ENV 106 Chapter 11

Climate and global climate

Climate - describes average weather conditions over a significant period of time for a particular region of Earth.

Global climate - describes the average weather conditions over a significant period of time for the planet as a whole.

Instrumental period

current era in which we have access to temperature readings taken directly with instruments such as thermometers.

Weather satellites have added a level of sophistication with infrared radiation to record temperature in various layers of the atmosphere.

Since the instrumental period, confidence in plotting annual average temperatures has improved

Before the instrumental period, reliable temperature data were collected by drilling bores deep into Earth’s crust.

Temperature

Along with collecting surface air temperatures (SAT) over land, scientists also collect average marine air temperatures (MAT) and sea-surface water temperatures (SST)

Geothermal gradient

The crust gets progressively hotter at deeper depths, resulting in the geothermal gradient, which describes how temperature increases with depth in Earth’s crust due to decaying radioactive elements.

Sustained temperature changes at the Earth’s surface diffuse through the crust and affect geothermal gradients, providing historical data on past surface temperatures

Proxy

an observable and measurable phenomenon that serves as an indirect indicator of changes in climate.

Examples - tree rings, ice cores, coral skeletons

Not a proxy - satellite temperature data

Paleoclimates

ancient climate conditions understood through use of proxies.

• Examining the ratio of heavier to lighter oxygen in the air bubbles in ice cores

from glaciers can tell us how cool past temperatures were.

• Heavier oxygen isotopes (18O) in water condense faster than lighter oxygen

isotopes (16O), and the colder the temperature is, the quicker the heavier

isotope is depleted from the air.

Greenhouse effect

happens in any system where a barrier causes an inflow of energy that outpaces the outflow such that the interior warms.

On Earth, the warming effect is due to atmospheric greenhouse gases preventing radiant heat emitted from the surface escaping into space.

Greenhouse Gases

Earth is surrounded by greenhouse gases (GHGs), e.g., carbon dioxide and water vapor. In the atmosphere, these GHGs redirect heat rising from Earth’s surface back down, causing a warming effect.

Albedo

Light colored surfaces on Earth increase albedo, a measure of the reflectivity of a surface.

Darker surfaces absorb radiation and heat Earth’s surface; lighter surfaces reflect it back into atmosphere and help cool Earth’s surface.

Continental Drift

The positions of drifting continents relative to the equator affects the amount of solar radiation that reaches land to warm it, and movement of continents also influences ocean currents, which affects global heat distribution.

• Colliding land masses create hills and mountains that affect climate by

increasing land surface area exposure to natural acid in rain drops,

which is created when CO2 dissolves in water droplets.

• These rain drops remove CO2 from the atmosphere and store it in

oceans and marine organisms.

Milankovitch Cycles

regular patterns of variation in the shape of the Earth’s orbit, and the tilt and direction of Earth’s rotational axis.

• These alter the amount of the Sun’s radiation and energy that reach Earth and its atmosphere

These cycles contribute to temperature changes in the atmosphere and oceans, and long-term cycles and can even affect ice ages

Oceans Influence on the Climate

Saltwater covers most of Earth and has a major impact on global climate.

• The ocean is always moving as a connected flowing mass that transports energy around the globe, affecting areas thousands of miles from shore.

Ocean Currents, Surface Currents, and gryes

Ocean currents are the “rivers” of the ocean.

Surface currents are ocean currents affecting the top 400 meters of water that starts from air blowing across the surface.

These travel in gyres, large circular ocean currents.

• 5 main gyres in the oceans.

Gyres travel in circular patterns due to the Coriolis effect, a force

driven by Earth’s rotation that deflects objects, winds, and currents on

the surface of the Earth and in the ocean or the atmosphere.

• This causes gyres in the Northern Hemisphere to rotate clockwise, and

those in the Southern Hemisphere to rotate counterclockwise.

Deep currents

the flow of water below the surface caused by variations in density, temperature, and salinity.

Salinity

the concentration of salt in the water, generally measured in parts per thousand

Thermohaline Conveyor

Deep currents and salinity contribute to this.

It’s a large-scale ocean circulation driven by surface and deepwater ocean currents and changes in water temperature and salinity (density).

Countercurrents

changes in normal ocean currents.

Can change weather.

The El Nino-Souther Oscillation(ENSO)

a countercurrent that significantly weakens or even shifts the direction of trade winds and ocean currents in the southern Pacific.

Upwelling currents

where cold water is drawn up from deep in the ocean

CO2

Natural processes like photosynthesis and cellular respiration maintain a balance by cycling CO2 between living organisms and the atmosphere.

• CO2 is also absorbed into and released from the oceans in a natural balance.

• The natural atmospheric life of CO2 ranges from 50–200 years.

Humans emit much more CO2 through fossil fuel combustion and industrial processes.

Hindcasting

shows computer simulations in support of real-world observations; results over the past 30 years show that humans are driving global warming, especially by releasing carbon dioxide and methane.

Droughts

prolonged periods of low precipitation and high evaporation rates that can lead to

water shortages.

due to increased evaporation associated with warming, will affect regional

agricultural yields and wildfires.

Thermal expansion

the expansion of something as it warms, in particular, the water in the oceans,

which increases sea level, and melting ice from land and glaciers.

Ocean acidification

the ongoing decrease in pH of Earth’s oceans caused by absorption of CO2

from the atmosphere.

Phenology

the seasonal timing of biological activities, such as breeding, flowering, and

migration of various species.

• The ranges of many midlatitude species have been moving towards the poles

and up to higher elevations, where it is cooler.

Positive and negative feedback

Positive feedback enhances the original change, and negative feedback counters the original change.

Tipping points

where sudden changes can have a rapid and significant effect on global climate.

Carbon footprint calculators

can approximate how your daily actions contribute to GHG emissions

Industrialized countries have larger footprints than developing countries

Embodied energy

the energy used to make and transport goods; we want to choose goods with a lower amount of this.