1 Climate Change ScienceOctober 22, 2006 Thomas C. Peterson NOAA’s National Climatic Data Center Asheville, North Carolina Global Energy and Climate Change:

11Climate Change ScienceOctober 22, 2006

Thomas C. Peterson

NOAA’s National Climatic Data CenterAsheville, North Carolina

Global Energy and Climate Change:The Transportation – Land Use – Environment Connection

UCLA Lake Arrowhead Conference CenterLake Arrowhead, California

Climate Change Science:

What we know and don’t know

Climate Change Science:

What we know and don’t know


PHYSICAL

PROCESS

2) How well do we understand the climate system ?Outline

• Defining the Climate 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


A SCIENTIFIC STATUS REPORT:There is a natural greenhouse effect. It keeps the

Earth warmer than it would be otherwise.

Points . . .

In terms of basic physics:(A) If an object is

bathed in visible light . . .

(B) It warms up and . . .

(C) It emits infrared . . . LIGHT !

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“Confidence Index”

In terms of planet Earth:

}

Atmosphere AbundanceNitrogen . . . . . . . . . . . . . . 78%Oxygen . . . . . . . . . . . . . . . 20%

Water Vapor . . . . . . . . . . 2%Carbon Dioxide . . . . . . 0.04%

Greenhouse Gases


?

A SCIENTIFIC STATUS REPORT:There is a natural greenhouse effect. It keeps the

Earth warmer than it would be otherwise.(Cont’d.)

Key Aspects . . .

Water Vapor & Carbon Dioxide have been part of our atmosphere for millions of years.

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Their presence yields an average surface temperature of ~ 60oF.

Without them, the average would be ~ 5oF.

Q: So . . . What’s the problem?


GREENHOUSE GASES ARE INCREASING IN THE ATMOSPHERE BECAUSE OF HUMAN ACTIVITIES, & THEY ARE INCREASINGLY

TRAPPING MORE HEAT. Points . . .

Impeccable scientific measurements

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Other gases have increased too.

For Example:

• Methane (1/3 the effect of CO2)

• Sulfur (a cooling tendency)

The increases are human-caused.

CO2 - Combustion Methane - Agriculture

36% increase over the industrial era

ICE CORES

AIR SAMPLES


Climate Forcing Summary

From Ravishankara (2006)


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.)


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


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

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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)


MOST OF THE WARMING OVER THE PAST50 YEARS IS LIKELY TO BE DUE TO

GREENHOUSE GAS INCREASES.

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.

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?Q: What could this mean for the future?


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.

Indeed . . . To stabilize at doubled cuts in emissions

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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


Observed changes & projections “in the News”

- Heavy Precipitation

- Tropical storms

- Drought

Hurricane Katrina Forecast Track Overlay

Western U.S. Drought


Observed changes and projectionsHeavy Precipitation

Increasing levels of greenhouse gases

warm the climate and lead to increasesin very heavy precipitation events

Why: Increasing air temperatures result in a greater amounts of water vapor in the air

Facts from Climate Models and Theory

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Observed changes and projectionsHeavy Precipitation

Observed 3% increase in extreme precipitation frequency over last 50 years; middle & high latitudes (IPCC)

Warmer climates get more rainfall inextreme events compared to colder climates

Facts from Observations

Precipitable water (atmospheric water vapor) has increased ~ 0.5 mm per decade (~ 0.2 inches per century) latter half 20th century.

Alexander et al. (2005)

Contributes to Annual TotalHeavy Precip Days (>95th percentile

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Observed changes and projectionsTropical Storms

• Hurricanes respond to many environmental factors in addition to ocean temperatures.

– Tropical multi-decadal phenomena and the El Niño/La Niña cycle are important factors

• Research: global warming leads to increased hurricane intensity; less evidence for frequency

• Since 1995, significantly more

hurricanes and more intense that the previous two decades

• Past decade: increased US landfalls; higher landfalls frequency occurred in early century

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What factors influence seasonal to multi-decadal hurricane activity?

Atlantic hurricane activity during the 20th Century

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Observed changes and projectionsTropical Storms

• 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)

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Confidence Index

Confidence Index

How have ocean temperatures varied?

How long will the current active period last?• Varying Viewpoints. Increase in hurricane

intensity and frequency attributed to:– Natural Variability alone (cycles)……..

– Natural Variability and Global Warming……………


Observed changes and projectionsDrought Observations

• 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.

Drought activity during the 20th and early 21st Century

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Observed changes and projectionsDrought Observations

• 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).

• 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.

Drought as documented in the paleoclimatic record?

What about the Future?10

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IT IS A COMPLEX PLANET & WE HAVE IMPERFECT KNOWLEDGE, SO, SURPRISES LIKELY

Possible! Here’s why:

We are entering a new regime of climate perturbation.

Climate is a non- linear system.

} Surprises?

• Currently unknown geophysical processes activated?

• Methane releases as permafrost melts

• Ocean circulation changes

• Melting Ice Sheets

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


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) }Many details

hard to predict }Some aspects have more confidence than others


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.


YearTo the range of projected changes into perspective, the mean annual temperature

in Los Angeles is ~ 3.5 degrees C (or Kelvins) warmer than San Francisco.


Year


Precipitation Projections

YearTo put the range of projected changes into perspective, the annual precipitation in San Francisco is ~ 18 cm greater than Los Angeles


U.S. Area Averaged


U.S. Area Averaged



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.

1 Climate Change ScienceOctober 22, 2006 Thomas C. Peterson NOAA’s National Climatic Data Center Asheville, North Carolina Global Energy and Climate Change:

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