The Last 1,000 Years Summary The Medieval Warm Period The Little Ice Age Year Without a Summer Volcanoes and Climate Attribution of Climate Change Exam.

The Last 1,000 YearsSummaryThe Medieval Warm PeriodThe Little Ice AgeYear Without a SummerVolcanoes and ClimateAttribution of Climate ChangeExam 2 on Wednesday!

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Social Scientists

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All Occupations

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Instrumental: Red TrianglesTree Ring: Brown TrianglesBorehole: Black CirclesIce Core: Blue StarsOther: Purple Squares

Locations of Proxy Records

How might the locationsof proxy records influencethe climate reconstructions?

Medieval Warm PeriodAlso known as the Medieval Climate Anomaly (MCA)~1000 to 1200 ADMost pronounced in the North Atlantic region?Debate persists as to how significant this was globally.

Quite evident in tropical South America, however.

Figure 7. Reconstructed tropical South American temperature anomalies (normalized to the 1961–1990AD average) for the last 1600 years (red curve, smoothed with a 39‐year Gaussian ∼filter). The shaded region envelops the ±2s uncertainty as derived from the validation period. Poor core quality precluded any chemical analysis for the time interval between 1580 and 1640 AD.

Kellerhals et al. 2010

Viking Settlement of the North Atlantic

Little Ice Age~1500 to 1850 ADWidespread global cooling, particularly in the North Atlantic region (Europe and eastern North America).Glacier advance in most of the world, best chronicled in Europe.

Discussion QuestionWhat are believed to be the two most important climate forcings during the period 1000 to 1850 AD?

Alan RobockDepartment of Environmental Sciences

Tambora in 1815, together with an eruption from an unknown volcano in

1809, producedthe “Year Without a Summer” (1816)

Tambora -- 1815

Largest volcanic eruption of modern times

Located on Sumbawa Island along the east Sunda Arc

Heard up to 1400 km away! Ash remained in

atmosphere for several years, leading to pronounced cooling and the “Year without a summer” in the northeastern U.S. in 1816

Year without a Summerhttp://www.dandantheweatherman.com/

Alan RobockDepartment of Environmental Sciences

Global Surface Temperature Reconstruction

-0.4

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1700

1720

1740

1760

1780

1800

1820

1840

1860

1880

1900

1920

1940

1960

1980

Year

An

om

aly

(°C

)

Mann et al. (2000)

Tambora in 1815, together with an eruption from an unknown volcano in

1809, producedthe “Year Without a Summer” (1816)

Alan RobockDepartment of Environmental Sciences

Tambora, 1815, produced the “Year Without a Summer”

(1816)

George Gordon,

Lord Byron

Percy Bysshe Shelley Mary Shelley

Alan RobockDepartment of Environmental Sciences

Tambora, 1815, produced the “Year Without a Summer”

(1816)“Darkness” by Byron

I had a dream, which was not all a dream.The bright sun was extinguish'd, and the starsDid wander darkling in the eternal space,Rayless, and pathless, and the icy earthSwung blind and blackening in the moonless air;Morn came and went—and came, and brought no day,And men forgot their passions in the dreadOf this their desolation; and all heartsWere chill'd into a selfish prayer for light:And they did live by watchfires—and the thrones,The palaces of crowned kings—the huts,The habitations of all things which dwell,Were burnt for beacons; cities were consumed,And men were gather'd round their blazing homesTo look once more into each other's face; . . .

Discussion QuestionHow do volcanoes influence climate? What are the physical processes?

Volcanoes and ClimateLarge volcanic eruptions inject sulphate aerosols into the troposphere and stratosphere, reducing the amount of solar radiation reaching the surface and therefore resulting in a negative radiative forcing.

Alan RobockDepartment of Environmental Sciences

Explosive

NET COOLING

Stratospheric aerosols(Lifetime » 1-3 years)

Ash

Effectson cirrusclouds

absorption (IR)

IRHeating

emission

emission

IR Cooling

MoreDownward

IR Flux

LessUpwardIR Flux

forward scatter

Enhanced Diffuse FluxReduced

Direct Flux

Less TotalSolar Flux

Heterogeneous ® Less O3 depletion Solar

Heating

H2SSO2

NET HEATING

Tropospheric aerosols(Lifetime » 1-3 weeks)

Quiescen

t

SO2 ® H2SO4

® H2SO4

CO2

H2O

backscatter

absorption(near IR)

Solar Heating

More ReflectedSolar Flux

Indirect Effects on

Clouds

Alan RobockDepartment of Environmental Sciences

Krakatau, 1883The Loudest Explosion Ever

Heard

http://www.springerlink.com/content/f40022142221l168/fulltext.html

Projected Cooling following a “Mega-Colossal” Eruption

Solar Forcing

Historical records, paleo-archives, and model simulations suggest that the Medieval Warm Period was associated with positive solar irradiance forcing (relative to 1500 to 1899 mean values) while much of the Little Ice Age was associated with negative solar irradiance forcing.

Sunspots and ClimateThere is some evidence that sunspot activity positively correlates to surface temperature (e.g., greater sunspot activity is associated with higher temperatures).The Maunder Minimum of sunspot activity occurred at the heart of the Little Ice Age.

Discussion QuestionHow/why does sunspot activity appear to be an important climate forcing?

Sunspots and Solar IrradianceDuring periods of low sunspot activity, total solar irradiance decreases. During years when sunspots are abundant, the amount of radiation emitted in solar flares is a maximum.Mechanisms operating within the sun simultaneously regulate both sunspots and net solar emissions.Recent observations from space suggests that the decrease in ultraviolet (UV) irradiance during low sunspot activity may be considerably greater than previously thought.

Sunspot Cycle 24The current data for Sunspot Cycle 24 gives a smoothed sunspot number maximum of about 101. We are currently over six years into Cycle 24. The current predicted size makes this the smallest sunspot cycle in about 100 years.

http://solarscience.msfc.nasa.gov/predict.shtml

Solar Forcing in the Newshttp://www.nature.com/news/2010/101006/full/news.2010.519.html

http://www.nature.com/nature/journal/v467/n7316/pdf/nature09426.pdf

http://science.nasa.gov/science-news/science-at-nasa/2013/08jan_sunclimate/