Chapter 7 The Issue of Global Warming

Developing the Case of Human Responsibility

Greenhouse gases maintain the temperature on Earth at a level for live.

Human activities increase the amount of GHGs in the atmosphere. Increased GHGs may lead to warming of the atmosphere and

climate change. Increased GHGs may alter weather patterns, shift biomes and

increase sea levels. Feedback mechanisms are very comples and changes may lead to

positive or negative results. Governments & individuals can act to reduce GHG emissions. There is still much controversy & varying preceptions about global

warming.

Key Points

Short Term Objective 1.

Describe the functioning of the atmospheric system in terms of the energy balance between solar and long-wave radiation.

(ν): The number of waves that pass a fixed point per second

Wavelength, Amplitude, Peak & Valley

Peak

Valley Valley

Peak

What do you know already

Make a list of causes of climatic change. Burning fossil fuels Volcanic activity & astroid impacts Changes in Earth’s orbit Progression of the equinoxes Milankovitch Cycles Sun spot activity

What are the percentages?

Questions????

The Earth’s atmosphere is an example of an open system

What does this mean and why is it important?

The Greenhouse effect is natural and important to the earth. Why?

What is albedo? Use figures from the table to describe how the

albedo of the atmosphere can change the amount of solar radiation arriving at the ground surface.

Use figures from the table above to describe how the albedo of the ground surface can change the amount of long wave radiation emitted by the earth

Albedo may affect the energy balance between short and long term radiation

N S

If the Greenhouse effect is natural then what’s the problem?

Climate changes all the time but what has happened recently?

The problem is that the rate of change seems to have risen rapidly since the Industrial Revolution.

Hence it is sometimes called the Enhanced Greenhouse Effect.

Why?

The causes of climate change

1. Increasing levels of Greenhouse Gases in the atmosphere

Climate Change is not a new thing!

The worlds climate has been changing over the last 18,000 years, sometimes getting hotter and sometimes colder as you can see from the graph below.

Paleoclimate Cycles

During most of Earth history, global temp. was 8-10°C warmer than today, but there have been a few long

periods of sustained globally cold periods.ice ages:

2500 Myr,

700 Myr,

300 Myr

and 42 Myr

Even over short periods there are fairly large fluctuations

Proof of Global Warming?

What do you think?

Does it matter whether the causes of global warming are natural or human?

How do the causes of global warming impact the way we mediate the problem?

How to Change Global Climate

The ways in which global climate may be influenced

include:

•changes in Earth’s orbit

•variable solar output

•changes in ocean circulation

patterns

•albedo (reflectivity) effects

•greenhouse effect

Is climate change natural or human induced (anthropogenic)?

There are 3 main natural events that scientists believe affect the worlds climate:

1.Variation in solar output

2.Variation in the earths orbit

3.Volcanic eruptions and cosmic causes

1: Variations in Solar Output

The sun’s output is not constant; it also varies. A variety of cycles have been detected, most are short term. The most obvious is due to the 11-year sun spot activity cycle.

The effect of sunspots is to blast more solar radiation towards the earth

Some scientists have suggested that around 20% of 20th Century warming may be because of solar output variation

However a study in 2006 showed no major increase in solar output since mid 1970s

Sun Spot Activity: Q & A

What are sunspots? How are they linked with the amount of solar radiation the earth receives? Describe the pattern of sunspot activity. What is the link between sunspot activity and global temperature anomalies?

2: Variations in the Earth’s Orbit

Milankovitch Cycles A Serbian physicist working at the beginning

of the 20th century. He identified 3 variations in the Earth’s orbit

around the Sun Link

Milutin Milankovitch 1879 - 1958

Eccentricity of Earth’s orbit

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

Obliquity of the Earth’s Axis

The Earth’s axis is tilted at 23.5o, this changes over a 41,000 yrcycle between 22o & 24.5o,

affecting solar input, especially in higher latitudes.

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.

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.

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 Aledo 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.

Also Tundra?? What effect does the tundra have in GW?

Milankovitch Cycles

3. Volcanoes & Cosmic Collisions

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 0.4-0.7 degrees C

An asteroid smashing into the Yucatan peninsular is thought to have contributed to extinction of the dinosaurs.

Unprecedented Global warming?

Never been seen before! So is Global warming unprecedented? Not unprecedented as we have had periods of global

warming in the past. The IPCC* sums up the current views on Global warming:

What does this phrase mean?

“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”

Anthropogenic Causes Seem To Be Confirmed!

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

Facts

Where do we get the long term evidence for climate change

from?1. Ice Cores

• Best evidence for climate change comes from Greenland and Antarctic ice cores

• Ice cores are a frozen record of past climates. Like a time capsule!!

• Within these layers the ice contains air bubbles which contain carbon dioxide and oxygen isotopes.

• From looking at the graph you can see clearly the periods of low concentrations of CO2 occur during glacial periods

• High concentrations of CO2 link with warmer periods of time- like the Holocene interglacial we are going through now!

How accurate and reliable are these sources of data?

The sequences of sea level change links very closely with oxygen and CO2 isotope levels suggesting that this is a very reliable source!

2. Pollen Analysis

Pollen was extracted from sediment cores in peat bogs and lake beds.

Pollen grains are preserved in waterlogged sediments.

By analysing pollen we can see how ecosystems have changed in response to climate change.

Where do we get the long term evidence for climate change

from?

Not as reliable - as accurate pollen reconstructions rely on good preservation of pollen. Long pollen sequences are rare, and vegetation change may lag behind “climate change”.

How accurate and reliable are these sources of data?

2. Pollen Analysis

Where do we get the medium term evidence for climate change from?

1. Tree Rings (Dendrochronology)

Many trees are sensitive to changes in temp, sunlight and precipitation

In warm years trees have wide rings & vice versa

Record can go back 10,000years+

How accurate and reliable are these sources of data?

Good reliability – However, tree records only give localised records!

1. Tree Rings (Dendrochronology)

2. Paintings and written accounts

Bruegel Painting 1565

London Frost Fair 1789

Where do we get the medium term evidence for climate change from?

How accurate and reliable are these sources of data?

Paintings are a good line of evidence

Dickensian Winters

Where do we get the medium term evidence for climate change from?

The written word

How accurate and reliable are these sources of data?

The written word is also good evidence

Where do we get the medium term evidence for climate change from?

2. Historical records

Unreliable – These sources did not set out to record climate, and must be used with care. They are usually local, and difficult to generalise.

How accurate and reliable are these sources of data?

2. Historical records

Glaciers change in response to climate change. We can look at old photos/maps/paintings to measure

direct differences in glacial positions

Where do we get the medium term evidence for climate change from?

3. Glacier Retreat

Reliable – Good records stretch back to around 1880, before this the record is patchy.

3. Glacier Retreat

How accurate and reliable are these sources of data?

The last 128yrs of data suggest the Earth is 0.7 – 0.8 oC warmer 11 of the world’s hottest 12 years occurred in the decade 1995-2006 Global warming or natural?

Where do we get the short term evidence for climate change from?

Link between CO2 & temperature

How accurate and reliable are these sources of data?

Good evidence of the

Three possible effects of climate change.

1. Rise in Global Mean Temperature

2. Rise in Average Sea Level

3. Decline in Northern Hemisphere Snow |Cover

Homework

“An Inconvenient Truth” or “The Death of the Oceans” Watch it and fill in the sheets ready for

discussion next lesson.

Most scientists agree Anthropogenic causes are producing the enhanced greenhouse effect and leading to unprecident global warming.

Is the Carbon Anthropogenic (human) or Natural?