Climate Change: The Physical Basis, Causes, Consequences, and Solutions

Comprehensive practice flashcards covering climate science fundamentals, energy balance, greenhouse gases, paleoclimate, the Anthropocene, extreme weather, terrestrial ecosystems, and mitigation pathways.

What is the primary problem driving modern climate change according to Lecture 1?

Anthropogenic emissions of too many greenhouse gases into the atmosphere.

What percentage of global warming is attributed specifically to $\text{CO}_2$ emissions?

$74\%$ of global warming is attributed to $\text{CO}_2$.

What proportion of anthropogenic $\text{CO}_2$ emissions originates from fossil fuels (coal, oil, and gas)?

$90\%$ comes from coal, oil, and gas combustion.

What percentage of anthropogenic $\text{CO}_2$ emissions is caused by deforestation?

$10\%$ of $\text{CO}_2$ emissions is caused by deforestation.

According to the lecture timeline, in what year did global mean warming reach $1.0\,^\circ\text{C}$ above pre-industrial levels?

Global mean warming reached $1.0\,^\circ\text{C}$ in $2021$.

In what year does the lecture note that global mean warming reached $1.5\,^\circ\text{C}$?

Global warming reached $1.5\,^\circ\text{C}$ in $2025$.

What physical environmental impacts of global temperature rise are listed on Page 1?

Melting glaciers, drier forests, and increasing wildfires.

What three human impacts of temperature rise are highlighted in the introductory lecture?

Adverse effects on agriculture, water shortages, and silent deaths of humans.

How is climate mitigation defined?

Mitigation comprises the actions taken to avoid further warming.

How is climate adaptation defined?

Adaptation comprises the actions taken to adapt to the climate changes we are already facing.

What does the acronym IPCC stand for?

Intergovernmental Panel on Climate Change.

In what year was the IPCC established?

The IPCC was established in $1988$.

What is the primary objective of the IPCC?

To provide policymakers with objective information regarding climate change causes, impacts, and potential actions.

Why are IPCC assessment reports characterized as conservative?

Because they are consensus reports where every participating member must agree.

What is the name and publication timeframe of the IPCC's latest assessment report referenced?

The Sixth Assessment Report, or $\text{AR6}$, published in $2021\text{--}2022$.

According to IPCC $\text{AR6}$, by how much must global $\text{CO}_2$ emissions be quickly decreased?

$\text{CO}_2$ emissions must be quickly reduced by half.

What ultimate target must global $\text{CO}_2$ emissions reach according to $\text{AR6}$?

Emissions must reach net zero, after which additional $\text{CO}_2$ must still be removed from the atmosphere.

What does it mean that the climate system will "overshoot" $1.5\,^\circ\text{C}$?

Global mean surface temperature will exceed the $1.5\,^\circ\text{C}$ warming threshold before potentially coming back down.

In an overshoot scenario, what two factors must humanity actively strive to reduce?

The magnitude (how high temperatures peak) and the duration (for how long temperatures remain elevated).

What is the definition of weather provided in Lecture 2?

The atmospheric condition at a given time and place, possessing a chaotic element.

Beyond what time horizon cannot weather be accurately predicted due to its chaotic nature?

Weather cannot be predicted more than $10\text{--}14\,\text{days}$ in advance.

What is the definition of climate provided in Lecture 2?

The statistics of weather, encompassing the mean and extreme conditions of the atmosphere over a long period.

What is the standard time period used to calculate climate statistics?

A standard period of $30\,\text{years}$.

Which five Earth system spheres must interact to understand the global climate system?

The atmosphere, cryosphere, lithosphere, biosphere, and hydrosphere.

What principle governs the radiation balance of the Earth?

There is a fundamental balance between incoming solar radiation from the Sun and outgoing terrestrial radiation from the Earth.

What formula describes the Earth's incoming and outgoing radiation balance on Page 2?

$S(1-\alpha) = \varepsilon \sigma T^4$, or $G(1-\alpha) = \varepsilon \sigma T^4$.

What is the formula used to calculate Earth's effective global mean temperature ($T$)?

$T = \left( \frac{S(1-\alpha)}{4\sigma} \right)^{\frac{1}{4}}$, derived from the planetary Stefan-Boltzmann equilibrium.

What vital role do greenhouse gases play in Earth's atmosphere?

They produce the natural greenhouse effect, warming the planet and making life possible.

What is Earth's actual global mean surface temperature due to the natural greenhouse effect?

Approximately $+15\,^\circ\text{C}$.

What would Earth's surface temperature be without the natural greenhouse effect?

Approximately $-18\,^\circ\text{C}$.

What is the temperature difference produced by Earth's natural greenhouse effect?

A warming difference of $33\,^\circ\text{C}$ ($15\,^\circ\text{C} - (-18\,^\circ\text{C}) = 33\,^\circ\text{C}$).

What is the most abundant greenhouse gas in Earth's atmosphere, and what proportion of the effect does it represent?

Water vapor, accounting for approximately $60\%$ of the natural greenhouse effect.

Can human activity directly control the concentration of atmospheric water vapor?

No, humans cannot directly control atmospheric water vapor.

How does human emission of $\text{CO}_2$ indirectly increase atmospheric water vapor?

Increasing $\text{CO}_2$ warms the atmosphere, which increases its capacity to hold water vapor, triggering a reinforcing warming feedback.

What is the current measured energy imbalance between incoming and outgoing radiation at the top of Earth's atmosphere?

An imbalance of approximately $0.6\,\text{W}\,\text{m}^{-2}$.

Why does an increase in atmospheric $\text{CO}_2$ cause Earth's surface to warm up?

$\text{CO}_2$ absorbs outgoing longwave radiation, requiring Earth to warm up to emit sufficient longwave radiation to restore balance.

In the enhanced greenhouse effect model, what are the initial baseline incoming ($S$) and outgoing ($L$) radiation values?

Incoming solar radiation $S = 240\,\text{W}\,\text{m}^{-2}$ and outgoing longwave radiation $L = 240\,\text{W}\,\text{m}^{-2}$.

Immediately upon doubling $\text{CO}_2$ concentration ($\text{CO}_2 \times 2$), what value does outgoing radiation ($L$) drop to before thermal adjustment?

Outgoing radiation drops from $240\,\text{W}\,\text{m}^{-2}$ down to $236\,\text{W}\,\text{m}^{-2}$.

What is Earth's surface temperature increase after doubling $\text{CO}_2$ without climate feedbacks once equilibrium is restored?

A temperature rise of $+1.2\,^\circ\text{C}$, reaching $15 + 1.2\,^\circ\text{C}$.

What is Earth's surface temperature increase after doubling $\text{CO}_2$ when positive climate feedbacks are included?

A temperature rise of $+2.5\,^\circ\text{C}$, reaching $15 + 2.5\,^\circ\text{C}$.

What are the three main greenhouse gases released by human activity?

Carbon dioxide ($\text{CO}_2$), methane ($\text{CH}_4$), and nitrous oxide ($\text{N}_2\text{O}$).

For how long have atmospheric $\text{CO}_2$ concentrations not been as high as they are currently?

Current atmospheric $\text{CO}_2$ concentrations have not been seen since $2\,\text{million years ago}$.

How does the simultaneous decline in atmospheric $\text{O}_2$ prove that rising $\text{CO}_2$ is from fossil fuel combustion?

Burning fossil carbon consumes atmospheric oxygen, causing a drop in $\text{O}_2$ that parallels the rise in $\text{CO}_2$.

How does the interhemispheric gradient of atmospheric $\text{CO}_2$ point to human origin?

The difference in $\text{CO}_2$ concentration between the Northern and Southern Hemispheres correlates directly with the spatial distribution of fossil fuel emissions.

Why is atmospheric $\text{CO}_2$ accumulating rather than remaining in equilibrium?

Because humans are perturbing the natural carbon cycle balance by releasing fossilized carbon faster than natural sinks can absorb it.

What fraction of extra anthropogenic $\text{CO}_2$ emitted into the atmosphere remains airborne?

Approximately half of the emitted $\text{CO}_2$ stays in the atmosphere, while the other half is absorbed by land and sea.

What is the Global Warming Potential (GWP) of methane ($\text{CH}_4$) compared to $\text{CO}_2$?

Methane has a global warming potential $28\,\text{times}$ higher than that of $\text{CO}_2$.

What is the atmospheric lifespan of methane ($\text{CH}_4$)?

Methane has a relatively short atmospheric lifespan of about $20\,\text{years}$.

What are aerosols?

Suspended liquid or solid microscopic particles in the air.

What are the primary anthropogenic sources of aerosols?

Fossil fuel combustion, industrial carbon emissions, and biomass burning.

What are the primary natural sources of aerosols?

Mineral dust from deserts, sea salt spray, and volcanic eruptions.

What is the net radiative climatic effect of aerosols in the atmosphere?

A net cooling effect, because they increase Earth's reflectivity and scatter solar radiation.

What natural solar cycle causes variations in solar irradiance?

The $11\text{-year}$ sunspot cycle.

What is the typical atmospheric residence time of volcanic aerosol forcing?

Volcanic aerosol forcing is transitory, typically lasting only $1\text{--}2\,\text{years}$.

What role does the sun's radiation wavelength or solar trends play in current global warming?

None; it is irrelevant to current warming because all solar trends over the past 20 years run in the opposite direction of observed temperature rise.

By how much has Earth's global mean surface temperature warmed since 1880?

Earth has warmed by approximately $1.1\,^\circ\text{C}$ since $1880$.

How does the spatial pattern of observed warming compare between land and ocean surfaces?

Warming is significantly larger over land surfaces than over the ocean.

Where and during what season is modern global warming observed to be largest?

Warming is largest over high northern latitudes, especially during winter.

What localized regional cooling trend has been observed in the ocean, and what is its cause?

Cooling over the North Atlantic Ocean, caused by the weakening of the ocean overturning circulation.

What are the sequential consequences of reduced deep-water overturning in the North Atlantic?

Less deep-water overturning causes less northward heat transport, producing regional cooling and shifts in atmospheric circulation and climate.

Why does temperature increase faster over land than over the oceans?

Because land has a lower heat capacity than water, allowing it to heat up much more rapidly.

What observed trend occurred in global mean total column water vapor from 1979 to 2020?

A consistent increase in total atmospheric water vapor, driven by warmer air temperatures.

What is the general trend in precipitation over land observed from 1901 to 2019?

Data is incomplete, but precipitation over land has likely increased since $1950$.

What does historical observational data indicate regarding the frequency of tropical cyclones since 1970?

There is no significant trend indicating an increase in the total number or frequency of hurricanes.

What has been observed regarding the intensity of tropical cyclones since 1970?

Cyclones have become stronger, showing an increase in the proportion of intense Category 4 and 5 storms.

What is the cryosphere?

The component of the Earth system encompassing all frozen water and soil on Earth's surface.

What are the eight major physical components of the cryosphere listed on Page 4?

Ice sheets, ice shelves, glaciers and ice caps, sea ice, seasonal snow cover, river ice, lake ice, and ground ice (permafrost).

Why do changes occurring in remote cryospheric regions have global consequences?

Because changes in snow and ice alter planetary albedo, global radiation balance, weather patterns, and global sea level.

Why does the melting of land-based ice raise global sea level, whereas melting sea ice does not?

Land ice adds new mass to the ocean, while sea ice is already floating and displacing its liquid equivalent volume.

How do snow surfaces influence planetary temperature?

They have high albedo, reflecting solar radiation back into space and cooling the planet.

Explain the positive albedo feedback mechanism caused by cryospheric melting.

Warmer temperatures melt snow and ice, exposing darker land and sea surfaces that absorb more solar radiation, accelerating warming.

What trend has been recorded for seasonal snow cover in the Northern Hemisphere?

A significant decrease in seasonal snow cover extent.

By how many days did the average ice duration on rivers and lakes decrease between 1850 and 2000?

An average decrease of $12\,\text{days}$ of ice cover (lakes freeze later and thaw earlier).

What has been the trend in Northern Hemisphere sea ice extent since 1900–2011?

A clear and pronounced retreat, with Arctic sea ice reaching levels lowest since at least $1850$.

In what year did Arctic sea ice extent reach its historic recorded minimum?

Arctic sea ice hit its lowest recorded minimum in $2012$.

What trend has been observed in Antarctic sea ice extent in the Southern Hemisphere?

There is no clear, long-term continuous trend in Antarctic sea ice evolution.

What global pattern is revealed by glacier terminus records across all continents?

A consistent, widespread recession and retreat of glacier tongues due to climate change.

How far did the Morteratsch Glacier retreat between 1864 and 2000?

It retreated by approximately $2\,\text{km}$, with accelerated retreat occurring after 2000.

What percentage of their total mass did Swiss glaciers lose between 2000 and the present?

Swiss glaciers lost $40\%$ of their total mass since $2000$.

What proportion of Swiss glacier mass was lost during the years 2022 and 2023 alone?

$10\%$ of total Swiss glacier mass was lost in the years $2022\text{ and }2023$ alone.

What are the two greatest ice sheets on Earth that hold the largest sea-level rise potential?

The Greenland Ice Sheet and the Antarctic Ice Sheet.

What has been the mass balance trend of both the Greenland and Antarctic ice sheets since 1992?

Both ice sheets have experienced continuous, accelerating mass loss.

Through what primary mechanisms do continental ice sheets gain and lose mass?

They gain mass via surface snowfall and lose mass via surface melt and dynamical ice discharge.

What specific spatial pattern of thickness change characterizes the Greenland Ice Sheet?

Small central interior thickening combined with much larger marginal thinning.

Until approximately what year was the Greenland Ice Sheet in mass equilibrium?

It remained in approximate mass equilibrium until $1990$.

What has driven the significant volume decrease of the Greenland Ice Sheet over the last two decades?

Surface mass balance decreases and accelerating dynamic ice discharge into the sea.

Which major Antarctic glacier is singled out in the lecture notes for massive overall ice loss?

Pine Island Glacier.

What does the acronym MISI stand for in glaciology?

Marine Ice Sheet Instability.

How does Marine Ice Sheet Instability (MISI) operate?

Warm seawater melts floating ice shelves; as the grounding line retreats down a retrograde slope into deeper water, ice discharge increases unstoppably.

What does the acronym MICI stand for?

Marine Ice Cliff Instability.

According to the MICI hypothesis, above what exposed vertical height can an ice cliff become structurally unstable?

Vertical ice cliffs exceeding $800\,\text{m}$ can become structurally unstable and collapse under their own weight.

Has Marine Ice Cliff Instability (MICI) been directly observed in nature?

No, it remains a controversial theory and has never been observed in nature.

What is the technical definition of permafrost?

Ground (soil or rock) that remains at or below $0\,^\circ\text{C}$ for at least two consecutive years.

What change in permafrost has been documented across Siberia and Russia?

A significant decrease in permafrost depth and active layer thawing.

What percentage of the excess energy trapped by Earth's radiative imbalance has warmed the global oceans?

Approximately $90\%$ of excess thermal energy has entered and warmed the oceans.

What is thermal expansion of seawater?

The physical expansion of water molecules as ocean temperature increases, directly driving sea-level rise.

What is the current estimated rate of global mean sea-level rise?

The current rate of sea-level rise is approximately $3.7\,\text{mm/yr}$.

What was the single largest contributing factor to sea-level rise between 2006 and 2018?

Ocean thermal expansion (ocean warming), accounting for $34\%$ of sea-level rise.

What percentage of sea-level rise (2006–2018) came from the Greenland Ice Sheet?

The Greenland Ice Sheet contributed $23\%$.

What percentage of sea-level rise (2006–2018) came from land glaciers and ice caps?

Mountain glaciers contributed $15\%$.