# Contents

## Idea

Quoting Wikipedia:

A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth’s surface would be on average about 33 °C (59 °F) colder than at present.

Since the beginning of the Industrial revolution, the burning of fossil fuels has increased the levels of carbon dioxide in the atmosphere from 280ppm to 390ppm.

For an explanation of why certain gases, that is certain molecules, react to (far) infrared radiation and some do not, see molecular emission spectrum.

## Causes

According to Vaclav Smil:

The level of high mobility of carbon, nitrogen and sulfur makes these three elements fairly readily available in spite of their relative biospheric scarcity, Their cycles are complex both in terms of the number of major reservoirs, fluxes and compounds involved in the cycling processes and in temporal as well. The three cycles are not just essential for the biosphere; they are also fundamentally its creations.

Unfortunately the easy mobility of these three elements - the result of their volatile and highly water-soluble compounds - also means that human inference in these cycles has become evident on the global level, above all as rising atmospheric concentrations of CO2 (carbon dioxide?), CH4 (methane) and N2O (nitrous oxide).

## Effects

Vaclav Smil also mentions:

Environmental problems arising from these changes - potentially rapid global warming, widespread acidification of soils and waters, growing eutrophication? of aquatic and terrestrial ecosystems - have been receiving a great deal of research attention in the last decade.

Short term trends of four greenhouse gases, from Wikipedia:

The radiative forcings caused by various greenhouse gases and other agents, (converted from Wikipedia):

# Research

Several research groups in climate physics or climate science are trying to get a better understanding of positive (reinforcing) and negative (counteracting) feedback in coupled climate systems.

# References

Data on the global warming potential of greenhouse gases can be found at webpages

• ghgprotocol.org: Global warming potential values, pdf
• International Panel of Climate Change – Climate Change 2007: Working Group I: The Physical Science Basis, 2.10.2 Direct Global Warming Potentials
• United Nations framework convention on climate change: GHG data and its own source is Climate Change 1995, The Science of Climate Change: Summary for Policymakers and Technical Summary of the Working Group I Report, page 22.

Other references

Abstract: In a series of equilibrium experiments the climate response to present-day radiative forcings of anthropogenic greenhouse gases and aerosol particles is calculated. The study was performed with a model system consisting of the ECHAM4 atmospheric general circulation model coupled to a slab ocean and thermodynamic sea ice model. The model includes transport of the relevant chemical constituents, a sulfur chemistry model that calculates sulfate production in the gas and aqueous phase, and an aerosol model that accounts for source and sink processes. The aerosol cycle, the hydrological cycle, and the atmospheric dynamics are fully interactive. The climate response to aerosol forcing is not just a mirror image of the response to greenhouse forcing. This applies to the temperature changes, which are regionally more uniform for greenhouse forcing than for aerosol forcing as is already well known, and, in particular, to the hydrological cycle: the global hydrological sensitivity - $\Delta_{precip}/\Delta_{temp}$ - to a 1-K surface temperature change is almost 3 times higher for aerosol forcing than for greenhouse forcing.

When both forcings are combined, a global warming is simulated while evaporation and precipitation decrease by about 2% K−1, resulting in a negative hydrological sensitivity. A strong dependency of the response to the type of forcing has also been found for the cloud water content and, consequently, for the change in cloud radiative forcing, which is substantially larger in the combined forcing experiment than in either of the individual forcing experiments. Consequently, the global warming for combined forcing is significantly smaller (0.57 K) than that obtained by adding the individual changes (0.85 K). Due to feedbacks between temperature changes and the hydrological cycle the simulated aerosol load, applying the same source strength, is considerably lower in a warmer climate (−17% K−1 warming). A consequence of this aerosol–temperature feedback could be that a future increase in greenhouse gases may reduce the aerosol burden even if the source strength would not change.

Abstract: The authors investigate the change of atmospheric angular momentum (AAM) in long, transient, coupled atmosphere–ocean model simulations with increasing atmospheric greenhouse gas concentration and sulfate aerosol loading. A significant increase of global AAM, on the order of $4 \times 10^{25}$ kg m2 s−1 for tripled CO2, was simulated by the Canadian Centre for Climate Modelling and Analysis (CCCma) coupled model. The increase was mainly contributed by the relative component of total AAM in the form of an acceleration of zonal mean zonal wind in the tropical–subtropical upper troposphere. Thus, under strong global warming, a superrotational state emerged in the tropical upper troposphere. The trend in zonal mean zonal wind in the meridional plane was characterized by 1) a tropical–subtropical pattern with two maxima near 30° in the upper troposphere, and 2) a tripole pattern in the Southern Hemisphere extending through the entire troposphere and having a positive maximum at 60°S. The implication of the projected increase of global AAM for future changes of the length of day is discussed.

The CCCma coupled global warming simulation, like many previous studies, shows a significant increase of tropical SST and includes a zonally asymmetric component that resembles El Niño SST anomalies. In the CCCma transient simulations, even though the tropical SST and global AAM both increased nonlinearly with time, the ratio of their time increments ΔAAM/ΔSST remained approximately constant at about $0.9 \times 10^{25}$ kg m2 s−1 (°C)−1. This number is close to its counterpart for the observed global AAM response to El Niño. It is suggested that this ratio may be useful as an index for intercomparisons of different coupled model simulations

Abstract: Emissions of a broad range of greenhouse gases of varying lifetimes contribute to global climate change. Carbon dioxide displays exceptional persistence that renders its warming nearly irreversible for more than 1,000 y. Here we show that the warming due to non-CO2 greenhouse gases, although not irreversible, persists notably longer than the anthropogenic changes in the greenhouse gas concentrations themselves. We explore why the persistence of warming depends not just on the decay of a given greenhouse gas concentration but also on climate system behavior, particularly the timescales of heat transfer linked to the ocean. For carbon dioxide and methane, nonlinear optical absorption effects also play a smaller but significant role in prolonging the warming. In effect, dampening factors that slow temperature increase during periods of increasing concentration also slow the loss of energy from the Earth’s climate system if radiative forcing is reduced. Approaches to climate change mitigation options through reduction of greenhouse gas or aerosol emissions therefore should not be expected to decrease climate change impacts as rapidly as the gas or aerosol lifetime, even for short-lived species; such actions can have their greatest effect if undertaken soon enough to avoid transfer of heat to the deep ocean.

category: climate