A new satellite was launched at the end of October 2011 to monitor weather and climate from space. The first measurements were made in November 2011. By comparing the heat output from the Earth with the energy absorbed from the sun, scientists expect to be able to measure directly the extent to which the future global climate will change, extending the record that began in 1997.
The New Satellite
The NPP satellite has 5 instruments on board, supplied by the National Oceanic and Atmospheric Administration (NOAA).
The main image shows a scan from the Visible Infrared Imager Radiometer Suite (VIIRS). Its role is to provide data in the visible and infrared. The instrument will be critical to monitor how the Earth’s surface is changing for assistance in weather forecasting and climate monitoring.
The satellite is a “polar orbiter”, that is, its orbit goes close to the poles with an orbital period of 102 minutes. This enables the satellite to scan the whole Earth in 14 orbits per day. Although not every part of the Earth can be viewed simultaneously, daily measurements are sufficient to be able to produce long-term climate means. By comparison, geostationary satellites orbit around the Equator and have an orbital period of 24 hours. They scan the same part of the surface continuously, but are able to observe only a small part of the Earth.
Other Instruments on NPP
The other instruments provide maps and profiles of ozone in the atmosphere, and 2 instruments provide the atmospheric temperature variation with height. A 4th instrument, Clouds and Earth’s Radiant Energy System (CERES) will monitor the energy entering and leaving the Earth’s atmosphere.
CERES instruments have previously been launched on earlier satellites, starting in 1997. The latest instrument will continue the record and allow any trends to be determined.
Earth’s Equilibrium Climate
Scientists refer to radiation from the sun, not to be confused with nuclear radiation, as consisting of all the energy in the electromagnetic spectrum from the ultraviolet to the infra-red. The Earth emits radiation in the infra-red. The total solar radiation can be measured from space and compared with the energy emitted from the Earth. If the two are the same, then the global climate would be in balance. If the solar energy exceeded the Earth’s emitted heat, then the Earth would tend to warm.
Energy from the Sun and Earth
The average total energy from the sun is 1361.5 W, measured in overhead sun over 1 square metre of the Earth’s surface. The area of the sun’s beam that is intercepted by the Earth is \pi r^2, where r is the Earth radius. This energy is spread over the total surface area of the Earth of 4 \pi r^2, i.e. 4 times as much. So, the average energy absorbed by the Earth is 1361.5/4 = 340.4 W/m^2.
Measurements suggest that the energy emitted by the Earth is out of balance by 0.85 W/m^2, implying with the new measurements that the Earth emits 339.5 W/m^2.
The Figure shows slight differences from the currently understood values. This relates to prior instruments which read high due to errors that are now better understood (Kopp and Lean, 2011).
Although there is a small difference, between incoming and outgoing radiation, the suggestion is that the climate is being warmed by 0.85 W/m2. The new measurements will help to provide more detailed analysis which is expected to confirm current understanding.
Changes in Clouds
It has been suggested that the climate changes that have ben observed are natural fluctuations due to changes in clouds, amongst other (unidentified) factors. The advantage of the CERES instrument is that it will be able to monitor any changes in clouds directly. In principle, increases in cloud amount could reflect more sunlight to space, and ensure that the climate stabilizes. If this were the case, then the energy from the sun and Earth would be found to be in balance, as in the figure.
If, as seems likely, the new instruments confirm previous results, then the data would imply that the global climate would have to warm before equilibrium climate is reached. This is in accordance with theoretical expectations from, for example, reports of the Intergovernmental Panel on Climate Change.
Kopp, G. and Lean, J.L. (2011), A New, Lower Value of Total Solar Irradiance: Evidence and Climate Significance, Geophys. Res. Letters Frontier article, 38, L01706, doi:10.1029/2010GL045777. Accessed 23 November, 2011.