Global Warming 101
Roy W. Spencer, Ph.D
Principal Research Scientist
The University of Alabama In Huntsville
19 March 2007
Due to greenhouse effect
We are probably not
as warm as during
Medieval Warm Period
The GRIP (Greenland) borehole record is one of the best records because it is not a proxy, it is a
DIRECT measure of temperature. Shown are the last 2000 years. (Dahl-Jensen et al. 1998, Science,
282, 268-271 "Past Temperatures Directly the Greenland Ice Sheet"). A similar reconstruction occurs
for the Ural Mountain borehole temperatures (i.e. warmer 1000 years ago, Bemeshko, D., V.A.
Schapov, Global and Planetary Change, 2001.
Global Warming Basic Hypothesis:
1. Carbon Dioxide is a greenhouse gas,
2. it is increasing in the atmosphere (at ½ rate of human production),
3. therefore, the lower atmosphere MUST warm
CO2 concentration is now about
40% above pre-industrial times.
Most of our atmosphere is being continuously
recycled by precipitation systems, which then
determine the strength of the Greenhouse Effect
Cooling (loss of IR radiation)
by dry air to space
released through
causes air to rise,
rain falls to surface
Air sinks in
response to precipitation systems:
Sinking air is relatively dry
Sunlight absorbed
at surface
Boundary layer
warm, humid air
cool, dry air
removes heat
Ocean or Land
• Evidence for climate change
• Predictions of future climates
• Assessing response of natural ecosystems
• Future directions
GLOBAL WARMING BASICS: “Radiative Energy Balance” (= const. Temp.)
Incoming Sunlight = Emitted Infrared Radiation
Global average input = output =
≈235 Watts per square meter
=> Greenhouse gases affect Infrared Radiation
“Global Warming”
(at least since 1920) is Real…
But how unusual is it?
How much of it is natural versus man-made?
“Little Ice Age”
Data source: J. Hansen/ GISS
Niagara Falls NY - 1911
GLOBAL WARMING: Early Warning Signs
Fingerprints and Harbingers
Spreading disease
Coral reef bleaching
Heat waves and periods of
unusually warm weather
Glaciers melting
Earlier spring arrival
Downpours, heavy
snowfalls, and flooding
Sea level rise and coastal
Arctic and Antarctic
Plant and animal
range shifts and
population declines
Droughts and fires
Changes in
US 20th century
Global 20th century
A 1000-year record of temperatures
Borehole temperatures
Retreat of glaciers
Grinnell glacier, 1938
Grinnell glacier, 1981
Retreat of glaciers
Sea ice extent and mass
Coral reef bleaching
Bleaching hot
spots in last 15
Rising sea levels
Rising sea levels
Rising sea levels
Insect pests and disease
Changes in growing season length
Mauna Loa, HI
Thoning and Tans
Changes in US precipitation regimes
20th c.
Arctic Climate Impact Assessment (ACIA)
Sources: Claire Parkinson and Robert Taylor
Greenland Mass Loss – From Gravity Satellite
Responsibility for CO2 Emissions and Climate Change