All life depends on a healthy planet, but the interwoven systems of atmosphere, oceans, watercourses, land, ice cover and biosphere, which form the natural environment, are threatened by human activities. The Global Atmosphere Watch (GAW) programme provides reliable scientific data and information on aerosols, greenhouse gases, selected reactive gases, ozone, ultraviolet radiation and precipitation chemistry (or atmospheric deposition). 

The natural environment suffers, for example, from lack of precipitation for extended periods and uncontrolled land use, leading to desertification. It is estimated that one-third of the Earth’s surface and one-fifth of the world’s population are threatened by desertification. WMO, therefore, directs its attention to the aspects of climate variability and change that impact the environment. The observational data of weather, climate and the atmosphere that are collected through the WMO networks of observing, data-transmitting and forecasting systems keep policy-makers informed of the state of the environment so that they are in a better position to prevent its further degradation and are used by used by the Intergovernmental Panel on Climate Change (IPCC) in its assessments of climate climate change, its potential impacts and options for adaptation and mitigation. 

WMO is the recognized, comprehensive source of unique global systematic observations on the state of a wide variety of geophysical phenomena, datasets and long-term archives, and scientific and technical expertise in support of policy advice on various critical environmental issues.

Biodiversity (the variety of life on Earth and the natural patterns it forms) helps keep the global environment working. Polluted air, depleted or contaminated water, degraded soil and urban growth are all threats to biodiversity. Rising ocean temperatures are responsible for the widespread bleaching of coral reefs that support vast populations of marine life and are also important tourist attractions. Ecosystems such as wetlands, forests and lakes are an important part of the natural regime of a river. They are a buffer between river and terrestrial ecosystems and play an important role in storing or attenuating floodwaters. Stratospheric ozone protects plants, marine life, animals and people from solar ultraviolet radiation, which is harmful for life on Earth. Chlorofluorocarbons and other anthropogenic chemicals are responsible for the destruction of ozone. It is necessary, therefore, to ensure that all these Earth systems remain healthy. 

An essential activity of National Meteorological and Hydrological Services is to monitor long-term changes in atmospheric greenhouse gases, ultraviolet radiation, aerosols and ozone, and to assess their consequent effects on people, climate, air and water quality and marine and terrestrial ecosystems. Another important activity is monitoring the atmospheric and water transport of dangerous particles in the wake of a volcanic explosion or an industrial accident.

The Global Atmosphere Watch (GAW) programme provides reliable scientific data and information on aerosols, greenhouse gases, selected reactive gases, ozone, ultraviolet radiation and precipitation chemistry (or atmospheric deposition). The GAW Urban Research Meteorology and Environment (GURME) project works together with the Group of Experts on Scientific Aspects of Marine Environmental Protection (GESAMP) as well as provides Sand and Dust Storms Warning (SDS-WAS). GAW recently initiated the Integrated Global Greenhouse Gas Information System (IG3S) that will use observations of greenhouse gases and inverse modelling techniques to support climate mitigations efforts. This new approach (explained in the animations below) supports of the UN Framework Convention on Climate Change (UNFCCC) and its Paris Agreement by providing an additional way of identifying and estimating urban and national emissions. It seeks to empower policymakers to take more effective action on mitigation.










The Global Atmosphere Watch monitors:

Sand and Dust Storms

Sand and dust storms are common meteorological hazards in arid and semi-arid regions. They are usually caused by thunderstorms – or strong pressure gradients associated with cyclones – which increase wind speed over a wide area. These strong winds lift large amounts of sand and dust from bare, dry soils into the atmosphere, transporting them hundreds to thousands of kilometres away. Some 40% of aerosols in the troposphere (the lowest layer of Earth’s atmosphere) are dust particles from wind erosion.


Ozone is a form of oxygen with molecules carrying three atoms instead of two. Ozone is found both in the troposphere, the lower 10 km of the atmosphere, and in the stratosphere, 10 to 50 km above the ground. Ozone acts as a shield protecting us against harmful ultraviolet radiation from the Sun. 

Greenhouse gases

The Earth has a natural greenhouse effect due to trace amounts of water vapour (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the atmosphere. These gases let the solar radiation reach the Earth’s surface, but they absorb infrared radiation emitted by the Earth and thereby lead to the heating of the surface of the planet. One needs to distinguish between the natural greenhouse effect and the enhanced greenhouse effect. The natural greenhouse effect is caused by the natural amounts of greenhouse gases, and is vital to life.


The impact of aerosols on the atmosphere is widely acknowledged as one of the most significant and uncertain aspects of climate change projections. The observed global warming trend is considerably less than expected from the increase in greenhouse gases, and much of the difference can be explained by aerosol effects. Aerosols impact climate through direct scattering and absorption of incoming solar radiation and trapping of outgoing long-wave radiation as well as through alteration of cloud optical properties and the formation of clouds and precipitation.

Reactive Gases

The reactive gases as a group are very diverse and include surface ozone (O3), carbon monoxide (CO), volatile organic compounds (VOCs), oxidised nitrogen compounds (NOx, NOy), and sulphur dioxide (SO2). All of these compounds play a major role in the chemistry of the atmosphere and as such are heavily involved in inter-relations between atmospheric chemistry and climate, either through control of ozone and the oxidising capacity of the atmosphere, or through the formation of aerosols. The global measurement base for most of them is unsatisfactory, the only exceptions being surface ozone and carbon monoxide. Reactive gases are measured at stations in the Global Atmosphere Watch (GAW) Programme of WMO. 

Solar Ultraviolet Radiation

The ozone layer protects us against harmful solar ultraviolet radiation. Ozone in the stratosphere absorbs some of the Sun’s biologically harmful ultraviolet radiation. Most of the short-wave radiation (so-called UV-B) is absorbed by the ozone layer, whereas long-wave UV (so-called UV-A) passes through the ozone layer and reaches the ground.

The intensity of UV radiation can be expressed by the UV index. WMO has issued, in collaboration with WHO and other organisations, a guide on how to report solar UV radiation to the public. Awareness on how to behave in the sun is important for curbing the rapid increase in skin cancer oberved in many populations. Solar ultraviolet radiation is measured at stations in the Global Atmosphere Watch (GAW) Programme of WMO. 

Atmospheric Deposition

Precipitation chemistry remains a major environmental issue in several parts of the world (e.g., eastern North America, south-east Asia, and Europe) due to concerns over acid deposition, eutrophication, trace metal deposition, ecosystem health, biogeochemical cycling, and global climate change. In more recent years, concerns have expanded from wet deposition alone to include such considerations as air concentrations, dry deposition, and surface-air exchange, particularly as they relate to the atmospheric lifetimes of acidifying species, greenhouse gases, and oxidizing species. In spite of these concerns, little has been done to bring these additional factors to the framework of GAW, primarily due to budgetary limitations. Deposition chemistry observations are performed at a number of sites in the Global Atmosphere Watch (GAW) Programme of WMO.

The Atmospheric Input of Chemicals to the Ocean

The atmospheric input of chemicals to the ocean is closely related to a number of important global change issues. The increasing input of atmospheric anthropogenic nitrogen species to much of the ocean may cause a low level fertilization of the ocean that could result in an increase in marine 'new' productivity of up to ~3% and thus impact carbon drawdown from the atmosphere. However, the increase in nitrogen inputs are also likely to increase the formation of nitrous oxide in the ocean. The increased emission of this powerful greenhouse gas will partially offset the climate forcing impact resulting from the increase in carbon dioxide drawdown produced by N fertilization. Similarly, much of the oceanic iron, which is a limiting nutrient in many areas of the ocean, originates from the atmospheric input of minerals as a result of the long-range transport of mineral dust from continental regions. The increased supply of soluble phosphorus from atmospheric anthropogenic sources (through large-scale use in fertilizers) may also have a significant impact on surface-ocean biogeochemistry, but estimates are highly uncertain. While it is possible that the inputs of sulphur and nitrogen oxides from the atmosphere can add to the rates of ocean acidification occurring due to rising levels of carbon dioxide, there is too little information on these processes to assess the potential impact. These inputs may be particularly critical in heavily trafficked shipping lanes and in ocean regions proximate to highly industrialized land areas. Other atmospheric substances may also have an impact on the ocean, in particular lead, cadmium, and persistent organic pollutants.