The Causes of these Changes in Climate

page 20

1. Natural fluctuations

We know that CO2 does naturally vary a lot

2. Anthropogenic cause (man-made)

Most of the observed changes have happened in the past 250 years.

So what happened about 250 years ago?

watermill

windmill

As long as we needed only a small source of power,

water, wind or horses were enough

To operate a large mill or factory, you need the power of steam.

And you make steam by boiling water

We used to burn wood,

but burning wood is not very efficient

We switched from burning a small amount of wood.

To burning a large amount of coal.

To power the factories and the mills of the Industrial Revolution

initially coal was main energy source

and remains a big source

but now oil and natural gas are also big

So is the burning of fossil fuels (coal & oil) causing changes in global climate?

If so, how?

This is a natural process in which atmospheric gases trap radiated heat

Remember, without this Earth would have Moon-like temperatures

So what’s the problem?

The Greenhouse Effect

If one blanket keeps you warm at night, what would be the effect of two blankets?

You’d be too warm!

What gas is the main contributor to the Greenhouse Effect?

CO2 the most famous greenhouse gas? No!

CH4 (methane) another gas in the news a lot? No!

N2O (nitrous oxide) a gas in the news a bit? No!

No!Some mysterious little known new gas?

Water vapor accounts for about 95% of Greenhouse Effect

So if it is a natural phenomena, mostly caused by water vapour, what’s the big deal?

Human activity is increasing the amount of the other greenhouse gases in the atmosphere

1. Deforestation

means less photosynthesis to soak up CO2.

as the forests are burned N2O is released

releases CO2 and N2O

2. Burning of fossil fuels

However neither releases a lot of CH4 (methane)

So where does the CH4 come from?

Ruminants such as cows and sheep breakdown cellulose

this produces waste methane

3. Methane from cows

with the help of bacteria in their rumen

But are there really more cows in North America than we used to have in our buffalo herds?

used to be 60 million buffalo now about 120 million cows

so has methane production only gone up by 2X?

No, methane production is way up! Why?

Buffalo eat grass at a slow and steady rate and grow slowly.

Cows eat grain, silage and hay at high rates to grow fast.

So one cow actually makes 2x or 3x as much methane as one buffalo. And remember, there are 2X more cows.

4. Other chemicals

a. fluorocarbons

No longer used in aerosol cans where CO2 has replaced them

Now used mostly as coolants in air conditioners

And as cleaners of circuit boards for computers

b. sulphur hexfluoride [SF6]

production of magnesium and magnesium alloys

the cleaning of aluminum

a. transportation fuels

b. waste disposal/processing

c. power stations

d. industrial processes

e. residential/commercial use

f. agricultural

g. obtaining/processing fossil fuel

What human activities actually are causing the most problems?

Rank these sources of Greenhouse Gases (in pencil)

Now let’s get the actual values.

Not all greenhouse gases are equal:

carbon dioxide CO2 1 GWP

methane CH4 24 GWP

nitrous oxide N2O 300 GWP

fluorocarbons XFC 2000 GWP

sulphur hexafluoride SF6 24000 GWP

GWP is global warming potential per molecule

a big GWP is bad!

Water (H2O) 0.28 GWP

So if CO2 has such a low GWP why are we so worried about that one gas?

Even though CO2 has a low GWP it is still the major greenhouse gas after water vapour

http://www.geocraft.com/WVFossils/greenhouse_data.html

Carbon dioxide accounts for 0.035% of the 1%.

The “other gases” (including the greenhouse gases) make up the 1%.

The percentage of carbon dioxide (and others) are increasing.

The percentage of oxygen would decrease.

What are the effects of all these excess Greenhouse Gases?

What can we do about it all?