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MET 112 Global Climate Change – Lecture 10
Recent Climate Change
Dr. Craig Clements
San Jose State University
Outline
 Recent trends in temperature
 Recent trends in GHGs
 Time scales
Modeled
temperature
changes
IPCC (2007)
(b) Additionally, the year by year (blue curve) and 50 year average (black curve) variations of the
average surface temperature of the Northern Hemisphere for the past 1000 years have been
reconstructed from “proxy” data calibrated against thermometer data (see list of the main proxy
data in the diagram). The 95% confidence range in the annual data is represented by the grey
region. These uncertainties increase in more distant times and are always much larger than in the
instrumental record due to the use of relatively sparse proxy data. Nevertheless the rate and
duration of warming of the 20th century has been much greater than in any of the previous nine
centuries. Similarly, it is likely7 that the 1990s have been the warmest decade and 1998 the
warmest year of the millennium.
Time series of
climate data
Time series of
climate data
Examples of Temperature Change




Trends
Periodic Oscillations
Random Variations
Jumps
Examples of Temperature Change

Draw the following:
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend + Oscillation
Random variations
Random + trend
Jump
Random + jump
Trend
Temperature
0
20
40
Time
60
80
100
This graphs represents
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
1.
2.
3.
4.
5.
6.
7.
0
20
40
Time
60
80
1
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
Time Frames -- Examples
 Seconds to minutes – Small-Scale Turbulence
 Hours – Diurnal Cycle (Caused by Earth’s
Rotation)
 Hours to Days – Weather Systems
 Months – Seasonal Cycle (Caused by tilt of
axis)
 Years – El Niño
 Decades -- Pacific Decadal Oscillation
 Centuries – Warming during 20th Century
(Increase in greenhouse gases?)
 Tens of thousands of Years – Irregularities in
Earth’s motions
 Millions of Years – Geologic Processes
Latest global temperatures
…“Over the last 140 years, the best estimate is that the
global average surface temperature has increased by
0.6 ± 0.2°C” (IPCC 2001)
 So the temperature trend is:
0.6°C ± 0.2°C
 What does this mean?
 Temperature trend is between 0.8°C and 0.4°C
 The Uncertainty (± 0.2°C ) is critical component to the
observed trend
Current CO2: ~383 ppm
What Changed Around 1800?
 Industrial Revolution
– Increased burning of fossil fuels
 Also, extensive changes in land use began
– the clearing and removal of forests
Burning of Fossil Fuels
 Fossil Fuels: Fuels obtained from the earth
are part of the buried organic carbon
“reservoir”
– Examples: Coal, petroleum products,
natural gas
 The burning of fossil fuels is essentially
– A large acceleration of the oxidation of
buried organic carbon
Land-Use Changes
 Deforestation:
– The intentional clearing of forests for
farmland and habitation
 This process is essentially an acceleration of
one part of the short-term carbon cycle:
– the decay of dead vegetation
 Also causes change in surface albedo
(generally cooling)
Carbon Budget Changes
 Units in Peta-grams (x1015) of Carbon per year
(PgC/yr)
 Atmosphere increase
3.3 ± 0.1
– Observations
 Emissions (fossil fuel, cement)
5.4 ± 0.3
– Estimates from industry
 Ocean-atmosphere flux
-1.9 ± 0.6
– Estimates from models/obs
 Final component is Land/atmosphere flux:
 What is the land/atmosphere flux?
Methane
Anthropogenic Methane Sources
 Leakage from natural gas pipelines and coal
mines
 Emissions from cattle
– Flatulence…gas
 Emissions from rice paddies
Nitrous Oxide
Anthropogenic Sources of Nitrous
Oxide
 Agriculture
CFCs
CFC-11
CFC-12
Sources of CFCs
 Leakage from old air conditioners and
refrigerators
 Production of CFCs was banned in 1987
because of stratospheric ozone destruction
– CFC concentrations appear to now be
decreasing
– There are no natural sources of CFCs
Lecture on ozone depletion to follow later in
semester…
Activity
1. Describe the 120 year temperature records in terms of
the seven above described types of variations (trend,
trend+oscillation etc.) by breaking up the time series
into periods (i.e. from 1930-1950, oscillation + positive
trend, from 1950-1970, negative trend)
2. Based on the past 120 years of globally averaged
temperatures:
a. What trend would you assign to this period. (i.e.
0.3°C over 120 years)
b. If you were to break up the data into time sections
provide trends over the following time periods i)
1880-1920; b) 1920-1940 and c) 1970-2000
Temperature over the last 10 years
The Land and Oceans have both warmed
Precipitation patterns have changed