Untitled Flashcard Set

Main Points:

  1. Global temperature does not exhibit the same, smooth increase over time as seen in the CO2 record.

  2. The oceans and atmosphere have a large amount of internal variability over annual to decadal time scales.

  3. Understanding the major “modes” of this variability, like the El Niño system, are key in distinguishing the climate change “signal” from the background climate “noise”.

  4. Climate change is expected to disrupt the normal patterns of ocean & atmosphere circulation, which will likely have a greater impact than warming temperatures.



Slide 1: 

  • 2024 was the warmest year on record 

  • 2023 was the second warmest

  • 2025 was the third warmest



Atmospheric circulation: 



Net Radiation: higher at the equator b/c sunlight hits more directly (at less of an angle = less atmosphere to pass through). 



Insolation Imbalance: 




Ocean Circulation

  • Oceans are responsible for heat circulation/transporting heat from the equator to the poles. . 

  • Thermohaline Circulation ("Conveyor Belt"): Driven by density differences (temperature and salinity), this deep-ocean movement circulates water and nutrients, taking centuries to complete a cycle.


Ocean’s Physical Structure





Major Ocean Surface Currents

  • Ag: Agulhas Current

  • K: Kuroshio Current

  • Al: Alaska Current

  • L: Labrador Current

  • Be: Benguela Current

  • N: Norwegian Current

  • Br: Brazil Current

  • NA: North Atlantic Current

  • Cal: California Current

  • NE: North Equatorial Current

  • Can: Canary Current

  • NP: North Pacific Current

  • EA: East Australian Current

  • O: Oyashio Current

  • EC: Equatorial Countercurrent

  • P: Peru (Humbolt) Current

  • EG: East Greenland Current

  • SE: South Equatorial Current

  • F: Florida Current

  • SP: South Pacific Current

  • G: Guinea Current

  • WA: West Australian Current

  • GS: Gulf Stream

  • ACC: Antarctic Circumpolar Current


Upwelling

  • Upwelling: where strong winds and the Coriolis effect push surface water away from a coastline or the equator, causing cold, nutrient-rich water to rise from deeper levels.

    • Ekman transport 



Ocean-Atmosphere Interactions



Teleconnections: 

  • Recurring, persistent, large-scale patterns of pressure and circulation anomalies that span vast geographical areas

  • Also called Ocean-Atmosphere Oscillations.


We will focus on El Niño, but are there other ocean-atmosphere oscillations / teleconnections?

  • Yes!

    • Pacific Decadal Oscillation (PDO)

    • North Atlantic Oscillation (NAO)

    • Arctic Oscillation (AO)

    • Atlantic Multidecadal Oscillation (AMO)

    • Madden / Julian Oscillation (MJO)

    • East Atlantic (EA)

    • West Pacific (WP)

    • East Pacific-North Pacific (EP-NP)

    • Pacific/North American (PNA)

    • Tropical/Northern Hemisphere (TNH)


The El Niño-Southern Oscillation System (ENSO)


Normal in tropical pacific: 

  • Trade winds blow E to W, pushing warm water near the surface. 

  • Warm water piles up on the W side around Asia; around S and Central AMerica, warm water is replaced by cooler water through upwelling, creating a temp difference across the tropical pacific. 

  • Warm water adds heat to air, causing more rapid rising. 

  • Leads to more clouds and rainfall. 

  • Cool, dry air moves W and influences easterly winds (pushing them forward; denser air moves faster). 

  • ENSO 

    • Starts by the equator in the Pacific 

    • weaken/maybe reverse trade winds

      • Less push of warm surface water to W, less upwelling of cold to E

        • Cancels out temp difference 

      • Changes rainfall over equatorial pacific and large scale wind patterns

    • Impacts: 

      • Increase in floods in Peru, increase in droughts in India, parts of Brazil, etc. 

      • Lots of energy is released into the atmosphere; may warm global temps (why el nino years are warmer) 

      • Peals around christmas, lasts several months

    • One of the only predictable parts of the climate system - can predict months in advance and put in warning systems ab what might happen. 

  • La nina: 

    • Stronger normal trade winds

    • Warm water pushed to W of tropical pacific, increased cool upwelling in E

    • Can make global temps lower. 

    • Opposite effects to el nino 

  • Southern oscillation index: measures atmospheric part of el nino 

    • Pressure, etc



Overall: 

  • La nina: warmer, dryer 

  • El nino: cooler, wetter 


El Niño and climate change

  • During el nino, the ocean releases heat. GHGs trap this increased heat 

  • This is why el nino years are often hottest on record 

  • Warming happens faster in periods of el nino than periods of la nina 


More La Niña – like?

  • “Ocean thermostat” mechanism

More El Niño – like?

  • Atmospheric circulation weakening as mechanism



Sea-Surface Temperature Indices




Relative Oceanic Niño Index (RONI)

  • three month running average of the relative Niño 3.4 index.

  • two primary benefits for ENSO monitoring and prediction:

  1. RONI better identifies current and past El Niño and La Niña events because it is less sensitive to the chosen base climatology period. This allows for comparison of events across the lengthy climate record. 

  2. A relative index is more related to changes in rainfall over the tropical Pacific than the traditional index. It is the change in tropical rainfall and heating that ultimately drives the subseasonal to seasonal variations we see in the midlatitudes and over the United States.



The Southern Oscillation Index

  • Calculated by the normalized pressure difference between Tahiti and Darwin, Australia. 

  • Sustained negative values indicate El Niño (warmer-than-average, weak trades)

  • Positive values signal La Niña (cooler-than-average, strong trades)