EVSC 305: Climate Change – EVSC 305: Climate Change – the Science and Local Impact the Science and Local Impact on a Global Environmental on a Global Environmental CrisisCrisis

EVSC 305…EVSC 305…This introductory course will give

students an integrated overview of the science of climate change and an analysis of the implications of this change for patterns of daily life in their own circumstance and around the world

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EVSC 305EVSC 305Your reader…Additional readings…The website (

www.greenresistance.wordpress.com)

Set up your own research database

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EVSC 305EVSC 3054 objectives

◦Science of Climate Change◦Impacts of Climate Change◦Policy Analysis◦Mitigation Objectives

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Writing AssignmentWriting Assignment2 page paper on recent news of climate change.Reference. Grammar. Your analysis.Due via email on Friday October 8

EVSC 305: Climate Change – EVSC 305: Climate Change – the Science and Local the Science and Local Impact on a Global Impact on a Global Environmental CrisisEnvironmental Crisis

Chapters 1 and 2

The start…The start…Climate is dynamicNothing simple about how the climate

changes: the behavior of the Earth’s climate is governed by a wide range of factors all of which are interlinked in an intricate web of physical processes

What are the factors that most matter?

What is climate change?What is climate?

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Weather and Climate: Weather and Climate: what is the what is the difference?difference?

◦“Weather is what we get; climate is what we expect. Weather is what is happening to the atmosphere at any given time; climate is what the statistics tell us should occur at any given time of the year”

◦Emphasis on average conditions◦In considering climate change: we are

concerned about the statistics of the weather phenomena that provide evidence of longer term changes

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Climate variability – climate Climate variability – climate changechange

Climate variability - the way climatic variables (such as temperature and precipitation) depart from some average state, either above or below the average value. (Although daily weather data depart from the climatic mean, we consider the climate to be stable if the long-term average does not significantly change.)

Climate change - a trend in one or more climatic variables characterized by a fairly smooth continuous increase or decrease of the average value during the period of record.

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Climate variability – climate Climate variability – climate changechangeOne basic interpretation: climate variability

is a matter or short-term fluctuations; climate change: longer-term shifts.

Potentially oversimplifying(1) no reason why the climate should not

fluctuate randomly on longer timescales; major challenge is to recognize this form of variability

(2) climate change may occur abruptlyDetecting fluctuations in the climate

involves measuring a range of past variations of meteorological parameters around the world over a wide variety of timescales

Unfortunately – variety in quality12

Connections, timescales and Connections, timescales and uncertaintiesuncertainties

Golden rule: do not oversimplify the workings of the climate

Need to understand feedback processes (a perturbation in one part of the system may produce effects elsewhere that bear no simple relation to the original stimulus) – positive and negative feedback processes◦ Positive: warming reduction in snow cover in winter

more sunlight absorbed at the surface more warming◦ Negative: warming more water vapor in the atmosphere

more clouds more sunlight reflected into space less heating of the surface

[supporting material on feedback systems on http://greenresistance.wordpress.com/climate-change-evsc-305/] 13

Challenge: which processes matter most involves: (1) knowing how a given alteration may disturb the climate; (2) knowing how different timescales affect the analysis of climate

Thus: need to know how changes occur and how they are linked to one another◦Continental drift – crucial when interpreting

geological records; more immediate consequences (volcanism) more dramatic impact on interannual climate variability

◦Fluctuations in the output of the Sun

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Big picture…Big picture…Everything in the system is

connected to everything elseThere is no simple answer to any

issue associated with climate changeHow do the changes in every aspect

of the Earth’s physical conditions and extraterrestrial influences combine?◦Atmospheric motions (ever-changing);

variations in land surface (…); sea-surface temperatures; pack-ice extent in polar regions; deep-ocean currents; ocean productivity; carbon dioxide levels in the atmosphere; and…

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Chapter 2: Radiation and the Chapter 2: Radiation and the Earth’s energy balanceEarth’s energy balanceEssential driving process: supply of

energy from the Sun1.Properties of solar radiation and how

the Earth re-radiates energy to space;

2.How the Earth’s atmosphere and surface absorb or reflect solar energy and also re-radiate energy to space;

3.How all these parameters change throughout the year and on longer timescales

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Solar and terrestrial Solar and terrestrial radiationradiationRadiative balance of the Earth:

over time the amount of solar radiation absorbed by atmosphere and the surface beneath it is equal to the amount of heat radiation emitted by the Earth to space

Global warming: retains some solar energy in the climate system

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What is radiation?What is radiation?electromagnetic wavesCharacteristics of a wave …

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What are typical What are typical wavelengths of radiation?wavelengths of radiation?units of

micrometers are often used to characterize the wavelength of radiation

1 micrometer = 10-6 meters

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Radiation lawsRadiation laws Any object not at a

temperature of absolute zero (-273.16 C) transmits energy to its surroundings by radiation in the form of electromagnetic waves travelling at the speed of light and requiring no intervening medium

Black body: a body which absorbs all the radiation and which, at any temperature, emits the maximum possible amount of radiant energy; no actual substance is truly ‘black’◦ Snow absorbs very little light but

is highly efficient emitter of infrared radiation

object does not have to appear "black"

sun and earth's surface behave approximately as black bodies

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Radiation Radiation lawslawsSpectrum:

wavelength dependence of the absorptivity and emissivity of a gas, liquid, or solid◦ Radiative properties

of the Earth are made up of the spectral characteristics of the constituents of the atmosphere, oceans, and land surface

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Black body…Stefan-Black body…Stefan-Boltzmann lawBoltzmann lawBlack body: the

intensity of radiation emitted and the wavelength distribution depend only on the absolute temperature

Expression for emitted radiation is the S-B law: flux of radiation from a black body is directly proportional to absolute temperature

E=sT4

◦ E/F = flux of radiation◦ T = absolute

temperature (K) of object

◦ s= constant called the Stefan-Boltzman constant = 5.67 x 10-8 Watts m-2 K-4

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Consider the earth and sun:Consider the earth and sun:

Sun: T = 6000 K◦so E = 5.67 x 10-8 Watts m-2 K-4 (6000

K)4 = 7.3 x 107 Watts m-2 ◦Q: is this a lot of radiation??? Compare

to a 100 Watt light bulb.....Earth: T = 288K

◦so E = 5.67 x 10-8 Watts m-2 K-4 (288 K)4 = 390 Watts m-2

◦Q: If you double the temperature of an object, how much more radiation will it emit? 

◦A: 16 times more radiation23

Wien displacement law:◦ Wavelength at which a

black body emits most strongly is inversely proportional to the absolute temperature

◦ the hotter the body, the shorter the wavelength of peak emission.

Most objects emit radiation at many wavelengths

However, there is one wavelength where an object emits the largest amount of radiation

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Weins lawWeins lawThis wavelength is

found with Weins Law: lmax = 2897 mm / T(K)

At what wavelength does the sun emit most of its radiation? – 0.5 micrometers

At what wavelength does the earth emit most of its radiation? – 10.0 micrometers

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Radiative equilibriumRadiative equilibrium If the temperature of an

object is constant with time, the object is in radiative equilibrium at its radiative equilibrium temperature (Te)

Q: What happens if energy input > energy output? 

A: object will be warmer Q: What happens if

energy input < energy output? 

A: object will be cooler Q: Is the earth in

radiative equilibrium?  A: Earth’s global average

is constant with time

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So…So…If the Earth were a black body and the

Sun emitted radiation as a black body of temperature 6000 K, then a relatively simple calculation of the planet’s radiation balance produces a figure for the average surface temperature of 270 K

Observed value is about 287 KWhy?Earth does not absorb all the radiation

from the Sun; in principle, should be even cooler – at around 254 K – i.e. FROZEN

Reason for the difference: properties of the Earth’s atmosphere, aka Greenhouse Effect

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How does the build up for radiatively active gases in the atmosphere alter the temperature?

To understand that…As the density of the atmosphere decreases

rapidly with altitude, any absorption of terrestrial radiation will take place principally near the surface

Since the most important absorber is water vapor, which is concentrated in the lowest levels of the atmosphere, the greatest part of the absorption of terrestrial radiation emitted by the Earth’s surface occurs at the bottom of the atmosphere

In achieving balance between income and outgoing radiation the surface and lower atmosphere are warmed and the upper atmosphere cooled

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Interaction of Long Wave Interaction of Long Wave Radiation and the Radiation and the AtmosphereAtmosphere Some of the long-wave

radiation emitted by the earth escapes to space

Some of the long-wave radiation is absorbed by gasses in the atmosphere

These gasses then re-emit some of the long wave radiation back to the ground

The additional long-wave radiation reaching the ground further warms the earth

This is known as the "greenhouse effect"

The gasses that absorb the LW emitted by the earth are called "greenhouse gasses"

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Greenhouse GasesGreenhouse Gases

Methane (CH4)Carbon Dioxide (CO2)Ozone (O3)

Water Vapor (H2O)Nitrous Oxide

(N2O)

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the wavelengths over which the Sun and Earth emit most of their radiation. The Sun being a much hotter body emits most of its radiation in the

shortwave end and the Earth in the longwave end of the spectrum. The division between shortwave and longwave radiation occurs at about 3

micrometers.

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Terrestrial radiationTerrestrial radiationThe principal atmospheric gases

(oxygen and nitrogen) do not absorb appreciable amounts of infrared radiation

Radiative properties of the atmosphere are dominated by certain trace gases (water vapor, carbon dioxide, ozone) – which interact with infrared radiation in their own way modifying surface radiation by absorption and re-emission in the atmosphere

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Remember…Greenhouse Remember…Greenhouse GasesGases

Methane (CH4)Carbon Dioxide (CO2)Ozone (O3)

Water Vapor (H2O)Nitrous Oxide

(N2O)

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How to quantify the impact of the How to quantify the impact of the naturally occurring radiatively naturally occurring radiatively active gases?active gases?What is their contribution to the

warming of the Earth above the figure of 254 K?

Water vapor 21 KCarbon dioxide 7 KOzone 2 KNote: if the climate warms - the

amount of water vapor in the atmosphere will increase. A positive feedback.

Methane, oxides of nitrogen, sulphur dioxide and CFCs also modify the radiative properties of the atmosphere

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Terrestrial radiationTerrestrial radiationWhere are these greenhouse

gases – how are they distributed in the atmosphere?

Most trace constituents are relatively uniform;

water vapor and ozone have a more complicated distribution

Hydrological cycle…Photochemical process…

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Hydrological cycleHydrological cycle

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Questions re: HQuestions re: H220 cycle0 cycleWhat is the extent to which global

warming will alter the [ ] of water vapor in the atmosphere?

Water vapor is dependent on the surface temperature of the Earth expected to impact future warming (+ive feedback) – depends on whether in a warmer world the increase in water vapor will occur throughout the troposphere

Also: most complicated absorption spectrum

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OzoneOzoneMajority of ozone is created by

photochemical action of sunlight on oxygen in the upper atmosphere

Depends on the amount of sunlight – thus have a marked annual cycle (esp at high latitudes); + pollution in urban areas can produce conditions for photochemical production of ozone significant widespread increases in lower atmosphere over much of the more populated parts of the world

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Energy balance of the Energy balance of the EarthEarth Earth’s orbit

around the Sun

Earth’s own rotation about its tilted axis

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Energy budgetEnergy budgetOverall – the total incoming flux

of solar radiation is balanced by the outgoing flux of both solar and terrestrial radiation

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Energy budgetEnergy budget

Key: amount of energy absorbed or reflected is dependent on the surface properties◦Snow: high proportion of incident sunlight

reflected◦Moist dark soil: efficient absorber of

sunlight

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Snow: selective Snow: selective absorptionabsorptionSnow is a

poor absorber of solar radiation, but is a great absorber and therefore emitter of long-wave radiation

during the daytime - snow surface stays cool

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Selective Absorption - Selective Absorption - Snow during night timeSnow during night time

during night time, snow is only emitting long wave radiation, and is doing it very effectively

so, snow covered surface gets quite cold at night

ski areas in the spring

thin snow cover in the late fall

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Energy budgetEnergy budgetAlbedo: amount of solar radiation reflected or

scattered into space w/o any change in wavelength (global albedo = ~30%) [yes, know table 2.1]◦ Eg: what are the implications of this new discovery? –

twice as much sunlight is reflected back to space by snow-covered croplands and grasslands as is reflected by snow-covered forests

Solar radiation is absorbed differently on land and at sea◦ Land: most of the energy absorbed close to the

surface, warms up rapidly, increases amount of terrestrial radiation leaving the surface

◦ Sea: solar radiation penetrates deeper; more than 20% reaching 10 m depth; more energy stored in top layer of ocean; less lost to space

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Clouds and Climate Clouds and Climate ChangeChange

Some clouds help cool the Earth, but other clouds help keep Earth warm – in part depending on how high up they are in our atmosphere.

So: what is the role of low-cloud cover?◦ Will climate change dissipate clouds, which would effectively speed

up the process of climate change, or increase cloud cover, which would slow it down?

◦ One study (July 2009, Science) level clouds tend to dissipate as the ocean warms — which means a warmer world could well have less cloud cover. … A positive feedback

Remember water vapor? The transition betw clouds and vapor …

“The physics of clouds is the greatest obstacle to improving predictions of climate change.”◦ Data from satellites (data only a few decades old)◦ Human observations (data back to the 1950s)◦ Read the scientific article

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Clouds and Climate Clouds and Climate ChangeChangea growing consensus among climate modelers

is that clouds will increase, rather than hold back, the warming triggered by greenhouse gases. That’s largely because water vapor itself is a powerful greenhouse gas, which means that clouds should trap more heat than they are likely to reflect back into space.

But uncertainty remains◦ what types of clouds will form and at what

altitude?◦ what particles will the clouds form around?◦ how can modelers go from predicting the ways

any given bank of clouds might behave as opposed to forecasting how the effects on systems of clouds on a regional or global scale?

◦ Plus incomplete cloud observations

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Role of particulatesRole of particulatesBetter reflectors of sunlight than

they are absorbers of terrestrial radiation

Impact: reduce the net amount received cooling effect

[eg: dust from drought-prone areas]

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Role of oceansRole of oceansNot separate from the

atmosphereContinual exchange of energy

◦In the form of heat, ◦momentum as winds stir up waves, ◦moisture in the form of both

evaporation from the oceans to atmosphere, and

◦precipitation from atmosphere to oceans

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Solar variabilitySolar variabilitySunspots: darker areas – seen at

lower latitudes between 30 N and 30 S crossing the face of the Sun as it rotates – cooler than surrounding chromosphere◦Chromosphere?

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The Sun explained... The Sun explained...

Core The energy of the Sun comes from nuclear fusion reactions that occur deep inside the core

Radiative zone The area that surrounds the core. Energy travels through it by radiation

Convective zone This zone extends from the radiative zone to the Sun’s surface. It consists of “boiling” convection cells

Photosphere The top layer of the Sun. It is this that we see when we look at the Sun in natural light

Filament A strand of solar plasma held up by the Sun’s magnetic field that can be seen against its surface

Chromosphere A layer of the Sun’s atmosphere above the photosphere, around 2000km deep

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Solar variabilitySolar variability Sunspots: darker areas – seen at lower latitudes

between 30 N and 30 S crossing the face of the Sun as it rotates – cooler than surrounding chromosphere◦ Vary in size, number, and duration◦ Sunspots are dark, cooler patches on the Sun’s surface

that come and go in a roughly 11-year cycle, first noticed in 1843.

Output of the Sun did rise and fall during the sunspot cycle. ◦ the Sun's activity waxes and wanes over an 11-year cycle

and that as its activity wanes, the overall amount of radiation reaching Earth decreases.

More sunspots more output more heat◦ during an 11-year solar cycle the Sun’s output changes by

only 0.1 per cent◦ Much of this change is concentrated in the UV part of the

spectrum; absorbed by oxygen and ozone molecules◦ Useful to know how solar UV energy affects upper

atmosphere

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Variability on solar Variability on solar variabilityvariability assumed that as solar activity – indicated by the number

of sunspots on the Sun's surface – increases, then so does the amount of solar radiation coming to the Earth to heat the planet.

a study based on satellite data of the Earth's atmosphere has shown there is a complicated interaction between the varying amounts of radiation from the Sun and the amount of ozone in the atmosphere.

A decline in solar activity does not necessarily mean a cooler Earth

This latest study looked at the Sun's activity over the period 2004-2007, when it was in a declining part of its 11-year activity cycle.

the amount of energy reaching Earth at visible wavelengths increased rather than decreased as the Sun's activity declined, causing this warming effect.

researchers behind the study believe it is possible that the inverse is also true and that in periods when the Sun's activity increases, it tends to cool, rather than warm, Earth.

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