NATS 101

Lecture 32

Climate Change (cont’d)

Outline• IPCC summary from Kevin Trenberth

• Current energy flow and balance

• How changing the GHG concentrations causes climate to change– Stephen Boltzmann law (reminder)

• Feedbacks and subsequent changes

Role of the IPCC:

The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. Review by experts and governments is an essential part of the IPCC process.

Role of the IPCC:

The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. Review by experts and governments is an essential part of the IPCC process.

1988 - The establishment of the IPCC WMO, UNEP

1990 - First IPCC Assessment Report1992 - IPCC Supplementary Reports

1994 - IPCC Special Report 1995 - Second IPCC Assessment Report

1996 - COP-2, 1997 - COP-3

2001 - Third IPCC Assessment Report 2002 - COP-8, 2003 - COP-9

2007 - Fourth IPCC Assessment Report

1992- Adoption of the UNFCCC1994- Entry into force of the UNFCCC

Ratified by 189 countries

1997- Adoption of Kyoto Protocol at COP-32005 Feb 16- Kyoto Protocol ratified by 164 countries

(But not by USA or Australia)

Scenarios of future emissionsof greenhouse gases, aerosols

Scenarios of future concentrationsof greenhouse gases and aerosols

Projections of future climate:The response, global, regional

Assessment of observations, processes and models

Impacts

Adaptation

MitigationPolicy options

A major strength of the IPCC processhas been the intergovernmental process, through reviews and then approval of the Summary for Policy Makers on a word-by-word basis.

A major strength of the IPCC processhas been the intergovernmental process, through reviews and then approval of the Summary for Policy Makers on a word-by-word basis.

But it has also been subject to criticism as it is much more political. In principle, this process is designed to provide a report in which the content is determined by the science while how it is stated is determined jointly with the governments. Hence it aids communication between scientists and politicians.

But it has also been subject to criticism as it is much more political. In principle, this process is designed to provide a report in which the content is determined by the science while how it is stated is determined jointly with the governments. Hence it aids communication between scientists and politicians.

The recent IPCC report has clearly stated that “Warming of the climate system is unequivocal” and it is “very likely” caused by human activities.

Moreover, most of the observed changes are now simulated by climate models over the past 50 years adding confidence to future projections.

IPCC report online

The recent IPCC report has clearly stated that “Warming of the climate system is unequivocal” and it is “very likely” caused by human activities.

Moreover, most of the observed changes are now simulated by climate models over the past 50 years adding confidence to future projections.

IPCC report online

IPCC 2007 Report on Climate

2007:The Nobel Peace Prize goes to the Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr. "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change".

2007:The Nobel Peace Prize goes to the Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr. "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change".

Nobel Peace Prize

GLOBAL Energy Flow Thru Atmosphere

Global Atmo Energy Balance

Ahrens, Fig. 2.14

Solar inSolar in

IR OutIR Out

In a stable climate, Solar Energy IN = IR Energy OUT

Water Vapor

Carbon Dioxide

Ozone

Methane,Nitrous Oxide

WaterWaterVaporVapor60%60%

CarbonCarbonDioxideDioxide26%26%

OO33

8%8%

CHCH44

NN2200 6%6%

Clouds also have a greenhouse effect Kiehl and Trenberth 1997

The Natural Greenhouse Effect: clear sky

Changing CO2 concentrations• CO2 concentrations have varied naturally by a factor of

2 over the past few hundred thousand years • Fossil fuel burning since the industrial revolution has

created a sharp increase in CO2 concentrations• CO2 concentrations are now higher than at any time in

past few hundred thousand years • And concentrations are increasing faster with time

Last 4 Ice Age cycles:400,000 years

See http://epa.gov/climatechange/science/recentac.html

Man made

You are here

Global Atmo Energy Imbalance

Ahrens, Fig. 2.14

Solar inSolar in

AtmosphereAtmosphere

IR OutIR Outis reducedis reduced

Increasing GHG concentrations decrease Energy outSo Energy IN > Energy OUT and the Earth warms

Radiative Forcing (RF) Components{Global-average estimates and ranges; typical geographical

extent and assessed level of scientific understanding}

Stefan-Boltzmann’s Law(review from Lecture 5)

• The hotter the object, the more radiation emitted.

• When the temperature is doubled, the emitted energy increases by a factor of 16!

• Stefan-Boltzmann’s LawE= (5.67x10-8 Wm-2K-4 )xT4

E=2x2x2x2=16 4 times

(T is temperature in Kelvin)

Sun Temp: 6000K

Earth Temp: 300K

Aguado, Fig. 2-7

Change in IR Emission to Space• Notice that because of Earth’s greenhouse gases, 91%

(=64/70) [195/235 = 83%] of the IR emitted to space comes from the atmosphere and only 9% (=6/70) [40/235 = 17%] comes from the surface

• When GHG’s are added to the atmosphere, the altitude of IR emission to space rises

• In the troposphere, air temperature decreases with altitude

• So the temperature of the emission to space decreases

• So the energy emission to space decreases because the emission energy decreases with decreasing temperature

Change in IR Emission to SpaceBEFORE GHG increase IN=OUT AFTER GHG increase IN>OUT

NH SHAhrens, Fig. 2.21

Alti

tud

e

Temperature Temperature

1. Altitude of IR emission to space rises

Altitude of IR emission to space

Temperature of IR emission to space

2. Temperature of IR emission to space decreases

3. IR emission to space decreasesbecause of colder emission temperature

IR emission to space

tropopause

Change in IR Emission to Space (cont’d)

AFTER GHG increase IN>OUT Eventual solution IN=OUT

SHAhrens, Fig. 2.21

Temperature

4. Atmosphere warms until…

5. Temperature of IR emission to space increase to original temperature

6. IR emission to space increases until it matches the original IR emission before GHG increases

SHAhrens, Fig. 2.21

Temperature

1. Altitude of IR emission to space rises

2. Temperature of IR emission to space decreases

3. IR emission to space decreasesbecause of colder emission temperature

Anthropogenically-Caused Warming

• Initially after increasing GHG concentrations, the IR radiation to space decreases, such that

Solar in > IR out – Causing the Earth to start warming

• IF GHG concentrations level off at some point, then eventually the Earth warms enough that

Solar in = IR out– “Eventually” depends on how fast the oceans warm

• The warmer Earth represents a new climate regime– With bad and good consequences that we partially understand

Complexity of Climate System

The climate system involves numerous, interrelated components.

Closer Look at Climate System

Climate Feedback Mechanisms

Positive and Negative Feedbacks

Assume that the Earth is warming.• Warming leads to more melting of ice• Less ice reduces Earth’s albedo• Earth absorbs more sunlight• Earth becomes warmer melting more ice

Works in the other direction as well:Cooling makes more ice which reflects sunlight which

makes Earth colder which makes more ice

=>’Positive’ Feedback Mechanism

Positive and Negative Feedbacks

Again assume that the Earth is warming.• Suppose as the atmosphere warms and moistens,

more low clouds form.• More low clouds reflect more solar radiation,

which decreases solar heating at the surface. • This slows the warming, which would counteract

a runaway greenhouse effect on Earth.

‘Negative’ Feedback Mechanism

Positive and Negative Feedbacks

• Atmosphere has a numerous checks and balances, some that counteract climate changes and some that enhance changes

• All feedback mechanisms operate simultaneously.

• The dominant effect is difficult to predict with complete certainty.

• Cause and effect is very challenging to prove.

Complexities of GHG caused WarmingSo, as the Earth starts warming, other things start to change… • The atmosphere can hold more water vapor

– Water vapor is a GHG => more warming (‘positive’ feedback)– More intense precipitation events and severe weather

• Land heats up faster than the oceans (remember sea breeze)– Less snowpack => earlier and smaller run-off => drier summers– Relative humidity over land will likely drop in general– Continental interiors will generally get drier?

• Clouds will change?????– Having more clouds increases albedo, cooling the Earth– More clouds increase Greenhouse effect warming the Earth

• Wind patterns start changing– Storm tracks and precipitation patterns change. – Winter storm tracks may move more poleward

• Ice starts melting – Reducing the albedo => more warming– Continental ice melt causes sea level to rise

SVP and Temperature (from Lecture 9)

Claussius Clapeyron equation defines water vapor saturation vapor pressure (SVP) versus temperature

SVP defines water holding capacity of air

SVP nearly doubles with a 10oC warming

Ahrens Fig. 4.5

Total water vaporTotal water vapor

Observations show that water vapor in LOWER troposphere is indeed increasing. Surface temperature increase: 0.6C since 1970 over global OCEANS and 4% more water vapor.

Observations show that water vapor in LOWER troposphere is indeed increasing. Surface temperature increase: 0.6C since 1970 over global OCEANS and 4% more water vapor.

Water holding capacity of atmosphere increases about 7% per oC (4% per F) increase in temperature.

Water holding capacity of atmosphere increases about 7% per oC (4% per F) increase in temperature.

From Trenberth/IPCC

Since late 1970’s, ocean surface has been warming at ~0.14C/decade => ~1% WV increase/decade. Observed WV trend since 1988 is ~1.2% per decade

Water vapor increase at higher temperatures

Water Vapor

Carbon Dioxide

Ozone

Methane,Nitrous Oxide

WaterWaterVaporVapor60%60%

CarbonCarbonDioxideDioxide26%26%

OO33

8%8%

CHCH44

NN2200 6%6%

Clouds also have a greenhouse effect Kiehl and Trenberth 1997

The Natural Greenhouse Effect: clear sky

Upper Tropospheric Water Vapor Trends

• Far less water vapor as in lower troposphere because temperatures are much colder (SVP much less)

• Fractional changes in UT WV are almost as important as in LT WV because temperatures are much colder

• so IR emitted from upper troposphere is small reducing outgoing IR to space

• Climate models generally predict UT WV should increase as climate warms

• Very challenging to measure UT WV • At least indirect inferences that UT WV is increasing

• Some doubt about the robustness of this result and its generality

Observational Evidence of Water Vapor Feedback• Increasing water vapor concentrations shift the altitude of water IR emission upward which

DECREASES its emission (because of colder temperatures)• Atmospheric temperatures have also been increasing over time (at least in theory) which

should INCREASE the IR emission from water vapor• To isolate the water vapor concentration change, Subtract the IR measured from water

(=‘T12’ from HIRS) from emission measured from O2 (whose concentrations have not changed) (=‘T2’ from MSU)

• If IR from water is becoming less than emission from O2, the atmospheric water concentrations have increased => THIS IS WHAT IS OBSERVED

Soden et al. 2005

Annual anomalies of global average SST and land surface air temperatureLand increased 0.4oC vs ocean suggesting 3% decrease in RH over land

SSTLand

Trenberth/IPCC

Land surface temperatures are rising faster than SSTs

Evidence for reality of climate changeEvidence for reality of climate change

Glaciers meltingGlaciers melting

1900 2003 Alpine glacier, Austria

1909

TobogganGlacierAlaska

2000

Muir Glacier, Alaska

Snow cover and Arctic sea ice are decreasing

Snow cover and Arctic sea ice are decreasing

Spring snow covershows 5% stepwise drop during 1980s

Arctic sea ice area decreased by 2.7% per decade(Summer: -7.4%/decade)

2007: 22% (106 km2) lower than 2005

Trenberth/IPCC

Arctic sea ice disappears in summer by 2050Already 2007 lowest on record by 22%

Abrupt Transitions in Summer Sea Ice

• Gradual forcing results in abrupt Sept ice decrease

• Extent decreases from 80 to 20% coverage in 10 years.

• Relevant factors:• Ice thinning• Arctic heat transport• Albedo feedback

Trenberth from Holland et al., GRL, 2006

2007 x

from ocean expansion and melting glaciers

from ocean expansion and melting glaciers

Since 1993 Global sea level has risen 43 mm (1.7 inches)

• 60% from expansion as ocean temperatures rise, • 40% from melting glaciers

Since 1993 Global sea level has risen 43 mm (1.7 inches)

• 60% from expansion as ocean temperatures rise, • 40% from melting glaciers

from Steve Nerem via Trenberth

Sea level is rising:

Today 125,000 years ago

Research indicates that less than 8°F of Arctic warming caused Greenland to lose enough water to raise sea level by up to 12 feet during the Last Interglacial Period

Image from Bette Otto-Bliesner, National Center for Atmospheric Research

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

www.gfdl.noaa.gov

1 meter

4 meters

2 meters

8 meters

Increasing melt zones.

Melt descending into a moulin: a vertical shaft carrying water to the base of the ice sheet.

NSIDC (above)Braithwaite: Univ. Manchester

Surface melt on Greenland

Greenland ice mass budget

Researchers Mass Change Method Time Span (GT/year)Krabill et al. 2000 -47 Aircraft Surveys 1994-1999Velicogna et al. 2006 -200 to -260 GRACE 2002-2006Luthcke et al. 2007* -145 to -175 GRACE 2003-2006Zwally et al. 2007* -80 to -100 ICESat 2003-2005

GRACE is a gravity recovery missionICESat is a lidar topographymission

NASA website on Greenland ice sheet

A great deal of effort is going into estimating how the Greenland ice sheet is changing

100 GT/yr ~ 0.3 mm/yr sea level rise

Key Points: Climate Change

• Increasing GHG concentrations warms the Earth• Proxy data are used to infer the past climate.• Data show that the Earth’s Climate

Has changed in the past

Is changing now

And will continue to change• Key question is determining whether recent

changes are due to natural causes or man.

Key Points: Climate Change

• The climate system is very complex.

Contains hundreds of feedback mechanisms

All feedbacks are not totally understood.

• Three general climate change mechanisms:

Astronomical

Atmospheric composition

Earth’s surface

Assignment for Next Lectures

• Topic - Anthropogenic Climate Change

• Reading - Ahrens, Ch 14: 373-400 (383-412)

• Problems - 14.5, 14.8, 14.10, 14.12, 14.13, 14.15, 14.16, 14.19