GEOG 3105

Weather

current conditions of the atmosphere over the course of a few days

Climate

statistical description of weather over a long time (temperature, precipitation, cycles)

Why is climate important?

• supports all life and services

• infrastructure design (impacted by climate - ex. roads)

• agriculture and food systems

• water availability

• human health + environment

IPCC stands for…

Intergovernmental Panel on Climate Change

How will climate change affect climate hazards?

Climate change alters the magnitude and probability of climate variables

• intensity and magnitude

• timing and seasonal shifts

• frequency

• spatial extent

• duration

What is confidence?

relates to evidence and agreement

What is likelihood?

Quantifies uncertainty in the statements. Usually derived from models or statistical evidence

Unless otherwise states, uncertainty is quantified at _______ intervals

90%

What is the UNFCCC?

The United Nations Framework Convention on Climate Change (UNFCCC) is an international environmental treaty that is meant to stabilize GHG emissions

When IPCC says virtually certain, the probability is…

99-100%

When IPCC says extremely likely, the probability is…

95-100%

When IPCC says very likely, the probability is…

90-100%

When IPCC says likely, the probability is…

66-100%

IPCC likelihoods

What is Electromagnetic Radiation (EMR)?

All objects above 0 Kelvins emit EMR. The way that energy is transported from the Sun to the Earth, can be in many different wavelengths that form the electromagnetic spectrum and determine physical properties (visual spectrum, x-rays, etc.).

What is Earth’s energy budget?

The balance between energy/radiation that the Earth receives from the sun (EMR in) and the the energy/radiation that the Earth emits back into space (EMR out)

What is Shortwave Radiation (SW)?

Shortwave radiation (SW) is shorter wavelengths (visual spectrum, UV, shortwave IR) that comes from the sun

• shortwave radiation (insolation) is received unevenly across the planet (earth is a sphere, angle of incidence)

  • Earth naturally balances this to maintain a steady state equilibrium (ex. hadley, ferrell and polar cells)

What factors influence how much shortwave radiation gets to the surface?

1. Albedo (surface reflectivity)

2. Latitude (angle of incidence)

3. Aerosols (scattering of sunlight - reflect cools, absorb warms)

4. Cloud Cover (reflect incoming sunlight, increase albedo)

5. Elevation (higher altitude has increased intensity of solar radiation)

What is Longwave Radiation (LW)?

Longwave Radiation (LW) have longer wavelengths (LW to space emitted by Earth, thermal IR)

Diurnal Longwave and Shortwave Radiation Patterns

SW peaks during day

LW throughout day and night

Sensible Heat

changes a substances temperature without changing phase (what we feel)

Latent Heat

Heat required or released during the phase change of a substance

Specific Heat Capacity

Amount of energy required to increase a substance by 1 degree

Conduction

molecule-molecule heat transfer to a substance

Convection

transfer of heat in liquids/gases through circulation (vertical mixing)

Radiation

energy that moves from one place to another as waves/particles

Forcing

external factor that affects climate

What are the three groups of forcings that impact Earth’s energy budget?

1. Change in solar radiation (S)

   • Ex. Milankovitch cycles

2. Change in albedo (𝜶)

   • Ex. snow cover

3. Change in longwave radiation to space (L↑)

   • Ex. GHG effect, aerosols

What is the Solar Constant (S)?

The amount of energy (EMR) that Earth receives from the sun = ~1360 W/m²

• Total Solar Irradiance (TSI) since S is not constant (S/4 because Earth is a sphere)

Approx. how much energy is driving our atmospheric processes?

238 W/m²

Black bodies

idealized bodies that perfectly absorb and emit EMR (ex. Earth and Sun)

Wein’s Displacement Law

relationship between an object’s temperature and peak of its emission spectrum

@ 300 K (~Earth) — emit longer wavelength + less power (ex. IR, microwave, radio)

@ 6000 K (~Sun) — emit shorter wavelength + more power (ex. visible spectrum)

@ ~1600 K — metal glows red hot, edge of IR and visible spectrum

What is this equation? What does it state?

Stephan Boltzmann equation; states that total power emitted by a black body increases as temperature increases

What is earth’s equilibrium temperature (with and without GHG effect)?

No greenhouse = -18.6°C

With greenhouse = 15°C

What is the greenhouse effect?

atmosphere and greenhouse effect keep the surface of the earth warmer by trapping heat radiating from the surface

Mechanism:

1. absorbs UV and IR light (not visible)

2. Visible light passes through

3. Heats surfaces inside greenhouse, which can re-emit heat (LW radiation) which can’t escape because atmosphere absorbs IR

Rayleigh Scattering

The elastic scattering of light particles much smaller than it’s wavelength — most intense for shorter wavelengths

What are not GHGs?

Nitrogen (N) — ~78%

Oxygen (O) — ~21%

N and O are not GHGs as they do not strongly absorb specific wavelengths

What is a greenhouse gas (GHG)?

gases that absorb longwave radiation

contribution of GHG depends on its absorbance across relevant wavelengths and concentrations

What is the largest single contributor to the greenhouse effect?

Water vapour (~36-72%) but is short-lived

Describe this diagram

• Diagram shows the atmospheric windows (electromagnetic wavelengths) of GHGs

• Longwave radiation moves freely through the atmosphere

• There is almost a direct relationship between energy and absorption

• Water vapour and CO2 absorb released IR energy

• Oxygen and Ozone absorb UV energy (smaller wave absorption)

How much extra energy does the greenhouse effect contribute to Earth (under equilibrium conditions)?

152 W/m² (natural GHG forcing)

Earth’s current energy balance indicates and imbalance of ____ at top of atmosphere (TOA)

0.7 W/m² — more heat going in than out

Atmospheric Window

limited region of the electromagnetic spectrum that can pass through the atmosphere of Earth

What is ERF?

Effective Radiative Forcing (ERF) is a quantification of change in energy budget at the top of the atmosphere that a radiative forcer (GHG, aerosols, etc.) has

• shows what contributes to the partition and retention of energy

• understand the physical mechanisms of climate change and supports solutions (remote sensing, policy, etc.)

What is the current total ERF?

2.72 W/m² (estimated change in solar radiative forcing =0.01 W/m²) ~5.4 bulbs

What are the different methods to measure temperature?

• weather stations

• satellites (measure temp. with LW converted with IR calculation — Stephan Boltzmann)

• weather balloons

• ships & buoys

Roughly how far back does climate data (evidence) go?

~1850-1880

What are the 2 types of satellites to monitor Earth’s temperature?

1. Infrared Emissions

2. Microwave Sounding Unit

Satellites don’t measure temperature, they measure brightness which is then converted to temperature (clouds cause issues)

How do weather balloons work?

• launched 2x daily

• carry radiosondes that measure temperature, pressure, relative humidity

• tracked with GPS + calculates windspeed & direction

• tephigrams are used to interpret information

How are ocean temperatures monitored?

• tidal gauges

• drifting buoys (slow movement)

• moored buoys (same spot)

• ships

What are issues with temperature records?

1. Representative sites (ex. if near a body of water, elevation, etc.)

2. Rural VS Urban locations (experience heat differently - ex. Urban Heat Island effect)

3. Maritime VS Continental locations (water has a certain specific heat capacity, changes in evaporation = cooling)

4. Measures skin temperature (not = to surface temp., measures skin temp. which is top layer of ground surface)

5. Exposure of instrument to sun (placed in different locations, albedo)

What are some solutions to issues with temperature records?

• look at the trend as opposed to actual temperatures

• look at anomalies and compare to a historical baseline

• compare multiple records

• interpolate missing data

What is a temperature anomaly?

difference between absolute temperature and a reference temperature (usually multi-decadal period)

• the difference between an observed temperature and a long-term average (baseline) for a specific location or time

• positive anomaly indicates warmer-than-average conditions, while a negative anomaly indicates cooler conditions

The atmosphere only absorbs ____ of excess energy

1%

Describe energy absorption of the ocean

• ocean absorbs most of the energy

• higher specific heat capacity

• convection in ocean causes energy (and heat) to move downwards)

• latent heat (melting, evaporation, sublimation)

• Between 1970-2019 energy in ocean has increased by ~380 ZJ ~ 24 trillion Hiroshima explosions (0.7 W/m² imbalance)

What is Arctic amplification?

Warming on Earth is not evenly distributed. The Arctic is warming 3-4x faster than the global average. This is because of many different temperature feedbacks like the positive sea-ice albedo feedback, where warming causes snow and ice to melt, reduces albedo and increasing the oceans temperature which causes melting from below and more warming. Other temperature feedbacks include the Lapse Rate Feedback, Planck Feedback, Cloud Feedback, and Oceanic Heat Transfer.

Lapse Rate Feedback

• As you go up in the atmosphere, the temperature gets cooler

• In the Tropics (-), tropopause is higher up which leads to increased convection that causes the troposphere to warm and resulting in cooling at the surface from lift

• In the Arctic (+), the tropopause is lower (in comparison to Tropics), causes GHG to pool/stay and is more stratified. This traps heat near the surface causing warming.

Planck Feedback

• negative feedback

• warmer surface increases outgoing LW radiation @ TOA and promotes cooling

  • Stephan Boltzmann equation (total power emitted increases with warmer temperatures)

• Planck feedback is strongest at Tropics due to warmer temperature, meaning that it is weakest in the Arctic

Cloud Feedbacks

Positive Feedback — As temperatures get warmer, there is more moisture which causes clouds to form at a higher altitude. Higher clouds have a lower reflectivity and trap GHG, more LW radiation, and heat causing more warming. This also decreases the amount of lower level clouds, resulting in less reflectivity and cooling (causes warming).

Cloud Feedbacks can also be a negative feedback as more moisture leads to more water droplets and increased reflectivity.

Oceanic Heat Transfer

Ocean is transporting heat energy to the Arctic through the Barents Sea opening, the Fram Straight, and the Bering Straight, contributing to warmer temperatures

Why is the stratosphere cooling while the troposphere warming?

• Troposphere is closer to the Earth’s surface and receives more SW radiation

• 2 Mechanisms

  • Ozone Depletion — less ozone layer has resulted in less UV absorption

  • GHGs — the troposphere traps GHGs causing warming but in the stratosphere there is less pressure which allows CO2 to be emitted more easily (causing cooling)

Clausius Clapeyron Relationship

Amount of water vapour in atmosphere has increased over time

Warmer atmosphere = warmer specific humidity

As temperature increases by 1°C, relative humidity decreases by 7%

Specific VS Relative Humidity

Specific humidity measures the actual mass of water vapor per unit mass of air (constant)

Relative humidity is a percentage comparing current water vapor to the air's maximum capacity at a specific temperature (changes with temperature)

Precipitation over land has _____________ since 1950 and humans have likely contributed to this. Why only likely?

Increased; because precipitation is more difficult to measure so we have lower confidence