• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

RealClimate

Climate science from climate scientists...

  • Start here
  • Model-Observation Comparisons
  • Miscellaneous Climate Graphics
  • Surface temperature graphics
You are here: Home / Archives for group

group

Forcings

28 Nov 2004 by group

Translations: (Français)

Forcings in the climate sense are external boundary conditions or inputs to a climate model. Obviously changes to the sun’s radiation are external, and so that is always a forcing. The same is true for changes to the Earth’s orbit (“Milankovitch cycles”). Things get a little more ambigous as you get closer to the surface. In models that do not contain a carbon cycle (and that is most of them), the level of CO2 is set externally, and so that can be considered a forcing too. However, in models that contain a carbon cycle, changes in CO2 concentrations will occur as a function of the climate itself and in changes in emissions from industrial activity. In that case, CO2 levels will be a feedback, and not a forcing. Almost all of the elements that make up the atmosphere can be considered feedbacks on some timescale, and so defining the forcing is really a function of what feedbacks you allow in the model and for what purpose you are using it. A good discussion of recent forcings can be found in Hansen et al (2002) and in Schmidt et al (2004).

Filed Under: Glossary

General Circulation Model (“GCM”)

28 Nov 2004 by group

Translations: (Français)

Typically refers to a three-dimensional model of the global atmosphere used in climate modeling (often erroneously called “Global Climate Model”). This term often requires additional qualification (e.g., as to whether or not the atmosphere is fully coupled to an ocean–see ‘Atmosphere-Ocean General Circulation Model’).

The length scales that are resolved in these models is typically on the order of 100s of kilometers (i.e. features that size or smaller are not directly resolved). The timestep for the models (how often the fields are updated) is usually 20 minutes to an hour. Thus in any day there would be 24 to 72 loops of the main calculations.

The basic variables are the temperature, humidity, liquid/ice water content and atmospheric mass. The physics usually consists of advection, radiation calculations, surface fluxes (latent, sensible heat etc.), convection, turbulence and clouds. More elaborate Earth System models often contain tracers related to atmospheric chemistry and aerosols (including dust and sea salt).

Filed Under: Glossary

Greenhouse Gases (“GHGs”)

28 Nov 2004 by group

Greenhouse Gases (GHGs) refer to any atmospheric gases that absorb long wave radiation (emitted from the surface), thereby causing the planet’s surface to be warmer than it would be otherwise. These gases include water vapour, CO2, CH4, N2O, many CFCs (chloro-fluro-carbons). Ozone (O3) as well as being a shortwave absorber (in the ultra-violet range) also has a small longwave greenhouse effect. Other components of the atmosphere also absorb longwave radition (specifically aerosols and clouds) and hence have a greenhouse effect while not being gases themselves.
Oxygen (O2) and nitrogen (N2) while being the dominant gases in the atmosphere do not have significant absorption lines in the relevant longwave range and so are not greenhouse gases.

Filed Under: Glossary

Hockey Stick

28 Nov 2004 by group

Instrumental data describing large-scale surface temperature changes are only available for roughly the past 150 years. Estimates of surface temperature changes further back in time must therefore make use of the few long available instrumental records and natural archives or ‘climate proxy’ indicators, such as tree rings, corals, ice cores and lake sediments, and historical documents, to reconstruct patterns of past surface temperature change. Due to the paucity of data in the Southern Hemisphere, recent studies have emphasized the reconstruction of Northern Hemisphere (NH) mean, rather than global mean temperatures over roughly the past 1000 years.

[Read more…] about Hockey Stick

Filed Under: Glossary

Little Ice Age (“LIA”)

28 Nov 2004 by group

Translations: (Français)

Term originally introduced in the late 1930s by Matthes (1939) to describe a broad interval of the late Holocene during which significant glacial advances were observed. In the climatological literature the LIA has now come to be used to characterize a more recent, shorter recent interval from around A.D. 1300 to 1450 until A.D. 1850 to 1900 during which regional evidence in Europe and elsewhere suggest generally cold conditions. Variations in the literature abound with regard to the precise definition, and the term is often used by paleoclimatologists and glaciologists without formal dates attached. The attribution of the term at regional scales is complicated by significant regional variations in temperature changes due to the the influence of modes of climate variability such as the North Atlantic Oscillation and the El Nino/Southern Oscillation. Indeed, the utility of the term in describing past climate changes at regional [Read more…] about Little Ice Age (“LIA”)

Filed Under: Glossary

Medieval Warm Period (“MWP”)

28 Nov 2004 by group

Period of relative warmth in some regions of the Northern Hemisphere in comparison with the subsequent several centuries. Also referred to as the Medieval Warm Epoch (MWE). As with the ‘Little Ice Age’ (LIA), no well-defined precise date range exists. The dates A.D. 900–1300 cover most ranges generally used in the literature. Origin is difficult to track down, but it is believed to have been first used in the 1960s (probably by Lamb in 1965). As with the LIA, the attribution of the term at regional scales is complicated by significant regional variations in temperature changes, and the utility of the term in describing regional climate changes in past centuries has been questioned in the literature. As with the LIA, numerous myths can still be found in the literature with regard to the details of this climate period. These include the citation of the cultivation of vines in Medieval England, and the [Read more…] about Medieval Warm Period (“MWP”)

Filed Under: Glossary

Microwave Sounding Unit (“MSU”)

28 Nov 2004 by group

A Microwave Sounding Unit (“MSU”) is a device that has been installed on polar orbiting satellites to measure, from space, the intensity of microwave radiation emitted by earth’s atmosphere. Different “channels” of the MSU measure different frequencies of radiation which can, in turn, be related to temperature averages of the atmosphere over different vertical regions. Channel 2 measurements provide a vertically-weighted temperature estimate that emphasizes the mid-troposphere (with small contributions from the stratosphere), while Channel 4 largely measures temperatures in the lower stratosphere. Information from MSUs have been used to generate the “MSU Temperature Record“. More information on MSU can be found here.

Filed Under: Glossary

Mid-Holocene Climatic Optimum

28 Nov 2004 by group

This is a somewhat outdated term used to refer to a sub-interval of the Holocene period from 5000-7000 years ago during which it was once thought that the earth was warmer than today. We now know that conditions at this time were probably warmer than today, but only in summer and only in the extratropics of the Northern Hemisphere. This summer warming appears to have been due to astronomical factors that favoured warmer Northern summers, but colder Northern winters and colder tropics, than today (see Hewitt and Mitchell, 1998; Ganopolski et al, 1998). The best available evidence from recent peer-reviewed studies suggests that annual, global mean warmth was probably similar to pre-20th century warmth, but less than late 20th century warmth, at this time (see Kitoh and Murakami, 2002).

[Read more…] about Mid-Holocene Climatic Optimum

Filed Under: Glossary

MSU Temperature Record

28 Nov 2004 by group

Combinations of different channels of individual Microwave Sounding Unit (“MSU”) measurements have been used to generate a record of estimated atmospheric temperature change back to 1979, the “MSU Temperature Record”. The complex vertical weighting functions relating the the various channels of the MSU to atmospheric temperatures complicate the interpretation of the MSU data. Moreover, while MSU measurements are available back to 1979, a single, continuous long record does not exist. Rather, measurements from different satellites have been combined to yield a single long record, further complicating the interpretation of the MSU record. Direct comparisons of the MSU Temperature Record with the surface temperature record are therefore difficult. More information on the MSU Temperature Record can be found here.

Filed Under: Glossary

North Atlantic Oscillation (“NAO”)

28 Nov 2004 by group

Translations: (Français)

Measure of the strength of the westerlies across the North Atlantic. Originally defined by Sir Gilbert Walker in 1932 as the difference in pressure between Ponta Delgada on the Azores and Stykkisholmur in Iceland. More information on the NAO can be found here. See also Arctic Oscillation (“AO”).

Filed Under: Glossary

  • « Go to Previous Page
  • Page 1
  • Interim pages omitted …
  • Page 51
  • Page 52
  • Page 53
  • Page 54
  • Go to Next Page »

Primary Sidebar

Search

Search for:

Email Notification

get new posts sent to you automatically (free)
Loading

Recent Posts

  • High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Unforced variations: Oct 2025
  • “But you said the ice was going to disappear in 10 years!”
  • Time and Tide Gauges wait for no Voortman
  • Lil’ NAS Express
  • DOE CWG Report “Moot”?

Our Books

Book covers
This list of books since 2005 (in reverse chronological order) that we have been involved in, accompanied by the publisher’s official description, and some comments of independent reviewers of the work.
All Books >>

Recent Comments

  • Mo Yunus on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Martin Smith on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Martin Smith on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Mo Yunus on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Pete Best on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • David on “But you said the ice was going to disappear in 10 years!”
  • Mo Yunus on Unforced variations: Oct 2025
  • Piotr on Unforced variations: Oct 2025
  • Keith Woollard on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Geoff Miell on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • David on “But you said the ice was going to disappear in 10 years!”
  • David on Unforced variations: Oct 2025
  • Piotr on “But you said the ice was going to disappear in 10 years!”
  • Atomsk's Sanakan on Unforced variations: Oct 2025
  • Mo Yunus on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • David on Unforced variations: Oct 2025
  • Atomsk's Sanakan on Unforced variations: Oct 2025
  • Mo Yunus on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Atomsk's Sanakan on Unforced variations: Oct 2025
  • Mal Adapted on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Piotr on “But you said the ice was going to disappear in 10 years!”
  • Russell Seitz on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Piotr on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Ken Towe on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Nigelj on Unforced variations: Oct 2025
  • Mal Adapted on “But you said the ice was going to disappear in 10 years!”
  • Susan Anderson on Unforced variations: Oct 2025
  • zebra on High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC)
  • Ray Ladbury on Unforced variations: Oct 2025
  • David on “But you said the ice was going to disappear in 10 years!”

Footer

ABOUT

  • About
  • Translations
  • Privacy Policy
  • Contact Page
  • Login

DATA AND GRAPHICS

  • Data Sources
  • Model-Observation Comparisons
  • Surface temperature graphics
  • Miscellaneous Climate Graphics

INDEX

  • Acronym index
  • Index
  • Archives
  • Contributors

Realclimate Stats

1,384 posts

11 pages

247,605 comments

Copyright © 2025 · RealClimate is a commentary site on climate science by working climate scientists for the interested public and journalists.