Selected Slides from Prof. Broccoli’s Two Guest Lectures Required reading for Greenhouse Effect...

Selected Slides from Prof. Broccoli’s Two Guest Lectures

• Required reading for Greenhouse Effect class at Rutgers University, Spring 2004

• Condensed by Sunil Somalwar

Alan Robock & Tony BroccoliDepartment of Environmental Sciences

Global WarmingAlan Robock

Tony BroccoliDepartment of Environmental Sciences

Rutgers University, New Brunswick, New Jersey USA

[email protected] [email protected]

http://envsci.rutgers.edu/~robock http://envsci.rutgers.edu/~broccoli


Mann et al.

(1999)


“The balance of evidence suggestsa discernible human influence on global

climate.”

Climate Change 1995 – The Second Assessment of the Intergovernmental Panel on Climate Change

(IPCC)“There is new and stronger evidence thatmost of the warming observed over the last

50 years is attributable to human activities.”

Climate Change 2000 – The Third Assessment Report of the IPCC

“The unequivocal detection of the enhanced greenhouse effect from observations is not likely for

a decade or more.”

Climate Change – The IPCC Scientific Assessment (1990)


At the request of U.S. President George W. Bush, the National Research Council of the U.S. National Academy of Sciences issued a special report, Climate Change Science: An Analysis of Some Key Questions, that endorsed the key conclusions of the IPCC assessment in 2001.

The U.S. Environmental Protection Agency in 2002 issued a report that again supported the IPCC assessement.


Actual 1994-98 observations


Climate System

1. Atmosphere

2. Hydrosphere (oceans)

3. Cryosphere (snow, ice, glaciers)

4. Biosphere (including people)

5. Lithosphere (soil, volcanoes)


The Climate System


Temperature Feedbacks

External forcing

++

–––

+

Start with temperature increase, e.g., from more CO2

–

–

+


Fundamental Determinants of Climate1. Input of solar radiation

2. Atmospheric composition (gases and aerosols)

3. Surface characteristics (albedo, roughness, potential evapotranspiration)Humans can change climate by affecting 2

or 3.


The climate system


Earth’s global, annual mean energy balance

Planetary albedo () is the average reflectivity of the Earth = 107/342 0.3


Earth’s global, annual mean energy balance

Greenhouse effect


Causes of Climate Change (Forcings)

Natural: Solar variationsVolcanic eruptionsChaotic weather variationsEl Niño/Southern OscillationOther ocean-atmosphere

interactions

Anthropogenic: GHG: CO2, CH4, CFCs, N2O, O3

Tropospheric aerosolsSulfates, black carbon,

organics, dustDirect and indirect effects

Ozone depletion (indirect effect of CFCs)

Land surface modificationContrails


(IPCC TAR, Chap. 3)


Mountain Glacier Trends


19912002


General Circulation Models (GCMs) 1

Basic Physical Laws:

Conservation of energy (First law of thermodynamics)

Conservation of momentum (Newton’s second law of motion)

Conservation of mass (Continuity equation)

Conservation of moisture

Hydrostatic equilibrium

Gas law


General Circulation Models (GCMs) 2

Physical Processes That Must or Can Be Included:Wind Sea iceRadiation SnowPrecipitation GlaciersSoil moisture VegetationGround water Ocean biotaAerosolsClouds, convective and large-scaleAir-sea exchanges of moisture, energy, and momentumAir-land exchanges of moisture, energy, and momentumChemistry, particularly O3 and CO2

Ocean temperature, salinity, and currents


Typical grid spacing of a GCM is 4° x 5° latitude-longitude by 2 km in the vertical.

In the near future, we will have global 1° x 1° models and the Japanese have designed the fastest computer in the world, the “Earth Simulator.” on which they will run a global 10 km x 10 km grid.

Each time the horizontal resolution is increased by a factor of 2, the time needed to run the model goes up by a factor of 8.

When the vertical resolution is doubled the time required doubles in general, but can go up by more, if winds become faster.


To include all the processes in a climate model which are of a scale smaller than is resolved by the model, they must be “parameterized.”

One of the most important and difficult climate elements to parameterize is cloudiness. Clouds have a much smaller spatial and temporal scale than a typical GCM grid box.

Usually, we consider separately 2 types of clouds, layer clouds and convective clouds. There is no fundamental prognostic equation for clouds (no conservation of clouds principle); rather they form when condensation takes place and dissipate due to precipitation and evaporation.


Future Sea Level Projections

Different scenarios Model

ranges


Third Assessment Report of the IPCC (2001):

General circulation model results


Third Assessment Report of the IPCC (2001):

General circulation model results

Pinatubo


Vinnikov et al.(1999)


How will climate change affect us?


Land Use Change Loss of

Biodiversity

Invasive Species Air

Pollution Acid Deposition

Pollutio

n

Algal

Bloom

s

Climate Change and other Environmental Stresses


Areas of Human Endeavor That Could BeAffected by Global Warming

Agriculture Electricity DemandWater Resources Wind Energy GenerationFisheries Solar Energy GenerationAir Pollution Hydroelectricity GenerationHuman Health Ocean TransportationRecreation Air TransportationInsurance Land TransportationWetlands Political SystemsForestry


The Global Warming Dilemma (Mahlman, 2002)

“On the one hand, large increases in atmospheric CO2 concentrations have occurred, with considerably more ‘in the pipeline.’ Yet, the magnitude of documented warming to date is comparatively small, about 0.6°C....Thus, there has been little motivation today to resort to a major effort to reduce global CO2 emissions.

“On the other hand, delaying major CO2 emissionsreductions until substantial climate warming occurs would very likely ‘wire in’ the world to globally troublesome global warming for many centuries....Therefore, the choices are quite daunting: we can make very large policy commitments now with little visible short-term payback, or we can delay policy action indefinitely (the de facto current strategy), with very large coping and adaptation costs decades and centuries from now.”



“The harsh reality of the Global Warming Dilemma: Consider the policymakers’ sincere question: “What can we do in a mitigation context to keep global warming from happening?” The blunt answer is almost nothing; climate change is well underway and it carries huge momentum. Clearly, the question needs to be restated: “What are the options available for us to manage this dauntingly difficult problem in the most globally responsible way?” In this form, the question is quite reasonable because it allows avenues for finding rational approaches for dealing with the real problem.”



“There are no quick policy fixes, nationally or globally. If we don't begin to chip away at the problem soon, it is very likely that serious consequences will be wired in for the world of our great-grandchildren and for their great-grandchildren. ...

The long time scales and robustness of the problem almost guarantees that our descendants in the 22nd century will, with historical perspective, see that we were actually confronted with a major planet-scale stewardship/ management problem.

They will most assuredly note how we responded, or how we did not respond to the problem.”

Frequently Asked QuestionsFrequently Asked Questions• What is the global warming controversy?• Was the mild weather of some recent winters a

result of global warming?• Does global warming mean that there won’t be

snowy winters anymore?• If global warming is occurring, why was

January so cold?• How can we project what the earth’s

temperature will be 50 years from now if we don’t always get tomorrow’s weather forecast right?

What is the global warming What is the global warming controversy?controversy?

Media Coverage Media Coverage of Global of Global WarmingWarming

“Climbing temperatures. Melting glaciers.Rising Seas. All over the earth we’refeeling the heat. Why isn’t Washington?”

Climate change is a big and very complex scientific and political issue. Media coverage naturally reports on both of these aspects – often blending the two. Time Magazine

April 9, 2001

The Global Warming The Global Warming ControversyControversy

• Is the earth warming? (Detection)

• Are human activities responsible for this warming? (Attribution)

• What should we do about it? (Policy)

Was the mild weather of some Was the mild weather of some recent winters a result of recent winters a result of

global warming?global warming?

A Baseball AnalogyA Baseball Analogy

• John Doe is a five-year veteran with career averages of .303 BA, 9 HR, 57 RBI.

• He undertakes an off-season weight-training program.

• In his first at-bat of the new season, he hits a towering, 470-foot home run.

• Was this monstrous blast a result of his off-season weight training?

Possible AnswersPossible Answers

• “Of course not. One home run doesn’t prove anything. The pitcher may have thrown a batting practice fastball that anybody could crush.”

• “I knew all his off-season work would pay off. He’s always been able to get his bat on the ball, he just needed some more strength. I bet he wins the home run title.”

A Better AnswerA Better Answer

• Global warming would alter the probability of warm winters, but the internal variability of the climate system is a powerful factor in year-to-year climate variations.

• A warm winter could be evidence of global warming, but only if it is part of a long-term trend.

• Time will tell.

No Snowy Winters Anymore?No Snowy Winters Anymore?• Global warming would alter the

probability of snowy winters, but the internal variability of the climate system (e.g., El Niño, North Atlantic Oscillation) is a powerful factor in year-to-year climate variations.

If global warming is occurring, If global warming is occurring, why was January so cold?why was January so cold?

Global Temperature TrendsGlobal Temperature Trends

Source: NASA Goddard Institute for Space Studies

How can we project what the How can we project what the earth’s temperature will be 50 earth’s temperature will be 50 years from now if tomorrow’s years from now if tomorrow’s weather forecast isn’t always weather forecast isn’t always

right?right?

Consider a prediction using the above equation of the future state of the variable X, say the surface air temperature. The subscript n indicates the time, say the day, and a is a constant representing the physics of the climate system. X for any day is a times its value on the previous day minus X squared on the previous day.

With such a simple equation, it should be possible to predict X indefinitely into the future. Right?

Let’s assume that a is exactly 3.930 and that a prediction with three decimal places is the exact solution.

Then let’s consider three types of errors: imprecise knowledge of the physics of the climate system, imprecise initial conditions, and rounding due to limited computer resources.

This example is from Edward Lorenz.

Xn+1 = a Xn - Xn2

0.00.51.01.52.02.53.03.54.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

n

Xn

Control Physics Initial Conditions Rounding

Sensitivity to Initial ConditionsSensitivity to Initial ConditionsResults from three different simulations, each starting from different initial conditions. Changes in atmospheric composition are identical.

Global Warming Occurs in All Global Warming Occurs in All ThreeThree

The global warming signal eventually emerges in all three simulations, despite the pronounced internal variability that is evident.

My Global Warming ForecastMy Global Warming Forecast• The global climate will continue to warm, and

as it does, any scientific controversy about the detection of climate change will end.

• Controversy about the attribution of climate change will last longer than controversy about the detection of climate change.

• The controversy will eventually shift toward the policy questions and remain for a long time.

However…However…

• Virtually all forecasts should be expressed as probability forecasts, and mine is no exception.

• We still have a lot to learn about how the climate system works.

• More work will be required to narrow the range of uncertainties about the future spatial and temporal evolution of climate.

Selected Slides from Prof. Broccoli’s Two Guest Lectures Required reading for Greenhouse Effect...

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