The Last 1,000 Years • The Medieval Warm Period • The Little Ice Age • Major Climate Forcings • Exam on Wednesday!!!
Locations of Proxy Records Instrumental: Red Thermometers Tree Ring: Brown Triangles Borehole: Black Circles Ice Core: Blue Stars Other: Purple Squares How might the locations of proxy records influence the climate reconstructions?
Climates of the recent millennium • Medieval Warm Period (1000 – 1200 AD) • Little Ice Age (1500 – 1850 AD) • Anomalously warm and cool periods • Significant fluctuations in Temp. and Precip. during these periods • Impacted global societies
Medieval Warm Period • Also known as the Medieval Climate Anomaly (MCA) • ~1000 to 1200 AD • Debate persists as to how significant this was globally. • Most pronounced in the North Atlantic region? • Quite evident in tropical South America, too • *MWP cooler than current global average temperatures.
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
Little Ice Age • ~1500 to 1850 AD • Widespread global cooling, particularly in the North Atlantic region (Europe and eastern North America). • Glaciers advanced in most of the world, best chronicled in Europe.
Radiative Forcing • The difference between radiant energy received by the Earth and energy radiated back to space • Medieval Warm Period - positive radiative forcing* • Little Ice Age - negative radiative forcing* *(relative to 1500 to 1899 mean values) • What are believed to be the two most important climate forcings during the period 1000 to 1850 AD?
Sunspots Photosphere – 5,800 K Sunspots – 3,800 K
Sunspots and Climate • Some evidence suggests greater sunspot activity is associated with higher surface temperatures
Sunspots and Solar Irradiance • Low sunspot activity = decrease total solar irradiance (When sunspots are abundant, the amount of radiation emitted in solar flares is at a maximum) • Sun spots and net solar emissions are regulated by magnetic field
Volcanoes and Climate • Large 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.
More Reflected Solar Flux Less Upward IR Flux backscatter absorption(near IR) Solar Heating emission IR Heating IR Cooling emission absorption(IR) forward scatter Explosive Enhanced Diffuse Flux Effects on cirrus clouds Reduced Direct Flux Ash More Downward IR Flux Less Total Solar Flux Quiescent Indirect Effects on Clouds Stratospheric aerosols (Lifetime » 1-3 years) H2S SO2 ® H2SO4 NET HEATING Heterogeneous® Less O3 depletionSolar Heating CO2 H2O Tropospheric aerosols (Lifetime » 1-3 weeks) SO2® H2SO4 NET COOLING
Major volcanic eruptions of the past 250 years
Tambora in 1815, together with an eruption from an unknown volcano in 1809, producedthe “Year Without a Summer” (1816)
Tambora in 1815, together with an eruption from an unknown volcano in 1809, producedthe “Year Without a Summer” (1816) Mann et al. (2000)
Mary Shelley Percy Bysshe Shelley George Gordon, Lord Byron Tambora, 1815, produced the “Year Without a Summer” (1816)
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 stars Did wander darkling in the eternal space, Rayless, and pathless, and the icy earth Swung blind and blackening in the moonless air; Morn came and went—and came, and brought no day, And men forgot their passions in the dread Of this their desolation; and all hearts Were 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 homes To look once more into each other's face; . . .