Leadership

The last glacial maximum occurred at 18Ka. By 14Ka, the ice sheets of the Northern Hemisphere had already began retreating, and by 6Ka, global climate reached a Holocene thermal maximum. The Holocene Epoch is thus delineated as a period of relative warmth, and is considered to be an example of […]

The importance of water vapour feedback in climate change has long been recognised (Manabe & Wetherald, 1967). The concentration of water vapour in the atmosphere increases rapidly with rising temperature (about 6%/C); this is the basis for the strong positive water vapour feedback seen in current climate models (whereby increases […]

Early attempts to produce a global surface temperature record from instrumental data were confined to land surface air temperatures (e.g. Jones, 1988; Hansen & Lebedeff, 1987, 1988). All analyses indicate that during the last decade globally averaged land temperatures have been higher than in any decade in the past 140 […]

The changing composition of the atmosphere, including its greenhouse gas and aerosol content, is a major internal forcing mechanism of climate change. As we have seen in section 1.2.4, the Earth’s natural greenhouse effect (involving an increase in the downward energy flux) plays an important role in the regulation of […]

During the last decade or so, a number of complex GCMs have attempted to simulate future anthropogenic climate change. Earlier models (e.g. Manabe & Stouffer, 1980; Hansen et al., 1984; Mitchell et al., 1989; see also IPCC, 1990a) studied equilibrium climate change associated between two, presumably stable, states of climate. […]

The major sinks for N2O are stratospheric photo-dissociation and photo-oxidation, estimated at 12.3Mt/a (3.5Mt/a). Consumption by soils may also be a small sink but, to date, this contribution has not been quantitatively evaluated.

Global-mean temperature has increased by around 0.3 to 0.6C over the past 100 years (section 6.7.1). At the same time, greenhouse gas concentrations, and atmospheric aerosol loadings have increased substantially (sections 6.4 and 6.6). To assess whether the two are associated requires the use of model simulations of the likely […]

4.1. Introduction Climate models attempt to simulate the behaviour of the climate system. The ultimate objective is to understand the key physical, chemical and biological processes which govern climate. Through understanding the climate system, it is possible to: obtain a clearer picture of past climates by comparison with empirical observation, […]

Halocarbons are compounds containing carbon, halogens such as chlorine, bromine and fluorine, and sometimes hydrogen. They may be wholly anthropogenic such as the CFCs or they may have natural sources, such as some of the methylhalides (see section 6.4.4). Chlorofluorocarbons (CFCs) are entirely anthropogenically produced by aerosol propellants, refrigerator coolants […]

Accompanying the increasing concentrations of greenhouse gases in the atmosphere has been an increase in greenhouse radiative forcing (enhanced greenhouse effect) due to the enhanced absorption of terrestrial infrared radiation. This radiative forcing can be quantified from the increases in greenhouse gases since the beginning of the Industrial Revolution.