A global concern
In New York on 9th May 1992, the UN Framework Convention on Climate Change (UNFCCC) was adopted; to date, the most significant global legal framework for international action to address climate change. By the start of 2005, 186 countries and the European Community had become Parties to the Convention.
The ultimate objective of this Convention is to achieve stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic (man-made) interference with the climate system.
The UNFCCC was strengthened at a meeting of the Conference of the Parties (COP) to the Convention in December 1997, where a legal instrument – named the Kyoto Protocol – was adopted. The Protocol subjects industrialised countries to legally-binding targets to limit their greenhouse gas emissions. These targets add up to a total reduction of 5% in greenhouse gas emissions from 1990 levels, for the five-year period 2008-2012. By November 2004, 127 countries had ratified the protocol; in order to enter into force, the Protocol is required to be ratified by 55 Parties to the Convention, including enough major industrialised Parties to account for at least 55% of the total carbon dioxide emissions by industrialised countries in 1990. This participation target was achieved when Russia ratified the treaty in late 2004 – and the Kyoto protocol became a legally binding agreement.
National commitments under the Kyoto Protocol were not offered lightly. The necessary reductions in greenhouse gas emissions will require changes in the way in which countries generate energy, provide transportation, and manage land use – issues which are all fundamental to future economic development. However, the necessary impetus to meet these challenges is the alarming realisation, based on the best available scientific assessment, that human activities are already affecting the Earth’s climate, and that the emission of greenhouse gases is the primary cause.
The term ‘climate change’ usually refers to changes in the climate system, notably a global warming trend caused by emissions of greenhouse gases that create a ‘human-induced greenhouse effect.’ The most important of these gases is carbon dioxide (CO2), which comes mainly from the burning of fossil fuels such as oil, gasoline, natural gas and coal. Other important greenhouse gases include methane (CH4), nitrous oxide (N2O), ozone (O3), and chlorofluorocarbons (CFCs).
The Intergovernmental Panel on Climate Change (IPCC) projects that greenhouse gas emissions due to fossil fuel burning are almost certain to be the dominant influence on trends in atmospheric greenhouse gas concentrations in the coming century and that with a ‘business as usual’ scenario, the global average surface temperature is expected to rise between 1.4oC and 5.8oC. This rate of warming is most likely without precedent in at least the last 45,000 years. Scientists anticipate profound consequences for sea level (a rise of 9-88cm in the 21st century), precipitation patterns and extreme weather, with consequent impacts on a wide range of ecological functions and human activities essential for individual and societal well-being.
The International Response
The relevant international communities are collaborating on an unprecedented global scale in order to observe, model, and understand the underlying Earth System processes and to implement policy measures to avert the worst effects of the ‘business as usual’ scenario. The main policy initiative is the Kyoto Protocol.
The Kyoto Protocol sets limits on the emission of six main greenhouse gases:
- carbon dioxide (CO2);
- methane (CH4);
- nitrous oxide (N2O);
- hydrofluorocarbons (HFCs);
- perfluorocarbons (PFCs);
- sulphur hexafluoride (SF6).
Some specified activities in the land-use change and forestry sector (namely, afforestation, deforestation and reforestation) that emit or remove carbon dioxide from the atmosphere are also covered. All changes in emissions, and in removals by so-called ‘sinks’ (absorbers), are considered equivalent for accounting purposes.
|Fossil fuel emissions and deforestation play major roles in climate change
||Fluxtowers monitor exchanges of CO2, water vapour and energy between land and atmosphere
The Protocol also establishes three innovative ‘mechanisms’, known as ‘joint implementation’, ‘emissions trading’, and the ‘clean development mechanism’, which are designed to help Parties reduce the costs of meeting their emissions targets by achieving or acquiring emission reductions more cheaply in other countries than at home. The clean development mechanism also aims to assist developing countries to achieve sustainable development by promoting environmentally-friendly investment in their economies from industrialised country governments and businesses.
The role for satellite Earth observations
For adaptation to be effective, governments as well as the private sector need information about past and current climate conditions, their variability and extremes, as well as sound projections of future conditions, not only on a year-over-year basis but for many decades into the future. The World Climate Research Programme (WCRP) was established in 1980 to co-ordinate international research in this domain, in order to determine the extent to which climate can be predicted and the extent of human influence on climate.
The climate system responds to both external forcings and to perturbations of internal processes; it is important that we can track climate change and variability in a way that causes can be determined, trends and variability predicted, and appropriate adaptation and mitigation strategies defined for implementation.
The Global Climate Observing System (GCOS), in consultation with its partners, has developed a plan which identifies the observations of the ‘essential climate variables’ required by the Parties to the United Nations Framework Convention on Climate Change (UNFCCC). These key Earth System parameters are shown in the table on the next page and include measurements of land, sea, ice, ocean, and atmosphere.
The GCOS Implementation Plan notes that this will require terrestrial, oceanic, and atmospheric observations from both in-situ and remote sensing platforms, which then must be transformed into products and information through analysis and integration in both time and space. Global observing systems for climate will comprise instruments at ground stations as well as on ships, buoys, floats, ocean profilers, balloons, samplers, aircraft, and satellites, since no single technology or source can provide all the needed information. Of these, in the future, Earth observation satellites providing global coverage and well calibrated measurements will become ‘the single most important contribution to global observations for climate’.
Since the dominant influence on future greenhouse gas trends is widely agreed to be the emission of CO2 from fossil fuel burning, an improved understanding of the global carbon cycle has become a policy imperative for the forthcoming decades, both globally and for individual countries. The focus of this case study on climate change is therefore on observations of the carbon cycle – a global concern. It should be noted that there are many other, equally significant, aspects of climate monitoring – including those which highlight the results of climate change as well as the causes. These include the water cycle and water resources, and the cryosphere. Both topics are the subject of individual IGOS Themes, and the cryosphere will be the focus for the planned International Polar Year in 2007-2008.
Satellite ocean colour sensors provide important information on the ocean’s role in the carbon cycle
Satellites already deliver global estimates of CO2 concentrations in our atmosphere
The Orbiting Carbon Observatory
||Essential Climate Variables
(over land, sea, and ice)
|Surface: Air temperature, Precipitation, Air pressure, Surface radiation budget, Wind speed and direction, Water vapour.
Upper-air: Earth radiation budget (including solar irradiance), Upper-air temperature (including MSU radiances), Wind speed and direction, Water vapour, Cloud properties.
Composition: Carbon dioxide, Methane, Ozone, Other long-lived greenhouse gases, Aerosol properties.
||Surface: Sea-surface temperature, Sea-surface salinity, Sea level, Sea state, Sea ice, Current, Ocean colour (for biological activity), Carbon dioxide partial pressure.
Sub-surface: Temperature, Salinity, Current, Nutrients, Carbon, Ocean tracers, Phytoplankton.
||River discharge, Water use, Ground water, Lake levels, Snow cover, Glaciers and ice caps, Permafrost and seasonally-frozen ground, Albedo, Land cover (including vegetation type), Fraction of absorbed photosynthetically active radiation (FAPAR), Leaf area index (LAI), Biomass, Fire disturbance.
Observing the Carbon Cycle
The global carbon cycle connects the three major components of the earth system: the atmosphere, oceans, and land. In each domain, large pools of readily exchangeable carbon are stored in various compartments (‘pools’ or ‘sinks’ and ‘sources’). Large amounts of carbon (‘fluxes’) are transferred between the pools over various time periods, from daily to annual and much longer. Although some of the fluxes are very large, the net change over a given time period need not be. For many centuries prior to the industrial revolution, the carbon pools were more or less in equilibrium, and the net transfer was close to zero for the planet as a whole.
The major changes have occurred following the development of agriculture and industry, with the accelerated transfer from the geological (fossil fuels) and terrestrial pools to the atmosphere. Because of the connections among pools, the increased atmospheric carbon concentration affects the other connected pools in oceans and on land. The processes governing the fluxes between the pools take place at various rates, from daily to centennial and longer.
The UNFCCC and the Kyoto Protocol represent the first attempt by mankind, acting collaboratively across the world, to manage, at least partly, a global element cycle of the Earth System – the global carbon cycle. The Kyoto Protocol recognizes the role of terrestrial systems as carbon sinks and sources, and it provides a basis for developing future ‘emission trading arrangements’ that involve forests and potentially other ecosystems. Understanding of the pathways through which the anthropogenic CO2 is absorbed from the atmosphere and into ecosystems (thus offsetting a portion of the anthropogenic emissions) is fragmentary and incomplete. These factors and dependencies make the quantification and study of the carbon cycle very challenging to model, observe, and predict.
This challenge requires the support of a coordinated set of international activities – scientific research (including modelling), observation, and assessment. Assessment is perhaps the most advanced, with the pioneering work of the IPCC providing the scientific assessment required for the policy action. In terms of scientific research, the International Geosphere-Biosphere Programme (IGBP) has recently joined forces with the International Human Dimensions Programme on Global Environmental Change (IHDP) and the World Climate Research Programme (WCRP) to build an international framework for integrated research on the carbon cycle (called the Global Carbon Project).
Observations of the global carbon cycle, including the land, oceans, and atmosphere compartments of the cycle, are being co-ordinated within the IGOS Partnership, by the Integrated Global Carbon Observations (IGCO) Theme (see annex B for more on IGOS Themes).
The IGCO Theme will build on a number of carbon cycle observation initiatives at the Earth’s surface that are underway or planned, including:
- global networks of atmospheric greenhouse gas measurement stations (such as GLOBALVIEW CO2)and the WMO World Data Center for Greenhouse Gases (Tokyo);
- global networks of measurement tower sites that monitor the exchanges of CO2, water vapour, and energy between terrestrial ecosystems and atmosphere; e.g. the FLUXNET system has over 260 tower sites operating on a long-term and continuous basis;
- measurement ships and arrays of buoys, including the TAO array in the equatorial Pacific.
Data from Earth observation satellites provide the only global, synoptic view of key measures of the carbon cycle and form an essential and central part of the envisaged integrated observation strategy planned within IGCO.
The major applications include:
- global mapping of land cover use, land cover change, and vegetation cover characteristics that are important to full carbon accounting – using sensors such as AATSR, AVHRR, Landsat TM/ETM/ETM+ and MODIS and carried out through the Global Observation of Forest Cover and Land Cover (GOFC-GOLD) project initiated by CEOS;
- seasonal growth characteristics, including important parameters such as fraction of absorbed photosynthetically active radiation and Leaf Area Index (LAI) are generated on a global scale (e.g. by AVHRR, MODIS, MERIS, and SPOT VEGETATION);
- fire detection and burn scar mapping: in many regions of the world, fires are the most significant disturbance of vegetation and drive large inter-annual variations in carbon emissions from ecosystems; large fires in forests and grasslands are detected and mapped from space using thermal and optical sensors (radar sensors also show promise for burn mapping);
- combinations of satellite measurements of parameters such as ocean chlorophyll, dissolved organic matter, and pigment composition and physical measurements from satellite of ocean waves, winds, and temperature are used to derive three main contributions for the study of ocean carbon:
- quantifying upper ocean biomass and ocean primary productivity;
- providing a synoptic link between the ocean ecosystem and physical processes;
- quantifying air-sea CO2 flux.
Another key role for satellites relates to monitoring of the Kyoto Protocol’s ‘carbon trading’ mechanisms, especially the Clean Development Mechanism (CDM). Existing archives of high resolution satellite imagery (e.g. from Landsat and SPOT) provide the capacity for determining eligibility of CDM reforestation projects by confirming compliance with the Kyoto Protocol’s rule that any proposed forestry project must be able to prove that the site “did not contain forest on 31st December 1989”. The same technologies can also provide the geographically explicit land use data for national inventory reports concerning carbon sinks, and provide important information in trade-offs and conflicts between mitigation/adaptation carbon initiatives involving land use, land-use change and forestry, and long-term sustainable development strategies.
Within the next few years, scientists are hopeful of an extraordinary and unique revolution in global monitoring of atmospheric CO2 concentrations, sources, and sinks – with the benefit of space-based high-precision measurements of column-integrated CO2 molecular density with global, frequent coverage.
The precision requirements for such measurements are extremely taxing – requiring concentrations as low as 0.3% (1 ppm) to be achieved in order to accurately characterise carbon sources and sinks. But a number of new missions, specifically dedicated to this challenge, are being planned to provide the first such data. NASA will launch the Orbiting Carbon Observatory (OCO) in 2007. This 2-year mission is seen as a pathfinder for future long-term CO2 monitoring missions – and will use measurements of reflected sunlight in the short-wave infrared to provide global, high-precision measurements of the column-integrated CO2 mixing ratio. A second satellite, launched by JAXA, also aims to provide information on CO2. GOSAT (Greenhouse gas Observing Satellite) will be operational from 2008.
In the interim, scientists continue to make advances in the retrieval of CO2 information from atmospheric sounding instruments on the NOAA polar orbiting satellites, and from atmospheric chemistry instruments such as SCIAMACHY on ENVISAT.
Part of the future challenge will be to support a monitoring system that is suitably accurate, robust, and sustained to effectively support the implementation and policing of treaties such as the Kyoto Protocol – since cold, hard evidence may on occasion be required to ensure their enforcement. For Earth observation satellites this will require a move from research to operational status to support international policy frameworks.
The necessary co-ordination of the relevant satellite missions will be undertaken by the Committee on Earth Observation Satellites (CEOS) including through their participation in the IGCO Theme. Part III of this document summarises the various plans of the world’s space agencies.
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