Earth’s Climate & Mankind ClimateClimate

Long-term (years and Long-term (years and longer) average condition longer) average condition of a regionof a regionRainfall or snowfallRainfall or snowfallSnow and ice coverSnow and ice coverTemperatureTemperature

WeatherWeather Short-term (hours to Short-term (hours to

weeks) fluctuationsweeks) fluctuations

Historical Examples of Climate Change?

Advance and retreat of glaciersAdvance and retreat of glaciers Alpine glaciers shrunk in 20Alpine glaciers shrunk in 20thth century century

Thinning of ice on NW GreenlandThinning of ice on NW Greenland See See NatureNature v. 414, 60-62 v. 414, 60-62

Sea level riseSea level rise El Nino/La Nina oscillationsEl Nino/La Nina oscillations Length of growing season in Alaska Length of growing season in Alaska

increased from 1950-2000increased from 1950-2000 Decrease in Arctic sea ice cover from Decrease in Arctic sea ice cover from

1970-20001970-2000

How We Will Study Climate Change

Time Scales of Climate Change

Earth’s Climate System Earth’s climate systemEarth’s climate system

Air, water, land and vegetationAir, water, land and vegetation Changes in Earth’s climate systemChanges in Earth’s climate system

Driven by Driven by causecause and and effecteffect Buzz words of climate scientists – Buzz words of climate scientists –

forcing and responseforcing and response Forcing – factors that drive or cause Forcing – factors that drive or cause

changeschanges Response – the climate change that Response – the climate change that

occursoccurs

Earth’s Climate System and the Interactions of its Components

Forcing & Response

Climate Forcing Tectonic ProcessesTectonic Processes

Slow movement of plates affects Slow movement of plates affects climate only very slowlyclimate only very slowly

Climate Forcing Earth-Orbital ChangesEarth-Orbital Changes

Variations in earth’s orbit around the Variations in earth’s orbit around the Sun affect the amount of solar Sun affect the amount of solar radiation received on Earth’s surface. radiation received on Earth’s surface. Orbital scale changes occur over tens Orbital scale changes occur over tens to hundreds of thousands of years.to hundreds of thousands of years.

Climate Forcing Changes in the Strength of the SunChanges in the Strength of the Sun

Affects the amount of solar radiation Affects the amount of solar radiation received on Earth’s surface. Can received on Earth’s surface. Can occur on long-term (100’s of millions occur on long-term (100’s of millions of years) or on short-term (10-1000’s of years) or on short-term (10-1000’s years)years)

Climate Forcing Anthropogenic ForcingAnthropogenic Forcing

Not part of the natural climate systemNot part of the natural climate system Affect of humans on climateAffect of humans on climate Byproduct of agricultural, industrial Byproduct of agricultural, industrial

and other human activitiesand other human activitiesExample is addition materials to the Example is addition materials to the atmosphere such as gases (COatmosphere such as gases (CO22, , NN22O, etc.), sulfate particles and soot.O, etc.), sulfate particles and soot.

Response Time Time it takes the climate system to Time it takes the climate system to

react to a change in forcing (reaction react to a change in forcing (reaction time)time)

Response time = amount of time it takesto get 50% of the way toward equilibrium

Response Time Response curve exponentialResponse curve exponential

System moves ½ the way to equilibrium with each System moves ½ the way to equilibrium with each passage of response timepassage of response time

Absolute amount of change decreases through time Absolute amount of change decreases through time but proportional change towards equilibrium is but proportional change towards equilibrium is constantconstant

Time Scale of Forcing vs. Response

Forcing is slow compared to responseForcing is slow compared to response Climate system tracks forcingClimate system tracks forcing Typical of climate change on tectonic time Typical of climate change on tectonic time

scalesscales

Time Scale of Forcing vs. Response

Forcing is fast compared to responseForcing is fast compared to response Little response to climate forcingLittle response to climate forcing Stochastic events with short-lived responseStochastic events with short-lived response

Time Scale of Forcing vs. Response

Time scale of forcing = response timeTime scale of forcing = response time Yields dynamic and realistic responseYields dynamic and realistic response

Frequency of forcinghas a direct effect onthe magnitude of theresponse

The time scale offorcing is not longenough to allow thesystem to reachequilibrium

Cyclic Forcing and Response Natural climate forcing may vary in a Natural climate forcing may vary in a

cyclic fashion producing cyclic responsecyclic fashion producing cyclic response Response time same; forcing is Response time same; forcing is

changingchanging

Cyclic Forcing and Response Since forcing is constantly changing, Since forcing is constantly changing,

equilibrium value of system also equilibrium value of system also changeschanges Equilibration values set by the rate Equilibration values set by the rate

and direction of change of the forcingand direction of change of the forcing Regardless of the forcing rate of Regardless of the forcing rate of

changechange Response rate of the system is is Response rate of the system is is

fastest when the system is furthest fastest when the system is furthest from equilibriumfrom equilibrium

Cyclic Forcing and Response Frequency of forcing Frequency of forcing

affects the amplitude affects the amplitude of the responseof the response Slower cycling Slower cycling

produces a larger produces a larger response – more response – more time to reacttime to react

Faster cycling Faster cycling produces a smaller produces a smaller response – less response – less time to react time to react

Cyclic Forcing and Response

Cycling forcing and response typical of Cycling forcing and response typical of Milankovitch type orbital cyclesMilankovitch type orbital cycles Changes in incoming solar radiation Changes in incoming solar radiation

due to changes in Earth’s orbit occur due to changes in Earth’s orbit occur cyclically over tens of thousands of cyclically over tens of thousands of yearsyears

Response time of large glacial ice Response time of large glacial ice sheets also tens of thousands of sheets also tens of thousands of years years

Response Rates & Interactions

Different Different components of the components of the climate system climate system have different have different response timesresponse times Different Different

components will components will respond to a respond to a change in forcing change in forcing at different ratesat different rates

Response Rates & Interactions

If climate forcing occurs in cycles, it will produce If climate forcing occurs in cycles, it will produce different cyclic responses in the climate systemdifferent cyclic responses in the climate system Fast responses track forcingFast responses track forcing Slow responses lag forcingSlow responses lag forcing

Response Rates & Interactions

What happens to air temperature near What happens to air temperature near the foot of the glacier if incoming solar the foot of the glacier if incoming solar radiation were to slowly increase?radiation were to slowly increase?

Interactions in the Climate System

Does the air warm Does the air warm due to increase in due to increase in solar luminosity?solar luminosity?

Does the air stay Does the air stay cool because of the cool because of the proximity to large proximity to large mass of glacial ice?mass of glacial ice?

Response time of air Response time of air influenced by bothinfluenced by both Response time of Response time of

air will be faster air will be faster than the response than the response of the ice but lag of the ice but lag behind forcing behind forcing from the Sunfrom the Sun

Interactions in the Climate System

Individual components within the Individual components within the climate system do not respond climate system do not respond passively to forcingpassively to forcing Dynamic interaction between Dynamic interaction between

systemssystems Interaction blurs the distinction Interaction blurs the distinction

between forcing and responsebetween forcing and response Difficult to determine what system or Difficult to determine what system or

systems are reacting to the forcingsystems are reacting to the forcing

Feedbacks in the Climate System

Interactions can Interactions can produce positive produce positive feedbackfeedback Positive feedbacks Positive feedbacks

produce additional produce additional climate change climate change beyond that beyond that triggered by the triggered by the initial forcinginitial forcing

Positive feedback Positive feedback amplify changesamplify changes

Feedbacks in the Climate System

Interactions can Interactions can produce negative produce negative feedbackfeedback Negative Negative

feedbacks reduce feedbacks reduce the response that the response that would be caused would be caused by the forcingby the forcing

Negative feedback Negative feedback suppress climate suppress climate changechange