Lecture 5: Energy, Climate, and Weather – Jan 22nd, 2026

Specific heat capacity:

• How much energy is required to change the temperature of 1 kg a substance by 1°C

Climate:

• based on what weather is

• Def: The long-term averaged weather for an area, and any departures from that average (what we expect form the weather in an area based on what has happened on the past) (personality)

Weather:

• Day-to-day (or even hour-to-hour) changes in atmospheric conditions

• mood in the moment

Diff cultures are used to diff climatic conditions

• ex) india vs france heat wave

  • architecture in cultures used to extreme heat (adapted to heat) vs architecture in cultures not used to extreme heat

*extreme or expected is based on current averages

Drivers of global and regional climate

• spatial variability

• temporal variability

Climatic oscillations:

• any recurring global or regional climate pattern

  • air temp, precipitation, air pressure, sea surface temperature etc.

    • can occur on a range of timescales, from inter-annual, to multianual, decadal, multidecadal, century-wide, millennial or even longer timescales

      • Some cyclical variations in climate do not follow annual cycles like the seasons

• ENSO oscillation (el Niño-southern oscillation)

  • regional climatic oscillation that affects global climate

  • cyclic variation in the sea surface temps and convection cells in the equatorial region of the pacific ocean

  • causes by typical regional patterns in ocean and atmospheric circulation in pacific:

    • surface winds (trade winds) at the equator drive surface ocean current westward

    • surface water moved westward is replaced by colder water from deeper in the ocean (upwelling)

    • El Niño pattern: warm surface water shifts eastward towards south America

      • warm water now distributes across the entire equatorial region → not concentrated in the west

      • warm water drives a convection cell

        • but the warm water is distributed across the region (starts more centrally in the ocean → collected more water) → more precipitation

      • less upwelling

      • etc. …..

    • La Niña pattern: strengthening of normal westward surface winds

      • intensifying of climatic patterns associated with an “avg” climatic perido w/o la niña or el niño

      • ….

    • DO NOT know the cause of el niño or la niña (why some last longer than others etc.)

    • warmer water collects westward

      • heats up the air through conduction and drives air circulation through convection

    • air circulation moves air eastward (then falling when it gets colder over the east)

    • outcome = convection cell (that continues to get stronger and stronger)

  • these oscillations cause short/medium term fluctuations to climate that can add to or mask the effects of other climatic forcings (la nina mask the increasing temps due to anthripigenic forcings etc. in the east)

local/regional climate forcings

• climate forcing: anything / factors that have the ability to influence climate

  • Global: planet-wide impact

  • Regional: local impact

• two main climate forcings (global climate today is determined by these):

  • energy received from solar radiation (temp)

    • solar radiation is a mjor driver of:

      • global air circulation

      • precipitation through the movement of water vapor and heat

    • solar radiation hitting the earths surface varies temporally per location

  • precipitation (also influenced by temp)

    • global precipitation pattens vary temporally too (dry and monsoon seasosn)

  • global climate varies spatially and temporally

  • * @ any one time pts of the planet tilted closest to the sun receive significantly more energy than parts tilted away (earths axis is not straight)

    • causes our seasons

    • northern & southern hemispheres

• Regional climate forcings:

  • Buffering effect of water:

    • water has a very specific heat capacity and can mix vertically over time

      • holds more heat energy than land

      • takes longer to loose heat than land

      • areas closer to water (on the coast) are warmer than areas further from water

    • Land loses heat quickly

    • water loses heat slowly

    • this diff in heating rates btw land and water drives daily cycles in air movement

    • Day: land heats up faster (warm air above land rises, bringing in cooler air from over water to replace it)

    • night: water warmed by the sun cools slower than land (warm air above water rises, bringing in cooler air from over the land to replace it) reverse direction of winds as during day

  • Ocean currents

  • Urban heat island effect:

    • Low albedo of many man-made surfaces absorbs much more solar radiation than natural surfaces (dark colors absorb more solar radiation than light colors)

      • energy emitted through conduction results in increase in localized temps relative to areas with higher albedo

      • temps in cities are much warmer than in less urbanized areas

  • Topography

  • Plants

    • Flying rivers:

      • system which brings moisture over large areas as a results of winds current and significant plant transpiration

      • when water that falls as precipitation is released back into the atmosphere by plants through transpiration(release water through the leaves), when enough plants are in one location doing this: the volume of water released can be significant enough to move water over vast distances (like terrestrial rivers)

      • *plants are the main way the center of continents get water

    • Cloud seeding: some plants release special chemicals that function to intentionally seed cloud formation

      • if there are enough of these plants (usually trees like pines) in one place then it can locally produce clouds and potentially precipitation

      • if too hot plants can make a cloud to protect from heat

      • if too dry then make a cloud to make rain to nourish them

      • why there are never singular trees and only large groups (forests)

changes in historic weather averages

• what used to be considered extreme weather conditions are starting to become more common

Jet stream: area of very fast air movement in the upper atmosphere created/ where convection cells split (bc convection cells surround the earth, so do the jet streams)

• move from west to east with the corolis effect, moving weather systems along

• where we have this it generally separates regions of warmer air from colder air

  • can increase severity or create new high or low pressure systems

  • stalling of the jet stream:

    • when the wind speed of the jet stream decreases, resulting in:

      • slow movement of the jet stream (makes a more disorganized stream, massive peaks and troughs)

      • fast movement = straighter

    • weather systems could also become “cut off” from the jet stream (weather systems stall over areas for significant periods of time)

• the greater the temp diff btw equator and poles:

  • the stronger/faster the polar jet stream

  • the straighter the polar jet stream

  • the closer the polar jet stream is to the equator

extreme weather event: a weather event which, based on historic averages, only occurs -10% of the time

• extreme heat:

  • 3+ days where daytime and nightime temps are excessive for the regional avg at a particular time of yeat (varies by location)

  • heat dome: type of extreme heat event increasing in frequency

    • result of extreme-heat retention driven by very high atmospheric pressure and a stalled jet stream (not mobile bc of stalled jet stream)

• extreme cold/ cold front:

  • same cause as extreme heat

  • increased waviness in the jet stream

• drought: prolonged period of regionally abnormally low precipitation (→very low soil moisture)

  • these conditions typically build over an extended period of time

    • continuous decrease in precipitation which fails to meet local water needs

    • slow on-set = possible to anticipate and plant for dealing with short-term drought conditions

  • Flash-drought: rapid onset of drought conditions (even though they come quickly, they ususally leave just as quickly)

    • have much worse effects on the ecosystem bc life has no time to prepare or to respond

    • cause: similar to heat done, caused by sudden dramatic increase in temp OR sudden drop in precipitation

• extreme precipitation:

  • rainfall within the top 1% of significant rainfall events for a region

  • warmer air holds more water vapor so as temp increases the more water vapor air can hold and that water vapor will then fall as precipitation

    • as global tmep increases → more water vapor in atmospjere

    • water vapor condenses → more water available to rain (consists of larger drops)

Atmospheric river:

• a long narrow band high in the atmosphere which contains very hogh concentrations of water vapir …