OVERVIEW OF CLIMATE OVERVIEW OF CLIMATE SCIENCESCIENCE

What is the difference between climate and weather?

ClimateClimate A composite of a region’s average conditions

ClimateClimate

• Applies to long-term changes • Measured in terms of:

– Temperature– Precipitation– Snow and ice cover– Winds

• Can refer to– The entire planet– Specific regions (continents or oceans)

WeatherWeather

WeatherWeather

• Shorter fluctuations lasting– Hours– Days– Weeks

• Can refer to very short changes

Climates on Earth are Favorable to Life

• Surface Temperature– Averages 15oC (59oF)– Much of the Surface Ranges from

0o C to 30oC

Temperature ScalesTemperature Scales

• Kelvin Scale– Divided into units of Kelvin

instead of degrees– Absolute scale

• Converting values between the Fahrenheit and Celsius Scales

Tc = (Tf – 32)

Tf = (Tc + 32)

59

59

Geologic Time

1 km = 1 million years LA to NY – 4,500

million yrs Precambrian: LA to

Pittsburgh, PA Paleozoic – entirely in

PA Mesozoic – 179 km

drive to NJ, 65 from NYC

End of ice age – 10 m from destination

2,000 AD years is 2 meters

Human life span<10 cm

Another Geologic Time Analogy . . .

If all Earth history had been recorded from its origin to the present as a motion picture

• Each frame would flash on the screen for 1/32 of a second which would equal 100 years

• To show all Earth history would take 16 days.• The last 2,000 years would take ¾ of a second• The present to the last ice age would be less than

7 seconds.• The last 65 million years would take almost six

hours• The Paleozoic Era would last two days

• We will focus on the last several million years of Earth’s history (about 10% of its total age)

• This can only be represented by:– A series of magnifications– Using a log scale that increases by factors of 10

Time Scales of Climate ChangeTime Scales of Climate Change

Longest Shortest

Tectonic Change: The Longest Time Tectonic Change: The Longest Time ScaleScale

• Shows a slow warming – Between 300 Myr and 100 Myr

• Last 100 million years– Gradual Cooling– Led to ice ages during the last 3

million years

• Note shorter oscillations

Time Scales of Climate ChangeTime Scales of Climate Change

• As the time scales become shorter– Progressively smaller time scales are magnified out

from the larger changes at longer time scales.

Degree of Degree of ResolutionResolution

• Amount of detail retrieved from records• Older records have less resolution

– Long term averages over millions of years

• Younger records have progressively greater resolution– Shorter term averages– Occur within intervals of:

• Thousands• Hundreds• Even tens of years

Development of Climate ScienceDevelopment of Climate Science

• Modern climatology is an interdisciplinary endeavor throughout the world– Universities– National Laboratories– Research Centers

National Center for Atmospheric ResearchBoulder, CO

Diversity of StudiesDiversity of Studies• Meteorology• Oceanography• Chemistry• Glaciology• Ecology• Geology

– Includes geophysics, geochemistry, paleontology

• Climate Modelers• Historians

Studying Climate Change –Studying Climate Change –The Scientific MethodThe Scientific Method

• Hypothesis– An informal idea that has not been widely

tested by the scientific community– Most are discarded.

• Theory– When a hypothesis is capable of explaining a

wide array of observations.– Additional observations support the theory

• New techniques for data analysis• Devise models

Theories can be discardedTheories can be discarded

Ongoing work may disprove the predictions of a current theory

An Historical Example . . .An Historical Example . . .The Geocentric Model of the Solar SystemThe Geocentric Model of the Solar System

• Devised by Ptolemy (Claudius Ptolemaeus) in the second century AD

• Accepted until 1543

The Heliocentric Model replaced the Geocentric Model

Pluto is no longer considered a planet!

Pluto’s Been Demoted!Pluto’s Been Demoted!

• On August 24, 2006 the International Astronomical Union redefined the definition of a planet as:– “a celestial body that is in orbit around the sun– has sufficient mass for its self-gravity to

overcome rigid body forces so that it assumes a nearly round shape,

– and has cleared the neighborhood around its orbit.”

Pluto is now considered a “Dwarf Planet”Pluto is now considered a “Dwarf Planet”• Pluto lost its status as a planet because

it’s highly eccentric orbit crosses over the orbit of Neptune.– As such it hasn’t “cleared the

neighborhood around its orbit.

• A dwarf planet like Pluto is– Any other round object that

• Has not “cleared the neighborhood around its orbit• Is not a satellite

A A LawLaw or or UnifyingUnifying Theory Theory

• If a theory has survived the test of time– Years or decades

• It’s the closest approximation to “the truth” as possible.

• It’s impossible to prove a theory as being true.

• We can only prove it’s untrue.

Revolutions in Climate ChangeRevolutions in Climate Change

• A scientific revolution that endeavors to understand climate change has accelerated.

• The mystery of climate change yields it’s secrets slowly.

• This revolution has achieved the status so that it has begun to take its place alongside two great earlier revolution in knowledge of Earth history.

EvolutionEvolution

Evolution of the Jaw in FishEvolution of the Jaw in Fish

Who is the Descendent of this Mammal?Who is the Descendent of this Mammal?

Plate TectonicsPlate Tectonics

The unifying theory of geology

Tectonic Plate BoundariesTectonic Plate Boundaries

Earth’s Climate SystemEarth’s Climate System

• Small number of external factors

• Force or drive changes in the climate system

Earth’s Climate SystemEarth’s Climate System

• Internal components respond to external factors

• They change and interact in many ways

Earth’s Climate SystemEarth’s Climate System

• End Result of interactions– A number of

observed variations in climate

– Can be measured– Analogous to a

machine’s output after input (factors)

Climate ForcingClimate Forcing

Three fundamental kinds of climate forcing

1. Tectonic Processes1. Tectonic Processes

• Part of Plate Tectonic Theory

• Alter the geography of Earth’s surface– Changes in distribution of land and sea– Changes in surface topography

• Formation of mountain ranges• Erosion of the land surface

– Slow processes• Occur on a scale of millions of years

2. Variations in Earth’s Orbit2. Variations in Earth’s Orbit

• Alter the amount of solar radiation received on Earth– By season– As a function of latitude

• Occur over tens to hundred of thousands of years.

3. Changes in the Sun’s Intensity3. Changes in the Sun’s Intensity

• Affects the amount of solar radiation arriving on Earth

• Long-term increase since Earth’s origin• Shorter-term variations may be partially

the cause for changes on shorter time scales of– Decades– Centuries– Millenia

A Fourth Factor to be ConsideredA Fourth Factor to be Considered

• Anthropogenic Forcing– In a strict sense, not part of the natural

system– The effect of humans on climate– Unintended byproduct of agricultural,

industrial, and other human activities– Results from additions of materials to the

atmosphere

Climate System ResponsesClimate System Responses

• Changes in global and regional temperatures• Extent of ice• Amounts of rainfall and snowfall• Wind strength and direction• Ocean circulation

– At Depth– At the surface

• Vegetation– Types– Amount

Response TimeResponse TimeAn Example . . .An Example . . .

• The rate at which water in the beaker warms

• Rate slows with time

Response TimeResponse TimeAn Example . . .An Example . . .

• Equilibrium is reached– Rate slows as response

nears this state

Variation in the Response Times of Variation in the Response Times of Climate System ComponentsClimate System Components

Time ScalesTime Scales of of

Forcing Vs. ResponseForcing Vs. Response

• Forcing is Slow in Comparison to Response• Forcing is Fast in Comparison to Response

• Forcing and Response Time Scales are Similar

Slow Slow Forcing in Comparison to ResponseForcing in Comparison to Response

• Response keeps pace with gradual forcing (i.e., Equivalent to slowly increasing the bunsen burner flame.)

• Typical of tectonic scales of climate change– Climate changes in response to movement of landmasses

• 1 degree of latitude per million years (100 km/million years)• Slow changes in solar heating• Average temperature over the continent keeps pace with average changes

in solar radiation because of the short response time of land and water

Earlier Time Later

Fast Fast Forcing in Comparison to ResponseForcing in Comparison to Response

• Response time of the climate system is much slower than the time scale of the change in forcing– Little or no response– Analogous to turning the Bunsen burner on and off so quickly

that temperature doesn’t respond

Earlier Time Later

Fast Fast Forcing in Comparison to ResponseForcing in Comparison to ResponseThe Eruption of Mt. Pinatubo - 1991The Eruption of Mt. Pinatubo - 1991

• Earth’s average temperature decreased by 0.5o C in less than a year• Most of the fine dust remained aloft for only a few years• No long-term climate change

Similar Forcing and Response Time Similar Forcing and Response Time ScalesScales

• Bunsen Burner Analogy– Abruptly turned on

• Left on for awhile

• Turned off

– Turned on again• And so on . . .

– Varying degrees of response

• In the natural world climate forcing rarely acts in an “on-or-of” way

Earlier Time Later

Similar Forcing and Response Time Similar Forcing and Response Time ScalesScales

• Climate forcing (Bunsen Burner) – Behaves as a “moving target”

• Climate system response (temperature) never catches up– lags behind

• Continuously changing series of equilibrium values – Created by the moving target

of climate forcing• Rate of response is always

fastest when the system is farthest from equilibrium

Earlier Time Later

Cycles of Forcing and ResponseCycles of Forcing and Response

• Response to a “moving target” forcing is usually cyclic

• Fundamentally the same as the physical response of the beaker of water.

Cycles of Forcing and ResponseCycles of Forcing and Response

• Larger climate change – The climate system has

ample time to respond

• The same amplitude of forcing produces – Smaller climate changes

if the climate system has less time to respond.

Cycles of Forcing and ResponseCycles of Forcing and Response

• Results from changes in Earth’s orbit– Over tens of thousands of years– The climate response time characteristic of

large ice sheets that advance and retreat

• Characteristic of Seasonal time lags between– Highest solar intensity and hottest

temperatures– Lowest solar intensity and lowest

temperatures

Response Times Can Vary with an Response Times Can Vary with an Abrupt Change in Climate ForcingAbrupt Change in Climate Forcing

• Climate responses can range from slow to fast within different components of the climate system.

• Depends on their inherent response times.

Variations in Cycles of ResponseVariations in Cycles of Response

• Some fast-response parts track right along with the climate forcing.

• Other slow-response parts lag behind the forcing.

Variations in Cycles of ResponseVariations in Cycles of Response

• Fast response– Seasonal changes in tropical monsoons

• Slow response– Ice sheets

Variations in Cycles of ResponseVariations in Cycles of Response

• Low position of asterisk on the cold slow-response curve– Ice sheet is at its maximum size – Heating from the Sun has begun a slow, long-term

increase• Has not yet begun to melt any of the ice

Single point of time - A huge ice sheet in Canada

and northern U.S.

This Has Happened in the PastThis Has Happened in the Past

Pleistocene Ice Age: 20,000 years ago to 11,000 years ago

Two Possible Responses of Air Temperatures Two Possible Responses of Air Temperatures Over Land South of the Ice SheetOver Land South of the Ice Sheet

• Would air warm with slow increase of solar radiation?– Climate response would track right along with the initial forcing

curve

• Would air temperature still be affected by the ice sheet?– If so, the response might follow a slower, delayed response

pattern of the ice.– The ice would also be exerting and influence of its own

Single point of time - A huge ice sheet in Canada

and northern U.S.

Both Explanations Both Explanations are are

Sound and PlausibleSound and Plausible

• The response of air temperatures could be influenced by both the Sun and the ice.

• Then, the air temperature response would fall between the fast and slow responses.– Faster than the response of the ice– Lagging behind the forcing of the Sun

Climate FeedbacksClimate Feedbacks

Processes that Alter Climate Changes Already Underway

Positive FeedbackPositive Feedback

• Produces additional climate beyond that caused by the original factor• Amplifies change underway• Not to be interpreted as a “good” change.• Example:

– Decrease in solar energy could result in glaciers at high latitudes– Increase in ice and snow cover could further result in lower temperatures.

Negative FeedbackNegative Feedback

• Climate change is muted.• Not to be considered a “bad” change.• After initial climate change is triggered, some components of the

climate system reduce it.• Example

– Effect of clouds on warming effects of increasing CO2 in the atmosphere.