Climate Change Exam 2

Effective Radiative Forcing (ERF)

The net change in Earth’s energy balance (measured in W/m²) caused by an external perturbation (such as greenhouse gases or aerosols) after allowing for rapid atmospheric adjustments to take place.

Global Warming Potential (GWP)

An index quantifying the cumulative radiative forcing of a gas pulse over a set time horizon (commonly 20 or 100 years) relative to that of an equivalent mass of CO2 (CO2-e). Governed by radiative absorption efficiency, atmospheric lifetime, and molecular weight.

Equilibrium Climate Sensitivity (ECS)

The long-term, steady-state global mean surface warming caused by doubling of pre-industrial CO2 concentrations (2xCO2), evaluated while holding continental ice sheets and vegetation fixed.

Transient Climate Response (TCR)

The global mean surface warming observed when atmospheric CO2 reaches twice its baseline level in an idealized simulation where CO2 increases steadily at 1% per year compounded (reached at year 70).

Effective Climate Sensitivity

A measure of climate sensitivity estimated from the response to a sudden quadrupling of CO2 (4xCO2) over a 150-year period, capturing rapid-to-intermediate feedbacks. Does not capture long-term feedbacks

Pattern Effect

The principle that global radiative feedbacks (particularly cloud feedbacks) depend on the geographic spatial pattern of surface warming and cooling, rather than purely on the global mean temperature change. (not directly from lecture slides)

Parameterization

The computational technique in numerical models of approximating the net bulk effect of physical processes that operate at sub-grid scales (e.g., cloud condensation, convection, turbulence) using resolved large-scale variables.

Atmosphere-Ocean General Circulation Model (AOGCM)

Captures the physical fluid dynamics, thermodynamics, and momentum equations of the atmosphere, ocean, land surface, and sea ice without interactive dynamic biogeochemical cycles. Seasonal to decadal; regional)

Earth System Model (ESM)

Current state-of-the-art climate model class that couples physical AOGCM dynamics with interactive biogeochemical cycles (carbon, nitrogen, sulfur, ozone, dynamic vegetation, and atmospheric chemistry).

Earth System Model of Intermediate Complexity (EMIC)

A lower-resolution, computationally efficient, idealized climate model designed to simulate millennial timescales and slow climate feedbacks.

Coupled Model Intercomparison Project Phase 6 (CMIP6)

An international collaborative climate modeling framework comparing simulations and projections across more than 20 distinct global climate models.

Regional Climate Model (RCM)

A fine-resolution numerical climate model (typically 10 to 50 km grid spacing) used to dynamically downscale global climate simulations over a specific geographic domain.

Modeling challenges (W6-1: Models)

• uncertainty for the future. Can use RCPs to represent scenarios

• Models depend on quality of observations

• Hard to capture wide variety of time and spatial scales

• Clouds remain a struggle with modeling

• Trees are a struggle for land surface models

• Models are able to reproduce large-scale, observed temperature changes very well

• Precip not reproduced as well as temp changes

Static-Equilibrium Sea Level Fingerprints

The distinct, non-uniform spatial patterns of local relative sea level change resulting from ice sheet melting, governed by changes in gravitational attraction, Earth rotation, and elastic crustal deformation.

Glacial-Isostatic Adjustment (GIA)

The ongoing rebound and deformation of Earth's crust and mantle in response to the melting and redistribution of ice sheet mass since the Last Glacial Maximum (LGM).

Peripheral Bulge Collapse (Subsidence)

The slow sinking of the mantle forebulge that was forced outward around the margins of heavy ice sheets during the LGM, currently driving accelerated local sea level rise in regions such as the U.S. Mid-Atlantic coast.

Far-Field Sea Level Rise

The above-average SLR experienced in ocean regions distant from a melting ice sheet, caused by the release and global dispersion of water previously held close by the ice sheet's gravitational attraction.

Near-Field Sea Level Response

The local sea level response within ~2,000 km of a melting ice sheet, where relative sea level falls or rises far less than the global average due to lost gravitational attraction and elastic bedrock rebound.

Committed Sea Level Rise

The irreversible, long-term sea level rise locked in over centuries to millennia due to the deep ocean's thermal inertia and the slow relaxation of ice sheets, persisting even after greenhouse gas emissions stop. (not discussed in detail in slides)

Meltwater Pulse 1a (MWP-1a)

An abrupt deglacial event (~14,600 to 14,300 years ago) during which global sea level rose at an extreme average rate of ~50 mm/year (2 inches/year), totaling 14 to 18 meters of rise in ~350 years.

Marine Isotope Stage 5e (MIS 5e)

The last interglacial warm period (~125,000 years ago) when temperatures were 0.8°C to 2.0°C warmer than pre-industrial and global sea levels reached 6 to 9 meters higher than present.

Mid-Pliocene Warm Period

A warm geological period (~3 million years ago) with atmospheric CO2 near ~400 ppm, temperatures 1.8°C to 3.6°C above pre-industrial, and equilibrium sea levels 10 to 30 meters higher than present.

Ocean Dynamic Topography

Spatial variations in the height of the sea surface shaped by surface wind stress, prevailing currents (e.g., western boundary currents), and spatial differences in seawater temperature and salinity.

Kelvin Wave

An eastward-traveling wave along the equator and up continental coasts (e.g., California) that depresses the thermocline and raises local coastal sea level temporarily by several inches to feet. Occurs during El Nino.

Ocean Acidification

The ongoing decline in seawater pH and carbonate ion concentration ([CO3²⁻]) caused by the uptake and chemical equilibration of anthropogenic CO2 from the atmosphere.

Carbonate Ion Consumption Reaction

The chemical reaction where excess hydrogen ions from dissolved CO2 react with carbonate ions to form bicarbonate: H⁺ + CO3²⁻ ⇌ HCO3⁻, which reduces the pool of free carbonate ions.

Aragonite Saturation State (Omega / Ω)

A thermodynamic index of calcium carbonate saturation defined as Ω = ([Ca²⁺][CO3²⁻]) / K'sp. Values where Ω > 1 indicate supersaturation (stable); values where Ω < 1 indicate undersaturation (corrosive dissolution).

Aragonite

A metastable, highly soluble orthorhombic crystal polymorph of calcium carbonate (CaCO3) used by corals, pteropods, and larval bivalves; it dissolves more easily than calcite.

Calcite

A stable, trigonal crystal polymorph of calcium carbonate (CaCO3) that is less soluble than aragonite under equivalent temperature and pressure conditions.

Pteropod ("Sea Butterfly")

A small pelagic swimming snail with a delicate aragonite shell that forms a vital food source for polar and subpolar fish (such as salmon and mackerel), highly vulnerable to ocean acidification.

Otolith

An internal ear stone composed of aragonite used by teleost fish for acoustic detection, spatial orientation, and balance.

Ocean Stratification

The layering of the water column into distinct horizontal density zones governed by temperature and salinity, which inhibits vertical turbulent mixing and interior ventilation.

Thermal Solubility Effect (Deoxygenation)

The physical principle (Henry's Law) dictating that gas solubility decreases as water temperature increases, accounting for roughly half of upper-ocean oxygen loss.

Biological Oxygen Demand (BOD)

The amount of dissolved oxygen required by aerobic microbes and marine organisms to decompose sinking organic matter; it accelerates at higher ocean temperatures.

Oxygen Minimum Zone (OMZ)

A mid-depth oceanic layer (typically 100 to 1,000 meters) where biological respiration consumes dissolved oxygen faster than physical circulation and mixing can replenish it.

drivers of deoxygenation (W7-2 Ocean Impacts)

• Stratification: warming and increased freshwater input to ocean reduce mixing.

• Warming: lower solubility of O2 in warmer water •

• Biological effects: Warmer ocean temperatures increase BOD; increased nutrient inputs (through coastal runoff or through upwelling) lead to oxygen depletion at mid-depths (100-1000 m).

• Circulation changes: Slowing circulation and increased upwelling of oxygen-poor deep-water are linked to cc, can reduce O2 content.

SLR during last deglaciation (17,00-18,000 yrs ago)

12mm/yr

meltwater pulse 1a SLR (14,600 - 14,300 yrs ago)

50mm/yr

Current SLR

3.7mm/yr

Jet stream climate timescale

24 hrs

Fluid dynamics + precip timescale

36 hrs

Radiation + clouds + atm chem + land surf timescale

3-5 days

Ocean surface timescale

15 days (statistics)

Upper ocean layer + ice model timescale

3 months (statistics)

Deep ocean + biogeochemistry + volcanoes

years (statistics)

active vegetation + GHG emissions + particulate emissions

decades (statistics)

tipping element

aspect of the climate system that may have multiple stable states, transitions from one state to another due to reinforcing feedback loops

tipping point

the level of a particular forcing factor at which a tipping element commits to transition to a new stable state

ways to avoid overshooting tipping points

avoid thresholds, build resilience (reduce vulnerability to shocks) and control rate of forcing

Critical, near-term tipping point examples (discussed in W8-1 lecture)

1. Greenland: melt-elevation feedback

2. West Antarctic Ice Sheet

3. Permafrost thaw and thermokarst feedbacks

4. Amazon feedback

I highly anticipate she’ll ask us to discuss at least one of these on the exam

Greenland feedback

• 30 cm SLR may already be locked in

• Mass loss greater than 0.4 m SLE would require 10,000s years at pre-industrial GHG concentrations to reverse

• GMST of 3.2-3.4 ˚C >> potential for near-full melt of Greenland Ice Sheet over millennia

West Antarctic ice sheet feedback

• long term SLR of 3-5 m

• WAIS collapse w/0.5 - 1 C ocean warming above pre-industrial

• May already be commited to collapse

• (no causal loop diagram in slides)

Permafrost thaw and thermokarst feedback

• Arctic ecosystems may have already shifted from carbon sinks to carbon sources

• Regional scale tipping element

Amazon feedback

• High confidence in local and regional tipping point

• Low confidence that it is a continental-scale tipping point

• Note also drought-fire (local) and climate-carbon cycle feedback (global, low confidence

Atlantic Meridional Overturning Circulation (AMOC)

• warm salty surface water flows north (for example, thru Gulf Stream)

• water sinks (near Greenland), becomes colder and saltier

  • meltwater and rain weakens sinking

• cold, dense deep water returns south

• slow upwelling

AMOC collapse and consequences

• Evidence that AMOC is weakening, studies estimate collapse this century (now - 2095)

• Actual tipping point is highly uncertain

• Consequences of AMOC collapse include heat and precip distribution changes, higher sea levels along Eastern US

  • Colder northwestern European winters

  • Shifts in tropical rainbelts

  • Effects on other tipping elements

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Agriculture’s share of CH4 emissions

38% of all CH4 emissions (23% comes from enteric fermentation)

Agriculture’s share of N2O emissions

80% of all N2O emissions (28% comes from synthetic fertilizers)