The rationale for the Global Atmosphere Watch (as formulated in the GAW Strategic Plan: 2008-2015) is the need to understand and control the increasing influence of human activity on the global atmosphere. Among the grand challenges are:
Many of these have socio-economic consequences affecting weather, climate, human and ecosystem health, water supply and quality, and agricultural production.
The mission of GAW, taking into account the Integrated Global Atmospheric Chemistry Observations (IGACO) strategy, is to
GAW also fulfils a mandate from WMO Members by responding to the needs and clearly linking to the plans of national, regional, and international observing projects, programmes, systems and strategies, e.g.
Monitoring of trace atmospheric constituents was originally driven by scientific curiosity. It was not long before questions were raised as to what extent the observed increases in certain trace chemicals are connected to human activities and what the consequences would be for humanity if it should continue unabated.
WMO provided a substantial contribution in converting scientifically driven events into regular monitoring. It formally embarked on a programme of atmospheric chemistry and meteorological aspects of air pollution during the 1950s. Need for adequate information on the chemical composition of the atmosphere and on the consequences of the anthropogenic impact can be estimated on a global scale only if all measurements of the component of interest are expressed in the same units or on the same scale, i.e. the measurements performed by different countries are comparable.
The first step has been made by WMO in the international coordination of chemical measurements during the 1957 International Geophysical Year. WMO has taken a responsibility for development of standard procedures for uniform ozone observations and establishing the Global Ozone Observing System (GO3OS). It presented a coordinated Dobson and later Breuer spectrophotometer network to measure total atmospheric ozone. The system included ozonesondes intercomparisons, preparation of the Ozone Bulletins and Ozone Assessments and support of Ozone data center in Canada.
In the late 1960s, the Background Air Pollution Monitoring Network (BAPMoN) was established. It focused on precipitation chemistry, aerosol and carbon dioxide measurements, included regional and background stations and had WMO World data center established in USA
During the 1970s three important atmospheric issues were addressed: (a) the threat of CFC's to the ozone layer, (b) acidification of lakes and forests in large parts of North America and Europe, caused principally by the conversion of sulphur dioxide into sulphuric acid by precipitation processes in the atmosphere and, (c) potential global warming caused by the build-up of greenhouse gases in the atmosphere. Each of these issues is now the subject of international treaties or conventions. The initial development of these agreements and the subsequent assessments of the mitigation measures they contain, rely heavily on the information derived from WMO's atmospheric composition monitoring programme.In 1989 two observing networks BAPMoN and GO3OS were consolidated into the current WMO Global Atmosphere Watch (GAW) programme
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