1.a Climate proxies and natural forcing

Climate Change

Long-term shifts in temperatures and weather patterns, which may be natural or anthropogenic.

Anthropogenic Climate Change

Climate change driven by human activities, typically noted as starting post-1800.

Climate Proxy

Something used to reconstruct variations of past climatically relevant factors like temperature and CO2.

Incremental Climate Proxy

Proxies formed by the regular additions of material, such as ice cores and tree rings.

Radiometric Climate Proxy

Proxies that use absolute dating methods like radiocarbon dating on organic materials.

Palynology

The study of pollen grains to determine past plant types and environments.

Marine Sediments Proxy

Sea floor sediments containing foraminifera shells that reveal climate and sea temperatures.

Lake Sediments Proxy

Sediments accumulating in lakes containing leaf waxes, pollen, charcoal, and diatoms.

Ice Cores Proxy

Cores drilled from ice sheets containing air bubbles for CO2 levels, volcanic dust, and isotopes.

Tree Rings Proxy

Annual growth rings recording climate; trees grow faster in warmer conditions.

Fossils Proxy

Remains preserved in sedimentary rock, such as beetles for Pleistocene research.

Ice Cores (Table Details)

Frequency: Annual. Length: 100k years. Example: Col du Dome, France. Limit: Spatial limitations.

Marine Sediments (Table Details)

Frequency: Centuries/millennia. Length: Tens of millions of years. Example: Thatchpoint bluehole, Bahamas.

Lake Sediments (Table Details)

Frequency: Decades/centuries. Length: Millions of years. Example: Lake Redon, Spain.

Tree Rings (Table Details)

Frequency: Annual. Length: Thousands of years. Example: Rennes, France. Limit: Spatial implications.

Fossils (Table Details)

Frequency: Millennia. Length: Hundreds of millions of years. Example: Como Lake, Colorado.

Cambrian Period (541-485 Mya)

Characterized by the Cambrian explosion, when the largest number of creatures evolved in any single period.

Ordovician Period (485-444 Mya)

Area north of the tropics was almost entirely oceans and CO2 gradually declined.

Silurian Period (444-359 Mya)

A warmer period during which ice sheets retreated.

Devonian Period (419-359 Mya)

CO2 was removed from the atmosphere and fish were dominant.

Carboniferous Period (359-299 Mya)

Tropical swamps dominated with repeated glaciation.

Permian Period (299-252 Mya)

Pangea formed, creating very hot greenhouse conditions.

Jurassic Period (201-145 Mya)

Pangea broke up, dinosaurs began, CO2 was very high, and there were periods of increased rainfall.

Triassic Period (252-201 Mya)

Dinosaurs dominated, it was warm with temporary cooling events, and it had no permanent ice sheets.

Cretaceous Period (145-66 Mya)

Very hot with temperatures 6-8°C higher than today, polar forests, and the KT extinction impact in Yucatan.

Tertiary Period (66-2.6 Mya)

The age of mammals with 5 different eras and the Palaeocene Eocene thermal maximum.

Quaternary Period (2.6 Mya to present)

Characterized by severe drought, human evolution, and glacial-interglacial cycles.

Devensian Glacial

The last major glacial period in Britain, occurring 115,000-11,700 years ago.

Last Glacial Maximum (~20,000 years ago)

Global temps were 5-7°C colder, sea levels 120-130m lower, CO2 at 190 ppm, with extensive ice coverage.

Younger Dryas (~12,900-11,700 years ago)

A rapid return to colder conditions caused by freshwater melt disrupting North Atlantic ocean circulation.

Holocene (~11,700 years ago to present)

The current stable interglacial period where human agriculture and civilization developed.

Little Ice Age (1300-1850)

A cooler climatic period experienced in parts of Europe and North America.

Obliquity

Earth's axial tilt, currently 23.5° and varying between 22° and 24.5° over 40,000 years.

Effects of Obliquity

Less tilt causes cooler summers and warmer winters, spreading ice sheets; more tilt causes warmer summers and cooler winters, melting ice sheets.

Eccentricity

Earth's orbit changing from circular to elliptical over a 95,000 to 415,000 year cycle.

Effects of Eccentricity

Causes up to a 30% difference in solar radiation when Earth is closer or further from the sun, melting ice sheets.

Precession

The wobble of Earth on its axis, creating greater fluctuation than axial tilt.

Perihelion

The closest point at which the earth is to the sun.

Sun Spots

Cooler, darker areas created by magnetic activity on the Sun's surface associated with short-term climate events.

Sunspot Cycle

An 11-year cycle with a positive correlation between sunspot number and solar energy output, varying by only 0.1%.

Maunder Minimum

A period of zero sunspots that led to the Little Ice Age.

Plate Tectonics and Climate

Tectonic shifts like the formation of Pangea 250 million years ago created hot, dry climates due to paused ocean currents.

Himalayas and Weathering

The collision of India and the Asian plate formed the Himalayas, increasing chemical weathering which removed CO2 and cooled temperatures.

Ocean Upwelling and CO2

Upwelling brought phytoplankton to the surface to use CO2 for their shells, removing it from the atmosphere.

Volcanic Eruptions Climate Impact

Causes short-term global cooling and long-term global warming.

Sulphate Aerosols

Formed from volcanic SO2 converted to sulphuric acid in the stratosphere, reflecting solar radiation to cool the troposphere.

Mt Pinatubo (1991)

Eruption releasing 20 million tonnes of SO2, cooling global temperatures by 1.3°C over 3 years.

Deccan Traps

Volcanic eruptions in Western India 66 million years ago that released enormous amounts of greenhouse gases for long-term change.

Ocean Circulation Role

The primary role of ocean currents is to transfer and redistribute heat around the earth.

Gulf Stream Formation

Formed when South and North America joined, leading to the North Atlantic drift and Labrador corridor.

PETM (Palaeocene-Eocene Thermal Maximum)

An event 56 million years ago where CO2 levels reached 1000 ppm and temperatures were 10°C higher, triggered by volcanic activity.