GEOG 401 Natural Perturbationsclimate.socialsciences.hawaii.edu/Courses/GEOG401/GEOG...GEOG 401 Natural Perturbations.pptx Author Thomas Giambelluca Created Date 2/24/2015 7:40:20

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GEOG 401 Climate Change

Natural Climate Perturba:ons

Conceptualizing the Climate System

“Earth’s climate is the result of the physical requirement to maintain a balance between energy reaching and leaving the atmosphere.” (Cornell et al., eds., 2012, p. 72) “Heat is transported around the Earth in both the atmosphere and the ocean, and the paPerns of this transport modulate climate at any given loca:on.” (Cornell et al., eds., 2012, p. 72)

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Climate Perturba:ons

Defini:on: perturba:on – a devia:on of a system caused by an outside influence (hPp://oxforddic:onaries.com/defini:on/english/perturba:on)

Climate Forcings “In climate science, radia:ve forcing is defined as the difference between radiant energy received by the earth and energy radiated back to space.” (hPp://en.wikipedia.org/wiki/Climate_forcing) “A range of ‘primary’ forcings can be considered external to the climate system: these include changes in the amount of incoming solar radia:on (insola:on) caused by changes in the Earth’s orbit, or changes in solar ac:vity. Volcanic ac:vity, which releases trace gases and par:culates in the atmosphere, is also generally thought of as an external forcing on the climate system. Anthropogenic and geologic emissions of greenhouse gases area also generally considered as primary forcings.” (Cornell et al., eds., 2012, p. 73)

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Feedbacks “Feedback in general is the process in which changing one quan:ty changes a second quan:ty, and the change in the second quan:ty in turn changes the first. Posi:ve feedback amplifies the change in the first quan:ty while nega:ve feedback reduces it.” (hPp://en.wikipedia.org/wiki/Climate_change_feedback) “Climate change feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of each climate forcing, and so play an important part in determining the overall climate sensi:vity.” (hPp://en.wikipedia.org/wiki/Climate_change_feedback)

Climate Forcings and/or Feedbacks

•  Solar output (Forcing) –  Long-‐term increase –  Sunspot cycle –  Anomalies in sunspot cycle (e.g., Maunder Minimum)

•  Orbital characteris;cs (Forcing) –  Milankovitch Cycles

•  Atmospheric transmission (Forcing or Feedback) –  Volcanic erup:ons –  Dust, smoke, etc.

•  Earth albedo (Forcing or Feedback) –  Ice/snow cover changes –  Changes in cloud cover/characteris:cs

•  Atmospheric longwave radia;on absorp;on (Forcing or Feedback) –  Varia:ons in greenhouse gas concentra:ons

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Greenhouse Gas Forcing

hPp://www.giss.nasa.gov/research/news/20020114/

Solar Output Solar Evolu;on Faint Early Sun Paradox: “4.5 billion years ago sun was ca. 8% smaller and 3% less luminous so solar constant was ca. 25% less.” (Walter and Barry, 1991) (hPp://www.geo.arizona.edu/palynology/geos462/20climsolar.html)

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Solar Output Sunspot Cycle


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Milankovitch Cycles •  The characteris:cs of Earth’s orbit and axial :lt

change in regular cycles. •  This has liPle influence on the total annual

energy intercep:on of the whole Earth •  Seasonal and la:tudinal distribu:on of energy

is significantly affected causing changes in polar ice cover

•  Ice cover changes affect Earth’s albedo

Cycles •  Obliquity (22.1 – 24.5 degrees; 41,000-‐yr cycle;

currently 23.44 degrees) •  Eccentricity (0.005 – 0.058); 100,000-‐yr cycle;

currently 0.017) •  Precession (21,000-‐yr cycle)

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Milankovitch Cycles

ε is obliquity (axial :lt)

ϖ is longitude of perihelion

esin(ϖ) is the precession index (e is eccentricity)

is the calculated daily-‐averaged insola:on at the top of the atmosphere, on the day of the summer sols:ce at 65 N la:tude

Consequences of Orbital Varia:ons

Data from Vostok ice cores: hPp://www.usgcrp.gov/usgcrp/images/Vostok.jpg

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Volcanic Erup:ons

hPp://www.climate4you.com/ClimateAndVolcanoes.htm

Volcanic Erup:ons

hPp://www.geog.cam.ac.uk/research/projects/volcanoeffects/

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Volcanic Erup:ons Volcanic Emissions •  Dust par:cles •  Sulfur compounds •  Water vapor •  Carbon dioxide

Tambora (1815) •  150 km3 of ash •  900 km from the erup:on, 1 cm of ash fell •  Erup:on column es:mated to have been 45 km high •  Est. 92,000 people killed by erup:on •  Lowered global average temperature by 0.5-‐0.7 deg C

over 2-‐3 years •  Year without a summer (1816) •  London had snow in August

Volcanic Erup:ons Krakatau (Krakatoa) (1883)

•  Loudest sound in modern history (heard up to 4,800 miles away)

•  Op:cal effects for several years

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Volcanic Erup:ons Pinatubo (1991)

Volcanic Erup:ons Pinatubo (1991)

Longman (2012)

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Ice-‐Albedo Forcing/Feedback

Ice-‐Albedo Forcing/Feedback For the Arc;c Ocean, for example: •  Snow-‐covered ice albedo: 80-‐90% •  Open ocean albedo < 10% •  Changes in sea ice extent have large impacts on albedo of the polar region •  Ice-‐albedo effect on shortwave radia:on absorp:on is somewhat less

because of atmospheric reflec:on, especially by clouds •  Temperature varia:on affects sea ice extent only within a certain range;

when temperatures are very low, temperature varia:ons do not result in mel:ng; when temperatures are high, temperature varia:ons do not result in freezing

•  Effects on energy balance depend on the rela:ve effects of temperature change on albedo (affec:ng shortwave absorp:on) and emission (longwave)

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hPp://www.gfdl.noaa.gov/bibliography/related_files/mw0901.pdf



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Ice-‐Albedo Forcing/Feedback For land areas, such as Greenland and Antarc:ca : •  The ice vs. ice-‐free albedo contrast is

somewhat less than for the ocean

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Snow-‐Albedo Forcing/Feedback Vegetated land areas such as boreal forests: •  Evergreen tree cover reduces the albedo effect of snow

hPp://www-‐modis.bu.edu/brdf/userguide/publica:ons/2002_jin_2_etal.pdf

Cloud Forcings/Feedbacks

Albedo feedback

Longwave absorp:on feedback

hPp://earthobservatory.nasa.gov/Features/Clouds/

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Cloud Forcings/Feedbacks

Net Radia:on

Net Cloud Radia:ve Forcing

hPp://earthobservatory.nasa.gov/Features/Clouds/

Greenhouse Forcing/Feedback

AR5 WG1 Draq report (2013, Chapter 2)

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Radia:ve Forcing

Greenhouse Forcing/Feedback

hPp://www.giss.nasa.gov/research/briefs/schmidt_05/

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Climate Sensi:vity Climate Sensi;vity = change in mean surface air temperature in response to a given radia:ve forcing Two types of climate sensi;vity: ECS: Equilibrium Climate Sensi:vity TCR: Transient Climate Response

Climate Sensi:vity Climate Sensi:vity is a fundamental characteris:c of the climate system. If it were known with certainty, a simple energy balance model could be used to predict the temperature change.

ΔTs / RF = λwhere :Ts = Earth's mean surface air temperature ( C)RF = radiative forcing (W m−2 )λ = climate sensitivity ( C per W m−2 )

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Climate Sensi:vity

Climate Sensi:vity to increases in atmospheric greenhouse gases is usually given as the temperature change that will occur with a doubling of CO2 concentra:on rela:ve to the pre-‐industrial level.

Climate Sensi:vity Climate Sensi:vity is es:mated from global climate models and using paleo-‐analogues.

Model-‐based es:mates of climate sensi:vity: Differences among climate models in their climate sensi:vity is a measure of the uncertainty in climate projec:ons.

hPp://earthobservatory.nasa.gov/blogs/climateqa/what-‐if-‐global-‐warming-‐isnt-‐as-‐severe-‐as-‐predicted/

This image shows frequency distribu:on of climate sensi:vity, based on model simula:ons. Based on the cited Lindsey (2010) public-‐domain source: To understand how uncertainty about the underlying physics of the climate system affects climate predic:ons, scien:sts have a common test: they have a model predict what the average surface temperature would be if atmospheric carbon dioxide concentra:ons were to double pre-‐industrial levels (the climate sensi:vity)

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Climate Sensi:vity Paleo-‐analogue es:mates of climate sensi:vity:

Climate Sensi:vity Paleo-‐analogue es:mates of climate sensi:vity: 1.  How accurately known are the characteris:cs of

the past climates and forcings? 2.  Is the contemporary climate system response

unchanged from the :me of the paleo-‐analogues?

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Climate Sensi:vity

hPp://www.iac.ethz.ch/people/knutr/papers/knut08natgeo.pdf

Climate Sensi:vity

hPp://www.iac.ethz.ch/people/knutr/papers/knut08natgeo.pdf

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Climate Sensi:vity

hPp://www.iac.ethz.ch/pe

ople/knu

tr/pape

rs/knu

t08natgeo

.pdf

Climate Sensi:vity When will we get to doubled CO2?

RCP: Representa;ve Concentra;on Pathways Scenarios hPp://www.skep:calscience.com/print.php?n=1866

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AR5 Climate Sensi:vity Es:mates

•  Equilibrium Climate Sensi:vity (ECS): likely to be between 1.5°C and 4.5°C

•  ECS extremely unlikely to be less than 1°C •  ECS very unlikely to be greater than 6°C •  Transient Climate Response (TCR): likely to be between 1.0°C and 2.5°C

•  TCR extremely unlikely to be greater than 3°C

AR5 End of Century Warming

3.2°C to 5.4°C rela:ve to the 1850-‐1900 baseline for the high emissions scenario (RCP8.5)

Documents

GEOG 401 Natural Perturbationsclimate.socialsciences.hawaii.edu/Courses/GEOG401/GEOG...GEOG 401 Natural Perturbations.pptx Author Thomas Giambelluca Created Date 2/24/2015 7:40:20