What are greenhouse gases and how do they affect a planet's temperature?

Greenhouse gases (GHGs) are gases found in an atmosphere that trap heat. They absorb the infrared radiation that a planet emits, leading to a phenomenon known as the greenhouse effect. This process raises the surface temperature of astronomical bodies like Earth. Without these gases, Earth's average surface temperature would be significantly colder, around -18°C (0°F), rather than the current average of 15°C (59°F).

What are the five most abundant greenhouse gases in Earth's atmosphere, listed by their average mole fraction?

The five most abundant greenhouse gases in Earth's atmosphere, in decreasing order of average global mole fraction, are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.

Besides the five most abundant GHGs, what other gases are identified as concerns?

Other greenhouse gases of concern include chlorofluorocarbons (CFCs and HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons, sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3).

What is the approximate contribution of water vapor to the greenhouse effect, and how does it function in climate change?

Water vapor is responsible for about half of the greenhouse effect. It acts as a climate change feedback, meaning that as global temperatures increase, more water vapor enters the atmosphere, further amplifying the warming effect.

How have human activities since the Industrial Revolution impacted the concentrations of carbon dioxide and methane in the atmosphere?

Since the beginning of the Industrial Revolution (around 1750), human activities have significantly increased atmospheric concentrations. Carbon dioxide levels have risen by over 50%, and methane levels have increased by 150%. These increases are primary drivers of global warming.

Which greenhouse gas is the primary driver of global warming, and which contributes most of the rest?

Carbon dioxide emissions are the main cause of global warming, accounting for approximately three-quarters of the effect. Methane emissions are responsible for most of the remaining warming.

What are the primary human activities responsible for carbon dioxide and methane emissions?

The vast majority of human-caused carbon dioxide emissions stem from the burning of fossil fuels, with additional contributions from agriculture and industry. Methane emissions originate from agriculture, fossil fuel production, and waste management.

How long does it take for carbon dioxide and methane to be absorbed from the atmosphere?

The carbon cycle takes thousands of years to fully absorb carbon dioxide from the atmosphere. In contrast, methane has a much shorter atmospheric lifetime, averaging about 12 years.

What is the significance of natural carbon flows in maintaining atmospheric balance?

Natural flows of carbon between the atmosphere, terrestrial ecosystems, the ocean, and sediments have historically been balanced over the past million years, helping to keep greenhouse gas levels relatively stable. However, human activities have disrupted this balance.

How do current carbon dioxide levels compare to those in Earth's distant past?

Current carbon dioxide levels are higher than they have been in approximately three million years, indicating a significant departure from pre-industrial conditions.

What is the projected consequence if current greenhouse gas emission rates continue?

If current emission rates persist, global warming is projected to surpass 2.0°C (3.6°F) between 2040 and 2070. The Intergovernmental Panel on Climate Change (IPCC) considers this temperature increase level to be 'dangerous'.

What property makes greenhouse gases capable of trapping heat?

Greenhouse gases are infrared active, meaning their molecules can absorb and emit infrared radiation. This occurs in the same long wavelength range that Earth's surface, clouds, and atmosphere radiate heat, effectively trapping it.

Why are the most abundant gases in Earth's dry atmosphere, nitrogen (N2) and oxygen (O2), not considered greenhouse gases?

Nitrogen and oxygen molecules are composed of two identical atoms. This symmetry means there is no asymmetry in their electrical charge distribution, making them largely unaffected by infrared radiation. Consequently, they do not significantly contribute to the greenhouse effect, apart from a very minor effect from collision-induced absorption.

What characteristic of molecules like carbon dioxide allows them to interact with infrared radiation?

Molecules composed of atoms from different elements, such as carbon dioxide (CO2), have an asymmetry in their electrical charge distribution. This asymmetry allows their molecular vibrations to interact with electromagnetic radiation, making them infrared active and thus contributing to the greenhouse effect.

What is radiative forcing, and how does it relate to climate change?

Radiative forcing is a measure, typically in watts per square meter (W/m²), that quantifies the impact of an external factor on Earth's energy balance. A positive radiative forcing, like that from increased greenhouse gases, means more energy is entering the Earth system than leaving, leading to warming. Conversely, negative radiative forcing, such as from atmospheric sulfates, leads to cooling.

How do increasing concentrations of greenhouse gases affect the upper atmosphere?

As greenhouse gases increase in concentration in the lower atmosphere, they trap more heat, which leads to a cooling and contraction of the upper atmosphere. This occurs because any heat re-emitted by GHGs in the upper layers is more likely to escape directly into space due to the lower density of molecules.

What is the 'enhanced greenhouse effect'?

The 'enhanced greenhouse effect' refers to the changes in the natural greenhouse effect caused by human activities, primarily through the increase of greenhouse gas concentrations in the atmosphere.

According to the provided table, what are the approximate contributions of water vapor, clouds, and carbon dioxide to the greenhouse effect?

Based on the K&T (1997) and Schmidt (2010) estimates, water vapor contributes significantly (41-67%), clouds contribute substantially (up to 31% with clouds), and carbon dioxide (CO2) contributes around 18-26% to the total greenhouse effect.

What is Global Warming Potential (GWP)?

Global Warming Potential (GWP) is a metric used to measure how much heat a greenhouse gas traps in the atmosphere over a specific time period, relative to carbon dioxide (CO2). It is expressed as a multiple of the warming caused by the same mass of CO2, which has a GWP of 1 by definition.

How is the warming impact of methane compared to carbon dioxide using GWP?

Methane has a higher warming impact per unit mass than carbon dioxide over shorter time scales. For example, over a 20-year period, methane has a GWP of 81.2, meaning one tonne of methane emissions is equivalent to emitting 81.2 tonnes of CO2 over that timeframe. However, its GWP decreases significantly over longer periods due to its shorter atmospheric lifetime.

What is a carbon dioxide equivalent (CO2e)?

A carbon dioxide equivalent (CO2e) is a unit used to standardize the climate impact of different greenhouse gases. It represents the mass of CO2 that would produce the same amount of warming as a given mass of another greenhouse gas, calculated by multiplying the gas's mass by its GWP.

How has the rate of increase in atmospheric CO2 concentrations changed since the Industrial Revolution?

The rate of CO2 increase has accelerated significantly. The first 30 parts per million (ppm) increase took about 200 years (from the Industrial Revolution to 1958), while the subsequent 90 ppm increase occurred much faster, within just 56 years (from 1958 to 2014).

What determines the concentration of a greenhouse gas in the atmosphere?

The concentration of a greenhouse gas in the atmosphere is determined by the balance between its sources, which are the emissions from human activities and natural systems, and its sinks, which are the processes that remove the gas from the atmosphere.

What is the 'airborne fraction' of a greenhouse gas emission?

The airborne fraction (AF) refers to the proportion of a greenhouse gas emission that remains in the atmosphere after a specified period. The annual airborne fraction for CO2, for instance, indicates the percentage of annual emissions that stay in the atmosphere versus what is absorbed by natural sinks.

What is the atmospheric lifetime of a greenhouse gas?

The atmospheric lifetime of a greenhouse gas is the average time it takes for a molecule of that gas to be removed from the atmosphere and return to equilibrium following a sudden change in its concentration. This removal occurs through deposition, chemical reactions, or outflow.

Why does carbon dioxide have a variable atmospheric lifetime that cannot be specified by a single number?

Carbon dioxide's atmospheric lifetime is variable because it is not destroyed over time but rather moves between the atmosphere, ocean, and land systems. While some CO2 is absorbed relatively quickly, a significant portion remains in the atmosphere for centuries to millennia, and a small fraction can persist for tens of thousands of years.

How do current atmospheric carbon dioxide concentrations compare to those from millions of years ago?

Estimates suggest that current carbon dioxide levels may be the highest seen in the last 14 million years. Similar levels were also estimated to have occurred around 3 to 3.3 million years ago during the mid-Pliocene warm period.

What role might carbon dioxide have played in early Earth's climate?

Carbon dioxide is believed to have played a crucial role in regulating Earth's temperature throughout its history. Higher concentrations of CO2 in the early atmosphere might explain how Earth maintained liquid water and a warm climate, despite the Sun's output being significantly lower than it is today, addressing the 'faint young sun paradox'.

What is the NOAA Annual Greenhouse Gas Index (AGGI)?

The Annual Greenhouse Gas Index (AGGI) is calculated by NOAA atmospheric scientists. It represents the ratio of the total direct radiative forcing from long-lived, well-mixed greenhouse gases in a given year compared to the forcing in 1990. It reflects the cumulative commitment society has made to living in a changing climate.

What are the primary natural sources and sinks for carbon dioxide?

Natural sources of carbon dioxide include respiration from plants and animals, decomposition of organic matter, and volcanic activity. The primary natural sinks that remove CO2 from the atmosphere are photosynthesis by plants and absorption by the oceans.

What are the main human-made sources of carbon dioxide emissions?

The principal human-made sources of carbon dioxide emissions are the burning of fossil fuels (coal, oil, and natural gas) for energy, followed by industrial processes like cement manufacturing, fertilizer production, and land-use changes such as deforestation.

What is the significance of rice paddies in terms of greenhouse gas emissions?

Rice paddies are a notable source of greenhouse gases from agriculture, contributing approximately 22% of total agricultural methane emissions and 11% of agricultural nitrous oxide emissions globally.

What is the scientific consensus regarding the necessary emissions cuts to limit global warming?

According to the UNEP's 2022 Emissions Gap Report and the IPCC's Sixth Assessment Report, global annual greenhouse gas emissions must be significantly reduced to limit warming. To stay within the 1.5°C limit, emissions need to be cut by 45% by 2030, requiring rapid, economy-wide transformations and a drastic reduction in emissions starting immediately.

What are 'negative emissions' in the context of climate change mitigation?

Negative emissions refer to technologies and approaches designed to remove greenhouse gases, particularly carbon dioxide, directly from the atmosphere. Examples include bio-energy with carbon capture and storage (BECCS), direct air capture (DAC), and the use of biochar. Many climate models suggest large-scale negative emissions will be necessary to avoid severe climate change.

When was the term 'greenhouse' first applied to the phenomenon of atmospheric heat trapping?

The term 'greenhouse' was first applied to the phenomenon of atmospheric heat trapping by Nils Gustaf Ekholm in 1901.

What did early scientific experiments in the late 19th century reveal about atmospheric gases and infrared radiation?

In the late 19th century, scientists experimentally determined that diatomic gases like nitrogen (N2) and oxygen (O2) do not absorb infrared radiation. In contrast, gases like water vapor and carbon dioxide (CO2), which have molecules composed of multiple atoms, were found to absorb infrared radiation, indicating their role in heat trapping.

How does the greenhouse effect manifest on other planets?

Greenhouse gases create significant greenhouse effects on other planets. Notably, Venus has a very thick atmosphere dominated by carbon dioxide, leading to extremely high surface temperatures due to a runaway greenhouse effect. Mars and Titan also exhibit greenhouse effects due to their atmospheric compositions.

What is the role of the Montreal Protocol concerning greenhouse gases?

The Montreal Protocol primarily addresses ozone-depleting substances, such as CFCs. While these substances are also potent greenhouse gases, the protocol's motivation was ozone layer protection, not directly climate change mitigation, although its success has indirectly benefited climate efforts by phasing out these potent GHGs.

What is the Kigali Amendment, and what is its purpose?

The Kigali Amendment, adopted in 2016, is an international agreement to phase out the production and use of hydrofluorocarbons (HFCs). HFCs are potent greenhouse gases that were introduced as replacements for ozone-depleting substances but contribute significantly to global warming.

What is the difference between the natural and enhanced greenhouse effect?

The natural greenhouse effect is a vital process where atmospheric gases trap heat, maintaining Earth's habitable temperature. The enhanced greenhouse effect refers to the additional warming caused by the increased concentrations of these gases due to human activities since the Industrial Revolution.

How do scientists measure the relative impact of different greenhouse gases on global warming?

Scientists use Global Warming Potential (GWP) to measure the relative impact of different greenhouse gases. GWP compares the heat-trapping ability of a gas to that of carbon dioxide over a specified period, allowing for the calculation of carbon dioxide equivalents (CO2e) to standardize their climate effects.

What is the significance of the 'faint young sun paradox' in relation to early Earth's atmosphere?

The 'faint young sun paradox' refers to the observation that early Earth had liquid water despite the Sun being much dimmer than it is today. Scientists hypothesize that higher concentrations of greenhouse gases, like carbon dioxide and possibly methane, in the early atmosphere could have provided the necessary warming to maintain liquid water.

What is the purpose of the 'Atmospheric Carbon Cycle'?

The atmospheric carbon cycle describes the exchange of carbon compounds, primarily carbon dioxide, between Earth's atmosphere, oceans, and biosphere. It is a relatively fast-moving part of the overall carbon cycle, crucial for regulating atmospheric CO2 concentrations and supporting life through processes like photosynthesis.

What are the key areas of focus highlighted by leading climate scientists in 2023 regarding climate change policy?

In 2023, leading climate scientists identified several critical areas for policy implications. These include the likelihood of temporarily exceeding the 1.5°C warming limit, the urgent need for a rapid fossil fuel phase-out, challenges in scaling carbon dioxide removal technologies, uncertainties about future natural carbon sink contributions, and the interconnectedness of climate change with biodiversity loss.

What is the role of the IPCC in assessing climate change?

The Intergovernmental Panel on Climate Change (IPCC) assesses the scientific, technical, and socio-economic information relevant to understanding climate change, its potential impacts, and options for adaptation and mitigation. Its reports, like the Sixth Assessment Report (AR6), provide comprehensive scientific consensus on the state of climate change.

How do different IPCC assessment reports (TAR, AR4, AR5, AR6) reflect changes in understanding or data regarding greenhouse gases?

The different IPCC assessment reports (Third Assessment Report - TAR, Fourth Assessment Report - AR4, Fifth Assessment Report - AR5, and Sixth Assessment Report - AR6) show an evolution in data and understanding. For instance, they provide updated figures for greenhouse gas lifetimes, global warming potentials, atmospheric concentrations, and radiative forcings over time, reflecting ongoing scientific research and refinement.

What is the significance of the year 1750 and 1990 in the context of greenhouse gas data?

The year 1750 is often used as a baseline for pre-industrial greenhouse gas concentrations, against which changes due to human activities are measured. The year 1990 is significant as it serves as the baseline year for the Kyoto Protocol and the year of the first IPCC Scientific Assessment of Climate Change, making it a reference point for indices like NOAA's AGGI.

What are some examples of greenhouse gases with very long atmospheric lifetimes?

Greenhouse gases with notably long atmospheric lifetimes include perfluorocarbons (PFCs) like CF4 (PFC-14) with a lifetime of 50,000 years and C2F6 (PFC-116) with 10,000 years, and sulfur hexafluoride (SF6) with 3,200 years. These long lifetimes mean their warming effects persist for extremely extended periods.

What is the difference between ppm, ppb, and ppt when measuring atmospheric gas concentrations?

These units measure concentrations in parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt). For example, 1 ppm means one molecule of the gas per million molecules of air, 1 ppb is one per billion, and 1 ppt is one per trillion. These different scales are used depending on the abundance of the specific gas.

What is the role of 'climate feedbacks' in the context of greenhouse gases?

Climate feedbacks are processes that can amplify or dampen the effects of initial climate forcing. Water vapor is a key example; as the atmosphere warms due to other greenhouse gases, it holds more water vapor, which further enhances the greenhouse effect, creating a positive feedback loop.

Greenhouse Gas Wiki: Atmospheric Sentinels: The Science of Greenhouse Gases

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Introduction to Greenhouse Gases

Regulating Earth's Temperature

Greenhouse gases (GHGs) are atmospheric constituents that absorb and emit thermal infrared radiation. This fundamental property enables the greenhouse effect, a natural process crucial for maintaining planetary habitability. Without these gases, Earth's average surface temperature would be approximately -18°C (0°F), significantly colder than the current average of 15°C (59°F).^[2]^[3]

Key Atmospheric Components

The primary greenhouse gases in Earth's atmosphere, ranked by average global mole fraction, are water vapor (H₂O), carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone (O₃). Additionally, synthetic compounds like chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃) are potent GHGs, despite their lower atmospheric concentrations.^[5]^[6]

Anthropogenic Influence

Since the Industrial Revolution (circa 1750), human activities have significantly increased atmospheric concentrations of GHGs. Carbon dioxide levels have risen by over 50%, and methane levels by approximately 150%.^[8]^[9] CO₂ emissions, primarily from fossil fuel combustion, account for roughly three-quarters of the observed global warming, with methane contributing most of the remainder.^[10]

Molecular Properties and Mechanisms

Infrared Absorption

Greenhouse gases are characterized by their ability to absorb and emit infrared radiation. This occurs because their molecular structure, containing atoms of different elements, allows for vibrational modes that interact with electromagnetic waves in the infrared spectrum. In contrast, diatomic molecules composed of the same element, such as nitrogen (N₂) and oxygen (O₂), which constitute about 99% of Earth's dry atmosphere, lack the necessary charge asymmetry and are largely transparent to thermal radiation.^[20]

Atmospheric Transmission

The interaction between atmospheric gases and electromagnetic radiation varies significantly with wavelength. While certain wavelengths are readily absorbed by GHGs like CO₂ and water vapor, others pass through the atmosphere relatively unimpeded, creating "atmospheric windows." The absorption bands of CO₂, particularly around the 15-micron wavelength, coincide with the peak thermal emission from Earth's surface, explaining its significant heat-trapping capacity.^[19]

Upper Atmosphere Cooling

The increased concentration of GHGs in the lower atmosphere not only traps heat near the surface but also leads to a cooling effect in the upper atmosphere. This occurs because heat re-emitted at higher altitudes is less likely to be reabsorbed by the thinner atmospheric layers, facilitating its escape into space. This phenomenon contributes to the contraction of the upper atmosphere.^[30]

Major Greenhouse Gases

Gas Composition and Impact

The relative contribution of each gas to the greenhouse effect is determined by its atmospheric concentration, its ability to absorb infrared radiation, and its atmospheric lifetime. Water vapor, while the most abundant GHG and responsible for a substantial portion of the natural greenhouse effect (41-67%), acts primarily as a feedback mechanism in response to temperature changes, rather than a direct driver of warming.^[32]^[33]^[35]

Global Warming Potential (GWP)

Global Warming Potential (GWP) quantifies the heat-trapping ability of a greenhouse gas relative to carbon dioxide over a specified time horizon (e.g., 20, 100, or 500 years). For instance, methane has a GWP-100 of approximately 27.9, indicating it traps 27.9 times more heat than CO₂ over a century. This metric allows for the calculation of carbon dioxide equivalents (CO₂e) to compare the climate impact of different gases.^[39]

Key Greenhouse Gases Table

The following table details the primary long-lived greenhouse gases, their atmospheric lifetimes, 100-year Global Warming Potentials (GWPs), pre-industrial and current concentrations, and their associated radiative forcings.

IPCC list of greenhouse gases with lifetime, 100-year global warming potential, concentrations in the troposphere and radiative forcings. The abbreviations TAR, AR4, AR5 and AR6 refer to the different IPCC reports over the years. The baseline is pre-industrialization (year 1750).
Species	Lifetime (years) ^[48]^: 731	100-yr GWP ^[48]^: 731	Mole Fraction [ppt — except as noted]^[A] + Radiative forcing [W m⁻²]^[B]					Concentrations over time^[54]^[55] up to year 2022
Species	Lifetime (years) ^[48]^: 731	100-yr GWP ^[48]^: 731	Baseline Year 1750	TAR^[56] Year 1998	AR4^[57] Year 2005	AR5^[48]^: 678 Year 2011	AR6^[52]^: 4–9 Year 2019	Concentrations over time^[54]^[55] up to year 2022
CO₂ [ppm]	^[C]	1	278	365 (1.46)	379 (1.66)	391 (1.82)	410 (2.16)	$Mauna Loa CO2 monthly mean concentration.svg$
CH₄ [ppb]	12.4	28	700	1,745 (0.48)	1,774 (0.48)	1,801 (0.48)	1866 (0.54)	$CH4_mm.png$
N₂O [ppb]	121	265	270	314 (0.15)	319 (0.16)	324 (0.17)	332 (0.21)	$HATS_Nitrous_Oxide_concentration.png$
CFC-11	45	4,660	0	268 (0.07)	251 (0.063)	238 (0.062)	226 (0.066)	$Hats_f11_global.png$
CFC-12	100	10,200	0	533 (0.17)	538 (0.17)	528 (0.17)	503 (0.18)	$Hats_f12_global.png$
CFC-13	640	13,900	0	4 (0.001)	–	2.7 (0.0007)	3.28 (0.0009)	cfc13
CFC-113	85	6,490	0	84 (0.03)	79 (0.024)	74 (0.022)	70 (0.021)	$Hats_f113_global.png$
CFC-114	190	7,710	0	15 (0.005)	–	–	16 (0.005)	$BK_CFC114.jpg$
CFC-115	1,020	5,860	0	7 (0.001)	–	8.37 (0.0017)	8.67 (0.0021)	cfc115
HCFC-22	11.9	5,280	0	132 (0.03)	169 (0.033)	213 (0.0447)	247 (0.0528)	$HCFC22_concentration.jpg$
HCFC-141b	9.2	2,550	0	10 (0.001)	18 (0.0025)	21.4 (0.0034)	24.4 (0.0039)	$HCFC141b_concentration.jpg$
HCFC-142b	17.2	5,020	0	11 (0.002)	15 (0.0031)	21.2 (0.0040)	22.3 (0.0043)	$HCFC142b_concentration.jpg$
CH₃CCl₃	5	160	0	69 (0.004)	19 (0.0011)	6.32 (0.0004)	1.6 (0.0001)	$BK_MC.jpg$
CCl₄	26	1,730	0^[D]	102 (0.01)	93 (0.012)	85.8 (0.0146)	78 (0.0129)	$Hats_ccl4_global.png$
HFC-23	222	12,400	0	14 (0.002)	18 (0.0033)	24 (0.0043)	32.4 (0.0062)	$HFC-23_mm.png$
HFC-32	5.2	677	0	–	–	4.92 (0.0005)	20 (0.0022)	$BK_HFC32.jpg$
HFC-125	28.2	3,170	0	–	3.7 (0.0009)	9.58 (0.0022)	29.4 (0.0069)	$HFC125_concentration.jpg$
HFC-134a	13.4	1,300	0	7.5 (0.001)	35 (0.0055)	62.7 (0.0100)	107.6 (0.018)	$HFC-134a_mm.png$
HFC-143a	47.1	4,800	0	–	–	12.0 (0.0019)	24 (0.0040)	$HFC143a_concentration.jpg$
HFC-152a	1.5	138	0	0.5 (0.0000)	3.9 (0.0004)	6.4 (0.0006)	7.1 (0.0007)	$HFC152a_concentration.jpg$
CF₄ (PFC-14)	50,000	6,630	40^[63]^[E]	80 (0.003)	74 (0.0034)	79 (0.0040)	85.5 (0.0051)	$Tetrafluoromethane_concentration.jpg$
C₂F₆ (PFC-116)	10,000	11,100	40^[63]^[E]	3 (0.001)	2.9 (0.0008)	4.16 (0.0010)	4.85 (0.0013)	$Hexafluoroethane_concentration.jpg$
SF₆	3,200	23,500	0.01^[63]	4.2 (0.002)	5.6 (0.0029)	7.28 (0.0041)	9.95 (0.0056)	$Sulfur_Hexafluoride_concentration.png$
SO₂F₂	36	4,090	0	–	–	1.71 (0.0003)	2.5 (0.0005)	$SO2F2_mm.png$
NF₃	500	16,100	0	–	–	0.9 (0.0002)	2.05 (0.0004)	$Nitrogen_Trifluoride_concentration.jpg$

Note: Values in parentheses represent the radiative forcing in W/m². ppt = parts per trillion; ppm = parts per million; ppb = parts per billion.

Radiative Forcing

Balancing Energy Flows

Radiative forcing quantifies the impact of external factors on Earth's energy balance, measured in watts per square meter (W/m²). An increase in greenhouse gas concentrations results in positive radiative forcing, indicating more incoming energy than outgoing energy, which leads to warming. Conversely, factors like aerosols can exert negative radiative forcing, causing cooling.^[19]^[27]

Impact on Atmospheric Layers

While GHGs warm the lower atmosphere (troposphere), they simultaneously cause cooling and contraction in the upper atmosphere (stratosphere). This occurs because heat re-emitted by GHGs at higher altitudes escapes more readily into space due to the lower density of atmospheric molecules.^[30]

Contributions to the Greenhouse Effect

Quantifying Impact

Estimates of the contribution of various components to the total greenhouse effect vary slightly depending on the methodology and inclusion of factors like clouds. Water vapor and clouds together account for a significant portion of the total effect, while carbon dioxide is the next most significant contributor. Other gases like tropospheric ozone, methane, and nitrous oxide also play important roles.^[32]^[33]

Comparative Contributions Table

The table below illustrates the estimated percentage contributions to the total greenhouse effect, differentiating between clear sky and cloudy conditions, based on different scientific assessments.

Percent contribution to total greenhouse effect
	K&T (1997)^[32]		Schmidt (2010)^[33]
Contributor	Clear Sky	With Clouds	Clear Sky	With Clouds
Water vapor	60	41	67	50
Clouds		31		25
CO₂	26	18	24	19
Tropospheric O₃	8
N₂O + CH₄	6
Other		9	9	7
K&T (1997) used 353 ppm CO₂ and calculated 125 W/m² total clear-sky greenhouse effect; relied on single atmospheric profile and cloud model. "With Clouds" percentages are from Schmidt (2010) interpretation of K&T (1997). Schmidt (2010) used 1980 climatology with 339 ppm CO₂ and 155 W/m² total greenhouse effect; accounted for temporal and 3-D spatial distribution of absorbers.

Monitoring and Data Networks

Measuring Atmospheric Concentrations

The monitoring of greenhouse gases involves direct measurement of atmospheric concentrations and indirect calculation of emissions. Techniques include infrared analysis and manometry for CO₂, and specialized instruments like differential absorption lidar (DIAL) for methane and nitrous oxide. Satellite missions, such as the Orbiting Carbon Observatory (OCO), and ground-based networks like the Integrated Carbon Observation System (ICOS) provide crucial data.^[76]^[58]

Annual Greenhouse Gas Index (AGGI)

The Annual Greenhouse Gas Index (AGGI), developed by NOAA, tracks the cumulative radiative forcing of long-lived GHGs relative to 1990 levels. It serves as a key indicator of the ongoing commitment to climate change, reflecting the total warming influence from these gases and providing a low-uncertainty measure of societal impact.^[42]^[78]

Sources of Greenhouse Gases

Natural vs. Anthropogenic

While natural processes maintain a relative balance in the carbon cycle over geological timescales, human activities have significantly perturbed this equilibrium. Natural sources and sinks for GHGs exist, but anthropogenic emissions, particularly since the Industrial Revolution, have led to increased atmospheric concentrations.^[84]^[85]

Human-Caused Emissions

The primary anthropogenic source of carbon dioxide is the combustion of fossil fuels (coal, natural gas, oil) for energy production. Other significant contributors include cement manufacturing, industrial processes, and land-use changes like deforestation.^[12]^[11] Methane emissions stem from agriculture (e.g., rice cultivation, livestock), fossil fuel extraction and transport, and waste decomposition.^[13]

Mitigation Strategies

Emissions Reduction Targets

To limit global warming to 1.5°C, global greenhouse gas emissions must be drastically reduced. Scientific assessments indicate that emissions need to peak before 2025 and decline significantly thereafter, necessitating rapid, economy-wide transformations rather than incremental changes.^[100]

Negative Emissions Technologies

Technologies aimed at removing GHGs from the atmosphere, known as negative emissions, are considered crucial in climate mitigation scenarios. These include bio-energy with carbon capture and storage (BECCS), direct air capture (DAC), and biochar application. Research is also exploring methods for atmospheric methane removal.^[105]^[107]

Historical Context of Discovery

Early Scientific Understanding

In the late 19th century, scientists experimentally determined that gases like water vapor and carbon dioxide absorb infrared radiation, unlike nitrogen and oxygen. This laid the groundwork for understanding their role in regulating Earth's temperature. The term "greenhouse" was first applied to this phenomenon by Nils Gustaf Ekholm in 1901.^[111]^[112]

Early Recognition of Impact

As early as 1912, scientific publications noted the potential impact of industrial activities, specifically coal consumption, on atmospheric CO₂ levels and subsequent climate change, demonstrating an early awareness of anthropogenic influence.^[108] By the late 20th century, a scientific consensus emerged linking increased GHG concentrations to significant global temperature rises and broader climate system changes.^[113]

Greenhouse Effects on Other Planets

Planetary Atmospheres

Greenhouse gases are present in the atmospheres of various celestial bodies, influencing their surface temperatures. Notable examples include Mars, with its thin CO₂ atmosphere, and Titan, Saturn's moon, which possesses a dense atmosphere rich in nitrogen and methane. Venus exhibits an extreme greenhouse effect due to its extremely dense CO₂ atmosphere, leading to surface temperatures hot enough to melt lead.^[114]

Runaway Greenhouse Effect

While Venus serves as an example of a runaway greenhouse effect, the conditions required for such an extreme scenario (e.g., a significantly brighter sun) are not replicable through human-induced GHG emissions on Earth. The concept highlights the powerful role of atmospheric composition in determining planetary surface temperatures.^[115]

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References

Mole fractions: Î¼mol/mol = ppm = parts per million (106); nmol/mol = ppb = parts per billion (109); pmol/mol = ppt = parts per trillion (1012).

Figure is combined total natural abundance of all perfluorocarbons: no data exist for individual compounds.

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Atmospheric Sentinels

💡 Dive in with Flashcard Learning! 💡

Introduction to Greenhouse Gases 🌍

🌡️ Regulating Earth's Temperature

💨 Key Atmospheric Components

📈 Anthropogenic Influence

Molecular Properties and Mechanisms ⚛️

💡 Infrared Absorption

🌐 Atmospheric Transmission

⚡ Upper Atmosphere Cooling

Major Greenhouse Gases 💨

📊 Gas Composition and Impact

🧮 Global Warming Potential (GWP)

📈 Key Greenhouse Gases Table

Radiative Forcing 📈

⚖️ Balancing Energy Flows

⬆️ Impact on Atmospheric Layers

Contributions to the Greenhouse Effect 📊

⚖️ Quantifying Impact

📊 Comparative Contributions Table

Monitoring and Data Networks 🛰️

📡 Measuring Atmospheric Concentrations

📊 Annual Greenhouse Gas Index (AGGI)

Sources of Greenhouse Gases 🏭

🌳 Natural vs. Anthropogenic

🔥 Human-Caused Emissions

Mitigation Strategies ⬇️

🎯 Emissions Reduction Targets

🌱 Negative Emissions Technologies

Historical Context of Discovery 📜

🔬 Early Scientific Understanding

📰 Early Recognition of Impact

Greenhouse Effects on Other Planets 🪐

🪐 Planetary Atmospheres

⚠️ Runaway Greenhouse Effect

Teacher's Corner 🧑‍🏫

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❓ Test Your Knowledge! ❓

Gamer's Corner 🎮

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References

📜 References

Feedback & Support 👍

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Disclaimer ⚠️

📜 Important Notice

Dive in with Flashcard Learning!

Introduction to Greenhouse Gases

Regulating Earth's Temperature

Key Atmospheric Components

Anthropogenic Influence

Molecular Properties and Mechanisms

Infrared Absorption

Atmospheric Transmission

Upper Atmosphere Cooling

Major Greenhouse Gases

Gas Composition and Impact

Global Warming Potential (GWP)

Key Greenhouse Gases Table

Radiative Forcing

Balancing Energy Flows

Impact on Atmospheric Layers

Contributions to the Greenhouse Effect

Quantifying Impact

Comparative Contributions Table

Monitoring and Data Networks

Measuring Atmospheric Concentrations

Annual Greenhouse Gas Index (AGGI)

Sources of Greenhouse Gases

Natural vs. Anthropogenic

Human-Caused Emissions

Mitigation Strategies

Emissions Reduction Targets

Negative Emissions Technologies

Historical Context of Discovery

Early Scientific Understanding

Early Recognition of Impact

Greenhouse Effects on Other Planets

Planetary Atmospheres

Runaway Greenhouse Effect

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice