AP Environmental Science:: Unit 9 - Globalchange

Modern, human-caused climate change is best understood as resulting primarily from an intensification of the natural greenhouse effect (discussed in an earlier unit), specifically because human activity has:

- **A)** Substantially increased the atmospheric concentration of certain greenhouse gases (particularly carbon dioxide from fossil fuel combustion, discussed in an earlier unit) beyond their pre-industrial levels, causing the atmosphere to trap additional outgoing infrared radiation and thereby increase the average amount of heat retained near Earth's surface over time - this is distinct from the entirely natural greenhouse effect itself (which has existed long before humans and is necessary for a habitable surface temperature), since human-caused climate change instead concerns the additional, human-driven intensification of that already-existing natural process
- **B)** Eliminated the atmosphere's greenhouse effect entirely, the general opposite of human-caused climate change's own actual, well-established relationship to an intensified, rather than eliminated, greenhouse effect
- **C)** Human-caused climate change having no meaningful, describable relationship to greenhouse gas concentration, infrared radiation, or atmospheric heat retention of any kind
- **D)** Reduced atmospheric carbon dioxide concentration below its pre-industrial level, the general opposite of the well-documented, substantial increase in atmospheric carbon dioxide concentration actually observed since the industrial era began

Which of the following is the single most significant human-caused greenhouse gas, by total contribution to the enhanced greenhouse effect discussed above, primarily due to its very large cumulative emission quantity from fossil fuel combustion (discussed in an earlier unit)?

- **A)** Ozone (O3), a gas already discussed in an earlier unit as playing a significant, though chemically and functionally distinct, role in both the stratosphere (protective) and the troposphere (a harmful secondary pollutant), rather than being the single most significant greenhouse gas by total emission quantity
- **B)** Carbon dioxide (CO2), released in very large cumulative quantities primarily through the combustion of coal, petroleum, and natural gas (all discussed in an earlier unit), along with deforestation (discussed in an earlier unit, since removing forest biomass reduces the amount of CO2 that would otherwise be absorbed via photosynthesis) - while other greenhouse gases (such as methane) can be considerably more potent per individual molecule, CO2's very large total emitted quantity makes it the single most significant contributor to the overall enhanced greenhouse effect
- **C)** Nitrogen gas (N2), the atmosphere's single most abundant gas by overall volume (discussed in an earlier unit), but a gas that is not itself considered a significant greenhouse gas contributor, unlike carbon dioxide or methane
- **D)** Oxygen gas (O2), the atmosphere's second-most abundant gas by overall volume (discussed in an earlier unit), but a gas that is not itself considered a significant greenhouse gas contributor, unlike carbon dioxide or methane

Methane (CH4), a significant greenhouse gas already discussed in an earlier unit's coverage of natural gas leakage and landfill gas, is generally considered considerably more potent than carbon dioxide at trapping heat on a per-molecule, shorter-timescale basis, but is emitted in a considerably smaller total quantity than carbon dioxide. Methane emissions originate from sources including:

- **A)** Methane emissions having no meaningful, describable relationship to natural gas leakage, landfills, or livestock digestion of any kind
- **B)** Exclusively natural gas leakage, with no meaningful methane contribution from any landfill, agricultural, or livestock-related source discussed elsewhere in this curriculum
- **C)** Methane being emitted, in every documented case, only from a purely natural (non-human-caused) source, with no meaningful human-activity-driven methane emission of any kind
- **D)** Natural gas leakage during extraction, processing, and transport (discussed in an earlier unit), decomposing organic waste in landfills (also discussed in an earlier unit's coverage of landfill gas), and livestock digestion (particularly from cattle, whose digestive process produces methane as a byproduct) - because methane, though shorter-lived in the atmosphere than carbon dioxide, traps heat considerably more effectively per molecule over a shorter timescale, reducing methane emissions is sometimes discussed as a potentially faster-acting climate mitigation strategy than reducing carbon dioxide emissions alone

Global average surface temperature has risen measurably since the pre-industrial era, a trend that the great majority of climate scientists attribute primarily to:

- **A)** A significant, sustained increase in the sun's own total energy output over the same time period, a factor that measured solar output data does not support as the primary driver of the observed warming trend
- **B)** Global average surface temperature having no meaningful, describable relationship to atmospheric greenhouse gas concentration, human activity, or fossil fuel combustion of any kind
- **C)** The human-caused increase in atmospheric greenhouse gas concentration (particularly carbon dioxide and methane, both discussed above), rather than to natural climate variability alone - multiple independent lines of scientific evidence, including the observed timing and pattern of warming, support this human-caused attribution as the primary driver of the specific warming trend observed since the industrial era began
- **D)** A significant, sustained decrease in atmospheric greenhouse gas concentration over the same time period, the general opposite of the well-documented, substantial increase in atmospheric greenhouse gas concentration actually observed since the industrial era began

Ice cores, cylindrical samples drilled from deep glacial or polar ice sheets, provide scientists with a valuable historical climate record primarily because:

- **A)** Each successive annual layer of accumulated ice traps a small sample of the atmosphere from the specific time period when that layer originally formed (as tiny air bubbles), along with other climate-relevant indicators - by analyzing the trapped air's own greenhouse gas concentration and certain other chemical/isotopic signatures at different ice-core depths, scientists can reconstruct a detailed historical record of atmospheric composition and temperature extending back many hundreds of thousands of years, providing crucial historical context for evaluating the current, human-caused warming trend against past natural climate variability
- **B)** Ice cores have no meaningful, describable relationship to trapped atmospheric gas, historical climate reconstruction, or ice-sheet layering of any kind
- **C)** Ice cores can only provide climate information about the exact present day at which they are drilled, with no meaningful historical record of any kind extending backward in time
- **D)** Ice core analysis is, in fact, entirely incapable of revealing any information whatsoever about historical atmospheric greenhouse gas concentration, contradicting ice cores' own well-documented and extensively-used role in reconstructing past atmospheric composition

Rising global average temperatures are associated with accelerated melting of many of the world's glaciers and polar ice sheets, which in turn contributes to global sea-level rise primarily through:

- **A)** Melting glacial and polar ice having no meaningful, describable relationship to global sea-level rise, ocean water volume, or thermal expansion of any kind
- **B)** Adding meltwater directly into the ocean (increasing the ocean's total water volume) and, separately, through thermal expansion - since water (like most substances) expands slightly in volume as it warms, a warmer ocean occupies somewhat more physical space even without any additional meltwater volume being added at all - both mechanisms together contribute to the global sea-level rise observed in recent decades, with the relative contribution of each varying somewhat depending on the specific time period and region examined
- **C)** Melting glacial and polar ice always causing global sea levels to fall, rather than rise, the general opposite of the well-documented, observed relationship between glacial/polar ice melt and rising global sea levels
- **D)** A process that occurs, in every documented case, only via thermal expansion, with no meaningful direct meltwater contribution to global sea-level rise from any melting glacier or polar ice sheet

Coastal communities and low-lying island nations are of particular concern in discussions of climate-change-driven sea-level rise (discussed above) primarily because:

- **A)** Sea-level rise has no meaningful, describable relationship to coastal flooding risk, storm surge, or low-lying land area of any kind
- **B)** Rising sea levels always uniformly benefit every coastal community by increasing available land area, the general opposite of sea-level rise's own actual, well-established tendency to reduce, rather than increase, available dry land in a low-lying coastal area
- **C)** Sea-level rise affects only the open ocean itself, with no meaningful capacity to affect any coastal community or low-lying island nation located at the ocean's edge
- **D)** Even a comparatively modest rise in average sea level can meaningfully increase the frequency and severity of coastal flooding (particularly during a storm surge event) and can permanently submerge low-lying coastal land over time - island nations and coastal communities located at a very low average elevation above current sea level are therefore especially vulnerable to this specific climate change impact, in some cases facing the prospect of significant land loss or even full submersion of some low-lying areas over the coming decades

Ocean acidification, a chemical consequence of rising atmospheric carbon dioxide already introduced in an earlier unit, is considered a distinct climate-change-related concern from atmospheric/surface warming primarily because ocean acidification results directly from:

- **A)** Rising ocean surface temperature alone, with no meaningful direct chemical relationship to atmospheric carbon dioxide absorption or ocean pH of any kind
- **B)** A decrease, rather than an increase, in the ocean's overall absorption of atmospheric carbon dioxide, the general opposite of ocean acidification's own actual, well-established relationship to increased CO2 absorption already established in an earlier unit
- **C)** The ocean's own direct chemical absorption of a portion of the excess atmospheric carbon dioxide already discussed throughout this unit, which lowers ocean pH (as already established in an earlier unit) largely independent of any accompanying temperature change - meaning ocean acidification represents a distinct chemical impact of rising atmospheric CO2, separate from (though occurring alongside) the atmospheric/surface temperature warming that same excess CO2 also causes via the enhanced greenhouse effect discussed earlier in this unit
- **D)** A process that has no meaningful, describable relationship to atmospheric carbon dioxide, ocean pH, or ocean chemistry of any kind