Lecture 13 - Climate Change

Weather

Describes the temperature, precipitation, cloud cover, and winds observed at a particular location and time on Earth’s surface.

Climate

Describes averaging weather and other variables over many years of observation.

Examples of climate

• Ex: El Niño will cause a hot and dry summer.

• Ex: Annual global temperatures are rising.

Solar Forcing

Cyclical variations in the input of solar energy that cause changes in the surface environment.

Examples of solar forcing

• Temperature rises in day, falls in night

• Temperature rises in summer, falls in winter

Energy from the climate system is…

Driven by the Sun:

• Earth receives about 340 W/m2 of energy in the form of heat from the Sun

• Mantle convection emits 0.06 W/m2

• Earth as a system emits the same amount of heat back into space, otherwise Earth would heat or cool, called radiation balance.

Without an atmosphere, solar heat would…

Either be reflected to space or absorbed by the surface.

• White surfaces reflect light

• Black surfaces absorb light

Albedo

The fraction of solar energy reflected by the surface.

Examples of Albedo

• White clouds

• White icecaps

• Reflective oceans

The carbon cycle

The continual movement of carbon between different components of the Earth system.

• Each component of the Earth system that contains carbon is seen as a carbon reservoir.

• Each reservoir is linked by transport processes that can move carbon between reservoirs.

The Carbon Cycle absorption of CO2

• Oceans absorb 2.3 Gt/yr

• Land absorbs 2.6 Gt/yr

Residence Time

The average amount of time a single molecule of carbon will spend in a reservoir.

Humans and carbon

Humans inject 8.9 Gt/yr of CO2 into the atmosphere, but only 4.0 Gt/yr remain there.

• Why: Carbon cycle

The carbon cycle leads to…

Ocean acidification, killing off thousands of species of marine life.

• Plant removal of CO2 is still being studied

Natural Climate Change

Natural Factors:

Short Term:

• Solar Radiation

• Volcanic Eruptions

• El Niño/La Niña Cycles

Long Term:

• Ocean Currents

• Milankovitch Cycles

Solar Radiation

Energy that drives most biological and physical changes on Earth.

• ~11-year cycles

• Usually impacts regional climate, not global

• Changes are subtle

Volcanoes

Depends on released gases:

SO2 causes cooling

• Ex: Laki (1783)

CO2 causes warming

• Single eruption can release 24 coal power plants worth of CO2

• No warming has been directly linked to a single volcanic eruption

La Niña

Cooling in the eastern Pacific Ocean every 3-7 years

• Considered normal climate

• Moisture rides jet stream and moves north

El Niño

Warming in the eastern Pacific Ocean every 3-7 years

• Jet stream stays north

• Hot, humid air is unimpeded

Ocean Currents

Driven by density and temperature differences

• Makes some areas warmer than their latitude suggests

• Moves atmospheric heat away from the surface

• Changes over millions of years

Milankovitch Cycles

Periodic variations in Earth’s movement around the Sun.

Eccentricity

100,000 year cycle

Obliquity

41,000 year cycle

Precession

23,000 year cycles

The greenhouse effect

Thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases and is re-radiated in all directions.

Climate Forcing

Any process that disrupts Earth’s heat balance.

Positive feedback loops

Increasing CO2→ Global warming→ Increases evaporation→ Increased water vapor→ Warms atmosphere→ Repeats.

Negative Feedback loops

Increasing CO2→ Global warming→ Increases evaporation→ Increased low clouds→ Cools atmosphere→ Does not repeat to global warming.

Albedo feedback

Rising temperatures reduces accumulation of ice and snow, decreasing albedo and increasing temperature

Plant growth feedback

Increased CO2 increases plant growth which removes CO2 from the atmosphere.

How do we know so much about the Earth’s climate history?

• Ice is a rare material that expands and includes air in its structure when frozen

• Also deposits in annual layers and traps particulate matter in the air:

• Ash, Dust, Pollen

Isotope

Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei

O16 – Lighter

• Less Energy to Evaporate

O18 – Heavier

• More energy to evaporate

When climates are colder…

Sea water richer in heavy O18 and ice richer in

light O16.

How do we know fossil fuels emissions are causing the increases in CO2?

Isotopes

• Carbon has 16 isotope varieties.

• Oxygen has 18 isotope varieties.

• Radioactivity decays nearly all Carbon to an even more unique signature.

Timeline: Concentration of CO2 and Temperature fluctuations

• Cyanobacteria dominate

• dominate the land surface

• Dinos extinct, Mammals take over

• Homo sapiens show up

Consequences of Climate Change

• Increased global temperatures

• Melting ice

• Sea Level Rise

• Increased extreme weather events

• Changing migration patterns

• Proliferation of insects

• Melting permafrost

• Acidification of oceans

Benefits of Climate Change

Profit.

Demographics

Yay: Climate scientists, Insurance companies, Most American corporations, Major energy companies, 50% of the American population

Nay: 50% of the American population