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.

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. Moreover, while a fragile environment becomes more vulnerable to natural disasters, the natural disasters also degrade the environment in a pernicious circle of causes and effects.

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.

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 which impact the environment.

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, which support vast populations of marine life and are also an important tourist attraction. El Niño events are particularly critical.

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. It is necessary therefore to ensure they remain healthy. Structural flood-management interventions cannot fully control extreme flood events beyond the design standard and may have adverse impacts on the natural environment.

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

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. WMO observational data are 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.

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/NASAOzone 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. 

However, ozone at ground level is a pollutant. It can trigger breathing difficulties and damage plants and crops. It is one of the principal ingredients of smog. Therefore, whether ozone is good or bad depends on its altitude in the atmosphere.

The ozone layer has been under attack from chlorine (chlorofluorocarbon, CFC) and bromine (halon) compounds abundantly used in the past in products such as aerosol spray can propellants, refrigerants, pesticides, solvents and fire extinguishers. When these substances reach the stratosphere, the ultraviolet radiation from the Sun causes them to break apart and release chlorine and bromine atoms, which react with ozone. These reactions trigger chemical cycles of ozone destruction that deplete the protective ozone layer.

It has been calculated that just a single chlorine atom can obliterate more than 1 000 ozone molecules. Bromine atoms however, are some 50 times more efficient at destroying ozone. Fortunately, the atmospheric abundance of bromine containing compounds is much lower than that of CFCs.

Countries have been adhering to international agreements currently in place, such as the Vienna Convention and the Montreal Protocol and its Amendments. After peaking around year 2000, the total amount of chlorine and bromine containing compounds in the stratosphere is now slowly going down, but it will probably take 50 years before the amount of chlorine and bromine is back at where it was before 1980 (roughly when the first Antarctic ozone hole was observed).

Recent scientific reports show that ozone reduction has stopped in most regions of the globe, but it could take years before ozone starts to increase again. The Antarctic ozone hole, which appears every year in the September to November time period has not become worse in the last 5-10 years, but there is also no sign of a significant improvement yet.

Greenhouse Gases

Greenhouse Emissions / WMOThe 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. In the absence of the natural greenhouse effect the surface of the Earth would be approximately 33 degrees Celsius cooler. The enhanced greenhouse effect refers to the additional radiative forcing resulting from increased concentrations of greenhouse gases induced by human activities. The main greenhouse gases whose concentrations are rising are carbon dioxide, methane, nitrous oxide, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and ozone in the lower atmosphere. The Global Atmosphere Watch (GAW) Programme of WMO observes, analyses and publishes greenhouse gas data collected by fifty countries around the globe from the High Arctic to the South Pole. 


Aerosol Pollution / WMOThe 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. 

There is growing concern for the impact of aerosols on human health and interest by many sectors such as weather prediction, the green energy industry (regarding their influence on solar energy reaching the ground) and the commercial aircraft industry (regarding the impact of volcanic ash and dust storms on operations and aircraft).

Regional problems include potential impacts on human health and mortality and environmental impact such as visibility impairment. Major sources of aerosols include urban/industrial emissions, smoke from biomass burning, secondary formation from gaseous aerosol precursors, sea salt and dust. Outstanding problems include determining the natural sources of aerosols, and the organic fraction.

Various aerosol parameters, such as aerosol optical depth, are measured at stations in the Global Atmosphere Watch (GAW) Programme of WMO. 

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.  

Integrated Global Greenhouse Gas Information System (IG3IS)

WMO and its partners in the Global Atmosphere Watch (GAW) are developing a new approach to tracking greenhouse gas emissions in support 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, this approach seeks to empower policymakers to take more effective action on mitigation.

WMO has produced three animations to explain how this works. The animation on “The carbon cycle” provides basic background about rising atmospheric levels of greenhouse gases. “Measuring national emissions” and “Monitoring the atmosphere to reduce urban greenhouse gas emissions” describe how high-resolution monitoring of the atmosphere combined with modelling can now be used to more accurately estimate greenhouse gas emissions in order to support decision-making. The animations can be viewed below and on the  WMO YouTube Channel. High-resolution versions can be requested from cpa@wmo.int.

1 - “The carbon cycle” - Arabic / Chinese / English / French / Russian / Spanish / Excerpt for TV
2 - “Measuring national emissions” - Arabic / Chinese / English / French / Russian / Spanish / Excerpt for TV
3 - “Monitoring the atmosphere to reduce urban greenhouse gas emissions” - Arabic / Chinese / English / French / Russian / Spanish / Excerpt for TV

Support to Multilateral Environmental Agreements (MEAs)

WMO Members operate the WMO Integrated Global Observing System, which includes complex networks in space, the atmosphere, on land and at sea. These networks provide the data and derived value-added information that are the foundation of our knowledge of the environment. As the recognized, comprehensive source of unique global systematic observations of a wide variety of geophysical phenomena, datasets and long-term archives, WMO has the scientific and technical expertise required to support policy advice on various critical environmental issues. In particular, WMO reports on the state of the global climate system and the state of the atmospheric environment. The Organization also produces various scientific assessments, statements, bulletins and other advisories on the state of climate and environment.

In addition, WMO hosts and co-sponsors the Secretariats of the Intergovernmental Panel on Climate Change (IPCC) and the Global Climate Observing System (GCOS). The Organization also provides direct support to the United Nations Framework Convention on Climate Change (UNFCCC) and organizes the work of the Ozone Research Managers of the Vienna Convention on Protection of the Ozone Layer, which is supported by the Ozone Secretariat, hosted by the United Nations Environment Programme (UNEP).

WMO participates in the work of subsidiary bodies on scientific and technical advice with the following organizations:

United Nations Environment Programme (UNEP) Convention for the Protection of Marine Environment and the Coastal Region of the Mediterranean.