Summary of Lecture 1
• Introduction to Earth’s atmosphere
– origin
– composition
– structure
– comparison with other planets
• Stefan’s law
4 T  S 1   
4
s
Solar and Terrestrial Radiation
Sun ~ 6000 K
UV/vis lmax~0.6mm
Solar flux =1370 Wm-2
S (1-)/4=TE4
Earth ~ 255 K
IR
lmax~ 12mm
UV absorption
DUV
UVc
UVb
UVa /
Visible
Infra
Red
Absorption by atmospheric gases
Solar energy received
Radiation Balance
Notes:
• Surface has Ts=288 K and radiates Ts4 = 400 Wm-2
(117 units).
• Atmosphere at 250 K radiates 220 Wm-2 (64 units),
both up and down.
• 30% of surface radiation is reflected by the atmosphere
(32 units), giving a total downward flux of 96 units.
• Non-radiative flux of 100 Wm-2 (30 units) drives the
atmospheric circulation and weather
Seasonal net IR radiation
Global Climate
Net short, long and global
radiation entering and leaving
the top of our atmosphere
measured by satellite.
Data are from the Earth
Radiation Budget Experiment
(ERBE)
Global Warming
Global temperatures 1880-2015
Change in extent of Arctic sea ice
Rising CO2 levels
Carbon dioxide concentration
in the atmosphere, due to three emissions scenarios
700350
Business as usual emissions
Constant 1990 emissions
50% reduction in emissions
CO2 concentration ppm
300
600250
200
500150
100
400 50
350
0
1990
2000
2010 2020
2030
2040
2050
2060
2070 2080
2090
2100
Global temperature rise, degrees C
Global temperature rise
IPCC A1FI emissions
A2 emissions
B2 emissions
B1 emissions
Components of sea-level rise
Hadley Centre
Pattern of annual temperature changes
2080s relative to present day
Met Office / Hadley Centre
0
A1FI emissions scenario
1
2
3
4
5
6
Temperature rise
Medium-high emissions scenario, 2080s
winter
summer
Hadley Centre
Hadley Centre
°C
Pattern of annual precipitation changes
2080s relative to present day
Met Office / Hadley Centre
–3
–2
A1FI emissions scenario
–1
–0.5
–0.25
0
0.25
0.5
1
2
3
Change in precipitation
Medium-high emissions scenario, 2080s
winter
summer
Hadley Centre
Hadley Centre
%
Change in surface temperature
with forced THC collapse, but without change in greenhouse gases
Hadley Centre
Deg C