Climate Change Science:
What we know and don’t know
Thomas C. Peterson
NOAA’s National Climatic Data Center
Asheville, North Carolina
Global Energy and Climate Change:
The Transportation – Land Use – Environment Connection
UCLA Lake Arrowhead Conference Center
Lake Arrowhead, California
October 22, 2006
Climate Change Science
1
P
H
Y
S
I
C
Outline
A
• Defining the Climate L
•
•
•
•
P
R
O
C
E
S
S
2) How well do we
understand the climate
system ?
Change Issue
Common misperceptions
Understanding observed
changes
• Changes & projections
“In the News”
•
Heavy
Precipitation
•
U.S. Tropical
storms
•
Drought
General conclusions
Climate change and
transportation
October 22, 2006
Climate Change Science
2
A SCIENTIFIC STATUS REPORT:
10
There is a natural greenhouse effect. It keeps the
Earth warmer than it would be otherwise.
5
0
 Points . . .
 In terms of basic physics:
(B) It warms
up and . . .
(C) It emits
infrared . . .
 In terms of planet Earth:
Atmosphere
(A) If an object is
bathed in visible
light . . .
“Confidence
Index”
LIGHT !
Abundance
Nitrogen . . . . . . . . . . . . . . 78%
Oxygen . . . . . . . . . . . . . . . 20%
}
Water Vapor . . . . . . . . . . 2%
Carbon Dioxide . . . . . . 0.04%
Greenhouse Gases
October 22, 2006
Climate Change Science
3
A SCIENTIFIC STATUS REPORT:
10
There is a natural greenhouse effect. It keeps the
Earth warmer than it would be otherwise.
(Cont’d.)
5
0
 Key Aspects . . .
“Confidence
Index”
 Water Vapor & Carbon Dioxide have been part of our
atmosphere for millions of years.
 Their presence yields an average surface
temperature of ~ 60oF.
 Without them, the average would be ~ 5oF.
?
Q: So . . . What’s
the problem?
October 22, 2006
Climate Change Science
4

GREENHOUSE GASES ARE INCREASING IN
THE ATMOSPHERE BECAUSE OF HUMAN
ACTIVITIES, & THEY ARE INCREASINGLY
TRAPPING MORE HEAT.
Points . . .
5
0
“Confidence
Index”
 Impeccable scientific measurements
 Other gases have
increased too.
10
ICE
CORES
AIR
SAMPLES
 For Example:
•
•
Methane (1/3 the effect
of CO2)
Sulfur (a cooling tendency)
 The increases are human-caused.
 CO2 - Combustion
 Methane - Agriculture
October 22, 2006
36% increase over
the industrial era
Climate Change Science
5
Climate Forcing Summary
From Ravishankara (2006)
October 22, 2006
Climate Change Science
6
Common Misperceptions
 Last winter was cold & snowy in Europe & Asia - so much for global warming!
• Actually - - - last winter was much warmer than average
across the USA
• Probability of Northern Hemisphere cold winters are decreasing
(e.g., last 12 winters above average)
 Satellites show global cooling not warming!
• Thought to be true several years ago
• Now - - - more data and improved analyses
reveal significant warming at the surface and
in the troposphere
 Heat islands lead to over-exaggerated claims of observed warming!
• Strong warming over oceans (unaffected by
heat islands), snow and ice extent decreasing
• Heat island effect examined and addressed
in the temperature records
• Lake and river ice extent decreasing
• Paleo data reveal warming (bore holes, tree rings, ice cores, etc.)
October 22, 2006
Climate Change Science
7
Common Misperceptions (cont’d.)
 Solar variations are responsible for any global warming!


Best evidence today suggests warming in first part of the
20th century influenced by solar radiation
Since satellite measurements (late 1970s) no appreciable
changes in total solar output - - at time of rapid global temperature increases
 Global warming will be negligible due to the
planet’s self regulating thermostat (the “iris effect”)!


Redistribution of tropical clouds were
hypothesized to allow more heat to escape into space as
globe gets warmer
BUT - - Observational data (in-situ and satellite)
show the opposite
October 22, 2006
Climate Change Science
8
THERE IS A COLLECTIVE PICTURE OF A
WARMING WORLD, & HUMAN ACTIVITIES
HAVE LIKELY CONTRIBUTED
 Points . . .
 Global temperatures: Up 0.7 – 1.4o F over past 100 years
 Consistent with the warming:






Glacial retreat
10-15% reduction in Arctic sea ice extent (1970s)
Snow-cover decrease (10% since 1970s)
Freeze-free periods lengthened (20th century)
Sea-level increased 4-8 inches (since 19th century)
Lake and river ice shortened season
(~ 2 weeks, 19th to 20th century)
October 22, 2006
10
5
0
“Confidence
Index”
Climate Change Science
9
MOST OF THE WARMING OVER THE PAST
50 YEARS IS LIKELY TO BE DUE TO
GREENHOUSE GAS INCREASES.
10
5
0
“Confidence
Index”
 Reasons . . .
Comparisons of simulated
vs. observed temperatures:
 Simulations with natural and human
factors match observations best
 Correspondences increase with time
 Probability is low that a “natural only”
Earth would have such correspondences.
?
Q: What could this
mean for the future?
October 22, 2006
Climate Change Science
10
A CONTINUED GROWTH IN GREENHOUSE
GASES IS PROJECTED TO LEAD TO VERY
SIGNIFICANT INCREASES IN GLOBAL
TEMPERATURES & SEA LEVEL.
 Points . . .
 CO2 abundance will likely double by 2100.

10
5
0
“Confidence
Index”
Indeed . . . To stabilize at
doubled
cuts in emissions
 Predicted climate responses
 For a range of future emission scenarios
(Non-intervention, economics,
technology, population)
•
Global temperature rise of 2.5 to 10oF
by 2100
•
If so, this would exceed the natural
changes over the past 10,000 years
•
Corresponding sea level rise of
4 to 35 inches by 2100
October 22, 2006
Climate Change Science
11
Observed changes & projections
“in the News”
Hurricane Katrina Forecast Track Overlay
- Heavy Precipitation
- Tropical storms
Western U.S. Drought
- Drought
October 22, 2006
Climate Change Science
12
Observed changes and projections
Heavy Precipitation
Facts from Climate Models and Theory
10
 Increasing levels of
greenhouse gases
5
warm the climate
and lead to increases
0
in very heavy
“Confidence
precipitation events Index”
10
Why:
Increasing air
temperatures result in a
greater amounts of water
vapor in the air
October 22, 2006
5
0
“Confidence
Index”
Climate Change Science
13
Observed changes and projections
Heavy Precipitation
Facts from Observations
 Observed 3% increase in extreme
precipitation frequency over last
50 years; middle & high latitudes (IPCC)
Contributes to Annual Total
Heavy Precip Days (>95th percentile
 Warmer climates get more rainfall in
extreme events compared to colder climates
 Precipitable water
(atmospheric water vapor)
has increased ~ 0.5 mm per
decade (~ 0.2 inches per
century) latter half 20th
century.
October 22, 2006
10
5
Alexander et al. (2005)
0
“Confidence
Index”
Climate Change Science
14
Observed changes and projections
Tropical Storms
What factors influence seasonal to multi-decadal hurricane activity?
•
Hurricanes respond to many environmental factors in
addition to ocean temperatures.
10
– Tropical multi-decadal phenomena and the
El Niño/La Niña cycle are important factors
•
5
Confidence
0 Index
Research: global warming leads to increased hurricane
10
intensity; less evidence for frequency
5
Confidence
0 Index
Atlantic hurricane activity
during the 20th Century
•
•
October 22, 2006
Since 1995, significantly more
hurricanes and more intense that
the previous two decades
10
5
Confidence
0 Index
Past decade: increased US landfalls; higher
landfalls frequency occurred in early century
Climate Change Science
15
Observed changes and projections
Tropical Storms
How have ocean temperatures varied?
• Over the 20th Century, global ocean
temperatures have warmed and…
• Tropical Atlantic temperatures
significantly warmer than
the global average
– Part of this warming may be related
to the Atlantic Multi-decadal
Oscillation (AMO)
How long will the current active period last?
• Varying Viewpoints. Increase in hurricane
intensity and frequency attributed to: 10
– Natural Variability alone (cycles)……..
5
Confidence
0 Index
– Natural Variability and Global Warming……………
October 22, 2006
10
5
Confidence
0 Index
Climate Change Science
16
Observed changes and projections
Drought Observations
Drought activity during the 20th and early 21st Century
• Drought is a recurrent part of the U.S. climate.
• Widespread drought can affect the country for years
(e.g., 1930s “Dust Bowl”)
• U.S. droughts show
pronounced multi-year
to multi-decadal
variability, but no
convincing evidence
for long-term trends
toward more or
fewer events. 10
5
Confidence
0 Index
October 22, 2006
Climate Change Science
17
Observed changes and projections
Drought Observations
Drought as documented in the paleoclimatic record?
• Within the past millennium there have
been severe droughts in both the western
U.S. and Midwest that have lasted for
multiple decades (50 years).
10
5
Confidence
0 Index
What about the Future?
• As temperatures increase, it may lead to
more intense droughts during periods of
dry weather due to increases in evaporation.
• Models suggest that as the planet warms,
storminess and the jet stream tracks will
shift northward; may lead to drier conditions
in S and SW U.S.
October 22, 2006
10
5
Confidence
0 Index
10
5
Confidence
0 Index
Climate Change Science
18
IT IS A COMPLEX PLANET & WE HAVE IMPERFECT
KNOWLEDGE, SO, SURPRISES LIKELY
 Surprises?
Possible! Here’s why:
• Currently unknown geophysical
processes activated?
• Methane releases as
permafrost melts
• Ocean circulation changes
• Melting Ice Sheets
}
We are entering a
new regime of
climate perturbation.
Climate is a nonlinear system.
 Is there a safe level of greenhouse gas concentrations?
 Value judgment . . .
 On our way to concentrations larger than observed over past
500,000 years or more
October 22, 2006
Climate Change Science
19
GENERAL CONCLUDING COMMENTS
 Bottom lines
The VAST MAJORITY of the scientific viewpoint:
 Human-caused global climate change has occurred.
 Exactly - where (regions)
- when (rate of change)
- how much (magnitude)
October 22, 2006
}
Many details
hard to predict
}
Some aspects have more
confidence than others
Climate Change Science
20
Now a few details from our new paper
“Climate Variability and Change with
Implications for Transportation”
• Commissioned by the National Research
Council.
– Just submitted last month.
• Transportation is particularly sensitive to
changes in extremes.
• Used historical observations and model
projections that contributed to the IPCC
Fourth Assessment Report.
October 22, 2006
Climate Change Science
21
Year
To the range of projected changes into perspective, the mean annual temperature
October
2006 is ~ 3.5 degrees C (or Kelvins) warmer than San
Climate
Change
in Los22,
Angeles
Francisco
. Science
22
Year
October 22, 2006
Climate Change Science
23
Precipitation Projections
Year
To put the range of projected changes into perspective, the annual
October
22, 2006
Change Science
precipitation
in San Francisco is ~ 18 cm greater than LosClimate
Angeles
24
U.S. Area Averaged
October 22, 2006
Climate Change Science
25
U.S. Area Averaged
October 22, 2006
Climate Change Science
26
October 22, 2006
Climate Change Science
27
Climate Change and Transportation
Conclusions
• Climate change will definitely impact
transportation.
• Some impacts will be negative.
– E.g., increased potential for rail track buckling.
• Some impacts will be positive.
– E.g., likely opening of the Northwest Passage.
• In all cases, planning that considers climate
change will be important.
October 22, 2006
Climate Change Science
28