Monthly Archives: March 2006

Impacts of Land Use Change on Climate – Special Issue of the Journal of Applied Meteorology and Climatology Planned

There is a an opporunity to submit papers in the special issue of the Journal of Applied Meteorology and Climatology on “Impacts of Land Use Change on Climate” (see).

The Announcement reads,

“Recently, several special sessions on land use change and climate were organized at the 102nd Annual Meeting of the Association of American Geographers. Based on the quality of the papers, interest among authors, and importance of the topic highlighted by the IGBP, IPCC, and US Climate Change Science Program, we are organizing the publication of a special issue in the Journal of Applied Meteorology and Climatology (JAMC).

The theme issue will specifically focus on the role of land use and land cover change on all aspects of local, regional and global climate. Manuscripts may include modeling, observational, or experimental research. The manuscript submission deadline for this special issue is June 30th, 2006. The submission process will employ the current web-based submission platform of the American Meteorological Society. Authors must indicate in the “description” section of the submission web-page that the paper should be part this special issue, and include the special issue title (“Impacts of Land Use Change on Climate”).

Submitted manuscripts will be handled by the regular editors of JAMC and will go through the regular peer review process as per guidelines of the AMS and JAMC. To participate in this special issue or obtain further information, please contact the organizers: Rezaul Mahmood: rezaul.mahmood(at)wku.edu and Oliver W. Frauenfeld: oliver.frauenfeld(at)colorado.edu

AMS manuscript submission link: http://www.ametsoc.org/au_upload/index.cfm

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Response to CCSP Comment on the Pielke and Matsui GRL paper

The CCSP Response to the Public Comments includes a comment on the Pielke and Matsui 2005 paper entitled “Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same?”.

There has already been an informative exchange on this topic in William M. Connolley’s weblog STOAT.

The importance of this paper, and the identification of a warm bias in the surface temperature trend assessments, were summarized in the Climate Science weblog of January 23 2006.

This weblog dissects their reply in segements. The CCSP Response (page 140) stated,

1. ‘Since 1979, Tmin has not warmed relative to Tmax globally; see Vose et al Geophysical Research Letters, 32, doi:10.1029/2005GL024379(2005). In the tropics Vose et al do not make explicit calculations but scrutiny of their global map (their Figure 4) shows no evidence of relative warming of Tmin relative to Tmax in the tropics or extratropics separately since 1979.

The trend for HadCRUT3 global annual anomalies from 1979-2004 was 1.80 degrees/century. Halving the trend from Eurasia >45N in October-March reduces the global annual trend from 1979-2004 to 1.76 degrees/century. Removing the trend entirely from Eurasia >45N in October-March reduces the global annual trend from 1979-2004 to 1.72 degrees/century. The reason for this result is that warming over the period 1979-2004 is almost ubiquitous globally with the exception of most of Antarctica and a little of the Southern Ocean adjacent to it.”

This summary conflicts with the following text, which is based on peer reviewed papers also,

“Most of the recent warming has been in winter over the high mid-latitudes of the Northern Hemisphere continents, between 40 and 70° N (Nicholls et al., 1996). There has also been a general trend toward reduced diurnal temperature range, mostly because nights have warmed more than days. Since 1950, minimum temperatures on land have increased about twice as fast as maximum temperatures (Easterling et al., 1997). This may be attributable in part to increasing cloudiness, which reduces daytime warming by reflection of sunlight and retards the nighttime loss of heat (Karl et al., 1997)…….â€?

Part of the disagreement is possibly due to the different time periods selected. It is someone misleading in any case for the response to be in units of degrees per century, when the values thay quote should be, for example for the global average, 0.45 degrees per 25 years. Such a value is well within the range of amplified minimum temperature increases that we show to be realistic in the Pielke and Matsui GRL paper. We are also currently exploring a similar issue with respect to maximum temperatures and will report on this study when complete. Our research does support an increase of minumum temperature with time, but indicates that since the measurements are obtained near the surface, that the increase is overstated.

2. “The heights of the surface temperature observations are largely fixed, so an observed warming trend is not invalidated by any variation of trend with height.”

Where is their documentation that these heights are fixed? Studies are being performed because the heights of the temperature observations have been changed, and are funded by NOAA! See, for example,

Griffith, Brian D., and Thomas B. McKee, 2000:. Rooftop and Ground Standard Temperatures: A Comparison of Physical Differences. Climatology Report 00-2, Atmos. Sci. Paper 694, Dept. of Atmos. Sci., CSU, Fort Collins, CO, July, 49 pp.

3. “The cited paper by Pielke and Matsui appears to be an idealized calculation for some unspecified extreme nocturnal condition e.g. that might occur over the Prairies or Siberia.”

The model we used was based on obervations, as summarized in the classic textbook Stull, 1988: An Introduction to Boundary Layer Meteorology, Kluwer Academic Publishers. It accurately represents how the nightime boundary layer responds to a reduction in boundary layer cooling for any reason (i.e. with the result that there is an amplified increase of near surface air temperatures; thus sampling of temperatures near the surface results in a warm bias in terms of boundary layer averaged temperature trends). It is not an “extreme” case, but is true for any night which does not have significant horizontal temperature advection.

4. “Any attempt to quantify this effect globally or over the tropics requires a full assessment of the real mix of weather events that have occurred. This can only be approximately achieved by very carefully running a full climate model with a high-resolution boundary layer. “

The use of a model to evaluate a hypothesis is not appropriate. Models have serious deficiences in their representation of the nighttime boundary layer (see; also there will be a weblog on this issue as soon as the issue on the GABL study appears in Boundary Layer Meterology). Real observational data representing real weather needs to be used to examine the magnitude of the warm bias. This should have been a recommendation of the CCSP Report (it was but it was deleted with the replacement Chapter 6).

5. “Furthermore, Pielke and Matsui do not take account of the fact that the radiative imbalance driving global warming is fundamentally at the tropopause rather than at the surface. The long-term average radiative imbalance at the land surface is very small when greenhouse gases are increasing, because increasing downward longwave radiation from the warming atmosphere balances increased upward longwave radiation from the warming surface.”

As we have shown in

Eastman, J.L., M.B. Coughenour, and R.A. Pielke, 2001: The effects of CO2 and landscape change using a coupled plant and meteorological model. Global Change Biology, 7, 797-815.

there is a significant reduction of cooling at night (which elevated the minimum temperatures; see Figure 8 in that paper), due to an increase of carbon dioxide. A reduction of cooling by 1 watt per meter squared is a realistic value.

6. “So Pielke and Matsui’s paper may have limited application”

The casual dismissal of the science issue that we raised in Pielke and Matsui exists throughout the CCSP Report whenever a diverse view is presented that does not conform to the views of the Committee Chair and the majority of the other members of the Committee.

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A New Paper on the Importance of Regional Climate Forcings and Response

An important paper appeared in the March 22, 2006 issue of JGR-Atmosphere which further documents why we must focus on regional diabatic forcings and responses in order to provide a more scientifically sound understanding of climate variability and change. This paper by C. Erlick, V. Ramaswamy and L. Russell entitled “Differing regional responses to a perturbation in solar cloud absorption in the SKYHI general circulation model” has the following abstract,

“In this study we perform an idealized experiment to investigate the effect of solar absorption in clouds on climate using a general circulation model with prescribed sea surface temperatures, focusing on the manner of regional changes during the northern summer season. The response arising from this type of perturbation is akin to “semidirectâ€? effects of absorbing aerosols, namely, dissipation of clouds owing to a high aerosol absorption in the cloud layers. In the experiment, we apply a similar perturbation to all low-cloud layers, reducing their single-scattering albedo to a value of 0.99, which enables us to isolate the effect of such solar absorption from other aerosol related influences. We find that in both midlatitude and equatorial regions, the reduction in low-cloud single-scattering albedo causes a reduction in low-cloud amount and a warming of the surface. However, the dynamical response of the system varies from one continental region to another. In the midlatitude regions of the United States and Europe/east Asia, the diabatic heating perturbation leads to the dissipation of low clouds, an increase in shortwave flux to the surface, an increase in horizontal heat advection, and an increase in atmospheric stability. In the tropical region of North Africa, the diabatic heating perturbation translates into an increase in convection, a decrease in stability, an increase in middle- and high-level clouds, and a reduction in shortwave flux to the surface. In agreement with previous studies, these results demonstrate the distinctive response of the tropical versus midlatitude regions to a similar solar perturbation.”

In this study, while a uniform aerosol distribution is prescribed, the cloud cover is spatially heterogeneous such that the climate forcing is regional in scale.

The conclusion of the paper includes the following statement,

“…..the manner in which the diabatic warming input in any continental region translates into temperature increases versus increases in vertical velocity can vary between the tropics and midlatitudes, and this response can also be of differing magnitudes in different models. There can be considerable spatial heterogeneity as well, for example, subcontinental-scale changes can be quite different from continental-scale averages.

The results presented lend further support for the importance of taking into consideration the aerosol absorption effects on clouds in the lower troposphere and the ensuing effects on climate, including so-called semidirect effects. However, the global mean response of the climate is not an indication of the regional response, and a full understanding of the response of the climate to such a perturbation can only be gained by looking at the regional scale, and investigating both radiative and hydrologic budgets, where the mechanisms and effects prevailing in the tropical and midlatitude domains can be quite different from one another. Even when the radiative pattern of solar absorption in the atmosphere is well understood, as is the case in our idealized simulations, the responses of different regions may not follow in a similar manner. Our main conclusion is that even for an idealized uniform aerosol distribution, the response is not similar everywhere, not even qualitatively. Any departure from these globally uniform, idealized conditions could yield even more differences.”

A critically important conclusion in the above text is that,

“the global mean response of the climate is not an indication of the regional response, and a full understanding of the response of the climate to such a perturbation can only be gained by looking at the regional scale, and investigating both radiative and hydrologic budgets, ….”.

The importance of regional climate forcing and response has been discussed on the Climate Science weblog ; see

What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?

Why We Need to Focus on Regional Tropospheric Temperature Trends

As reported on both of these Climate Science weblog postings,

““The 2005 National Research Council report concluded that:

‘regional variations in radiative forcing may have important regional and global climate implications that are not resolved by the concept of global mean radiative forcing.’

And furthermore:

‘Regional diabatic heating can cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing.’

This regional diabatic heating produces temperature increases or decreases in the layer-averaged regional troposphere. This necessarily alters the regional pressure fields and thus the wind pattern. This pressure and wind pattern then affects the pressure and wind patterns at large distances from the region of the forcing which we refer to as teleconnections.�

The new Erlick et al JGR paper provides further scientific evidence on the validity of the National Research Council’s findings.

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Is the Nightime Warming in Arizona Due to Global Warming?

A news release on March 27, 2006 by Tony Davis of the Arizona Daily Star discusses the observed increase in winter nightime temperaturres in Arizona over the past 70 years. The article is generally well written, but it does not present the warm bias in minimum temperatures that we have discussed several times on this weblog (e.g see).

The article, which is headlined “Ariz. temps on the rise in winter for last 70 years” includes the text,

“Winter nights have warmed significantly across Arizona over 70 years, raising questions about whether human-caused global warming is part of the cause, said a University of Arizona researcher.

From 1931 to 2001, average wintertime low temperatures rose by as little as 0.03 a of a degree per decade in Safford to as much as 1.11 degrees in Mesa, according to the UA-analyzed data. “

As shown on Climate Science, however, any climate change that results in less cooling to space at night (such as a long term trend in increased cloud cover at night, greater air pollution, and/or greater water vapor in the air overhead) necessarily results in an amplified temperature increase at the surface. The radiative forcing of the added well-mixed greenhouse gases certainly can reduce cooling to space, but these other climate forcings also need to be considered.

As just one example, the role of aerosols in altering minumum temperatures was discussed in the Climate Science weblog of March 19, 2006 (see). An extract from the peer reviewed paper on this subject stated in part,

““A regional coupled climate-chemistry-aerosol model is developed to examine the impacts of anthropogenic aerosols on surface temperature and precipitation over East Asia. Besides their direct and indirect reduction of short-wave solar
radiation, the increased cloudiness and cloud liquid water generate a substantial downward positive long-wave surface forcing; consequently, nighttime temperature in winter increases by +0.7°C, and the diurnal temperature range decreases by -0.7°C averaged over the industrialized parts of China.”

With the urban growth in Arizona and the large amounts of aerosols transported into the state from industrial activities in adjacent areas of Mexico, the aerosol influence is also likely to be important in this region.

Thus, to use the observed surface temperature increase at night as support that the radiative forcing of CO2 and the other well-mixed greenhouse gases dominates climate variabiltiy and change in Arizona needs further scrutiny.

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Changes in global monsoon precipitation over the past 56 years

There is a significant new research contribution concerning an assessment of recent trends in the global monsoon systems. Monsoons are a critical component of the climate system in many parts of the world which includes their role in regional and local water resources.

The new paper by Bin Wang and Qinghua Ding is published in Geophysical Research Letters and is entitled,

“Changes in global monsoon precipitation over the past 56 years”. (Geophys. Res. Lett., 33, L06711, doi:10.1029/2005GL025347).

The abstract of the paper reads,

“Changes in the global monsoon rainfall over land were examined using four sets of rain-gauge precipitation data sets compiled for the period of 1948–2003 by climate diagnostic groups around the world. Here, we define a global monsoon rain domain according to annual precipitation range, using simple objective criteria; then, we propose metrics for quantifying the intensity of the global monsoon precipitation. The results suggest an overall weakening of the global land monsoon precipitation in the last 56 years, primarily due to weakening of the summer monsoon rainfall in the Northern Hemisphere. However, since 1980, the global land monsoon rainfall has seen no significant trend, which contrasts with the rapid intensification of global warming during the same period. Meanwhile the oceanic monsoon precipitation shows an increasing trend after 1980. The results provide a rigorous test for climate models that will be used in future climate-change assessment.”

This new paper is consistent with our earlier study,

Chase, T.N., J.A. Knaff, R.A. Pielke Sr. and E. Kalnay, 2003: Changes in global monsoon circulations since 1950. Natural Hazards, 29, 229-254,

where we concluded, as summarized in the abstract, that

“We examined changes in several independent intensity indices of four major tropical monsoonal circulations for the period 1950-1998. These intensity indices included observed land surface precipitation and observed ocean surface pressure in the monsoon regions as well as upper level divergence calculated at several standard levels from the NCAR/NCEP reanalysis. These values were averaged seasonally over appropriate regions of southeastern Asian, western Africa, eastern Africa and the Australia/Maritime continent and adjacent ocean areas. As a consistency check we also examined two secondary indices: mean sea level pressure trends and low level convergence both from the NCEP reanalysis.

We find that in each of the four regions examined, a consistent picture
emerges indicating significantly diminished monsoonal circulations over the period of record, evidence of diminished spatial maxima in the global hydrological cycle since 1950. Trends since 1979, the period of strongest reported surface warming, do not indicate any change in monsoon circulations. When strong ENSO years are removed from each of the time series the trends still show a general, significant reduction of monsoon intensity indicating that ENSO variability is not the direct cause for the observed weakening.

Most previously reported model simulations of the effects of rising CO2 show an increase in monsoonal activity with rising global surface temperature. We find no support in these data for an increasing hydrological cycle or increasing extremes as hypothesized by greenhouse warming scenarios.”

The Wang and Ding paper concludes with,

“The tropical atmospheric moisture content, latent heating, and overall hydrological cycle have been hypothesized to enhance with increasing tropospheric temperature [e.g., Intergovernmental Panel on Climate Change, 2001]. The numerical simulations with increasing greenhouse gas content generally show increased intensity of the Asian summer monsoonal circulations [e.g., Meehl and Washington, 1993; Hulme et al., 1998]. The inclusion of aerosols, however, seems to suppress the simulated increasing trends in southeast Asia seen in many general circulation model simulations [e.g., Mitchell and Johns, 1997], but not in all [e.g., Roeckner et al., 1999]. The present results provide a rigorous test for climate models that will be used in future climate change assessments………..

It is conceivable that the trend observed over the last 56 years reflects a transition from a strong phase to a weak phase in the multi-decadal variability. Previous studies have suggested that a rapid change occurred in atmospheric circulation and ENSO in the mid-1970s [e.g., Trenberth and Hurrell, 1994]. The results shown here (Figures 2a and 3b) suggest that changes in the NH monsoon strength reflects this “regime shift,â€? which may be a portion of the Interdecadal Pacific Oscillation, a period of 50 to 70 years [Folland et al., 1999], or caused by changes in tropical/sub-tropical land cover and high latitude snow cover [Meehl, 1994; Chase et al., 1996]. There is much we have yet to learn about the causes of observed trends in the global monsoon.”

There last sentence is very revealing with respect to the current understanding of the role of natural- and human-climate forcings and feedbacks.

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Further Confirmation of the Robustness of the Kalnay and Cai (2004) Nature paper on the Importance of the Land Surface With Respect to the Surface Temperature Trend Assessments

On several weblogs, we have discussed new research papers on the role of land surface processes on the surface temperature trend assessments (e.g. see and see).

Another new paper has appeared on March 24, 2006 that further confirms the important role of land surface processes in significantly influencing long term surface temperature trends;

Kalnay, Eugenia, Cai, Ming; Li, Hong, and Tobin, Jayakar: Estimation of the impact of land-surface forcings on temperature trends in eastern United States J. Geophys. Res., Vol. 111, No. D6, D06106

The abstract of the paper states,

“We use the “observation minus reanalysisâ€? difference (OMR) method to estimate the impact of land-use changes by computing the difference between the trends of the surface temperature observations (which reflect all the sources of climate forcing, including surface effects) and the NCEP-NCAR reanalysis surface temperatures (only influenced by the assimilated atmospheric temperature trends). This includes not only urbanization effects but also changes in agricultural practices, such as irrigation and deforestation, as well as other near-surface forcings related to industrialization, such as aerosols. We slightly correct previous results by including the year 1979 within the satellite decades and by excluding stations in the West Coast of the United States. The OMR estimate for surface impact on the mean temperature is similar to that obtained using satellite observations of night light to discriminate between rural and urban stations, with regions of large positive and negative trends, in contrast with the urban corrections based on population density, which are uniformly positive and much smaller. The OMR seasonal cycle results suggest that the impact of the greenhouse gases dominates in the winter, whereas it appears that the impact of surface forcings dominates in the summer. The impact of the USHCN adjustments for nonclimatic trends in the observations does not affect the geographical distribution of the OMR trends. The effect of using a model with constant CO2 in the reanalysis, the use of other reanalyses, and the possible use of the reanalyses to correct for nonclimatic jumps in the observations are also discussed. “

This paper provides an in-depth confirmation of the robustness of the conclusions of the 2004 Kalnay and Cai Nature paper. As was stated in the Climate Science weblog of December 1, 2005 with respect the earlier paper by Young-Kwon Lim, Ming Cai, Eugenia Kalnay, and Liming Zhou;

“The paper provides evidence on the robustness of the conclusions in the 2003 Kalnay and Cai paper entitled ‘Impact of urbanization and land-use on climate change’ (Nature, 423, 528-531); Corrigendum, which was (incorrectly as it now turns out) criticized in Nature in subsequent issues (Vose et al. 2003; Trenberth 2003 with reply by Cai and Kalnay 2003 ; subscription required) .”

The new Kalnay et al paper published on March 24, 2006 provides even further refutation of the comments by Vose et al and by Trenberth. Their paper provides additional evidence on the value of applying the NCEP Reanalysis to the assessment of long term climate trends, as they summarize in the following text extracted from their paper (see, subscription required);

“Since nonclimatic corrections are substantial, we suggest that reanalyses could be used to provide an alternative estimation of the nonclimatic adjustments taking advantage of the fact that they provide an accurate estimate of the expected value of the surface observations (absent sudden changes). If this method compares well with that used in the USHCN data set, it can be extended to other areas of the world where such careful corrections are not available”.

Their winter time attribution to greenhouse gases, however, also needs to be related to the results that we have found that a nighttime boundary layer decrease in cooling, for any reason, will result in an amplified near-surface air temperature increase. Attributing to greenhouse gases (by default) neglects the possible contributing influence due to increased nighttime cloud cover and or aerosols (e.g. see).

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A Current Example of The Value of the Vulnerability Paridigm – Water Resources in the Western United States

There was an accurate and well written media report in the NY Times on March 21 2006 by Kirk Johnson on the current water resource conditions in the western United States.

Entitled “More Western Drought, but With a Twist”, this news article illustrates the complexity of this issue as it relates to both weather conditions over the last several years, as well as the demand for use of this water. It also provides an example of why society is more vulnerable today to drought than if the same weather patterns had occurred, but with the societal conditions of early times. We found this to be true with the 2002 western USA drought as it affected Colorado (see), where the impacts of the 2002 drought far exceeded what were expected prior to that drought. It also provides examples of ways local and state governments, and the public are working to adapt to drought conditions and to ameliorate their consequences.

Excerpts from the news article are,

“Spring is here, and the West is dry and ready to burn. Winter is over, and the West is snowpacked and facing flood.

Meteorologists say both are true. What it adds up to, when the extremes of wet and dry are averaged out, is that the long Western drought, which began in the late 1990’s, is still on but without some of its past punch……

The Arkansas River is a case study in the region’s bipolar condition. It drains the Colorado Rockies south and east toward Kansas and is socked with snow at its headwaters around the town of Leadville, where the snowpack is nearly 140 percent of average for mid-March. Just a few hours south on the river, however, are places that have not had significant precipitation since October and are setting records for drought….

In some ways, experts say, the climatic situation is less dire than in past drought years. Experience itself has helped, with states and cities across the West adopting conservation policies, new monitoring systems and information-sharing operations that allow faster responses and better planning….

But scientists and government officials say the roller-coaster pattern has also underscored the fact that an uncertainty of water supply is becoming engrained in planning and Western life.

‘When two out of three, or three out of four years are bad, the issue that’s being driven home is how much competition there is for water in the West,’ said Michael J. Hayes, a climate impacts specialist at the National Drought Mitigation Center at the University of Nebraska-Lincoln.

Dr. Hayes said that in the ever more urbanized West, rolling water shortages highlighted all the tensions of land use and development, in issues like wildfires, endangered species protection and the conflict between recreation and agriculture in places where a reservoir can be important for tourism and equally crucial to farmers.

Those off-and-on shortages can be downright dispiriting, too. “In the Southwest, everybody was so excited about last year,” Dr. Hayes said, referring to the wet winter of 2004-5. ‘But the cautious among them were saying it could be a blip, and now we’ve gone back to the dryness, so the enthusiasm is gone.'”

Congratulations to the New York Times for a well written article on this important issue.

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