2009/06/22

1. 2009/06/22

2. outline • Paper review – IPCC Report CH6 Palaeoclimate • Data analysis Orbital influences Solar cycle

3. 6.2 Palaeoclimatic Methods How are Past Changes in Global Atmospheric Composition Known? • to derive time series of atmospheric trace gases and aerosols for the period from about 650 kyr to the present from air trapped in polar ice and from the ice itself

4. How Precisely Can Palaeoclimatic Records of Forcing and Response be Dated? • tree ring records are generally the most accurate • sediment records • with age determinations derived from independent radiometric systems such as uranium series. • documentary data (e.g., in the form of specific observations, logs and crop harvest data) multi-proxy series provide more rigorous estimates than a single proxy approach

5. 6.3 THE PRE-QUATERNARY CLIMATES • (Bottom), There are four primary proxies used • Two proxies apply the fact that biological entities in soils and seawater have carbon isotope ratios that are distinct from the atmosphere • The third proxy uses the ratio of boron isotopes • The fourth uses the empirical relationship between stomatal pores on tree leaves and atmospheric CO2 content (top panel), which shows that the warmth of the Mesozoic Era (230–65 Ma) was likely associated with high levels of CO2 and that the major glaciations around 300 Ma likely coincided with low CO2 concentrations relative to surrounding periods. (middle panel), are derived from O isotopes (corrected for variations in the global ice volume), as well as Mg/Ca in forams and alkenones.

6. The Mid-Pliocene (about 3.3 to 3.0 Ma) is the most recent time in Earth’s history when mean global temperatures were substantially warmer for a sustained period produced winter surface air temperature warming of 10°C to 20°C at high northern latitudes with 5°C to 10°C increases over the northern North Atlantic(~60°N), whereas there was essentially no tropical surface air temperature change (or even slight cooling) • 3°C to 5°C in the northern North Atlantic, and 1°C to 3°C in the tropics ,generally similar to the response to higher CO2

7. it may be the result of increased ocean heat transports due to either an enhanced thermohaline circulation • or increased flow of surface ocean currents due to greater wind stresses • or associated with the reduced extent of land and sea ice

8. THE PALAEOCENE-EOCENE THERMAL MAXIMUM • Warm temp • a large mass of carbon with low 13C concentration must have been released into the atmosphere and ocean. • The mass of carbon was sufficiently large to lower the pH of the ocean and drive widespread dissolution of seafloor carbonates

9. 6.4 Glacial-Interglacial Variability and Dynamics 100-kyr • characterised by 100-kyr glacial-interglacial cycles of very large amplitude • large climate changes corresponding to other orbital periods • 20% on average of each glacial-interglacial cycle was spent in the warm interglacial mode 20% High-resolution ice core records of temperature proxies and CO2 during deglaciation indicates that antarctic temperature starts to rise several hundred years before CO2

10. What Caused the Ice Ages and Other Important ClimateChanges Before the Industrial Era? • (1) changing the incoming solar radiation (e.g., by changes in the Earth’s orbit or in the Sun itself) • (2) changing the fraction of solar radiation that is reflected (by changes in cloud cover, small particles called aerosols or land cover) • (3) altering the longwave energy radiated back to space (e.g., by changes in greenhouse gas concentrations). • In addition, local climate also depends on how heat is distributed by winds and ocean currents. All of these factors have played a role in past climate changes. • There are three fundamental ways the Earth’s radiation balance can change, thereby causing a climate change:

11. Heinrich events are thought to have been caused by ice sheet instability. Iceberg discharge would have provided a large freshwater forcing to the Atlantic, which can be estimated from changes in the abundance of the isotope 18O. • Freshwater influx is the likely cause for the cold events at the end of the last ice age (i.e., the Younger Dryas and the 8.2 ka event). • The circulation changes in Southern Ocean, could have a larger impact on atmospheric CO2

12. 6.5 The Current Interglacial These local warm periods were very likely not globally synchronous and occurred at times when there is evidence that some areas of the tropical oceans were cooler than today

13. 6.6 The Last 2,000 Years • Records of NH temperature variation during the last 1.3 kyr.

14. Data analysis Solar cycle: • Reconstructed Solar Irradiance, 1200 Years • Reconstructed Solar Irradiance, 400 Years • Volcanic and Solar Forcing of the Tropical Pacific, 1,000 Years Orbital influences: • Orbital Variations, 5,000,000 Years • Integrated Summer Insolation, 5,000,000 Years, • Orbital Variations, -50 to +20 MYrs,

15. RECONSTRUCTED SOLAR IRRADIANCE, 1200 YEARS, BARD ET AL. 2000 Reconstructed total solar irradiance (TSI) data based on the variations of cosmogenic nuclides (10Be and 14C).

16. RECONSTRUCTED SOLAR IRRADIANCE, 400 YEARS, LEAN 2000 • Use the sunspot record of solar activity that extends over almost four centuries • (Blue line) is the solar irradiance reconstructed with the Schwabe cycle as the only cause of variability. • (Red line) combines the Schwabe irradiance cycle with a longer term irradiance variability component. 0.24%

17. VOLCANIC AND SOLAR FORCING OF THE TROPICAL PACIFIC, 1,000 YEARS, MANN ET AL. 2005 • The dynamics of El Niño thus appear to have played an important role in the response of the global climate to past changes in radiative forcing.

18. ORBITAL VARIATIONS, 5,000,000 YEARS, BERGER AND LOUTRE 1991 K year

20. INTEGRATED SUMMER INSOLATION, 5,000,000 YEARS, HUYBERS 2006

21. ORBITAL VARIATIONS, -50 TO +20 MYRS, PRELIMINARY, LASKAR ET AL.(FROM IMCCE)

22. The End~