climate change lectures

what are permanent gases, and what are some examples?

gases whose concentrations remain relatively constant, such as n2, o2, and ar

what are variable gases, and why are they important?

gases whose concentrations change significantly and that can trap radiant heat from earth

what is relative humidity?

the percentage of water vapor the air currently holds compared with how much it could hold at that temperature

what does 100% relative humidity mean?

the air is at the dew point

what happens to atmospheric pressure and density as altitude increases?

both decrease rapidly

what does atmospheric pressure represent?

the weight of the air column above a unit area

what is the ideal gas law?

p = prt

what happens to air when it rises?

it expands and cools

why does relative humidity increase when air rises?

cooler air can hold less water vapor

what happens when air reaches 100% relative humidity?

condensation occurs, which can lead to clouds and precipitation

why does condensation help keep rising air warm?

condensation releases heat (energy)

what causes clouds to form?

air becomes saturated, generally because rising air cools

what three conditions are needed for deep convection?

enough moisture, temperature decreasing rapidly with height, and uplift

what are the main characteristics of the troposphere?

temperature decreases with height, it contains water vapor, and all weather occurs there

how much of the atmosphere’s mass is in the troposphere?

about 80%

how does temperature change with height in the stratosphere, and why?

temperature increases with height because ozone absorbs radiation

where is the ozone layer located?

the stratosphere

what is the pressure force, and how does it move air?

it pushes air from high pressure toward low pressure

what are hadley cells?

large-scale circulation where warm air rises at the equator and cold air sinks at the poles

what is the coriolis force?

an apparent force caused by earth’s rotation that deflects moving air

how does the coriolis force affect air in each hemisphere?

right in the northern hemisphere; left in the southern hemisphere; zero at the equator

what are cyclones and anticyclones, and what weather do cyclones often bring?

cyclones are associated with low pressure, while anticyclones are associated with high pressure. extratropical cyclones usually bring clouds and rain/snow

what are the major patterns of global warming described in the lecture?

global mean surface temperature has increased since the late 19th century, with warming strongest over northern hemisphere continents, especially the arctic

what is the average rate of precipitation on earth?

~1 m/year

on average, how are evaporation (e) and precipitation (p) related?

e = p

if precipitation is greater than evaporation in one region, how is the difference balanced?

by winds transporting moisture

what causes precipitation?

rising air caused by convection, movement of air masses, or air flowing over mountains

when does precipitation take place?

when air becomes supersaturated with water vapor

what primarily causes monsoons?

temperature contrast between land and ocean

why does the indian summer monsoon bring heavy rainfall?

hot land drives moist air inland, where it rises over mountains and produces rainfall

what happens to the indian monsoon during winter?

the flow reverses

approximately what percentage of rainfall in the indian monsoon regions is due to monsoons?

80%

what percentage of the total greenhouse effect is water vapor responsible for, according to the lecture?

60%

how does atmospheric water vapor generally change as temperature rises?

it increases

what does the phrase “wet places get wetter and dry places get dryer” describe?

the strengthening of the water cycle as the atmosphere warms

what are aerosols?

tiny solid or liquid particles suspended in air

what is the most direct effect of aerosols on earth’s surface?

cooling

how do sulfate aerosols from burning fossil fuels cool the planet?

they reflect sunlight back into space

what is “los angeles-type smog” mainly produced by?

exhaust from cars

where are the largest concentrations of ozone found?

stratosphere

why is stratospheric ozone important?

it absorbs harmful uv radiation and protects life

why is tropospheric ozone considered “bad” ozone?

it is harmful to humans and plants, contributes to smog, and is a greenhouse gas

what caused the antarctic ozone hole?

ozone destruction involving chlorine from human-made cfcs

what happens during the antarctic winter that helps set up ozone destruction?

the polar vortex isolates antarctic air, which cools enough for polar stratospheric clouds to form

what was the montreal protocol, and why was it important?

a 1987 agreement restricting production of ozone-depleting chemicals such as cfcs

what was the reported death toll from the 2026 european heat waves by 5 july, and which two characteristics of a heat wave most affect the toll?

over 5,600 excess deaths. duration and night-time temperatures affect the toll

according to ipcc ar6 (1960-2018), what three things are happening with temperature extremes?

the hottest temperatures are getting hotter, the coldest temperatures are getting warmer, and the number of extreme hot days is increasing

what do the abbreviations txx, tnn, and tx90p measure?

txx is the annual hottest temperature. tnn is the annual coldest temperature. tx90p is the number of days exceeding the 90th percentile

what caused the 2024 european floods?

prolonged heavy rains

why is it hard to conclude whether river floods are becoming more frequent or intense? name the two contributing factors listed in the lecture

flooding depends on more than climate. the two factors are (i) land use (e.g., deforestation) and (ii) the timing and intensity of rain

in the ipcc map of stations with increasing annual maximum daily precipitation, how many trends were significant versus nonsignificant? which regions showed clusters of significant trends?

663 were significant and 4,146 were nonsignificant. significant clusters appear in the eastern us, europe (especially central and eastern), china, and southern africa

name the types of drought and what causes each.

meteorological drought is due to lack of rain. hydrological and agricultural drought is due to drying up of water supplies

in what three waves did the 1930s dust bowl drought arrive, and what human factor made it worse?

the waves were 1934, 1936, and 1939-1940. the human factor was the failure to use dryland farming methods, which led to severe dust storms

what were the impacts of the 2011-2017 california drought on trees?

it destroyed 102 million trees from 2011 to 2016, 62 million of them in 2016 alone

distinguish physical water scarcity from economic water scarcity

physical scarcity means there isn’t enough water for both people and ecosystems to function properly. economic scarcity means humans can’t meet their water demands because of lack of investment or insufficient infrastructure

describe how air moves in a tropical cyclone and why condensation is important

air spirals in near the ground and rises in the ring of deep convection, saturated with moisture. condensation releases huge amounts of heat/energy that feeds the storm

where are the strongest winds and heaviest rains, and what are conditions like inside the eye?

they are at the eyewall. in the eye, winds are weak, pressure is low, and the air is warm and dry

what is the “stadium effect”?

the eyewall slopes outward with height, like the seats in a stadium

in which direction do northern hemisphere hurricanes rotate?

counterclockwise

list the five conditions needed for hurricane formation

(1) strong coriolis force, (2) warm sea-surface temperature (typically >26.5 degrees C), (3) warm upper ocean (about 100 m), (4) winds that don’t change much with height, and (5) temperature that decreases with height

why can’t hurricanes form at the equator?

the coriolis force is too weak at the equator to produce the storm’s rotation

why do hurricanes often strengthen in the gulf of mexico?

the gulf’s warm water fuels and strengthens storms. temperatures at or above about 27.8 degrees C support tropical storms

put these stages in order and describe each: tropical depression, tropical disturbance, intensifying cyclone. what causes a storm to weaken and dissipate?

order: tropical disturbance (a cluster of thunderstorm clouds,) then tropical depression (winds and heat exchange intensify), then the cyclone intensifies and moves north-westward. it weakens and dissipates when it makes landfall or drifts into colder waters

what are the top three causes of death from atlantic cyclones, with percentages?

storm surge (49%), rain (27%), and wind (8%). surf and offshore are 6% each, tornado 3%, and other 1%. water causes most deaths

define storm surge and name two ways it is produced. how does coastline slope affect it?

storm surge is a rise in sea level driven by the storm. it is produced by low pressure near the eye pulling water higher (pressure surge) and by winds piling water up and pushing it toward shore (wind-driven surge). a shallow coastline slope produces a greater surge than a steeper one

match each even to its storm-surge image: katrina, sandy, ike

katrina (2005): surge breached the 17th street canal levee. sandy (2012): surge inundated mantoloking, nj. ike (2008): one home remained amid coastal flooding in gilchrist, tx

why is hurricane harvey (2017) notable? what about irma (2017) and dorian (2019)?

harvey was the second costliest ($125 billion) and the wettest in the contiguous us. irma was the strongest hurricane until dorian in 2019. dorian tied the 1935 labor day hurricane for the highest sustained winds at landfall

what conditions are needed for tornado formation, and what type of storm do tornadoes often develop from?

they often develop from supercells (a type of thunderstorm). they need dry air on top of moist air and winds that change direction with height

what air masses converge over “tornado alley,” where is it, and what scale rates tornado intensity?

warm moist air from the gulf, cold dry air from the north, and warm dry air from the southwest, along with the jet stream. tornado alley covers the plains: texas, oklahoma, kansas, nebraska, south dakota, and nearby states. intensity is rated on the f-scale (f0 to f5)

what percentage of earth’s surface do oceans cover, and what are their average and maximum depths?

about 71% of the surface. average depth is about 4 km, maximum about 11 km

compare the oceans to the atmosphere in terms of mass and the heat needed to warm them

the mass of the oceans is about 250 times that of the atmosphere. it takes about 1,000 times more heat to warm the oceans than the atmosphere by the same number of degrees

list four reasons the oceans are important for earth’s climate and life

(1) they store heat and move it around the planet. (2) sea surface temperature influences the atmosphere and sea ice. (3) sea level changes affect coastal areas. (4) they play a key role in the carbon cycle

what does it mean that “oceans moderate climate”?

air temperature changes would be much larger without oceans. oceans take in heat from the atmosphere, then store and redistribute it, buffering extremes

name three factors or features that shape sea surface temperature (sst) patterns, with an example of warming and of cooling

sst is shaped by latitude/solar heating, ocean currents, and upwelling. examples: the gulf stream warms the western north atlantic; the california current and upwelling cool the easter pacific coast, and upwelling also cools the tropical eastern pacific. sst patterns also influence the atmosphere, e.g., el niño/la niña involves changes in tropical sst

name and describe the three temperature layers of the ocean. how does the mixed layer vary with latitude and season?

mixed (surface) layer: uniform temperature. thermocline: temperature decreases rapidly with depth. deep ocean: nearly uniform and cold. the mixed layer is deepest and coldest at high latitudes, and in mid-latitudes it changes seasonally (deepens in winter). the deep ocean is cold everywhere, even in the tropics

how is the ocean different from land in how it handles heat?

the mixed layer alone can store more heat than the entire atmosphere. unlike land, heat in the ocean can be transferred to deeper layers by mixing and currents. mixing also carries co2 and oxygen downward

what is upwelling, how does it occur, and what does it bring to the surface? give two examples

upwelling is upward movement of water that brings deeper properties to the surface. it occurs when horizontal spreading of surface waters forces deeper water up. it brings cold, nutrient-rich water. examples: coastal upwelling (involving wind and the coriolis force) and upwelling within oceanic cyclones

define salinity and name the two factors that control sea-surface salinity. what is the extreme example given in the lecture?

salinity is the amount of dissolved salts in seawater. it is controlled by precipitation and evaporation, and by ocean currents. the extreme case is the dead sea, about 9 times more saline than seawater

How does pressure change with ocean depth? What two things cause small horizontal pressure differences?

Pressure rises rapidly with depth: each 10 m adds about one atmosphere. Small horizontal differences come from (1) "bending" of the ocean surface (1 m of height equals about 0.1 atmosphere of pressure) and (2) density differences (<1% variations, but important). These differences drive ocean circulation.

What determines seawater density, and which water is denser?

Temperature and salinity (and high pressure in the deep ocean can also change it). Colder, more saline water is denser than warmer, fresher water.

How do whales cope with high ocean pressure, and how deep can sperm whales dive?

Their ribcage is bound by cartilage and their lungs can collapse under large pressure. Sperm whales can dive to about 7,000 feet.

What drives wind-driven ocean circulation, and what are its main features?

Winds "bend" the ocean surface, creating pressure differences, and the circulation mirrors atmospheric winds. Main features: gyres (anticyclones), western boundary currents (e.g., the Gulf Stream), and zonal (east-west) currents.

Describe thermohaline circulation. Why do North Atlantic waters sink?

Warm, saline waters flow northward in the North Atlantic. Evaporation makes them more saline, and cooling in polar regions makes them even denser, so they sink to the bottom (forming North Atlantic Deep Water) and spread at depth.

How large is the "Great Conveyor Belt," and what does it transport?

It is slow but massive: 10-20 million cubic meters per second (about 100 Amazon rivers). It moves heat and carbon to the deep ocean.

How do the atmosphere and oceans transport heat? Which is larger, and where is ocean transport most important?

Both move heat from low to high latitudes, driven by atmospheric winds and oceanic currents. Atmospheric transport is larger; oceanic transport is important at low latitudes. If ocean temperature or circulation changes, heat transport and climate change too.

How does ocean surface warming compare to land warming?

Ocean surface warming is weaker than land warming, but the course of change is consistent with that over land.

Where does the extra heat from the atmosphere go? What share does the ocean absorb (1971-2010), and what share goes to the upper 700 m?

It goes into warming the atmosphere and land, melting ice, and storage in the ocean. The oceans take about 93% of the increase between 1971 and 2010, and the upper 0-700 m accounts for about 64% of the total warming.

Is upper-ocean warming uniform? Explain.

No. Some regions show strong warming while others show cooling.

What do climate models predict for the thermohaline circulation (AMOC), and which three factors weaken it? What is the main uncertainty?

Most models predict weakening. Warming, increased precipitation, and ice melt act to weaken it. The specific numbers differ widely across models, so measurements of its strength are needed to improve predictions and monitor change.

What is RAPID/MOCHA? Where, since when, and how does it work?

A large international effort to monitor the overturning circulation at 26.5°N, in place since 2004. It uses moorings across the Atlantic that take density profiles, combined with wind data and submarine telephone cable data in the Florida Straits, to calculate large-scale transport (Florida Strait, Ekman, and open-ocean geostrophic components).

Where is anthropogenic carbon stored most heavily in the ocean, and why? What does CO2 uptake do to ocean chemistry, and what is the trade-off?

The North Atlantic (due to AMOC) and the Southern Ocean, where water is mixed vertically. The ocean's anthropogenic carbon inventory increased from 1994 to 2010. CO2 uptake gradually acidifies the ocean (lowers pH). The trade-off is that it reduces atmospheric greenhouse gas levels but stresses the marine environment (e.g., coral reefs).

Why is the upper ocean losing oxygen? Where are the largest declines?

Two reasons: (1) less oxygen dissolves in warmer surface waters, and (2) in the tropics, mixing with the oxygen-rich surface ocean is reduced. The largest declines are in the Pacific and Southern Ocean.

How has global sea level changed over the last ~150 years, and how many people live within 1 meter of the current high tide line?

Global sea level has been rising over the last ~150 years faster than ever before. Around 280 million people live within 1 meter of the current high tide line, and this number could grow.

What are the two main causes of global sea level rise?

(1) Warming of the ocean and the resulting thermal expansion. (2) Melting of land ice and changes in land water storage. (Per the IPCC AR6 budget, components include the upper ocean, glaciers, Greenland, Antarctica, and land water storage.)

How can regional sea level change differ from the global average?

Regional changes can be very different from the global change. The IPCC map shows some regions rising much faster than the global rate (e.g., the western tropical Pacific near Manila) while others show little change or a decline (e.g., parts of the eastern Pacific).

Describe the regional pattern of ocean warming. Where is warming slower, and where is it faster?

Warming is uneven. It is slower in the North Atlantic and faster in the Indian and Southern Oceans.

What explanation does the lecture suggest for cooling in the North Atlantic, and what happens to heat delivery as AMOC weakens?

The cooling may be due to changes in thermohaline circulation. As AMOC weakens, less heat is delivered to the North Atlantic.

In a warmer world, what happens to the AMOC and Gulf Stream? Describe the changes in the North Atlantic that cause this.

Climate change weakens the AMOC, which slows the Gulf Stream. Water becomes fresher and lighter and sinks less near the poles, much less heat and water are transferred from the tropics to northern latitudes, and the Gulf Stream weakens, though the portion pushed by winds remains.

How do equatorial trade winds affect sea level in the Pacific?

Trade winds pile up water in the west. Stronger winds increase the west-east difference in sea level.

Define flood tide, high tide, ebb tide, and low tide.

Flood tide: sea level rises over several hours. High tide: the water reaches its highest level. Ebb tide: sea level falls over several hours. Low tide: the water stops falling and reaches its lowest level.