Global Warming and the Global Warming and the Dominican RepublicDominican Republic

Kerry EmanuelKerry Emanuel

Program in Atmospheres, Oceans, Program in Atmospheres, Oceans, and Climateand Climate

Department of Earth, Atmospheric Department of Earth, Atmospheric and Planetary Sciencesand Planetary Sciences

MITMIT

ProgramProgram

• History of the earth’s climateHistory of the earth’s climate

• The science of global warmingThe science of global warming

• Possible effects of climate change on the Possible effects of climate change on the Dominican RepublicDominican Republic

The Faint Young Sun Paradox: Why The Faint Young Sun Paradox: Why didn’t the Earth Freeze?didn’t the Earth Freeze?

The Snowball EarthThe Snowball Earth

A detailed record of the earth’s climate has A detailed record of the earth’s climate has emerged over the last few decades, from analyses emerged over the last few decades, from analyses

of ice cores and deep sea sedimentsof ice cores and deep sea sediments

Ice Cover, Last Glacial Maximum Ice Cover, Last Glacial Maximum (~18,000 years ago)(~18,000 years ago)

http://upload.wikimedia.org/wikipedia/commons/1/1d/Post-Glacial_Sea_Level.png

Paleo reconstructions of temperature change Paleo reconstructions of temperature change over the last 2000 yearsover the last 2000 years

Year

Instrumental Record

Estimates of Global Mean Surface Temperature Estimates of Global Mean Surface Temperature from the Instrumental Recordfrom the Instrumental Record

Some Characteristics of Climate Some Characteristics of Climate ScienceScience

• Described by some as the most difficult scientific problem ever faced

• Draws on all the major scientific disciplines:– Chemistry, geology, atmospheric science,

oceanography, solar physics, orbital mechanics, biology

– Climate prediction also requires understanding of economics, politics, human psychology

• Very much a frontier science

John Tyndall (1820-1893)

The Greenhouse EffectThe Greenhouse Effect

Tyndall’s Discovery:

Oxygen (O2) and Nitrogen (N2), which together comprise about 97% of the atmosphere, are transparent to solar and infrared radiation

If that’s all there were: 40

1(1 )4sT a S

= Stefan-Boltzmann constant

a = Planetary albedo

= Solar constant

0S

255 0sT K F

But certain trace gases interact strongly with radiation:

H20 (water vapor)

CO2 (carbon dioxide)

CH4 (methane)

Clouds also interact strongly with radiation. Together, they yield:

288 60sT K F

Elements of the Greenhouse EffectElements of the Greenhouse Effect

If the Only Feedback Were If the Only Feedback Were Temperature, Doubling Carbon Temperature, Doubling Carbon Dioxide would Increase Surface Dioxide would Increase Surface Temperature by about 1.1 Temperature by about 1.1 ooC.C.

Feedbacks in Climate ModelsFeedbacks in Climate Models

Water vapor Cloud Surface albedo

Lapse rate Water vapor + lapse rate

Climate Climate Forcing Forcing

by Orbital by Orbital VariationsVariations

Milutin Milanković, 1879-1958

Climate Forcing and ResponseClimate Forcing and Response

Black: Time rate of change of ice volumeBlack: Time rate of change of ice volume

Red: Summer high latitude sunlightRed: Summer high latitude sunlight

Strong Correlation between High Latitude Summer Strong Correlation between High Latitude Summer Insolation and Ice VolumeInsolation and Ice Volume

P. Huybers, Science, 2006

Causes of Recent Climate Causes of Recent Climate ChangeChange

http://upload.wikimedia.org/wikipedia/commons/f/f4/Instrumental_Temperature_Record.png

Variation in Variation in carbon dioxide carbon dioxide and methane and methane over the past over the past 20,000 years, 20,000 years, based on ice based on ice core and other core and other recordsrecords

Contributions to net radiative forcing change, 1750-2004:Contributions to net radiative forcing change, 1750-2004:

Distribution of temperature change, 1901-2005Distribution of temperature change, 1901-2005

Global Climate Models: Global Climate Models: How Good Are They, and What How Good Are They, and What

Do They Tell Us about The Do They Tell Us about The Future?Future?

Global Climate ModelingGlobal Climate Modeling

• General philosophyGeneral philosophy:– Simulate large-scale motions of atmosphere,

oceans, ice– Solve approximations to full radiative transfer

equations– Parameterize processes too small to resolve– Some models also try to simulate

biogeochemical processes– First GCMs developed in 1960s

Equations solved by discretizing Equations solved by discretizing to finite volumesto finite volumes

Unresolved physical processes Unresolved physical processes must be handled parametricallymust be handled parametrically• Convection

• Thin and/or broken clouds

• Cloud microphysics

• Aerosols and chemistry (e.g. photochemical processes, ozone

• Turbulence, including surface fluxes

• Sea ice

• Land ice

• Land surface processes

Global mean temperature Global mean temperature (black) and simulations (black) and simulations using many different using many different global models (colors) global models (colors) including all forcingsincluding all forcings

Same as above, but Same as above, but models run with only models run with only natural forcingsnatural forcings

Projected Warming:Projected Warming:

Climate Risks to the Climate Risks to the Dominican RepublicDominican Republic

Warming RisksWarming Risks

• Rising sea level• Concentration of rainfall into fewer but more

intense events...more drought, floods• Increased incidence of some tropical diseases• Increased production of allergens• Increased mortality from heat waves• Increased consumption of electricity• Increase in violent hurricanes• Ocean acidification, increased species

extinctions

Sea Level, 1860-2003Sea Level, 1860-2003

Reconstructed

Tide Gauge

Satellite altimetry

Arctic Minimum Sea Ice ExtentArctic Minimum Sea Ice Extent

Greenland Greenland surface elevation surface elevation

change, 1989-change, 1989-20052005

Hurricane Power is Changing in Concert with Hurricane Power is Changing in Concert with Tropical Ocean TemperatureTropical Ocean Temperature

Today’s global climate Today’s global climate models are far too coarse to models are far too coarse to simulate tropical cyclonessimulate tropical cyclones

Our ApproachOur Approach• Step 1: Seed each ocean basin with a very large

number of weak, randomly located cyclones

• Step 2: Cyclones are assumed to move with the large scale atmospheric flow in which they are embedded

• Step 3: Run a coupled, ocean-atmosphere computer model for each cyclone, and note how many achieve at least tropical storm strength

• Step 4: Using the small fraction of surviving events, determine storm statistics.

200 Synthetic U.S. Landfalling tracks (color 200 Synthetic U.S. Landfalling tracks (color coded by Saffir-Simpson Scale)coded by Saffir-Simpson Scale)

Present Climate: Spatial Present Climate: Spatial Distribution of Genesis PointsDistribution of Genesis Points

Observed

Synthetic

Now Use Daily Output from IPCC Now Use Daily Output from IPCC Models to Derive Wind Models to Derive Wind

Statistics, Thermodynamic State Statistics, Thermodynamic State Needed by Synthetic Track Needed by Synthetic Track

TechniqueTechnique

1. Last 20 years of 20Last 20 years of 20thth century century simulationssimulations

2.2. Years 2180-2200 of IPCC Years 2180-2200 of IPCC Scenario A1b (COScenario A1b (CO22 stabilized at stabilized at

720 ppm)720 ppm)

Compare two simulations each Compare two simulations each from 7 IPCC models:from 7 IPCC models:

Change in Destructiveness of HurricanesChange in Destructiveness of Hurricanes

Return PeriodsReturn Periods

Sample Wind SwathSample Wind Swath

Sample Storm SurgeSample Storm Surge

Sample Rain SwathSample Rain Swath

Sample Rain Rate at Santa DomingoSample Rain Rate at Santa Domingo

Change in Landslide RiskChange in Landslide Risk

SummarySummary

• Earth’s climate has changed radically and often abruptly through time

• Primary culprits:– Changing insolation, through solar evolution and

orbital variations– Changing concentrations of trace greenhouse

gases– Changing concentration of aerosols: Volcanic

eruptions

• Evidence for human-induced climate change now very compelling

• Principle risks of Global Warming to the Dominican Republic:– Increased incidence of flash floods– Ocean acidification and damage to marine

ecosystems– Coastal flooding owing to sea level rise– Increased frequency and severity of

hurricanes, including storm surge and fresh-water flooding

http://upload.wikimedia.org/wikipedia/commons/7/7e/Satellite_Temperatures.png

Possible Benefits of Warming:Possible Benefits of Warming:

• Fewer deaths from exposure

• More vigorous plant growth

• Increase of arable land at high latitudes

• Increased mining potential in current permafrost regions

• Arctic waterways become navigable

• Reduced heating costs

Changing Distributions of PrecipitationChanging Distributions of Precipitation