Global Climate Change

Weather

Short-term atmospheric conditions (minutes to days)
ex: temperature, precipitation, humidity, wind

Climate

Long-term average patterns (30+ years) and statistics of weather

Five Earth Spheres

atmosphere - air, gases, weather systems
hydrosphere - oceans, lakes, rivers, water cycle

cryosphere - frozen water: glaciers, sea ice, ice sheets

biosphere - all living organisms

lithosphere - earth’s solid crust and upper mantle

What do the spheres exchange?

energy, water, momentum, and carbon

Climate Change Indicators: Temperature

+1.2 degrees Celsius above pre-industrial, strongest warming at poles

Climate Change Indicators: Artic Sea Ice

~30% decline since 1979

Climate Change Indicators: Sea Level

rising ~4 mm/year today

Tipping Point

Threshold beyond which change becomes self-perpetuating due to feedback

West Antarctic Ice Sheet (WAIS)

is a tipping point - grounded below sea level, which means it’s vulnerable to ocean warming. Once WAIS retreats, the collapse may be irreversible, meaning meters of sea level rise, even if it stops warming

Positive Feedback

amplifies the initial change
ex: ice-albedo feedback

Ice-albedo feedback

warming melts ice —> lowers reflectivity —> absorbs more heat —> more warming

Negative Feedback

dampens initial change

ex: increased outgoing infrared radiation as Earth warms (energy loss helps cool Earth)

Two land masses that contribute to Glacial melt and Sea Level Rise?

Greenland and Antarctica, Antarctica has more ice but is slower to melt, Greenland currently contributes more

Sea level rise throughout time…

velocity is increasing (accelerating)

Thermal Expansion

warming water expands, which is historically the biggest driver, this is why melting ice sheets/glaciers are becoming increasingly more important

Paleoclimate - contemporary versus Past Change

Past Changes: much slower (thousands of years)

Today: warming is much faster (decades to centuries)

ex: CO2 now > 420 ppm, highest ever in at least 3 million years

Equilibrium Climate Sensitivity (ECS)

how much Earth warms from a doubling of CO2 (relative to preindustrial ~280 ppm)

likely range: 2.5-4 C

Hard to estimate because of uncertainties in feedbacks (clouds)

Heavy Oxygen Isotope

18O - condenses more easily

Light Oxygen Isotope

O16 - evaporates more easily

What happens with Isotopes when it is warm?

Ice melts, Oceans become enriched in 16O

What happens with isotopes when it is cold?

Ice traps O16, leading to oceans being enriched in O18

*ratios in ice cores and sediments tell us about past temperatures

Milankovitch Cycles (3)

Eccentricity of Earths Orbit (shape)

Variation in tilt of Earths axis

Variation in precession of Earths axis (wobble)

What do the Milankovitch Cycles change together?

They change the distribution of sunlight and drive glacial-interglacial cycles

Greenhouse Effect

Absorption and re-admission of infrared radiation emitted by the Earth by some chemicals (greenhouse gases) in the atmosphere

What would Earth’s temperature be without the Greenhouse Effect?

-18 C

What is Earths temperature with Greenhouse Effect?

12-15 C

Main Problem of Greenhouse Effect

Human emissions strengthen the effect of raising global temperatures

UV vs IR radiation

Sun —> mostly shortwave (UV/visible)

Earth —> re-radiates longwave (IR)

Which radiation do greenhouse gases absorb?

IR, trapping heat

Greenhouse Gases

CO2, CH4, N2O, H2O vapor, O3

Greenhouse gases - Water Vapor

the strongest of the gases

Greenhouse Gases - CO2/CH4

drive the long-term changes because water vapor responds quickly to temperature

Carbon Cycle - Pools

atmosphere, oceans, soils, land plants, fossil fuels

Carbon Cycle - Fluxes

Photosynthesis, respiration, ocean uptake/release, combustion

Carbon Cycle - GPP

Gross Primary Productivity - total photosynthesis

Carbon Cycle - NPP

Net Primary Productivity - (GPP - plant respiration = biomass growth)

Permafrost tipping point

Frozen soils contain vast carbon stocks

*warming thaws permafrost —> microbes release CO2 and CH4

*Positive Feedback: more warming —> more thawing —> more GHG release

Ocean acidification

CO2 dissolves in seawater —> carbonic acid —> lowers pH

*harms calcifying organisms (corals, shellfish)

*independent of warming (direct chemical effect of CO2)

How much do humans add yearly of C

~9-10 Gt C/year

*mostly fossil fuels, deforestation

*upsets carbon cycle balance —> rising atmospheric CO2

Uneven heating (equator vs poles) drives what?

Circulation

Three-cell system:

Hadley (0-30C) - rising at ITCZ, descending at subtropics

Ferrel (30-60C) - mid-latitude westerlies

Polar (60-90C)

*redistributes heat poleward

Earth’s energy budget - Incoming Solar

~340 W/m²

Earths Energy budget - albedo

~30% reflected

Earths Energy Budget - Rest absorbed = ?

re-emitted as IR

Earths Energy Budget - Balance

incoming = outgoing (over long term)…but human GHGs upset this balance

Ocean Acidification equation

CO2 + H2O ←> H2CO3 ←> HCO3- + H + ←> CO3² - +2H +

H2CO3

CARBONIC ACID

HCO3-

BICARBONATE

CO3² - 

CARBONATE