Week 10: Global Change and Paleoclimate

List some unidirectional change processes?

Volcanism

Addition of O and reduction of Hydrogen in the atmosphere

Differentiation

Mass extinction

List some Cyclic changes?

Glacial periods

Sea Level rise

Sea level rise

Mountain building

Supercontinent cycles

Biogeochemical cycles

Define forcing and response?

Forcing: Any process or disturbance that drives climate change

Response: Any change in the climate system caused by a change in climate forcing (and associated feedbacks)

What is a paleoclimate archive?

A physical repository from which paleoclimate records are obtained

What is a paleoclimate proxy?

A chemical, physical, or biological parameters preserved in natural archives that reflect climate at the time of formationWha

What is a paleoclimate model?

A simulation of past climates under different boundary conditions

What are long term and short-term climate changes?

Long-term: Changes that occur over millions to trillions of year

Short-term: Changes that occur under 10,000 years

What are long-term climate changes controlled by?

Plate tectonics (continent position, volcanic activity, mountain building, ocean and atmospheric circulation)

Greenhouse gas concentrations

Solar radiation

What were conditions like during the Middle cretaceous period and why?

Warm, greenhouse gas, ice-free climate

Coral reefs grew closer to the poles

Sea level was 100-200 m higher (no ice sheets)

Global temperatures were 6-14 degrees warmer

Why:

1. Continent positions changed Earth’s albedo and ocean circulation

2. CO2 levels were between 8-10 times higher than of today (3900 ppm) because of increased volcanic activity

What are Milankovitch cycles and how do they cause glaciation?

Milankovitch cycles are changes in Earth’s orbital cycles (shape of orbit, tilt, wobbling) that drive climate variations over 1000 to 100,0000 of years

When the Northern Hemisphere summers are warm (receive more solar radiation), large ice sheets do not grow

What are the 3 components of Milankovitch cycles?

Eccentricity: The shape of Earth’s orbit varies (100,000-year cyclicity)

Obliquity: The tilt of the Earth’s axis varies from 22.5-24.5 degrees (41,000 years)

Precession: Earth’s axis wobbles like a top (23,000 years)

How do oxygen isotopes provide evidence of temperature and ice volume changes?

Colder ocean temperatures allow more 18O isotopes to be incorporated

Land ice incorporates more 16O isotopes so when ice sheets are bigger, more 18O isotopes are left behind in the ocean

What were conditions like during the Last Glacial Maximum?

Global temperatures were 4 degrees Celsius lower

pCO2 was 180 ppm

Large ice sheets dominated the Northern Hemisphere (more sea ice and mountain glaciers)

The sea level was lower by 120 m

Vegetation zones shifted south

Most of the world was windier and dustier

What was the climate like in the Western U.S. during the Last Glacial Maximum?

Pluvial lakes formed during the ice age

The American Southwest and Great Basin were much wetter

Large lakes occupied today’s desert

What causes short term climate changes?

Large and abrupt climate changes occur during glacial and deglacial climates

Linked to AMOC and large discharges of icebergs in the North Atlantic

What are trends regarding current atmospheric CO2 concentrations

Atmospheric CO2 levels are highest they have ever been

The world has been warmer and colder than today in Earth’s history, but those changes happened over longer time scales

The rate of climate change is likely 10 times faster than any change in the last 65 million years