Global Warming and the Dominican Republic Kerry Emanuel Program in Atmospheres, Oceans, and Climate Department of Earth, Atmospheric and Planetary Sciences MIT

Program 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 Dominican RepublicPossible effects of climate change on the Dominican Republic

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

The Snowball Earth

A detailed record of the earth’s climate has emerged over the last few decades, from analyses of ice cores and deep sea sediments

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

Paleo reconstructions of temperature change over the last 2000 years Year Instrumental Record

Estimates of Global Mean Surface Temperature from the Instrumental Record

Some Characteristics of Climate Science 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 ( ) The Greenhouse Effect

Tyndall’s Discovery: Oxygen (O 2 ) and Nitrogen (N 2 ), which together comprise about 97% of the atmosphere, are transparent to solar and infrared radiation If that’s all there were: = Stefan-Boltzmann constant a = Planetary albedo = Solar constant

But certain trace gases interact strongly with radiation: H 2 0 (water vapor) CO 2 (carbon dioxide) CH 4 (methane) Clouds also interact strongly with radiation. Together, they yield:

Elements of the Greenhouse Effect

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

Feedbacks in Climate Models Water vaporCloudSurface albedo Lapse rateWater vapor + lapse rate

Climate Forcing by Orbital Variations Milutin Milanković,

Climate Forcing and Response

Black: Time rate of change of ice volume Red: Summer high latitude sunlight Strong Correlation between High Latitude Summer Insolation and Ice Volume P. Huybers, Science, 2006

Causes of Recent Climate Change

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

Contributions to net radiative forcing change, :

Distribution of temperature change,

Global Climate Models: How Good Are They, and What Do They Tell Us about The Future?

Global 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 to finite volumes

Unresolved physical processes must 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 (black) and simulations using many different global models (colors) including all forcings Same as above, but models run with only natural forcings

Projected Warming:

Climate Risks to the Dominican Republic

Warming 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, Reconstructed Tide Gauge Satellite altimetry

Arctic Minimum Sea Ice Extent

Greenland surface elevation change,

Hurricane Power is Changing in Concert with Tropical Ocean Temperature

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

Our 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 coded by Saffir-Simpson Scale)

Present Climate: Spatial Distribution of Genesis Points Observed Synthetic

Now Use Daily Output from IPCC Models to Derive Wind Statistics, Thermodynamic State Needed by Synthetic Track Technique

Last 20 years of 20 th century simulations 2. Years of IPCC Scenario A1b (CO 2 stabilized at 720 ppm) 1. Last 20 years of 20 th century simulations 2. Years of IPCC Scenario A1b (CO 2 stabilized at 720 ppm) Compare two simulations each from 7 IPCC models:

Change in Destructiveness of Hurricanes

Return Periods

Sample Wind Swath

Sample Storm Surge

Sample Rain Swath

Sample Rain Rate at Santa Domingo

Change in Landslide Risk

Summary 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

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 Precipitation