Category Archives: Definition of Climate

The Terms “Global Warming” And “Climate Change” – What Do They Mean?

There continues to be considerable misunderstanding of the terms “global warming” and “climate change”. I have posted in previous years about these terms; e.g. see these posts in 2005;

What is Climate Change?

Is Global Warming the Same as Climate Change?

What is Climate? Why Does it Matter How We Define Climate?
 

Is Global Warming Spatially Complex?

but there continue to be misunderstandings.

I have attempted below to succinctly define these terms below:

Global Warming is an increase in the heat (in Joules) contained within the climate system. The majority of this accumulation of heat occurs in the upper 700m of the oceans.

Global Cooling is a decrease in the heat (in Joules) contained within the climate system. The majority of this accumulation of heat occurs in the upper 700m of the oceans.

Global warming and cooling occur within each year as shown, for example, in Figure 4 in

Ellis et al. 1978: The annual variation in the global heat balance of the Earth. J. Geophys. Res., 83, 1958-1962.

Multi-decadal global warming or cooling involves a long-term imbalance between the global warming and cooling that occurs each year.

Climate Change involves any alteration in the  climate system , which is schematically illustrated  in the figure below (from NRC, 2005)

which persists for an (arbitrarily defined) long enough time period.

 Shorter term climate change is referred to as climate variability.  An example of a climate change is if a growing season 20 year average  of 100 days was reduced by 10 days in the following 20 years.  Climate change includes changes in the statistics of weather (e.g. extreme events such as droughts, land falling hurricanes, etc), but also include changes in other climate system components (e.g. alterations in the pH of the oceans, changes in the spatial distribution of malaria carrying mosquitos, etc).

The recognition that climate involves much more than global warming and cooling is a very important issue. We can have climate change (as defined in this weblog post) without any long-term global warming or cooling.  Such climate change can occur both due to natural and human causes.

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Recommended Definitions of “Global Warming” And “Climate Change”

As discussed often in my posts; e.g.

What is Climate? Why Does it Matter How We Define Climate?

What is Climate Change?

Is Global Warming the Same as Climate Change?

there is lack of clarity in how these terms are defined. In today’s post, I offer the following short definitions:

Global Warming is an increase in the global annual average heat content measured in Joules.

Climate Change is any multi-decadal or longer alteration in one or more physical, chemical and/or biological components of the climate system.

The figure below (from NRC, 2005) schematically illustrates the Earth’s climate system 

 

Thus climate change includes, for example, changes in fauna and flora, snow cover, etc which persists for decades and longer. Climate variability can then be defined as changes which occur on shorter time periods.

Global warming involves the accumulation of heat in Joules within these components of the climate system, which is predominently the oceans, as shown in Table 1 in Levitis et al 2001.  The current use of the global average annual surface temperature trend to diagnose global warming involves only the two dimensional land, cryosphere and ocean surface.

As I wrote in

Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.

“Unlike temperature at some specific depth in the ocean or height in the atmosphere, where there is a time lag in the response to radiative forcing, no time lags are associated with heat changes, since the actual amount of heat present at any time is accounted for. Moreover, because the surface temperature is a massless two-dimensional global field while heat content involves mass, the use of surface temperature as a monitor of climate change is not accurate for evaluating heat storage changes. “

My recommendation is that the next IPCC assessment adopt these definitions for global warming and climate change.

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Weather And Climate – Well Summarized By On Tomas Milanovic On Climate Etc.

Tomas Milanovic has a accurate succinct summary of the relationship between weather and climate on the weblog post The Uncertainty Monster at Climate Etc.

The comment reads

“Weather is chaotic, nobody disputes that. The “climate” is exactly the same system, obeying to the same laws and described by the same equations like weather. The only difference being that the variables of the system “climate” are space and time averages instead of the instantaneous values. In addition for practical purposes the weather time scale is defined in days so that many slow variables are considered constant what spares computing time. However it is clear that if the system is chaotic with these constant coefficients , it will be chaotic with variable coefficients on longer time scales too.”

The issue of what is climate is discussed further in the article

Pielke, R.A., 1998: Climate prediction as an initial value problem. Bull. Amer. Meteor. Soc., 79, 2743-2746

where I wrote

“….weather prediction is a subset of climate prediction. Societally useful (i.e. reliable, accurate,etc.) requires that all of the feedbacks and other physical processes included in weather prediction be represented in the climate prediction model. In addition, longer-term feedback and physical processes must be included. This makes climate prediction a much more difficult problem than weather prediction.”

Indeed, climate models must not only be able to simulate weather features such as high and low pressure systems including tropical cyclones are well as operational numerical weather prediction models, but must be able to accurately simulate a diverse variety of physical, chemical and biological processes. Even then, nonlinear interactions between the many components of the climate system (e.g. as illustrated in Figure 1 in Rial et al 2004) can result in limiting skillful prediction decades into the future.  The Milanovic comment on Climate Etc. effectively summarizes this issue. A subject that is not properly assessed in the 2007 IPCC report.

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Q&A “On GCMs, Weather, and Climate”

 Dan Hughes has sent in a question on climate science (thanks Dan!).

The title is  “GCMs, weather, and climate”, and following is his question.

Hello Professor Pielke,

I have a candidate for Question for the Day.

GCMs do not resolve weather, either spatially or temporally.  Even if sufficient spatial and temporal resolution were used at run time, GCMs are not applied in the same manner as NWP models and codes are applied.  All NWP calculations immediately begin to derivate from reality, and after a relatively short period of time ( a very few days ) the calculated numbers exhibit almost no fidelity to the real world.  The NWP models and codes, knowing that the forecast window into future time is severely limited, inject updated measured information into the calculations.  Obviously, GCMs applied to calculations of future states of the Earth’s climate systems cannot be applied in this manner.

If the above is a correct, but rough, description of the situation, how can the variability seen in the numbers calculated by GCMs be assigned to be weather.  If the numbers are weather, then it is clear that it cannot be the correct weather.  If climate is taken to be the average of weather, how can the average of the weather calculated by GCMs be expected to have any fidelity to actual future states of the Earth’s climate systems.

Kindly let me know if I have presented an incorrect description.

Thank you for taking time to consider this candidate question.

Dan

There is a fundamental difference in how scientists who have prompted the 2007 IPCC WG1 report view climate modeling and how other climate scientists view this modeling. The IPCC perspective is that numerical weather prediction is an initial value problem while  climate prediction is a boundary value problem in which levels of atmospheric CO2 and aerosols are the primary “boundary forcing”.  With this perspective, they claim that changes in the statistics of weather (and other climate features) can be skillfully predicted.

However, our research has shown this is a seriously flawed view as climate prediction is really an initial value problem. It even more complicated than weather prediction since there are more variables that need to be initialized accurately (e.g. ocean temperatures and salinity; land ice depth and area, vegetation type, amount and distribution, etc).  Moreover, there are feedbacks between components of the climate system (e.g. see Figure in NRC, 2005), which become important on time periods of seasons, years and decades.

The need for treating climate as an initial value problem has been documented in a number of publications, including

Pielke, R.A., 1998: Climate prediction as an initial value problem. Bull. Amer. Meteor. Soc., 79, 2743-2746.

Pielke Sr., R.A., G.E. Liston, J.L. Eastman, L. Lu, and M. Coughenour, 1999: Seasonal weather prediction as an initial value problem. J. Geophys. Res., 104, 19463-19479.

Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38. 

Indeed, the broader climate community is starting to come around to this view, as illustrated in the concept of “seamless climate prediction“, which I have discussed on my weblog (e.g. see).

They have a difficult challenge. On time scales longer than perhaps a single season, there is no demonstrated skill in regional predictions.

I hope this addresses your question and appreciate your input!

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What is Climate? Why Does it Matter How We Define Climate?

Originally Posted on July 11, 2005.

The title of this weblog is “Climate Science,” so the first thing we need to do is define “climate.” For many, the term refers to long-term weather statistics. However, on this blog we are adopting the definition that is provided in the 2005 National Research Council (NRC) report where the climate is the system consisting of the atmosphere, hydrosphere, lithosphere, and biosphere. Physical, chemical, and biological processes are involved in interactions among the components of the climate system. Figure 1-1 and 1-2 in the report illustrate this definition of climate very clearly. In the NRC report, climate forcings were extended beyond the radiative forcing of carbon dioxide to include the biogeochemical influence of carbon dioxide, but also a variety of aerosol forcings (see Table 2-2 in the report), nitrogen deposition, and land-cover changes. Each of these forcings has been determined to influence long-term weather statisitics as well as other aspects of the climate.

However, this concept of climate and its alterations by humans, has been generally ignored. The NRC report listed above certainly appears to have been incompletely missed by policymakers. As an example, at the G-8 meeting, the term “climate change” is used interchangably with “global warming.” However, the human influence on climate is much more complex and multi-dimensional than captured by the term “global warming” (see, for example, http://www.climatesci.org/publications/pdf/R-260.pdf; http://www.nap.edu/books/0309095069/html/15.html and http://www.climatesci.org/pdf/R-225.pdf). The term “global warming” is generally used to refer to an increase in the globally-averaged surface temperature in response to the increase of well-mixed greenhouse gases, particularly CO2.

If, however, we are interested in atmospheric and ocean circulation changes, which, afterall is what creates our weather, we need to focus on how humans are altering these circulations. Ocean heat content changes are the much more appropriate metric than a globally-averaged surface temperature when evaluating “global warming” in any case (http://www.climatesci.org.edu/publications/pdf/R-247.pdf).

Thus it matters how we define climate and climate forcing (http://www.nap.edu/books/0309095069/html/15.html). By ignoring a number of the other first-order climate forcings, we are not properly addressing the threat we face in the future, but instead relying on the overly simplistic view of focusing on reductions in carbon dioxide emissions as the way to reduce our “dangerous intervention” in the climate. With respect to the changes of circulations, and therefore, weather, we need to identify and quantify the role of spatially heterogeneous climate forcings such as from aerosols and land-cover change, in addition to the influence of well-mixed greenhouse gases. These heterogeneous climate forcings could represent a more significant threat to our future climate system than the risk of an increase in the atmospheric concentration of CO2.

Hopefully, this blog will stimulate discussion, as well as illuminate reasons why this broader perspective on climate variability and change has been mostly ignored.

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What is Climate Change?

For the next several weeks Climate Science is reposting a number of weblogs that are worth repeating. We have quite a few more readers now than we did when my weblog started. The first reposting appears below.

Originally posted on July 29, 2005.

The different definitions of climate, have done much to confuse policymakers in the discussion of climate science.

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.

As one example of the misuse by policymakers, the Royal Society released the following statement by Lord May:

“The science points to the need for a Herculean effort to make massive cuts in the amount of greenhouse gases that we pump into the atmosphere. So, while this encouraging new deal may play a role in this, it will only be part, and not all, of the solution.”

“But we have serious concerns that the apparent lack of targets in this deal means that there is no sense of what it is ultimately trying to achieve or the urgency of taking action to combat climate change. And the developed countries involved with this agreement must not be tempted to use it as an excuse to avoid tackling their own emissions.”

“All eyes should be on the United Nations Framework Convention on Climate Change in Montreal at the end of November [2005]. Top of the agenda at this meeting should be the initiation of a study into what concentration of greenhouse gases in the atmosphere we can allow without suffering the most catastrophic effects of climate change. This would allow us to plan cuts in worldwide emissions accordingly and provide direction to such efforts to tackle what is the biggest environmental threat we face today.”

Here the conclusion is made that to “combat climate change” we must initiate “a study into what concentration of greenhouse gases in the atmosphere we can allow without suffering the most catastrophic effectsof climate change.”

Ignored in this statement is the role of the other anthropogenic climate forcings that we identified in the National Research Council report.

Lord May, President of the Royal Society, has clearly overlooked a very critical definition of what really constitutes the climate system and what the anthropogenic forcings and feedbacks are that influence climate. He is, unfortunately, cherrypicking climate science.

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New Article In Physics Today Titled “A Broader View Of The Role Of Humans In The Climate System.”

Physics Today has just published an invited opinion piece

Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.

The article starts with the text

“The 2007 report from the Intergovernmental Panel on Climate Change Working Group I presents a narrow view of the state of climate science. Attempts to significantly influence regional and local-scale climate based on controlling carbon dioxide emissions alone cannot succeed since humans are significantly altering the global climate in a variety of diverse ways beyond the radiative effect of CO2. The IPCC assessments have been too conservative in recognizing the importance of these human climate forcings as they alter regional and global climate. When the IPCC focuses its policy attention on CO2, it neglects other important aspects of the impact of human activities on climate.”

The conclusion of the article reads

 “Humans are significantly altering the global climate, but in a variety of diverse ways beyond the radiative effect of CO2. Significant, societally important climate change on the regional and local scales, due to both natural and human climate forcings, can occur due to these diverse influences. The result of the more complex interference of humans in the climate system is that attempts to significantly influence regional and local-scale climate based on controlling CO2 emissions alone is an inadequate policy for this purpose. There is a need to minimize the human disturbance of the climate by limiting the amount of CO2 that is emitted into the atmosphere by human activities, but the diversity of human climate forcings should not be ignored.”

The entire article can be read  at http://www.climatesci.org/publications/pdf/R-334.pdf.

 

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