water), by respiration of worms, bacteria, etc.
E
CO2 degassing
dissolved carbon in surface sea water (or fresh water) is released into the atmosphere as CO2
F
Atmospheric CO2 dissolution
CO2 from the atmosphere dissolves in surface sea water and becomes dissolved carbon
G
Upwelling
dissolved carbon is transferred from the deep ocean to the surface ocean
H
Sinking
dissolved carbon in the surface ocean is transferred to the deep ocean
I
Biological pump
particulate carbon (organic carbon and carbonate carbon) is transferred from the surface ocean to the deep ocean
J
Sedimentation
particulate from the deep ocean is transferred to organic and carbonate sediments
K
dissolution and respiration of sediment
carbonate carbon sediments and organic carbon sediments are transferred into dissolved carbon in the deep ocean
L
Rock formation (Ocean)
organic carbon or carbonate in sediments is converted into organic sedimentary rock or carbonate rock
M
Rock formation (Land)
deep buried (mostly organic) carbon from undecomposed vegetation becomes lithified (converted into organic rock)
N
Weathering
carbonate or organic carbon rock is released into streams and lakes, and then on the surface ocean as dissolved carbon
O
Volcanism
organic and carbonate carbon stored in rock is released to the atmosphere as CO2
Summary of section 8 - The carbon cycle
One of the factors that determines the Earths surface temperature is the amount of the green house gas carbon dioxide (CO2) in the atmosphere. The amount of CO2 in the atmosphere is controlled by the global carbon cycle, which is summarised in the diagram and table above.
The global carbon cycle can be broken into a biological cycle where carbon moves rapidly though the atmosphere, living things, soil and surface ocean (1 - 10 years). And a geochemical cycle where carbon moves slowly through the deep ocean, sediment and rock (103 - 106 years).
Small changes in either the biological cycle or the geochemical cycle can have a large effect on the amount of CO2 in the atmosphere. Through the greenhouse effect, the amount of CO2 in the atmosphere is linked to climate. burning fossil fuels has increased the rate at which carbon is released into the atmosphere by about 20 times. This has led to a significant increase in the level of CO2 in the atmosphere.
• Section 1 - Variations in the global mean surface temperature of a few degrees can have significant consequences for life on Earth.
• Section 2 - There's evidence to show that the Earth's surface temperature has varied in the recent past.
• Section 3 - There's evidence to show that the Earth's surface temperature has varied in the distant past.
• Section 4 - An overview of what determines the Earth's GMST using the leaky tank analogy.
• Section 5 - A closer look at the Earth's GMST and explanation of the greenhouse effect.
• Section 6 - An explanation of the Earth's atmosphere.
• Section 7 - An explanation of the water cycle.
• Section 8 - An explanation of the carbon cycle.
Summary of section 9 - Can we explain past variations in GMST?
Changes in the Earth's orbit around the sun and in the tilt of it's rotation axis seem to be the main trigger for changes in the GMST over the past few million years. During the whole of the Earth's 4 600 Ma history, the shapes of the ocean, increases in solar luminosity, and variations in the composition of the atmosphere become important.
Our understanding of changes in the GMST in the distant past is poor because the Earth's climate system is very complicated, and the climates and many factors that affect the climates are unknown.
Summary of section 10 - The Earth's temperature in the future
There is no proof that the increase in CO2 in the atmosphere has caused the GMST to rise. However, the GMST has risen in the past few hundred years, and climate models indicate that the rise in GMST could be due to the increase in CO2in the atmosphere.
The most optimistic predictions of future CO2 emissions suggest the amount of CO2in the atmosphere will increase until at least 2100.
Climate models estimate that the GMST will rise by between 1.0 and 3.5°C.
Slow moving deep ocean currents may release dissolved carbon into the atmosphere as CO2 in hundreds of years.
Some species will become extinct reducing the Earth's biodiversity, others will adapt to life at higher temperatures.
A higher GMST will:
• have a major effect on agriculture
• influence other climate features such as precipitation and evaporation
• cause a rise in sea level through melting ice caps and thermal expansion of sea water
• could lead to problems with pests and disease
• affect transport, and require the heating or cooling of buildings
On the surface, the subject of global warming could come across as controversial and difficult to understand. However, I've really enjoyed this course, the course material is well written and easy to follow with all new concepts fully explained. The activities are enjoyable, and the sort that you want to complete. There was the right mix of reading, written work, and cdrom / video media. I thoroughly recommend this course to anyone wishing to get back into the study of science.
The ECA was enjoyable to complete and reinforced many of the things I had learn. One minor point - I would have preferred to have the choice of submitting a totally Word processed document rather than having to submit a separate hand drawn graph. I also found the word limits for some questions slightly restrictive, but then that helps with creating concise and accurate answers.
In addition to 
Week one started with the study file introduction and getting used to the layout of the course. The introduction covered study skills that I was already familiar with from previous OU study. I went on to work through section 2 of the 'A temperate Earth?' book.
This section focuses on finding evidence of climate change in the distant past before written records began. Evidence is based on the link between climate, and changes in landscape, and the animal / plant life of a region.
The majority of the solar radiation reaching the Earth is in the form of light, but there is also some ultraviolet and infrared radiation. There are different forms of electro magnetic radiation, each with a different wavelength, but they all travel through space at the speed of light and transfer energy from one place to another.
Composition
The amount of water vapour affects the GMST because water vapour is a greenhouse gas.
