Lecture 30: Historical ClimateLecture 30: Historical Climate

Part V, 270-271; Ch. 17, p. 287-308

• Were climate changes during the last 1000 years similar in pattern across the globe, or did they vary from region to region?

• Can we see an imprint from millennial-scale and orbital-scale changes during this interval?

Historical Climate: The Little Ice Age

• What evidence indicates a cooler climate in Europe and nearby regions during the Little Ice Age? What were its causes?

•Why are climate changes during the last millennium difficult to detect?

Part V, 270-271; Ch. 17, p. 287-308

Climate Change at Different Time ScalesClimate Change at Different Time Scales

Hundreds of Hundreds of millions of millions of yearsyears

Tectonic-scaleTectonic-scale

Tens to hundreds Tens to hundreds of thousands of of thousands of yearsyears

Orbital-scaleOrbital-scale

Thousands of Thousands of yearsyears

Millennial-scaleMillennial-scale(Cycles)(Cycles) (Oscillations)(Oscillations)

Decades to Decades to hundreds of yearshundreds of years

Historical-scaleHistorical-scale

• Proxies that record annual growth patterns can indicate year to year variations in climate

-tree rings -ice cores -deep lake sediments -coral reefs

Proxy Records of Climate

Climate Change Since the Last Glacial MaximumClimate Change Since the Last Glacial Maximum

Data important for estimating past climate include:Data important for estimating past climate include:lake bottom sedimentlake bottom sediment, , ice coresice cores, , fossil evidencefossil evidence, , written documentswritten documents, , coral isotopescoral isotopes, , calcium carbonate layers in cavescalcium carbonate layers in caves, , borehole borehole temperaturetemperature, and , and dendrochronologydendrochronology or or tree ringtree ring data. data.

These data have helped identify several important These data have helped identify several important climate change climate change eventsevents in the past 18,000 years. in the past 18,000 years.

The Little Ice Age: Local or Global?The Little Ice Age: Local or Global?

Sea ice on the coast of IcelandSea ice on the coast of Iceland

The Little Ice Age was not a true ice age.The Little Ice Age was not a true ice age.

Major ice sheets did not develop.Major ice sheets did not develop.

The cooling in Europe (1400-1900): colder winters and shorter growing seasonsThe cooling in Europe (1400-1900): colder winters and shorter growing seasons

EvidenceEvidenceThe European population The European population seriously affectedseriously affected..Lakes, rivers, and ports in Europe Lakes, rivers, and ports in Europe frozefroze..

Mountain glaciers in the Alps of Switzerland and Austria Mountain glaciers in the Alps of Switzerland and Austria advancedadvanced..

Small (<1Small (<1°°C) drop in global temperature.C) drop in global temperature.Widely scattered land-based records, but few records from the oceans.Widely scattered land-based records, but few records from the oceans.

The Hunters in the Snow by Pieter Brueghel the Elder (Kunshistorisches Museum,

Vienna)

Historical documentsHistorical documents

February, from the Très Riches Heures

du duc de Berry, ca.1410

Little Ice AgeLittle Ice Age

The Reverend Robert Walker

Skating on Duddingston Loch attributed to Henry Raeburn, 1790's

Little Ice AgeLittle Ice Age

Two Interpretations of The Little Ice AgeTwo Interpretations of The Little Ice Age

The Little Ice Age in The Little Ice Age in Europe Europe could have could have resulted from resulted from

A continuation of A continuation of slow orbital-scale slow orbital-scale coolingcooling

Part of a millennial-Part of a millennial-scale oscillationscale oscillation

Causes of The Little Ice AgeCauses of The Little Ice Age

Low solar activity Low solar activity (1645-1715): 50 sunspots over a 30-yr period (1645-1715): 50 sunspots over a 30-yr period compared to normally 40,000 to 50,000 spots.compared to normally 40,000 to 50,000 spots.

Causes of The Little Ice Age (2)Causes of The Little Ice Age (2)

More volcanic More volcanic eruptionseruptions

The Year without The Year without summer in 1816 caused summer in 1816 caused by the 1815 eruption of by the 1815 eruption of Mt TamboraMt Tambora

Ice Core in Ice Core in GreenlandGreenland

Mt Tambora in Mt Tambora in IndonesiaIndonesia

Causes of The Little Ice Age (3)Causes of The Little Ice Age (3)

Shutdown of thermohaline circulationShutdown of thermohaline circulation

Yearly Temperature Change for the Last 2000 YearsYearly Temperature Change for the Last 2000 Years

Data from Data from tree rings, corals, ice cores, and historical recordstree rings, corals, ice cores, and historical records are are shown in shown in various colorsvarious colors. . ThermometersThermometers data in data in blackblack. .

Red: recent Red: recent estimates;estimates;

Blue: Blue: earlier earlier estimatesestimates

About 1000 y.a., Medieval Warm Period. About 1000 y.a., Medieval Warm Period. Certain regions were Certain regions were warmer than others.warmer than others. Warm and dry summers in England (1000-1300): vineyards flourished and wine was produced. Vikings colonized vineyards flourished and wine was produced. Vikings colonized Iceland and Greenland. Iceland and Greenland.

Global Global WarmingWarming

http://upload.wikimedia.org/wikipedia/commons/b/bb/1000_Year_Temperature_Comparison.png

Yearly Temperature Change Since 1850Yearly Temperature Change Since 1850

Data from Data from thermometersthermometers

19981998

http://commons.wikimedia.org/wiki/Image:Instrumental_Temperature_Record.png

The Earth’s Climate History1. Over the last century, the earth’s surface temperature has increased by

about 0.75°C (about 1.35°F).

2. Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C, alpine glaciers increased; few sunspots, low solar output)

3. Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized Iceland & Greenland)

4. Holocene Maximum = 5,000-6,000 ybp (1°C warmer than now, warmest of the current interglacial period)

5. Younger-Dryas Event = 12,000 ybp (sudden drop in temperature and portions of N.H. reverted back to glacial conditions)

6. Last Glacial Maximum = 21,000 ybp (maximum North American continental glaciers, lower sea level exposed Bering land bridge allowing human migration from Asia to North America)

7. We are presently living in a long-term Icehouse climate period, which is comprised of shorter-term glacial (e.g., 21,000 ybp) and interglacial (e.g., today) periods. There were four periods of Icehouse prior to the current one.

8. For most of the earth’s history, the climate was much warmer than today.