a collection of airborne particles, typically less than 100th of a millimetre in size, that reside in the atmosphere.

a measure of how much light airborne particles prevent from passing through a column of atmosphere. Aerosols tend to absorb or reflect incoming sunlight, thus reducing visibility and increasing optical depth.

caused or produced by humans.

the process of assigning causes to detected climate change, whether man-made or natural.    

the mass of living organisms, and dead matter such as wood, leaves, and other organic matter.

that part of the Earth consisting of living organisms, including in the atmosphere, on land and in the ocean.

representative temperature of a roughly triangular area of the United Kingdom enclosed by Bristol, Lancashire and London.

The level at which half of possible outcomes lie above and half below; often referred to as the median.

carbon dioxide, a gas in Earth's atmosphere. It occurs naturally and is also a by-product of human activity such as burning fossil fuels and land-use change. It is the principal anthropogenic greenhouse gas.

average weather and its variability over a period of time, ranging from months to millions of years. The World Meteorological Organization standard is a 30-year average.

a change in the climate's mean and variability for an extended period of decades, or more.

an initial process in the climate leads to a change in another process in the climate, which in turn influences the initial one. A positive feedback intensifies the original process, and a negative feedback reduces it. A warming climate could increase the release of carbon dioxide from soils. Since carbon dioxide is a greenhouse gas, the additional release of carbon dioxide would further warm the climate - this is an example of a positive feedback.

a mathematical representation of the climate system based on its physical, chemical and biological components, in the form of a computer program. The computer climate models used at the Met Office Hadley Centre are detailed three-dimensional representations of major components of the climate system. Coupled climate models are the most complex, combining various components such as atmosphere, ocean, sea ice and land surface. They are run on the Met Office's supercomputer.

the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change.

El Niño is a periodic warming  of the tropical Eastern Pacific Ocean associated with a fluctuation in the low latitude pressure system known as the Southern Oscillation. This atmosphere-ocean interaction is known as ENSO, and normally occurs on timescales of between two to seven years.

biomass lain down in the Earth millions of years ago, such as coal, oil, and natural gas, which when burnt produce carbon dioxide.

the non-living, solid portion of the Earth, including rocks.

the reduction in the amount of solar radiation at the Earth's surface, through the presence of aerosols.

a rise in the Earth's temperature, often used with respect to the observed increase since the early 20th century.

gases in the atmosphere, which absorb thermal infra-red radiation emitted by the Earth's surface, the atmosphere and clouds e.g. water vapour, carbon dioxide, methane and nitrous oxide.

the Gulf Stream is a warm ocean current originating near the Caribbean and the Gulf of Mexico which follows the east coast of the USA before turning into the North Atlantic Drift towards north west Europe. This combined system transports heat from low to high latitudes, keeping north west European winter temperatures higher than they would otherwise be.

the Met Office Hadley Centre's third generation climate model

the Met Office Hadley Centre's Global Environment Model.

the cold phase of ENSO leading to extensive cooling of the central and eastern Pacific.

an international protocol adopted in Montreal in 1989 controlling the production and use of stratospheric ozone depleting gases.

a molecule, which in the upper atmosphere (stratosphere) filters potentially damaging ultraviolet light from reaching the Earth's surface.

climate prior to the development of climate measuring instruments, details of which are acquired from so-called proxy data, e.g. from ice sheets, tree rings, sediment, and rocks.  

climate models split the Earth's atmosphere and ocean into a finite number of gridboxes (similar to the pixels on a digital camera) - the higher the number of gridboxes, the higher (or finer) the spatial resolution. For example, a model with a horizontal resolution of 1 degree would have 360 (latitude) x 180 (longitude) = 64,800 gridboxes. The height of the atmosphere, and the depth of the ocean are split into distinct layers - so the number of these layers determines the vertical resolution of the model.

a synthetic description of an event or series of actions and events.

is a branch of physics and of chemistry that studies the effects of changes in temperature, pressure, and volume on physical systems.

the world's large-scale ocean circulation driven by differences in temperature and salinity of the water masses.

the degree to which a value is unknown. In the context of climate change uncertainty arises from imperfect understanding of the physics of the atmosphere; imperfect representation of the real climate in climate models owing to limited computer power and unknown future greenhouse gas emissions.

a metropolitan area which is significantly warmer than its surroundings.

the loss removal of the rural characteristics of a town or area, a process associated with the development of civilization and technology.