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Introduction to ClimatologyGEOGRAPHY 300

Tom GiambellucaUniversity of Hawai‘i at Mānoa

Climate Change

The Coupled Climate System

Defining Climate Change• Changes in a system can be ascribed to

changes in:– Boundary conditions– Internal characteristics

• However a given change in boundary or external conditions will not always produce the same climate response.

Climates of the Past

Ice AgesEarth's climate history reveals alternating warm and cold periods, with peaks roughly 150 million years apart. Note that the the graph below shows time going back from right to left.

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Climates of the Past

Ice AgesHere the graph is oriented more conventionally with time proceeding from left to right. But note that the scale increases as you move closer to the present.

Climates of the PastIce AgesWe are currently in one of the cold periods or ice ages, which began with gradual cooling that started about 55 MYA.

Climates of the PastIce AgesWe are currently in one of the cold periods or ice ages, which began with gradual cooling that started about 55 MYA.

Geological Time Scale

Earth is about 4.54 billion years old.

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Climates of the PastQuaternary PeriodThe most recent (current) geological period within the Cenozoic Era, beginning around 2.6 million years ago.

Pleistocene:Period of repeated glaciations, 2.6 million to 12,000 years ago.

Holocene: Relatively warm period since 12,000 years ago.

Anthropocene: Some scientists recognize the past 150-200 years as a new geological epoch. Others suggest that this period started 8,000 years ago with the expansion of agriculture.

1.806–2.588Gelasian (Lower)

0.781–1.806Calabrian (Lower)

0.126–0.781Ionian (Middle)

0.0117–0.126Tarantian (Upper)

Pleistocene

0–0.0117Holocene

Quaternary

Age (Ma)StageSeriesSystem

Subdivisions of the Quaternary Period

Climates of the PastPleistocene EpochDuring the Pleistocene Epoch, periods of cold climate, called glacials, and warm climate, called interglacials, alternated on a roughly 100,000-yr cycle. The most recent Pleistocene glacial peaked around 18,000 years ago.

PaleoclimatologyThe study of past climates using non-instrumental records, including:

1. oral and written histories of extreme weather, crop failure, famine, floods, droughts, commodity price fluctuations, etc.,

2. biological evidence, including live tree rings, fossil tree rings, fossil pollen, coral layers, marine sediments

3. ice cores, glacial ice deposited as annual layers which trap bubbles of air (atmospheric samples), organisms, and other material; stable water isotopes used to estimate temperature

4. geological evidence, including evidence of glaciation, evidence of inundation, sediments

5. isotopic evidence , radioisotopes used for dating other evidence; ratios of stable water isotopes indicate temperature; other isotope ratios used for a variety of purposes

Examples of Proxy Data

Pollen Tree Rings Ice Cores

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Tree Ring Data

Using an increment borer to obtain a core for tree ring analysis

Bristlecone Pines are the oldest known living trees,

up to 5000 years old

Tree Ring Data

Extended continuous records can be constructed from overlapping life spans of trees, a process called cross-dating

Only certain areas have been sampled for tree ring chrologogies

Ice Core Data

Ice cores taken during experimental ice core drilling in Greenland, 2005 (Riebeek, 2006)

Source: NOAA Arctic Theme Page

Causes of Climate ChangeThe climate is highly variable on all space and time scales.But what causes sustained changes over time?

Solar OutputSun spots:

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Causes of Climate ChangeSolar OutputSun spots:

Maunder Minimum (1645-1715) coincides with the “Little Ice Age”

Causes of Climate ChangeSolar OutputFaint Early Sun Paradox:

Sun's output has increased by about 1/3 since formation of solarsystem, but Earth surface temperatures were relative high duringearly times. This paradox was first framed by Carl Sagan and George Mullen in 1972, and focused on the contradiction between low solar radiation and the evidence that liquid water existed on the earth 4 billion years ago. The paradox can be resolved by taking into consideration the changing atmospheric gas composition. The early atmosphere has low in oxygen and rich in methane. As life evolved, oxygen became abundant, which facilitated conversion of method into CO2. Methane is a much more potent greenhouse gas than CO2.

Causes of Climate ChangeOrbital ChangesCharacteristics:

Eccentricity: elliptical shape of earth's orbit

Obliquity: tilt of earth's axis

Precession: timing of equinox or solstice with respect to aphelion

Causes of Climate ChangeOrbital Changes:Milankovitch Cycles

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Causes of Climate ChangeOrbital Changes:Milankovitch Cycles

Berger's (1991) solution for 65 degrees north latitude from the present to 1 million years ago. In the Northern Hemisphere, peak summer insolation occurred about 9,000 years ago when the last of the large ice sheets melted. Since that time Northern Hemisphere summers have seen less solar radiation.

Causes of Climate ChangeInternal Forcing Factors:

• Changes in land configuration: continental drift• Changes in surface characteristics: deforestation,

desertification influences on albedo and ET• Changes in atmospheric turbidity: increasing aerosol

concentrations; volcanic eruptions• Changes in radiatively active gases: early faint sun

paradox; recent greenhouse gas increases

Causes of Climate ChangePossible Feedback Mechanisms:

• Ice-Albedo Feedback (Positive Feedback)• Water Vapor Feedback (Positive Feedback)• Cloud-Albedo Feedback (Negative Feedback)• Cloud-LW Absorption Feedback (Positive Feedback)• Ocean-Atmosphere Interaction• Land-Atmosphere Interaction

Global WarmingBecause of increasing concentrations of greenhouse gases in the atmosphere, concerns were raised among scientists that the global average air temperature near the surface would increase. Evidence now strongly points to enhanced greenhouse warming as the cause of the observed increases in global average temperature over the past century and a half. The scientific debate has shifted from the question of whether or not global warming is occuring to what are the consequences of various options to combat (mitigation) and adjust to (adaptation) future climate changes.

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Intergovernmental Panel on Climate Change (IPCC)

International scientific body charged with evaluating the risk of climate change caused by human activity.

Established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP)

1990: First Assessment Report (FAR)

1992: Supplementary Report

1995: Second Assessment Report (SAR)

2001: Third Assessment Report (TAR)

2007: Fourth Assessment Report (AR4)

Shared 2007 Nobel Peace Prize with Al Gore

Climate Change DeniersDespite scientific consensus, some segments of our society continue to question the validity of contemporary global warming.

The group of so-called "global warming skeptics" includes people and organizations, such as:

Rush LimbaughFox NewsWall Street JournalExxon-MobileFred Singer (Univ. of Virginia)Bill Gray (Colorado State Univ.)See Greenpeace-sponsored web site EXXONSECRETS.ORG, which exposes the connections between phony climate science and oil industry funding.

Global Warming: The Facts1. Greenhouse gases, such as CO2 (carbon dioxide)

and CH4 (methane), cause air temperature near the surface to be higher.

Global Warming: The Facts2. Greenhouse gas concentrations are increasing.

MLO:

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Global Warming: The Facts2. Greenhouse gas concentrations are increasing.

CO2 increases are seen in both hemispheres, compensating decrease in O2 also observed, global carbon emissions trend matches observed changes in ratio of carbon isotopes, identifying human activities as the source of increasing CO2 concentrations:

Global Warming: The Facts2. Greenhouse gas concentrations are increasing.

Global methane concentration has also been increasing. The rate of increase (bottom panel) has been declining, but large up-spike was observed this year (not shown):

Global Warming: The Facts3. Mean global air temperature is increasing.

Global Warming: The Facts3. Mean global air temperature is increasing.

The pace of temperature increase is increasing

0.177 + 0.052Past 25 years:

0.128 + 0.026Past 50 years:

0.074 + 0.018Past 100 years:

0.045 + 0.012Past 150 years:

Rate (oC per decade)Period:

Observed Mean Global Temperature Change

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Global Warming: The Facts4. Air temperature increase is global.

Both hemispheres:

Global Warming: The Facts5. Global and hemispheric sea surface temperature

(SST) is increasing.

Global Warming: The Facts6. Global and hemispheric sea surface temperature

(SST) is increasing.

Global Warming: The Facts7. Oceanic dissolved CO2 is increasing and oceanic

pH is decreasing (sea water is acidifying).

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Global Warming: The Facts8. Mean global sea level is rising.

Important Scientific QuestionsHow fast will temperature increase over the coming decades?To what extent will the cooling effects of increased aerosols offset greenhouse warming?How will caused by decreasing ice and snow cover and increasing cloud cover affect the rate of temperature change?How will extreme events (droughts, floods, severe storms) changein terms of frequency or severity?How will regional weather (temperature, precipitation, storm frequency) change?What will be the regional impacts of global warming? Which nations will suffer/benefit the most?

Other Important Quesions

How can we best respond to global warming?

Whom should pay the costs?

Modeling Climate Processes

The Coupled Climate System

• Heated by incoming shortwave radiation, strongest at low latitudes

• Cooled by outgoing longwave radiation, predominant at high latitudes

• Latitudinal gradient drives large-scale atmospheric and oceanic circulations.

• Incomplete understanding of feedbacks cause uncertainties about the effects of changes within the system

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Modeling Climate Processes

Components of the Climate System

• atmosphere

• ocean

• cryosphere

• biosphere

• geosphere

Modeling Climate Processes

Biogeochemical Cycles

• nitrogen cycle• oxygen cycle• carbon cycle• phosphorus cycle• sulfur cycle• water cycle• hydrogen cycle

Modeling Climate ProcessesBiogeochemical Cycles

• nitrogen cycle

Modeling Climate ProcessesBiogeochemical Cycles

• carbon cycle

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Approaches to predicting changes in the climatic system

• Palaeo-analogue method• Coupled numerical general circulation models GCMs

Palaeo-analogue method• Approach: Identify periods in the past in which

conditions were similar to those for which the prediction is needed.

• Uses: – Estimate global temperature sensitivity to carbon dioxide

increases– Examine regional climatic patterns associated with higher or

lower global average temperatures.

• Problems:– Uncertainty of reconstructions– Extending limited data to global scale– Interpreting effects of changing orography and equilibrium vs.

non-equilibrium conditions– Determining the relative influences of various factors that caused

past changes in climate

Numerical Modeling ApproachEquilibrium climate change Time dependent climate change

• Equilibrium climate: the mean climate after a long period of without change in boundary conditions or internal characteristics; radiative balance.

• The current climate system is not in equilibrium due to changes in GHG and surface characteristics. So why do equilibrium experiments?

• Simpler GCMs (requiring less computer time) ignore ocean circulation changes and deep ocean interaction, both of which must be included in time-dependent simulations.

• Easier to compare equilibrium experiments. Good for doing "sensitivity studies" to see the relative effects of different factors.

• Can be scaled to approximate time-dependent change.

Time Dependent Climate Simulation Strategy:

(IPCC, 2007)

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Coupled numerical general circulation models (GCMs) GCMs

How they work

• Grid points, layers, time steps

• Movement and distribution of mass calculated using differential equations solved numerically

• Four basic equations:– Conservatrion of energy (1st law of thermodynamics)– Conservation of momentum (Newton's second law of motion)– Conservation of mass– Ideal gas law

GCMsModel components and interactions

• Radiative exchange• Atmospheric dynamics• Atmospheric Chemistry• Carbon Cycle• Clouds• Ocean• Ice• Land Surface--Vegetation

GCMs

Issues

• Sub-grid-scale processes (e.g. convection)• Prescribed vs. interactive process• Horizontal and vertical resolution• Emissions scenarios• Flux correction• Regional models• Data assimilation• Reanalysis

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GCM Results

CO2 doubling experiments: climate sensitivity

2oC to 4.5oC, most likely about 3oC

Time-Dependent Changes

• To run time-dependent simulations, the timing of future increases in greenhouse gas concentrations needs to be estimated

• This requires future emissions time series• Future emissions cannot be “predicted”• Instead, emissions “scenarios” are used

Emissions Scenarios

• SRES: Special Report on Emission Scenarios

• Scenario Families• Story lines

Emissions ScenariosA1The A1 scenarios are of a more integrated world. The A1 family of scenarios is characterized by:• Rapid economic growth.• A global population that reaches 9 billion in 2050 and then gradually

declines.• The quick spread of new and efficient technologies.• A convergent world - income and way of life converge between

regions. Extensive social and cultural interactions worldwide.There are subsets to the A1 family based on their technological

emphasis:• A1FI - An emphasis on fossil-fuels.• A1B - A balanced emphasis on all energy sources.• A1T - Emphasis on non-fossil energy sources.

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Emissions ScenariosA2The A2 scenarios are of a more divided world. The A2 family of scenarios is characterized by:

• A world of independently operating, self-reliant nations.• Continuously increasing population.• Regionally oriented economic development.• Slower and more fragmented technological changes and

improvements to per capita income.

Emissions ScenariosB1The B1 scenarios are of a world more integrated, and more

ecologically friendly.The B1 scenarios are characterized by:

• Rapid economic growth as in A1, but with rapid changes towards a service and information economy.

• Population rising to 9 billion in 2050 and then declining as in A1.

• Reductions in material intensity and the introduction of clean and resource efficient technologies.

• An emphasis on global solutions to economic, social and environmental stability.

Emissions ScenariosB2The B2 scenarios are of a world more divided, but more

ecologically friendly. The B2 scenarios are characterized by:

• Continuously increasing population, but at a slower rate than in A2.• Emphasis on local rather than global solutions to economic, social

and environmental stability.• Intermediate levels of economic development.• Less rapid and more fragmented technological change than in B1

and A1.

Emissions Scenarios

Standard Scenarios Used in AR4 Simulations:

• A2

• A1B

• B2

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Simulated Temperature Change

(IPCC, 2007)

Simulated Temperature Change

(IPCC, 2007)

Simulated Hydrological Change

(IPCC, 2007)

Simulated Change in Sea Ice Extent

(IPCC, 2007)

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Simulated Change in Weather Extremes

(IPCC, 2007)

Important Questions about What to Do

• Response: Mitigation vs. Adaptation• Who pays for reducing emissions?