Lecture 3 Lecture 3 How Real is Global How Real is Global Warming?Warming?

Will Human-Induced Climate Will Human-Induced Climate Change Destroy the World?Change Destroy the World?

Global warming is the increase in the average Global warming is the increase in the average measured temperature of the Earth's near-measured temperature of the Earth's near-surface air and oceans since the mid-20surface air and oceans since the mid-20 thth century, and its projected continuation.century, and its projected continuation.

The average global air temperature near the The average global air temperature near the Earth's surface increased 0.74 ± 0.18 °C (1.33 ± Earth's surface increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in 2005.0.32 °F) during the 100 years ending in 2005.

Global WarmingGlobal Warming

Source: Intergovernmental Panel on Climate Change

• Global average temperature has risen by approximately 1ºF over the last century

Temperatures over last 140 years

?

““Hockey Stick” ControversyHockey Stick” Controversy

1000 1200 1400 1600 1800 2000-0.8

Year

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Tem

per

atu

re C

han

ge

(°C

)

Direct temperature measurementsMann et al. 1999

Mann,1998,1999

The map shows the 10-year average (2000-2009) global mean temperature anomaly relative to the 1951-1980 mean. 

Global Climate History

Geologic evidence clearly indicates relative long-term climate stability that has allowed liquid H2O to exist for most of geologic history

Tectonics plays an important role in regulating atmospheric CO2 and therefore climate

The Earth’s Climate System - very complex!!

Indicators of the human influence on the atmosphere (IPCC, 2001).

Human activities have changed the composition Human activities have changed the composition of the atmosphere since the pre- industrial eraof the atmosphere since the pre- industrial era

McIntyre, S., and R. McKitrick (2003), Corrections to the Mann et al. (1998) proxy data base and Northern Hemispheric average temperature series, Energy Environ., 14, 751–771.

McIntyre, S., and R. McKitrick (2005), Hockey sticks, principal components, and spurious significance, Geophys. Res. Lett., 32, L03710, doi:10.1029/2004GL021750.

Martin Durkin,The Great Global Warming Martin Durkin,The Great Global Warming Swindle:2007Swindle:2007

1﹑1﹑ 大气运动是个很复杂的过程，太阳大气运动是个很复杂的过程，太阳﹑﹑洋流洋流﹑﹑宇宙射线都会参与其中，怎宇宙射线都会参与其中，怎么能简单地都怪罪于二氧化碳呢么能简单地都怪罪于二氧化碳呢﹖﹖    2﹑2﹑ 二氧化碳只是地球大气很小的组成部分，而且这么小部分的气体增加，二氧化碳只是地球大气很小的组成部分，而且这么小部分的气体增加，有多少是人引起的也很难说。有多少是人引起的也很难说。 3﹑3﹑ 温度和二氧化碳的相关曲线和人类发展的进程曲线不符，人类工业高温度和二氧化碳的相关曲线和人类发展的进程曲线不符，人类工业高速发展发生在速发展发生在 19701970 年代，但是温度急速增长却在年代，但是温度急速增长却在 19401940 年代。年代。 4﹑4﹑ 温度和二氧化碳的相互关系更像是因为气温上升了，二氧化碳总量跟温度和二氧化碳的相互关系更像是因为气温上升了，二氧化碳总量跟着增加，可否解释为：因为海洋本身能存储二氧化碳，如果温度升高肯定会着增加，可否解释为：因为海洋本身能存储二氧化碳，如果温度升高肯定会有二氧化碳从裡面释放出来有二氧化碳从裡面释放出来﹖﹖    5﹑5﹑ 温室气体最主要的是水蒸气。温室气体最主要的是水蒸气。 6﹑6﹑ 一万年内就有过两次大的温暖期，一次在一万年内就有过两次大的温暖期，一次在 1414 世纪，一次在大禹治水时世纪，一次在大禹治水时期，这如何解释期，这如何解释﹖﹖    7﹑7﹑ 新能源（太阳能新能源（太阳能﹑﹑风能）成本高昂而且不稳定，因此造成的损失谁来风能）成本高昂而且不稳定，因此造成的损失谁来负责负责﹖﹖这影响了很多发展中国家的发展。这影响了很多发展中国家的发展。 8﹑8﹑ 现在大量的研究经费用于研究全球变暖的影响和预测，但是有多少经现在大量的研究经费用于研究全球变暖的影响和预测，但是有多少经费是给这些反对全球变暖的科学家进行研究的呢费是给这些反对全球变暖的科学家进行研究的呢﹖﹖    9﹑9﹑ 历史上就曾经有过格陵兰冰架完全融化的事情，是否有此事历史上就曾经有过格陵兰冰架完全融化的事情，是否有此事﹖﹖    10﹑10﹑ 全球变暖的重要证据 全球变暖的重要证据 —“—“曲棍球棒”气温曲线在科学界到底有没有可曲棍球棒”气温曲线在科学界到底有没有可信度信度 ﹖ ﹖

“ 曲棍球门” “ 气候门” “ 冰川门” “ 亚马逊门”

逻辑链条貌似严谨：人类排放二氧化碳→大气中温室气体增加→温室效应更加显著→地球气温升高→冰川融化、海平面上升以及一系列灾难性气候接踵而至→人类面临生存危机。仿佛一切顺理成章，人类在毁灭地球

路线图 路线图 19881988 年，欧洲人推动下年，欧洲人推动下 IPCCIPCC 成立，开始谋划成立，开始谋划应对“暖化危机”；应对“暖化危机”；19901990 年，欧共体代表在“第二次世界气候大会年，欧共体代表在“第二次世界气候大会部长级会议”中，首次提出保护大气层和控制二部长级会议”中，首次提出保护大气层和控制二氧化碳排放的主张，并提议立即开始关于“气候氧化碳排放的主张，并提议立即开始关于“气候变化公约”的谈判，从而拉开变化公约”的谈判，从而拉开《《气候变化框架公气候变化框架公约约》》谈判的序幕；谈判的序幕；19921992 各国首脑奔赴巴西里约热内卢，签订各国首脑奔赴巴西里约热内卢，签订《《联联合国气候变化框架公约合国气候变化框架公约》》，开始把矛头对准二氧，开始把矛头对准二氧化碳，但没有具体规定各国承担义务；化碳，但没有具体规定各国承担义务；19951995 年年 33 月月 2828 日，公约第一次缔约方大会在德日，公约第一次缔约方大会在德国柏林召开；国柏林召开；

哥本哈根大会，全称哥本哈根大会，全称《《联合国气候变化框联合国气候变化框架公约架公约》》第第 1515 次缔约方会议暨次缔约方会议暨《《京都议定京都议定书书》》第第 55 次缔约方会议，于次缔约方会议，于 20092009 年年 1212 月月77 －－ 1818 日在丹麦首都哥本哈根召开。来自日在丹麦首都哥本哈根召开。来自192192 个国家的谈判代表召开峰会，商讨个国家的谈判代表召开峰会，商讨《《京京都议定书都议定书》》一期承诺到期后的后续方案，一期承诺到期后的后续方案，即即 20122012 年至年至 20202020 年的全球减排协议。年的全球减排协议。以碳排权为主题 以碳排权为主题

19971997 年年 1212 月月 1111 日，第三次缔约方大会在日本东日，第三次缔约方大会在日本东京召开，京召开， 149149 个国家和地区签署通过了个国家和地区签署通过了《《京都议京都议定书定书》》，开始明确发达国家碳排放量；，开始明确发达国家碳排放量；

20072007 年年 1212 月，第十三次缔约方大会在印度尼西月，第十三次缔约方大会在印度尼西亚的巴厘岛召开，协商“后京都”问题，即亚的巴厘岛召开，协商“后京都”问题，即《《京京都议定书都议定书》》到期后的进一步减排事项，会议通过到期后的进一步减排事项，会议通过“巴厘路线图”；“巴厘路线图”；20082008 年年 88 月，西方月，西方 G8G8 领导人会议上就温室气体领导人会议上就温室气体减排长远目标达成一致意见，八国领导人在一项减排长远目标达成一致意见，八国领导人在一项声明中说，八国将与声明中说，八国将与《《气候框架公约气候框架公约》》其他缔约其他缔约国共同实现国共同实现 20502050 年温室气体至少减半的长期目年温室气体至少减半的长期目标，在相关缔约方谈判中与其他国家讨论并通过标，在相关缔约方谈判中与其他国家讨论并通过

Topics to be coveredTopics to be covered

Is the world getting warmer?Is the world getting warmer?

If so, are the actions of mankind to blame If so, are the actions of mankind to blame for earth’s temperature increases?for earth’s temperature increases?

What can/should be done about these What can/should be done about these issues?issues?

Are the potential resolutions worth the Are the potential resolutions worth the costs to implement them? costs to implement them?

What the unconvinced people are saying…

1. “Theory remains entirely unproved.”

2. “One-in-three chance … that experts are wrong.”

3. “Models are incapable of handling … water vapor.”

4. “Troposphere should be warming faster than the

surface.”

5. “If the weather folk can’t figure out what’s happening

for the rest of the week, how can they tell us what the

climate will be for the next 50 years?”

6. “Guess what? Antarctica’s getting colder, not

warmer.”

7. “Global warming is still just a theory.”

Facts…

1. Global mean temperature has been going up in the last 140 years

2. The magnitude of this variability does not exceed natural variability

3. Concentration of carbon dioxide has been going up as well as other greenhouse gases

4. Radiative theory of atmospheric gases (greenhouse) and aerosols is important

5. Climate change involves the entire “earth system” not just the atmosphere

6. Future projections face uncertainties in emission production, modeling, and impacts

7. Several thousand scientists from 40+ countries all over the world have been involved

Challenges A. Nature of climate system

1. Analysis must consider entire climate system and all of humanity2. Extensive natural climate variability3. Global connections for both climate forcing and climatic response4. Uncertainties in outcomes involve uncertainties in many components5. A small change in global means can translate to large changes in

local means/extremesB. Needs for research

1. Improve data – longer data, error analysis, more global coverage2. Improve theory – radiation-aerosol, cloud drops-aerosol( 气溶胶 )3. Improve models – parameterization for small scale components4. Separating naturally-induced fluctuations from human effects

C. Nature of people1. Implement controls on human impacts on the environment2. World cooperation3. Look at ourselves

Paleo-ClimatePaleo-Climate

Climate is the Climate is the mean statemean state of the of the environment, long-term average of daily environment, long-term average of daily variationsvariations

““Climate change” depends on the Climate change” depends on the resolution of the proxies and the length of resolution of the proxies and the length of the “mean state” in considerationthe “mean state” in consideration

Climate Change EventsClimate Change Events

Tectonic scale (Millions of years ago)Tectonic scale (Millions of years ago)

Orbital Scale, when Milankovich Orbital Scale, when Milankovich

started showing up (3 Ma)started showing up (3 Ma)

Deglacial and Millennial ScaleDeglacial and Millennial Scale

Historical climate changesHistorical climate changes

Time lineTime line

600-750 Ma: Snowball Earth (600-750 Ma: Snowball Earth (NeoproterozoicNeoproterozoic))

300 Ma-5Ma:300 Ma-5Ma: Hot house world ( Hot house world (Mesozoic/Cenozoic )Mesozoic/Cenozoic )

3 Myr-present: Orbital-scale variability: series of 3 Myr-present: Orbital-scale variability: series of glaciation and retreatglaciation and retreat

20 Kyr: Last glacial maximum (LGM) 20 Kyr: Last glacial maximum (LGM)

~13 Kyr:Bolling/Allerod warming ~13 Kyr:Bolling/Allerod warming

~12 Kyr: Younger Dryas (YD)~12 Kyr: Younger Dryas (YD)

Heinrich events and D-O cycles;Heinrich events and D-O cycles;

1000-1300 BP: Medieval Warm Period1000-1300 BP: Medieval Warm Period

1400-1800 BP: Little Ice Age1400-1800 BP: Little Ice Age

Life appeared ~3.8 billion years agoLife appeared ~3.8 billion years agoPhotosynthesis began 3.5-2.5 billion years Photosynthesis began 3.5-2.5 billion years agoago– Produced oxygen and removed carbon Produced oxygen and removed carbon

dioxide and methane (greenhouse gases)dioxide and methane (greenhouse gases)– Earth went through periods of cooling Earth went through periods of cooling

(“Snowball Earth”) and warming(“Snowball Earth”) and warming

Earth began cycles of glacial and Earth began cycles of glacial and interglacial periods ~3 million years agointerglacial periods ~3 million years ago

History of Earth’s ClimateHistory of Earth’s ClimateHistory of Earth’s ClimateHistory of Earth’s Climate

Earth’s Atmospheric GasesEarth’s Atmospheric Gases

Nitrogen (N2)

Oxygen (O2)

Water (H2O)

Carbon Dioxide (CO2)

99%

Methane (CH4)

1%

Non-Greenhouse

Gases

GreenhouseGases

Sun Runaway Greenhouse EffectRunaway Greenhouse Effect

• 97% carbon dioxide• 3% nitrogen• Water & sulfuric

acid clouds• Temperature:

860°F

Venus

Carbon Dioxide

170

220

270

320

370

420

200000400000600000Time (YBP)

CO

2 (p

pm

)

Vostok Ice CoreDome Concordia

Carbon Dioxide LevelsCarbon Dioxide Levels

0

Muana Loa ReadingsCO2 Levels Since 1958

310330350370

10203040

CO

2 (

pp

m)

0

Worldwide Carbon EmissionsWorldwide Carbon EmissionsC

arb

on

(10

9 m

etri

c to

ns)

0

1

2

3

4

5

6

7

8

1750 1800 1850 1900 1950 2000Year

Liquid fuelLiquid fuelTotalTotal

Gas fuelGas fuelSolid fuelSolid fuel

Annual Carbon EmissionsAnnual Carbon Emissions

Annual carbon emissionsAtmospheric CO2

Atmospheric CO2 average

1955 1965 1975 1985 1995 20050

4

6

8

2

Year

Car

bo

n (

109

met

ric

ton

s)

Future Carbon Dioxide LevelsFuture Carbon Dioxide Levels

• Increasing CO2 emissions, especially in China and developing countries

• Likely to double within 150 years: Increased coal usage Increased natural gas usage Decreased petroleum usage (increased

cost and decreasing supply)

Kyoto ProtocolKyoto Protocol

• Adopted in 1997

• Cut CO2 emissions by 5% from 1990 levels for 2008-2012

• Symbolic only, since cuts will not significantly impact global warming

How to study paleoclimate? How to study paleoclimate?

MarineMarineOcean sediment cores (more regional)Ocean sediment cores (more regional)

Terrestrial (more local)Terrestrial (more local)Lakes and wetlands coresLakes and wetlands coresTree ring/Coral (growth response)Tree ring/Coral (growth response)Ice coresIce coresSpeleothemSpeleothemIce coresIce coresSedimentary rocks/uplifted sedimentsSedimentary rocks/uplifted sediments

• Uses of proxy records of climate depend on both

- time span of record - resolution of record

• Proxies that record annual growth patterns can indicate year to year variations in climate

-tree rings -ice cores -deep lake sediments -coral reefs

• Limited to last 500-1000 years except ice cores

three cores (taken from three trees growing in El Malpais National Monument in New Mexico) have ring patterns in common. For example…

three cores (taken from three trees growing in El Malpais National Monument in New Mexico) have ring patterns in common. For example…

1793 = wide ring with thick latewood

1793 = wide ring with thick latewood

1806 = narrow ring (absent on bottom)1806 = narrow ring (absent on bottom)

1816 Year Without a Summer wide ring

1816 Year Without a Summer wide ring

1840 = wide ring1840 = wide ring

1847 = verynarrow ring1847 = verynarrow ring

Corals: The geologic record of El Niño

CORALS from the tropical Pacific record El Niño’s in the geochemistry of their skeletons

Living Porites corals provide recordsfor the last 200 years

Fossil Porites corals enable us to extend the record back many centuries

Good reproducibility between coral geochemical recordsincreases confidence in coral climate reconstructions.

Overlapping fossil corals: ancient El Niño events

Varved Lake Sediments

• Study site was an alpine lake in Ecuador 75 km east of the Pacific Ocean and east of the continental divide

• During moderate to severe El Ninos bursts of torrential rainfall deposit layers of mainly inorganic sediment (light-colored material in these cores)

• These flood deposits are less frequent before 5000 year ago

Glaciers as records of climate

• Ice cores:

– Detailed records of temperature, precipitation, volcanic eruptions

– Go back hundred of thousands years

Proxies: plant and animal remainsProxies: plant and animal remains

Pollens, foramsPollens, forams

Molecular techniques (transformation of molecules at a Molecular techniques (transformation of molecules at a

specific condition, or specific remains of group of living specific condition, or specific remains of group of living

organism).i.e. alkenonesorganism).i.e. alkenones （（长链烯酮 ）长链烯酮 ） , lignin, lignin （（木质素木质素 ） ）Each species has a specific range of habitat (precip, T, soil Each species has a specific range of habitat (precip, T, soil

type, nutrients, salinity)type, nutrients, salinity)

i.e. found foram in freshwater wetland cores: must have been saltier, i.e. found foram in freshwater wetland cores: must have been saltier,

Tropic pollen in the arctic = warmerTropic pollen in the arctic = warmer

Emiliania huxleyi Emiliania huxleyi Makes AlkenonesMakes Alkenones

UK’37 Varies with TemperatureUK’37 Varies with Temperature

Proxies:Stable IsotopesProxies:Stable Isotopes

If relative ratios of the selected pair changes If relative ratios of the selected pair changes

systematically according to climatic systematically according to climatic

parameters (T, precip, pH, etc)parameters (T, precip, pH, etc)

Mg/Ca: TMg/Ca: T

δδ1313C: ocean circulation, productivity, C cycleC: ocean circulation, productivity, C cycle

δδ1818O:Temperature/Salinity/Sea levelO:Temperature/Salinity/Sea level

– More ice on land: ocean More ice on land: ocean δδ1818O becomes heavier O becomes heavier

Seasonal variation in Mg/Ca ratio and 18O for various foram species

At lower temperatures, there is less Mg so the Mg/Caforam is more sensitive (steeper slope)

Planktonic

Benthic

A correlation of O isotope ratios and annual cycles was made by using recorded temperatures and the decreasing cycle length indicates slower growth at an age of 10 years, probably related to the onset of sexual maturity.

ChronologyChronology

RadiometricRadiometric

– C-14, U/Th, Ar/Ar, etc.C-14, U/Th, Ar/Ar, etc.

PaleomagneticPaleomagnetic

Wiggle match (cross dated): matching the Wiggle match (cross dated): matching the

same featuressame features

Understanding the Past ClimateUnderstanding the Past Climate

Many explanation are theoretical without Many explanation are theoretical without

consensusconsensus

A lot of underlying hypothesis has to do A lot of underlying hypothesis has to do

with the equilibrium of earth cycling with the equilibrium of earth cycling

process: weathering, precipitationprocess: weathering, precipitation

Think in term of feedbacksThink in term of feedbacks

Hot House WorldHot House World (300-5 Ma) Mesozoic/Cenozoic)(300-5 Ma) Mesozoic/Cenozoic)

Thermal max: 55 Ma (Cenozoic)Thermal max: 55 Ma (Cenozoic)Clues: Clues: – Marine T proxiesMarine T proxies– Tropical plants fossils, Tropical plants fossils, alligator, & alligator, & pollens up pollens up

in the arcticin the arctic– Organic-rich deposit (anoxia)Organic-rich deposit (anoxia) （（ north Atlantic north Atlantic

Ocean Ocean ））– Much lighter in Much lighter in δδ1818O O (-40‰ vs. 0 of ocean, and vs. (-40‰ vs. 0 of ocean, and vs.

-25 ‰ if melt all ice now. Must have additional T -25 ‰ if melt all ice now. Must have additional T effects.)effects.)

– No glaciomarine depositNo glaciomarine deposit

Causes of the hot house?Causes of the hot house?

Tectonic block circum polar current Tectonic block circum polar current can’t form arctic ice sheet?can’t form arctic ice sheet?

Can’t form deep water since there is no Can’t form deep water since there is no strong T gradient (est. 12ºC vs. ~0 now)strong T gradient (est. 12ºC vs. ~0 now)

CHCH44 Clathrate release>> positive Clathrate release>> positive

greenhouse feedbackgreenhouse feedback– supported by lighter δsupported by lighter δ1313CC

Global Climate Cooling: Was it BLAG? Global Climate Cooling: Was it BLAG? Rate of plate movement influences global climate by Rate of plate movement influences global climate by controlling atmospheric COcontrolling atmospheric CO22 concentrations concentrations

Support: faster seafloor spreading rate 100 Ma than nowSupport: faster seafloor spreading rate 100 Ma than now

Weathering: CaSiO3 + CO2 --> CaCO3 + SiO2

If BLAG explains the cooling, there should be evidence of If BLAG explains the cooling, there should be evidence of

slower-spreading rates from 55 Myr ago until present day. slower-spreading rates from 55 Myr ago until present day.

Recall that slower BLAG rates means less CORecall that slower BLAG rates means less CO22 is added is added

to the atmosphere which would cause a cooling trend. to the atmosphere which would cause a cooling trend.

the spreading rate was slower until about 15 Myr ago. In the spreading rate was slower until about 15 Myr ago. In

the last 15 Myr, the rate has increased. However, ice in the last 15 Myr, the rate has increased. However, ice in

the northern hemisphere the northern hemisphere first appeared in the last 15 Myr!first appeared in the last 15 Myr!

In summary, the BLAG hypothesis may have caused the In summary, the BLAG hypothesis may have caused the

global cooling before 15 Myr ago, but it cannot explain the global cooling before 15 Myr ago, but it cannot explain the

cooling since then. cooling since then.

Uplift weathering hypothesisUplift weathering hypothesis

Uplift accelerates chemical weathering, Uplift accelerates chemical weathering, drawing down COdrawing down CO22, and cooling the global , and cooling the global climate.climate.

Support of the Uplift HypothesisSupport of the Uplift Hypothesis

Tibetan Paleau Tibetan Paleau (also high monsoon strength which (also high monsoon strength which

encourages weatheringencourages weathering), Colorado Paleau, the ), Colorado Paleau, the Andes uplifted about that time.Andes uplifted about that time.

High High 87 87 SrSr //8686 Sr ratio = higher weathering Sr ratio = higher weathering

Summary: influence of plate tectonics on Summary: influence of plate tectonics on climateclimate

1. Location of continents1. Location of continents

2. Mountain building- alters atmospheric flow2. Mountain building- alters atmospheric flow

3. Open/close ocean gateways3. Open/close ocean gateways

4. Sea-level change- modifies ratio of land to ocean4. Sea-level change- modifies ratio of land to ocean

5. Altering weathering rates- linked to concentration 5. Altering weathering rates- linked to concentration

of COof CO22 in atmosphere in atmosphere

6. Altering rates of outgassing- linked to 6. Altering rates of outgassing- linked to

concentration of COconcentration of CO22 in atmosphere in atmosphere

Temperature History of the EarthTemperature History of the Earth

• For the past 3 million years, the earth has been experiencing ~100,000 year long cycles of glaciation followed by ~10,000 year long interglacial periods

• These climate periods are largely the result of cycles in the earth’s orbit – precession, obliquity, and eccentricity

Orbital Parameters: PrecessionOrbital Parameters: Precession

PerihelionApehelion

Orbital Parameters: ObliquityOrbital Parameters: Obliquity22.5°24.5°

Orbital Parameters: EccentricityOrbital Parameters: Eccentricity

PerihelionApehelionApehelion

Minimum: 0.005Minimum: 0.005

Maximum: 0.061Maximum: 0.061

Not to scale!Not to scale!To Scale!To Scale!

Orbital Parameters & Earth’s ClimateOrbital Parameters & Earth’s Climate

Age (kya)1000900 800 700 600 500 400 300 200 100 0

Eccentricity(100 ky)

Temperature

Obliquity(41 ky)

Precession(22 ky)

Temperature History of the EarthTemperature History of the Earth

• For the past 3 million years, the earth has been experiencing ~100,000 year long cycles of glaciation followed by ~10,000 year long interglacial periods

• Last ice age began to thaw 15,000 years ago, but was interrupted by the “Younger Dryas” event 12,900 years ago

Northern Hemisphere Ice sheet HistoryNorthern Hemisphere Ice sheet History

41 and 23 kyr 41 and 23 kyr cycles from ~.7-3 cycles from ~.7-3 MaMa

But why 100 ky But why 100 ky cycles dominate cycles dominate climate records of climate records of the last 700 ky?the last 700 ky?

Millenial Scale Climate Millenial Scale Climate ChangeChange

Last glacial maximum (LGM): ~21kyaLast glacial maximum (LGM): ~21kya

Bolling/Allerod warming-> Younger Bolling/Allerod warming-> Younger Dryas cooling:~13-11.9kyaDryas cooling:~13-11.9kya

Heinrich eventsHeinrich events

Dansgaard-Oeschger eventsDansgaard-Oeschger events

Last glacial maximum (~20 Ky)Last glacial maximum (~20 Ky)

Cold, dry and windy Cold, dry and windy

Continent-sized ice sheets Continent-sized ice sheets

(Laurentide ice sheet over North (Laurentide ice sheet over North

America)America)

110m lower sea level than present110m lower sea level than present

Tropical debate over LGM coolingTropical debate over LGM cooling

Small tropical cooling (~2°C ) : CLIMAP Small tropical cooling (~2°C ) : CLIMAP reconstruction based on the changes in planktic reconstruction based on the changes in planktic fauna and flora in the low-latitude oceans. Other fauna and flora in the low-latitude oceans. Other evidences: biochemical composition of plankton evidences: biochemical composition of plankton shells (double bonds of alkenones), shells (double bonds of alkenones), δδ1818O O measurements on the CaCOmeasurements on the CaCO33 shells of plankton shells of plankton..

Large tropical cooling (~5°C ): Mountain glacial Large tropical cooling (~5°C ): Mountain glacial ice line change, noble gases dissolved in glacial-ice line change, noble gases dissolved in glacial-age groundwater.age groundwater.GCMs can only get level of ice sheet and tropical GCMs can only get level of ice sheet and tropical glacier growth with ~5ºC shift in tropical glacier growth with ~5ºC shift in tropical temperaturetemperature

Abrupt climate changeAbrupt climate change

Heinrich events: ice-rafted debris & Heinrich events: ice-rafted debris & terrigenous material found in deep-terrigenous material found in deep-sea cores, corresponding to sea cores, corresponding to Greenland ice core low Greenland ice core low δδ1818O. O. Dansgaard-Oeschger cycle: A series Dansgaard-Oeschger cycle: A series of warm-cold oscillation punctuated of warm-cold oscillation punctuated the last glaciation from 15 to 110 Kyr the last glaciation from 15 to 110 Kyr BP. The D-O cycles have been BP. The D-O cycles have been marked by abrupt terminations, and marked by abrupt terminations, and often by abrupt onsets.often by abrupt onsets.

Climate Change over the Last Glacial CycleClimate Change over the Last Glacial CycleDansgaard-Oeschger Oscillations and Heinrich Events

Schematic diagram taken from: Alley, 1998: Nature, 392, 335 - 337

Younger DryasYounger Dryas

YoungerDryas

YoungerDryas

Younger Dryas EventYounger Dryas Event

-55-55

-50-50

-45-45

-40-40

-35-35

-30-30

-25-25

05101520Age (kya)

Tem

per

atu

re (

°C)

Tem

per

atu

re (

°C)

0.050.05

0.100.10

0.150.15

0.200.20

0.250.25

0.300.30

0.350.35

Sn

ow

Acc

um

ula

tio

n (

m/y

r)S

no

w A

ccu

mu

lati

on

(m

/yr)

Little Ice AgeLittle Ice AgeIce Age

Medieval WarmMedieval Warm

Younger Dryas EventYounger Dryas Event

-44-44-43-43-42-42

-41-41-40-40-39-39-38-38-37-37

-36-36-35-35-34-34

18O

(G

reen

lan

d)

18O

(G

reen

lan

d)

-8.0-8.0

-7.5-7.5

-7.0-7.0

-6.5-6.5

-6.0-6.0

-5.5-5.5

-5.0-5.0

-4.5-4.5

-4.0-4.010111213141516

18O

(C

hin

a)18

O (

Ch

ina)

YoungerDryas

YoungerDryas

Age (kya)

Medieval WarmingMedieval Warming

10th century-14th century in Europe; 10th century-14th century in Europe; May recent finding in North AmericaMay recent finding in North America

Coincided with a peak in solar Coincided with a peak in solar activityactivity

Little Ice AgeLittle Ice AgeA period of cooling from approx. 14th-19th A period of cooling from approx. 14th-19th century, occurs after the medieval century, occurs after the medieval warming, though there seems to be little warming, though there seems to be little global agreement on the timing. global agreement on the timing.

Most evidence in Europe and north AmericaMost evidence in Europe and north America

Hypotheses of the cause include decreased Hypotheses of the cause include decreased sunspot activity (Maunder minimum) and sunspot activity (Maunder minimum) and increased volcanic activity, others claim it increased volcanic activity, others claim it had to do with a decrease in population had to do with a decrease in population resulting from the black death and thus a resulting from the black death and thus a decrease in agricultural activitydecrease in agricultural activity

Recent Temperature Changes

百年尺度

千年尺度

十万年尺度

Or

地史时期气温变化"The farther backward you can look,the farther forward you are likely to see."- Winston Churchill