Confusion in the Definitions of Global Warming and Climate Change
24 Apr, 2007 01:16 pm
The terms climate change and global warming are often used interchangeably. However, even within professional science organizations, there is confusion on the definitions of these terms. This has resulted in the communication of climate change science to policymakers that are seriously flawed.
The American Meteorological Society (AMS) definition of “climate change” is
“(Also called climatic change.) Any systematic change in the long-term statistics of climate elements (such as temperature, pressure, or winds) sustained over several decades or longer. Climate change may be due to natural external forcings, such as changes in solar emission or slow changes in the earth’s orbital elements; natural internal processes of the climate system; or anthropogenic forcing.”
The AMS defines anthropogenic forcing as
“Human-induced or resulting from human activities; often used to refer to environmental changes, global or local in scale.
The AMS defines the climate system as the
“system, consisting of the atmosphere, hydrosphere, lithosphere, and biosphere, determining the earth’s climate as the result of mutual interactions and responses to external influences (forcing). Physical, chemical, and biological processes are involved in the interactions among the components of the climate system.”
Here we have an inconsistency with the definition even by a very distinguished professional society! Climate, as defined by the AMS, is focused on the atmosphere, while the climate system consists of the atmosphere, hydrosphere, lithosphere, and biosphere. No wonder policymakers misapply this terminology.
Even more misleading is the use of the term "global warming" and "climate change" interchangeably. The AMS Glossary of Meteorology does not even include this term (see)!
Global warming (or global cooling) means that heat content changes have occurred in the Earth’s climate system. The surface average temperature trend has been the traditional metric used to assess this heat content change (e.g. see the text in the 2005 National Research Council report that starts on page 19 ).
However, as discussed in
Pielke Sr., R.A., 2003: Heat storage within the Earth system . Bull. Amer. Meteor. Soc., 84, 331-335.
and analyzed in detail in
Willis, J.K., D. Roemmich, and B. Cornuelle, 2004: Interannual variability in upper ocean heat content, temperature, and thermosteric expansion on global scales . J. Geophys. Res., 109, C12036, doi: 10.1029/2003JC00226
ocean heat content change is the preferred metric to use to assess climate system heat changes since this where most heat storage change occurs in comparison to land, continental ice and the atmosphere heat changes. Global warming, therefore, can be most appropriately estimated by the Joules that have accumulated in the ocean.
Global warming or cooling is determined by the difference in Joules between incoming heat (from the Sun) and radiative heat loss from the climate system. This difference between them is referred to as the radiative forcing of the climate system.
The broader human climate change issue, however, is how are humans altering the climate system in response to the diversity of climate forcings that are identified in the 2005 National Research Council report. This is the more inclusive term "climate change", as contrasted with the term "global warming".
As stated in that report on page 5 of that Report,
Regional variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing. Tropospheric aerosols and landscape changes have particularly heterogeneous forcings
These climate implications can result in substantial alterations in the global climate patterns, even if there is no global warming or cooling. A example of a study which documents just such a response (i.e. due to landscape change) is
Feddema et al. 2005: The importance of land-cover change in simulating future climates., 310, 1674-1678.
The policy significance of such an important role of landscape change in the climate system is reported in the multi-authored paper
Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, P.C. Frumhoff, S.T. Jackson, L. Joyce, P. Kauppi, J. Katzenberger, K.G. MacDicken, R. Neilson, J.O. Niles, D. dutta S. Niyogi, R.J. Norby, N. Pena, N. Sampson, and Y. Xue, 2003: The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy . Climate Policy, 3, 149-157.
The abstract of that paper states in part,
….climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in terrestrial vegetation and to work toward a better understanding of the full climate system.
The greater importance of heterogeneous aerosol and landscape human climate forcing relative to the more spatially homogeneous radiative forcing of added CO2 in terms of how atmospheric weather features are affected was documented in
Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing . Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974.
These heterogeneous human climate forcings can occur with or without global warming, and appear to alter the climate system to the greater extent than does the radiative effect of CO2.
It is time for the assessment and policy communities and the media to recognize that an equivalence of global warming and climate change is erroneous. The 2007 IPCC Statement for Policymakers, unfortunately, has not corrected this misconception.