Climate and Weather: Key Concepts and Units in Climate Science

Climate vs Weather

Climate refers to long-term atmospheric conditions, while weather refers to short-term atmospheric conditions.

Climate Normal

30-year averages for climate variables like temperature and precipitation, serving as a baseline for comparing current weather to average weather.

Greenhouse Gases List

H2O (water vapor), CO2 (carbon dioxide), N2O (nitrous oxide), and CH4 (methane).

Temperature Units

Temperature can be measured in degrees Celsius (degC), degrees Fahrenheit (degF), or Kelvin (K).

Wind Speed Unit

Wind speed is measured in kilometers per hour (km/h).

Relative Humidity Unit

Relative humidity is expressed as a percentage (%).

Pressure Unit

Pressure is measured in bars.

Salinity Unit

Salinity is measured in parts per million (ppm).

Density Unit

Density is measured in kilograms per cubic meter (kg/m^3).

Indicators of Climate Change

Indicators include increasing temperatures, rising CO2 levels, increasing sea levels, and decreasing sea ice.

Heat Capacity

Heat capacity refers to the amount of heat required to change the temperature of a substance, differing between water and air.

Albedo

Albedo is the reflectivity of a surface, impacting the absorption and emission of radiation.

Shortwave vs Longwave Radiation

Shortwave radiation is emitted by the sun, while longwave radiation is emitted by Earth.

Ocean as Heat Sink

The ocean absorbs 90% of excess heat, acting as a heat sink.

Circulation Patterns

Circulation patterns in the ocean are driven by salinity, temperature, and density changes.

Atlantic Meridional Overturning Circulation (AMOC)

AMOC is a major component of the global conveyor belt of thermohaline circulation in the Atlantic Ocean.

Glacial vs Inter-glacial Periods

Glacial periods are characterized by colder temperatures, while inter-glacial periods are warmer.

Important Climate Events

Significant events include the Younger Dryas, AMOC Shutdown, End-Permian Extinction, Cretaceous/Paleogene Boundary, and Paleocene-Eocene thermal maximum.

Milankovitch Cycles

Milankovitch cycles are variations in Earth's orbit that impact glacial periods.

Paleoclimate Information Sources

Information on paleoclimate is obtained from ice cores, sediment cores, chemical isotopes, and proxies.

Climate

Conditions of the atmosphere, ocean, land-cover and ice over a long term, including fluctuations and processes, described by statistical models.

Weather

State of the atmosphere at a given time and place, short term (minutes to days), measured in temperature, precipitation, cloudiness, humidity, air pressure, and wind.

Carbon Dioxide (CO2)

A greenhouse gas produced by burning fossil fuels, contributing to ocean acidification.

Methane (CH4)

A greenhouse gas emitted from livestock, gas and oil production, and glacial melting.

Water Vapor (H2O)

A greenhouse gas that results from evaporation; warmer air holds more water vapor, creating positive feedback.

Nitrous Oxide (N2O)

A greenhouse gas primarily from agriculture, mostly from synthetic fertilizers.

Temperature

A measurement of heat, expressed in degrees Celsius (°C), degrees Fahrenheit (°F), or Kelvin (K).

Wind Speed

The rate at which air moves, measured in kilometers per hour (km/h).

Relative Humidity

The amount of water vapor in the air relative to how much it can hold at a given temperature, expressed as a percentage (%).

Pressure

The force exerted by the weight of air, measured in bars, where 1 bar is approximately one atmosphere of pressure.

Salinity

The concentration of salt in water, measured in parts per million (ppm).

Density

The mass of a substance per unit volume, expressed in kilograms per cubic meter (kg/m^3).

Absorption

Energy taken in by the surface, resulting in heating.

Reflection

Energy bouncing off the surface.

Emission

Re-radiating heat from Earth as infrared heat, which is different from reflection.

Shortwave Radiation

Incoming radiation from the Sun, including visible light and ultraviolet (UV) light.

Longwave Radiation

Infrared radiation emitted by the Earth's surface, atmosphere, and clouds as heat energy.

Incoming solar energy

The amount of solar energy that reaches Earth.

Outgoing infrared radiation

The amount of infrared radiation emitted back into space by Earth.

What are Greenhouse gases (GHGs)?

Gases in Earth's atmosphere that absorb infrared radiation and trap heat.

H2O

Water vapor - a natural greenhouse gas.

CO2

Carbon Dioxide - a greenhouse gas that is both natural and man-made.

CH4

Methane - a greenhouse gas that is both natural and man-made.

N2O

Nitrous Oxide - a man-made greenhouse gas.

Greenhouse gas effect

The process where greenhouse gases trap infrared radiation in the atmosphere, warming up Earth. Adding more blankets = insulate and warm the surface.

Venus Runaway Greenhouse Effect

A hypothesis suggesting that Venus' atmosphere used to have a lot of water vapor, leading to extreme warming.

Concentration of solar radiation at 90deg

warmer, stable temperatures occur at the equator due to more concentrated and intense radiation.

Stratosphere

The layer of the atmosphere 10-50 km above Earth where temperature increases with altitude.

Troposphere

The layer of the atmosphere 0-10 km above Earth where temperature decreases with altitude.

Adiabatic cooling

The process where air expands due to decreasing pressure, leading to a decrease in temperature.

Heat Index

A measure of what the water feels like, calculated from temperature and relative humidity.

Younger Dryas

A climate event occurring around 13,000 years ago characterized by sharp cooling linked to AMOC shutdown.

Paleocene-Eocene Thermal Maximum (PETM)

A climate event occurring 55.8 million years ago marked by rapid global warming from massive carbon release.

Jet stream

A fast-flowing air current formed when warm and cool air masses meet, helping to separate temperatures.

High-low pressure systems

Weather systems driven by the interaction of high and low pressure in the atmosphere.

Climate change effects

The varying impacts of climate change, which are less intense near the equator.

Atmospheric structure

The layered composition of the atmosphere, including the troposphere and stratosphere.

Cretaceous-Paleogene Boundary

Asteroid impact → sudden cooling, mass extinction of dinosaurs.

End-Permian Extinction

Volcanic CO₂ release → extreme warming, ocean anoxia, largest extinction.

Siberian Traps eruption

High CO2 in atmosphere leading to global warming, ocean acidification, ocean deoxygenation.

End of Dinosaurs

K-Pg extinction.

Earth's Past Temperature

Past global climates were much warmer than today's temperatures.

A key driver of temperature changes

higher CO₂ levels led to warmer climates.

Himalayas Uplift

Increased silicate rock weathering, removing CO₂ from the atmosphere.

Decreased Volcanic Activity

Reduced natural CO₂ input to the atmosphere.

Oxygen Isotopes (δ¹⁸O)

Reflect global temperature and past atmospheric greenhouse gas concentrations.

Ice Cores

Measured from air bubbles trapped in ice cores (e.g., Antarctica, Greenland).

Heavy to Light Oxygen Isotope Ratio

The ratio (18O/16O) changes with temperature and ice volume.

Climate-Carbon Feedbacks

CO₂ variations closely track glacial-interglacial cycles.

Eccentricity

How elliptical Earth's orbit is; controls seasonal contrast over long periods.

Obliquity

Tilt of Earth's axis (21.5°-24.5°); controls seasonal intensity, especially at high latitudes.

Precession

Wobble of Earth's axis; changes which season occurs at perihelion/aphelion.

Graph Analysis

Look at the x- and y-axes, check the units on the labels, examine the data itself.

Coriolis Effect

Moving objects are deflected due to Earth's rotation

High CO2

1 cycle ~ 100ky; associated with warmer temperatures.

Low CO2

Associated with colder temperatures.

Younger Dryas Period

A sudden return to cold conditions as the globe exited the most recent Ice Age.

Atmospheric Circulation

The large-scale movement of air that distributes thermal energy across the surface of the Earth.

Oceanic Circulation - Surface Currents

Wind patterns drive large gyres (circulation patterns) in the ocean surface currents.

Warm, salty surface water

Flows northward from the equator via the Gulf Stream.

Deep water circulation

Occurs when colder, saltier water sinks to the deep ocean, forming the lower part of the AMOC.

Freshwater input

Prevents surface water from sinking in the North Atlantic, which can weaken or shut down the AMOC.

Glacial meltwater

Introduces a layer of freshwater to the surface of the North Atlantic ocean, preventing deep water formation.

Thermohaline circulation

The global conveyor belt of ocean currents driven by temperature and salinity differences.

Northern Hemisphere

The half of the Earth that is north of the equator, where the Coriolis effect causes deflection to the right.

Southern Hemisphere

The half of the Earth that is south of the equator, where the Coriolis effect causes deflection to the left.

Circulation cells

Patterns of air movement caused by the Coriolis force that break up into smaller cells.

30° latitude

The latitude where warm air rises at the equator and is deflected by the Coriolis force, causing it to turn and sink.

Cooling and glacial-like conditions

Result of an AMOC shutdown, as experienced during the Younger Dryas period.

Gulf Stream

A warm ocean current that flows northward from the equator to the North Atlantic.

Ice sheets melting

Could trigger a future AMOC shutdown by increasing freshwater input in the North Atlantic.

Rapid cooling

A potential consequence of an AMOC shutdown, leading to glacial-like conditions.

Gyres

Large circular currents in the ocean, rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

Deep ocean currents

Follow the global conveyor belt of thermohaline circulation.

AMOC shutdown

Occurs when freshwater input prevents surface water from sinking, leading to significant climate changes.

Climate models

Simulations that predict the effects of various factors, including freshwater input, on thermohaline circulation.

North Atlantic

Region where the AMOC plays a crucial role in maintaining warmer temperatures compared to other regions at similar latitudes.

Heat Capacity for Water

~4000J/Cdeg

Slow to warm up and cool down

Heat Capacity for Air

~1000J/Cdeg

Quick to warm up and cool down