What We Know About Climate Change Kerry Emanuel Department of Earth, Atmospheric, and Planetary Sciences, MIT

Common Misperceptions about Climate and Climate Science Earth’s climate is inherently stable Climate science is very young Human activities can have only a minuscule effect compared to nature The idea that we are altering climate is based exclusively on complex, unreliable models

Common Misperceptions about Climate and Climate Science Earth’s climate is inherently stable Climate science is very young Human activities can have only a minuscule effect compared to nature The idea that we are altering climate is based exclusively on complex, unreliable models

Last 450 Thousand Years

The Snowball Earth, mya

Common Misperceptions about Climate and Climate Science Earth’s climate is inherently stable Climate science is very young Human activities can have only a minuscule effect compared to nature The idea that we are altering climate is based exclusively on complex, unreliable models

John Tyndall ( ) Jean Baptiste Joseph Fourier ( )

Climate Forcing by Orbital Variations (1912) Milutin Milanković,

Last 450 Thousand Years

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

Svante Arrhenius, “Any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4°; and if the carbon dioxide were increased fourfold, the temperature would rise by 8°.” – Världarnas utveckling (Worlds in the Making), 1906

Guy Stewart Callendar ( )

Carbon Dioxide and Climate: A Scientific Assessment Report to the National Academy of Sciences Jule G. Charney and co-authors 1979 When it is assumed that the CO2 content of the atmosphere is doubled and statistical thermal equilibrium is achieved, the more realistic of the modeling efforts predict a global surface warming of between 2°C and 3.5 °C, with greater increases at high latitudes.

Common Misperceptions about Climate and Climate Science Earth’s climate is inherently stable Climate science is very young Human activities can have only a minuscule effect compared to nature The idea that we are altering climate is based exclusively on complex, unreliable models

John Tyndall ( )

Tyndall’s Essential Results: Oxygen (O 2 ) and nitrogen (N 2 ), though they make up ~98% of the atmosphere, are almost entirely transparent to solar and terrestrial radiation Water vapor (H 2 O), carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and a handful of other trace gases make the lower atmosphere nearly opaque to infrared radiation, though still largely transparent to solar radiation (but clouds have strong effects on radiation at all wavelengths)

Water Vapor (H 2 O) is the most important greenhouse gas, but responds to atmospheric temperature change on a time scale of about 2 weeks Climate is therefore strongly influenced by long- lived greenhouse gases (e.g. CO 2, CH 4, N 2 O) that together comprise about 0.03% molar fraction of the atmosphere

Common Misperceptions about Climate and Climate Science Earth’s climate is inherently stable Climate science is very young Human activities can have only a minuscule effect compared to nature The idea that we are altering climate is based exclusively on complex, unreliable models

Paleoclimate

Last 450 Thousand Years

Paleo reconstructions of temperature change over the last 2000 years Year Instrument al Record “Hockey Stick”

Arctic air temperature change reconstructed (blue), observed (red) The long-term cooling trend in the Arctic was reversed during recent decades. The blue line shows the estimated Arctic average summer temperature over the last 2000 years, based on proxy records from lake sediments, ice cores, and tree rings. The shaded area represents variability among the 23 sites use for the reconstruction. The red line shows the recent warming based on instrumental temperatures. From Kaufman et al. (2009).

Instrumental Record

Distribution of temperature change,

High vs Low Temperature Records :1

Credit: National Snow and Ice Data Center courtesy Stroeve et al September Arctic Sea Ice Extent

Carbon Dioxide from Ice Cores and Direct Measurements

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

Simple Models

MIT Single Column Model

Global Climate Models

20 th Century With and Without Human Influences

Sources of Uncertainty Cloud Feedback Water Vapor Feedback Ocean Response Aerosols

Source: PAGE09 runs Our best estimate of how much global climate will warm as a result of doubling CO 2 : a probability distribution Chris Hope, U. Cambridge courtesy Tim Palmer

Climate Roulette Credit: MIT Center for Global Change Science

Atmospheric CO 2 assuming that emissions stop altogether after peak concentrations Global mean surface temperature corresponding to atmospheric CO 2 above IPCC 2007: Doubling CO 2 will lead to an increase in mean global surface temperature of 2 to 4.5 o C. Courtesy Susan Solomon

Consequences

(Source: WBGU after David Archer 2006) Past and Projected Sea Level vs. Temperature

Hydrological Extremes Increase with Temperature Floods

Drought

Hurricanes

Projected Global Tropical Cyclone Power Dissipation Global annual tropical cyclone power dissipation averaged in 10-year blocks for the period , using historical simulations for the period and the RCP 8.5 scenario for the period In each box, the red line represents the median among the 5 models, and the bottom and tops of the boxes represent the 25 th and 75 th percentiles, respectively. The whiskers extent to the most extreme points not considered outliers, which are represented by the red + signs. Points are considered outliers if they lie more than 1.5 times the box height above or below the box.

Severe Thunderstorms

Tornadoes

Hail Storms

55 The Oceans are Turning Sour  Acidification through CO 2 threatens marine life Plankton Coral Reefs

“Climate change could have significant geopolitical impacts around the world, contributing to poverty, environmental degradation, and the further weakening of fragile governments. Climate change will contribute to food and water scarcity, will increase the spread of disease, and may spur or exacerbate mass migration.” -- Quadrennial Defense Review, U.S. Department of Defense, February, 2010

Dealing with Climate Change Reduce emissions – gasification of coal—potential CO 2 capture – alternative sources– nuclear, wind, etc. – unlikely to effect major reductions – focus on non-CO 2 greenhouse gases Carbon capture and sequestration Other geoengineering – technically feasible, $20-30 billion/year – side effects, e.g. reduced precipitation Adaptation

Climate Politics

The New York Times December 9 th 1953

NY Times article on smoking-cancer connection Beginning of industry disinformation campaign

1991 the Western Fuels Association established the Information Council for the Environment (ICE) to “demonstrate that a consumer-based media awareness program can positively change the opinions of a selected population regarding the validity of global warming.” [1] The Council planned an ad campaign that would “directly attack the proponents of global warming by relating irrefutable evidence to the contrary, delivered by a believable spokesperson” and would “attack proponents through comparison of global warming to historical or mythical instances of gloom and doom.” The campaign specifically targeted older, less-educated males and younger, lower-income women. [1] 1991: Western Fuels Association establishes the Information Council for the Environment (ICE) to “demonstrate that a consumer-based media awareness program can positively change the opinions of a selected population regarding the validity of global warming.” Ad campaign that “will directly attack the proponents of global warming by relating irrefutable evidence to the contrary, delivered by a believable spokesperson”, and “will attack proponents through comparison of global warming to historical or mythical instances of gloom and doom.” The campaign specifically targeted “older, less-educated males and younger, lower-income women”.

RESULTS:

Summary of Main Points Several aspects of climate science are well established Projections remain highly uncertain, particularly at the regional scale Ill effects felt mostly through weather extremes and through indirect fallout, such as global armed conflict

Summary of Main Points Highly asymmetric risk function Rational response to risk impeded by well- funded and highly effective marketing campaign

Atlantic Sea Surface Temperatures and Storm Max Power Dissipation (Smoothed with a filter) Years included: Data Sources: NOAA/TPC, UKMO/HADSST1

Annual power dissipation of North Atlantic tropical cyclones downscaled from AGCMs and the NCAR/NCEP reanalysis using the technique of Emanuel et al. (2008), compared to estimated actual tropical cyclone power dissipation. The series have been smoothed using a filter.

Sandy?

An example It’s getting warmer!.... Time

It’s getting warmer!.... No, it’s not! Warming stopped at 13! In fact, 13 was warmer than at any time since then! Time

Note: We can forecast that summer will be warmer than winter, even though we cannot forecast the weather beyond a few days