| Overview | Details | Data Sources | Links | References |
| Atmosphere | • | Ocean | • | Terrestrial | • | Satellite |
Observations of climate variables at the surface of the Earth are vitally important as they characterise the climate of the atmospheric layer in which we live. Nevertheless, measurements are also required in the upper atmosphere because of its influence on weather and climate evolution at the surface. The concentrations of different components such as Carbon Dioxide and other greenhouse gasses as well as small particles known as aerosols are also measured because of their significant impact on climate.
Some of the key variables that need to be measured in the atmosphere are shown in the table.
| Surface | Upper Air | Composition |
| Temperature | Temperature | Carbon dioxide |
| Air pressure | Wind speed/direction | Methane & other greenhouse gases |
| Wind speed/direction | Water Vapour | Ozone |
| Precipitation | Cloud properties | Aerosol properties |
| Water vapour | Earth radiation budget | |
| Surface radiation budget |
Surface
A range of instruments such as thermometers (temperature), barometers (pressure), anemometers (wind), rain gauges, hygrometers (humidity) and radiation meters are housed in a weather station to collect surface variables on land.
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| Climatological weather station at Newport Co. Galway. |
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Click here to view a map of weather stations in the Republic of Ireland. |
Upper Air
The measurement of climate variables in the upper atmosphere is generally carried out using a radiosonde. This device consists of a box housing a number of weather sensing instruments and a radio transmitter. The box is launched into the atmosphere attached to a helium inflated balloon. Measurements are made and transmitted constantly while the balloon ascends to approximately 30 km, where it bursts due to the low atmospheric pressure, and the box falls back to the ground by means of a small parachute and can be recovered. Two radiosonde stations are located in Ireland one at Valentia Island Observatory in Co. Kerry and the other at Castor Bay in Co. Down where four sets of radiosonde measurements are made every day.
Composition
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| The atmospheric research station at Mace Head Co. Galway is part of the Global Atmospheric Watch network. Photo: NUI, Galway |
Oceanic Measurements
The oceans cover over 70% of the Earth's surface. Therefore, they have a significant impact on climate. The essential variables required to understand and predict oceanic influence on climate are listed in the table. Variability in the global ocean affects coastal regions; without sufficient knowledge of the ocean it is difficult to predict the effects of sea level rise or changes in wave climates at the regional or national level. The current infrastructure for oceanic climate observations is much more sparse than the atmospheric one, especially in the southern hemisphere. Nevertheless, progress on expanding the observation network is being made through programmes such as the Global Climate Observing System and the Global Ocean Observing System.
| Surface | Sub-surface |
| Sea surface temperature | Temperature |
| Sea surface salinity | Salinity |
| Sea level | Current |
| Sea ice | Nutrients |
| Sea state (variables relating to height, direction, length and time period of waves.) | Earth radiation budget |
| Ocean colour | Carbon |
| CO2 partial pressure | Phytoplankton |
Surface
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| Fixed buoys located around Ireland make a range of atmospheric and sea measurements. |
There are over 1250 surface drifting buoys deployed in the world's oceans by nations participating in the Global Oceans Observing System. These drifters consist of a floating buoy on which the instrumentation is mounted and a "drogue" or sea- anchor which is tethered to the buoy at a depth of approximately 15m. A transmitter relays the measurements to a telecommunications satellite which then forwards the information to various data centres. The drifters are carried by the surface water flow, therefore they are ideal for the measurement of ocean surface current direction and speed. Many drifters also measure surface and subsurface temperature, salinity, wind speed, air pressure and the quantity of chlorophyll in the water (ocean colour).
Voluntary observing ships also make a range of surface measurements. These ships are generally commercial transport vessels which sign up with national weather forecasting centres to provide regular observations. A suite of meteorological instruments is supplied to the participating ships and these are used to make regular measurements either manually or automatically. There are an estimated 5400 ships worldwide which currently participate in the programme. Although there are a significant number of measurements from the world's main shipping routes, there are large areas of ocean, mainly situated in the southern hemisphere, from which there are few measurements.
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Click here to view a map of the marine data buoys around Ireland. |
Sub-surface
Sub-surface ocean measurements need to take place up to the full depth of many thousand metres in the deep oceans off the continental shelves. Deep ocean currents, which form part of the thermohaline circulation system, are responsible for transporting cold and warm water around the Earth and therefore have a key role in determining the state of the climate. The recording of many sub-surface variables does not have as long a history as surface measurements and it is only recently that a comprehensive global observing system has been put in place. The main devices used to make sub-surface measurements are attached to moored buoys and sub-surface drifters while some are deployed from ships.
A network of about 100 moored buoys , the majority of which are located in tropical oceans,measures temperature, salinity, pressure and currents at depths of up to 500 m. In general these buoys have a float at the ocean surface with attached instruments for weather measurements. The measurement devices are mounted underwater at a range of intervals on a wired rope which is attached to the float. The buoy is anchored to the sea bed by a large weight which can be up to 4000kg. Depth measurements of temperature, pressure and salinity are logged by a data recorder mounted on the buoy and then beamed by an antenna via a satellite to the appropriate data centre. On some moorings instrumentation is attached which measures oceanic variables down to the ocean floor at 4000m and beyond.
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| An Argo float being readied for deployment off the west coast of Ireland. |
Since the year 2000 over 2700 drifters known as Argo floats have been released in the oceans. These floats measure temperature, salinity and currents at depths of up to 2000m. Once a float is activated it begins to descend to a depth of approximately 2000 m at 6m/s. It then floats at this depth for about 9 days after which it begins its re-ascent measuring temperature and salinity as it goes. It then remains at the surface from 6 to 12 hours while transmitting the collected data via satellite to the relevant data centre. The Marine Institute deployed four floats in 2008 and intends to deploy a further eight before 2010.
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| This Multinet plankton sampler holds five nets which can be opened and closed sequentially, thus collecting plankton samples from discrete water depths. |
Ships of opportunity, research vessels and navy ships also carry instruments for sub-surface measurements. The most developed programme measures water temperature at depths of up to 1000m using an Expandable BathyThermograph (XBT). As the temperature probe drops through the water, it sends back measurements of temperature at approximately one-meter intervals on a thin connecting wire to a data acquisition system on board the ship. The International XBT programme now concentrates on making line or transect measurements, as the Argo floats programme expands to make measurements in more dispersed locations. It is hoped to have 41 transects frequently repeated around the Globe.
Terrestrial Measurements
Given that the world's human population lives on land, there is a real need to monitor climate and understand how its changes can affect terrestrial environments. The key climate variables that should be monitored are listed in the table below and can be considered under three headings: hydrology; snow and ice and vegetation.
| Hydrology | Snow & Ice | Vegetation |
| Water use | Snow cover | Land cover |
| River discharge | Glaciers & ice caps | Fraction of absorbed photosynthetically active radiation |
| Lake levels | Permafrost | Leaf area index |
| Ground water | Biomass | |
| Fire disturbance | ||
| Albedo |
Hydrology
Approximately 20% of the world's croplands are irrigated accounting for over 70% of all freshwater consumption worldwide and as food needs grow it is expected that more freshwater will be used in irrigation. Many countries document the amount and areas of land under irrigation. However, there is no standard methodology for how this is done. Mapping and monitoring the acreage of land irrigated and the quantities of water used does not constitute the monitoring of climate change itself. It does, however, provide information to help understand how lake levels, river volumes and land cover changes are influenced by climate change as distinct from land use and water use changes.
In Ireland 10% of freshwater usage is in agriculture. Although at the moment there is limited use of irrigation, this could change in the future as drier and warmer summers are predicted, especially in southern and eastern areas.
Ground water is held in aquifers and permeable zones below the water table. It can come to the surface in springs and may also form the source of rivers. Groundwater levels are affected by rainfall amounts, river runoff and the quantities extracted. In the Republic of Ireland over 20% of drinking water comes from groundwater sources. Overexploitation of reserves can cause subsidence and reduced water quality as the volume of water decreases. Saltwater infiltration can be an issue in coastal areas. Water quality has been monitored by the Environmental Protection Agency since 1995, while groundwater protection schemes are administered by the Geological Survey of Ireland in a number of counties. In Northern Ireland responsibility for the management and protection of groundwater rests with the Environment and Heritage Service.
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| A staff gauge is used to measure water levels on rivers and lakes. |
Snow and Ice
About one-third of the Earth's land surface is seasonally covered in snow. It has a key role to play in water runoff, soil moisture and vegetation type and growth. Snowfall and snow cover are key indicators of climate change.
Reductions in the size of mountain glaciers and ice caps provide some of the clearest evidence of climate change and their monitoring is therefore fundamental to provide early warning. Glacial melt waters impact on the terrestrial water cycle, increasing river and lake water volumes in spring and early summer. Many regions depend on such melt waters for a range of purposes including agriculture and drinking water.
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| Glaciers in the Svalbard islands in the Arctic have been retreating over the last century. |
When ground material remains frozen for a long period of time it is known as permafrost. Changes over time of permafrost temperature and depth of seasonal freezing/thawing are reliable indicators of climate change in high latitudes and mountain regions. Warming may result in a reduction in the extent of permafrost which can influence terrain stability as well as affecting summer water availability.
Although in-situ measurement systems are in place to gather data regarding these variables, satellites are also important for providing data on the extent of ice sheets, glaciers and snow cover.
Vegetation
Land cover and its change influence climate by modifying water and energy exchanges with the atmosphere. In addition, when land cover consists of actively growing vegetation it acts as an absorber of Carbon Dioxide, however when areas are converted to urban use or deforestation occurs, this ability to absorb Carbon Dioxide is reduced or eliminated. Land cover distribution is partly determined by regional climate, so changes in cover may indicate climate change. Land cover mapping is now generally carried out by interpretation and classification of images collected by spacecraft or aircraft.
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Click here to view a land cover map of Ireland. |
Biomass or vegetative material plays an important role in the climate system as via photosynthesis it withdraws CO2 from the atmosphere and stores it. When biomass is burned as happens in vegetation fires, CO2, other GHG and aerosols are emitted to the atmosphere.
Leaf Area Index is a measure of the amount of leaf material in an ecosystem and has an important role to play in photosynthesis, respiration and rain interception. A related measure called the Fraction of Photosynthetically Absorbed Radiation (FaPAR), measures photosynthetic activity and indicates the presence and productivity of vegetation, which in turn is related to the amount of carbon stored in the vegetation. Another variable influenced by the amount of vegetation cover is surface albedo. This is a measure of the amount of the sun's radiation that is reflected by the Earth's surface. The higher the albedo the more heat is reflected. Reduction of snow cover, increases in artificial surfaces and the reduction of forested areas all tend to reduce albedo and therefore leads to more heat being trapped at the Earth's surface.
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| Vegetation fires are used as part of grassland management in Kakadu National Park, Australia. |
Satellite Observations
Earth observing satellites also play an important role in providing data from the atmosphere, oceans and land surface for climate studies. They give global coverage, collect data on a regular, repeatable basis and are particularly important for the gathering of data in inaccessible areas and regions poorly monitored on the ground. A large number of satellites have been launched by various national and international agencies (e.g NASA, ESA) and their important role in climate monitoring has been underpinned by international agreements such as the United Nations Framework Convention on Climate Change.