(mt/ag/ensc/enst 404/504 - global change) history (from ipcc wg-i, chapter 1) historical...

(Mt/Ag/EnSc/EnSt 404/504 - Global Change)(Mt/Ag/EnSc/EnSt 404/504 - Global Change) History (from IPCC WG-I, Chapter 1)History (from IPCC WG-I, Chapter 1)

Historical Perspectives Historical Perspectives onon

Climate Change ResearchClimate Change Research

Primary Source:

IPCC WG-I Chapter 1 - Historical Overview of Climate Change Science


The Scientific BasisThe Scientific Basis

1. Hypothesis testing

- Should be subject to peer analysis & review

- Can it be shown, in principle, to be false?

- Can it provide predictions (tests)?

2. Basis for scientific progress

- builds on previous work- self-correcting

3. For IPCC: Key questions• Has it been rigorously tested? • Did it appear in the peer-reviewed literature? • Did it build on the existing research record where appropriate?• What are the uncertainties?


How Do Climate Scientists Conduct Experiments?How Do Climate Scientists Conduct Experiments?

• There is only one planet.

• How can one test hypotheses?

1. Observed behavior (e.g., short-term climate perturbations, like volcanic emissions)

2. Simulation models

3. Fundamental theory


Rigorous Review is Essential!Rigorous Review is Essential!

Growth in the Peer-Reviewed LiteratureGrowth in the Peer-Reviewed Literature


What Determines Earth’s Climate?What Determines Earth’s Climate?

Earth’s Orbit


Earth’s Orbital ParametersEarth’s Orbital Parameters

Perihelion(~ Jan 3)

Vernal Equinox (~ March 21)

Aphelion(~ July 5)

Why is Iowa colder in January?


Earth’s Orbital ParametersEarth’s Orbital Parameters

Eccentricity = SQRT(a2 - b2)/a ; for circle, = 0

Longitude of perihelion (one choice: angle from NH vernal equinox)

Tilt of rotation axis (obliquity)

b

a


What Determines Earth’s Climate?What Determines Earth’s Climate?

Earth’s OrbitEarth’s Albedo Earth’s Emissions


The Greenhouse Effect


The Greenhouse Effect: Early DiscoveriesThe Greenhouse Effect: Early Discoveries

Edme Marriotte (1620-1684):

Sun’s heat passes through glass, other heat does not (1681).

(www.nndb.com)

Horace Bénédict de Saussure (1740-1799):

Air in mountains does not trap heat as much as air in low-lying regions

(www.eoearth.org)


The Greenhouse Effect: Atmospheric The Greenhouse Effect: Atmospheric Properties & Climate ChangeProperties & Climate Change

John Tyndall (1820-1893):

Measured infrared radiation absorption properties of atmospheric molecules

Changing H2O or CO2 could cause “all the mutations of climate which the researches of geologists reveal”

(en.wikipedia.org)

Svante August Arrhenius (1859 -1927):

40% or in CO2 could explain advance & retreat of glaciers. (2xCO2 T ~ 4˚C.) Human CO2

emissions could prevent another ice age.

Nobel Prize - Chemistry (1903)

(en.wikipedia.org)


The Greenhouse Effect: Impact of Humans?The Greenhouse Effect: Impact of Humans?

Guy Stuart Callendar (1897-1964)

2xCO2 T ~ 2˚C

Must treat atmosphere as set of interacting layers, not a single slab.

Speculated, with others, that T over first part of 20th Century was anthropogenic.

(www.aip.org)

Criticisms:

1. Overlap of H2O and CO2 absorption bands saturation no impact of increasing CO2.

2. Earth regulates CO2 amounts, esp. via ocean. Humans have negligible impact.


Other Atmospheric ConstituentsOther Atmospheric Constituents

Other Greenhouse Gases:

- Methane (CH4)

- Nitrous Oxide (N2O)

- CFCs

Anthropogenic Aerosols (particles):

• Scatter sunlight back to space

• Cause more, smaller cloud particles (increase albedo)

(oea.larc.nasa.gov)


The Climate SystemThe Climate System

How do we simulate this?How do we simulate this?


Development of Development of Global Climate Global Climate Models (GCMs)Models (GCMs)

What is this?

Increased computing power has allowed increased resolution …

Computing demand Computing demand increases inversely with increases inversely with cubecube of horizontal of horizontal resolution.resolution.


Development of Development of Global Climate Global Climate Models (GCMs)Models (GCMs)

… and increasing complexity.

Which should be Which should be favored?favored?


Complements to GCMsComplements to GCMs

Global stretched-grid modelsGlobal stretched-grid models

Regional (limited-area) Regional (limited-area) modelsmodels


Example Regional Model DomainExample Regional Model Domain

Contrast the Hadley Centre GCM …Contrast the Hadley Centre GCM …

2.5˚ (lat) x 3.75˚ (lon)


… … with a regional modelwith a regional model

~ 0.5˚ (lat) x ~ 0.5˚ (lat) x ~ 0.5˚ (lon)~ 0.5˚ (lon)



How Well Have GCMs performed?How Well Have GCMs performed?

One test: One test: Projected changes Projected changes in global in global temperaturetemperature

T [

˚C]

Much more detail later (AR4, Chapter 8)


ENDEND

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