The Last 2000 Years

Thousands of Years Before Present (log scale)

Where does the Temperature data come from?

• Tree Rings• Lake Sediments and pollen• Ice Cores (O-18)• Coral (local water temp and O-18)• Boreholes (local air temp)• Ocean Sediment O-18 (water temp)• REMEMBER! All temperatures are local!

Tree Rings

• In general, trees grow faster when it is milder and wetter.

• So the size of the rings show the local climate

• Since there are lots of trees we can get localized climate signals from lots of places

• In some places we have records going back 12,400 years

Complications

• But…..trees respond a bit differently in different areas

• Growth in cold regions depend largely on warm springs

• In arid regions, water is the critical factor (duh)

• CO2 is a serious complication since it stimulates growth

Medieval Warm Period

• The Medieval Warm Period (MWP) is generally thought to have occurred from about AD 950–1250

• It was probably cooler than now, but warm in comparison to ancient and later medieval times

• The Vikings took advantage of ice-free seas to colonize Iceland and Greenland

• Vineyards in the south of England were successful

Fall of Rome

Charlemagne

Vikings

First Crusade

Peak of theRoman Empire

Collapse of Mayan

Civilization

Knarr: TransAtlantic Cargo ShipLength 54 FtBeam: 16 ft

The BlackDeath

The IndustrialRevolution

The French

Revolution

What effects short-term climate?

• BIG volcanic eruptions

• Sunspots

• Climate Oscillations– El Nino– Pacific Decadal Oscillation– North Atlantic Oscillation

Volcanoes• Eruptions push gases high into stratosphere• Sulfur dioxide combines with water → sulfuric acid

• Tiny droplets of liquid → aerosols• Liquid sulfuric acid, type of aerosol, very reflective

• Thin layer of aerosols reflect sunlight, cool Earth

• Cooling lasts 1-2 years, until aerosols fall• 1815 – Tambora → “year without a summer”• Tropical eruptions usually more impact

The Year Without a Summer• A volcanic winter event caused by the 1815 eruption

of Mount Tambora, in the Dutch East Indies (Indonesia), the largest known eruption in over 1,300 years.– On 4 June 1816, frosts were reported in Connecticut– On 6 June 1816, snow fell in Albany, New York, and

Dennysville, Maine.– Nearly 12 inches (30 cm) of snow was observed in Quebec

City in early June, with consequent additional loss of crop.– In July and August, lake and river ice were observed as far

south as Pennsylvania. – Cool temperatures and heavy rains resulted in failed

harvests in Europe, food riots in England, France, Germany and Switzerland.

The Year Without a Summer• Hungary experienced brown snow. Italy

experienced something similar, with red snow falling throughout the year.

• In China, unusually low temperatures in summer and fall devastated rice production in Yunnan province in the southwest, resulting in widespread famine.

• In July 1816 "incessant rainfall" during that "wet, ungenial summer" forced Mary Shelley and their friends to stay indoors for much of their Swiss holiday. – They decided to have a contest to see who could write

the scariest story, leading Shelley to write Frankenstein.

The Year Without a Summer• High levels of ash in the atmosphere led to unusually

spectacular sunsets during this period, a feature celebrated in the paintings of J. M. W. Turner.

Sunspots

Sunspots

El Nino’s

Terracing dates back about 5,000 years….the only limiting factor is a source of water

Historical Records of El Nino

• This is pieced together from a lot of journal sources– Abundance of sea birds– Heavy rains and floods– Outbreaks of cholera and malaria– What else?

Pacific Decadal Oscillation• Changes in sea-surface temp over N. Pacific

• Produce variations in overlying pressure

• Warm phase:– NW US warm & dry– SW US wetter

• Cool phase:– NW US wet– SW US drought

• Phase may last2 decades

North Atlantic Oscillation• Departure in pressure between Azores high & Icelandic low

• High values:– Strong jet stream– Cold air restricted to northernmost regions

– NW Europe wet

• Low values:– Weak jet stream– Cold outbreaks in US– NW Europe dry

These effects mean a lot to us, but…• All this influences effect

climate…..a bit.• To us this effect seems pretty strong, BUT they are far less than the insolation effects on ice volume