Monthly Archives: January 2008

Current Status of Arctic and Antarctic Sea Ice Coverage

As we approach the time of year of the peak of areal coverage of Arctic sea ice and the minimum areal coverage in Antarctic sea ice, Climate Science is presenting a status report based on the excellent data analysis provided at the University of Illinois website The Cryosphere Today.  The coverage for January 31 2008 is about 900,000 square kilometers below average for the Arctic [Northern Hemisphere] (see) and about 500,000 square kilometers above average for the Antarctic [Southern Hemisphere] (see). The Illinois website has also introduced an effective display of past Arctic sea ice coverage at the same time of the year (see Compare Daily Sea Ice).

What has not been discussed, however, with respect to the global sea ice coverage is the relationship to albedo weighted by the time of year (i.e., an insolation-weighted albedo).  We presented this concept in our papers

Pielke Sr., R.A., G.E. Liston, and A. Robock, 2000: Insolation-weighted assessment of Northern Hemisphere snow-cover and sea-ice variability. J. Geophys. Res. Lett., 27, 3061-3064.

Pielke Sr., R.A., G.E. Liston, W.L. Chapman, and D.A. Robinson, 2004: Actual and insolation-weighted Northern Hemisphere snow cover and sea ice — 1974-2002. Climate Dynamics, 22, 591-595 DOI10.1007/s00382-004-0401-5.

In our second paper, the abstract reads

Actual and insolation-weighted Northern Hemisphere snow cover and sea ice are binned by latitude bands for the years 1973–2002. Antarctic sea-ice is also analyzed for the years 1980–2002. The use of insolation weighting provides an improved estimate of the radiative feedbacks of snow cover and sea-ice into the atmosphere. One conclusion of our assessment is that while a decrease in both areal and insolation weighted values have occurred, the data does not show a monotonic decrease of either Arctic sea-ice or Northern Hemisphere snow cover. If Arctic perennial sea-ice is decreasing since the total reduction in areal coverage is relatively small, a large portion of it is being replenished each year such that its radiative feedback to the atmosphere is muted. Antarctic sea-ice areal cover shows no significant long-term trend, while there is a slight decrease in the insolation-weighted values for the period 1980–2002. From the early 1990s to 2001, there was a slight increase in both values. The comparison of general circulation model simulations of changes over the last several decades to observed changes in insolation weighted sea-ice and snow cover should be a priority research topic.”Unfortunately, the IPCC did not make such an assessment (of insolation-weighted albedo) a priority.

With the data now available up through January 2008, it is clear that the global sea ice insolation-weighted albedo, using the methodology in our papers, is a global average negative radiative feedback at present (January 2008), as the above average sea ice coverage in the summertime in the Antarctic dominates this climate metric in the global average. This feedback is larger also since the Earth is closer to the Sun in January. If the Arctic sea ice areal coverage is again lower this northern hemispheric summer, this would be a global average positive radiative feedback.

Climate Science recommends the presentation of this insolation-weighted albedo on website such as at the University of Illinois and the National Snow and Ice Data Center.

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A Significant Warm Bias With The Diagnosis Of A Global Average Surface Temperature Anomaly To Diagnose Global Warming – Part II From Our JGR Paper

Part I of this series of weblogs (see), discussed the serious limited value of the use of a global average surface temperature anomaly to diagnose the global radiative imbalance (i.e., global climate heat system changes). In Part II, we discuss another serious issue that we raised in our paper

Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229.

Today’s weblog discusses Section 3 in this paper entitled

“Difficulties With the Use of Observed Nocturnal Warming Trends as a Measure of Climate Trends”

Because the land portion of the global average surface temperature trend is constructed using the average of the minimum and maximum daily temperatures, if there is a bias in either one of these temperatures, there will be a bias in the trends.

In our JGR paper and in our follow up study

Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652.
we have identified such a bias.

The bias is straightforward to describe. If there is overall warming of the lowest levels of the atmosphere at night (i.e. the nocturnal boundary layer), observations of this warming  near the surface overstates the warming simply because warming trends are not distributed evenly in the lower atmosphere. Similarly, if the nocturnal boundary layer experienced an overall cooling trend, the trend would be overstated  with measurents taken at and near the surface.

We have documented this bias both using boundary layer theory (see Pielke and Matsui 2005) and confirmed with observations (see Lin et al. 2007).  

We concluded in the Lin et al. 2007 paper cited above that

“Our results also indicate that the 1.5 or 2 m minimum long term temperature trends over land are not the same as the minimum long term temperatures at other heights within the surface boundary layer (e.g., 9 m), even over relatively flat landscapes such as Oklahoma. For landscapes with more terrain relief, this difference is expected to be even larger. Therefore, the use of minimum temperatures at 1.5 or 2 m for interpreting climate system heat change is not appropriate. This means that the 1.5 to 2 m observations of minimum temperatures that are used as part of the analysis to assess climate system heat changes (e.g., such as used to construct Figure SPM-3 of the Intergovernmental Panel on Climate Change Parker lead to a greater long term temperature trend than would be found if higher heights within the surface boundary layer were used. Our exploration of near-surface lapse rate changes including wind effects should, therefore, be extended to longer-term time series as well as cover larger spatial areas.”

The quantification of the magnitude of this bias has not been completed, but it is certainly significant, as shown below. 

Back of the Envelope Estimate of Bias in Minimum Temperature Measurements

To present a preliminary estimate, lets start with the value reported for the recent trend in the global average surface temperature.  The 2007 IPCC Report presents a global average surface temperature increase of  about 0.2C per decade since 1990 (see their Figure SPM.3). Their trend is derived from the average of the maximum and minimum surface temperatures; i.e.,

T(average) = [T(max) + T(min)]/2.

 From our papers (Pielke and Matsui 2005 and Lin et al. 2007), a conservative estimate of the warm bias resulting from measuring the temperature near the ground is around 0.21 C per decade (with the nightime T(min) contributing a large part of this bias) . Since land covers about 29% of the Earth’s surface (see), the warm bias due to this influence explains about 30% of the IPCC estimate of global warming. In other words, consideration of the bias in temperature would reduce the IPCC trend to about 0.14 degrees C per decade, still a warming, but not as large as indicated by the IPCC.

This is likely an underestimate, of course, as the value is not weighted for the larger bias that must occur at higher latitudes in the winter when the boundary layer is stably stratified most of the time even in the “daytime” Moreover, the warm bias over land in the high latitudes in the winter will be even larger than at lower latitudes, as the nightime surface layer of the atmosphere is typically more stably stratified than at lower latitudes, and this magnifies the bias in the assessment of temperature trends using surface and near surface measurements. [not coincidently, this is also where the largest warming is claimed; e.g., see the map on Andy Revkin's Dot Earth's weblog].

Land is also a higher fraction of the Earth’s surface at middle and higher latitudes in the northern hemisphere and at the highest latitudes in the southern hemisphere (see).

The documentation of this warm bias is found in the peer-reviewed literature [see also Walters et al. 2007)], and thus should be refuted or used in analyses such as that found in Figure SPM.3 in the 2007 IPCC Report. Thus far, this bias had been ignored.

Climate Science will present Part III in this series of presentations on our JGR paper within the next week or so.

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Important New Research Paper Published – Reconstructed Historical Land Cover And Biophysical Parameters For Studies Of Land-Atmosphere Interactions Within The Eastern United States”

An important new research paper has appeared which documents how dynamic human land management has been in altering the landscape component of the climate system. This seminal paper is

 Steyaert, L.T., and R.G. Knox, 2008: Reconstructed historical land cover and biophysical parameters for studies of land-atmosphere interactions within the eastern United States, J. Geophys. Res., 113, D02101, doi:10.1029/2006JD008277.

The abstract reads

“Over the past 350 years, the eastern half of the United States experienced extensive land cover changes. These began with land clearing in the 1600s, continued with widespread deforestation, wetland drainage, and intensive land use by 1920, and then evolved to the present-day landscape of forest regrowth, intensive agriculture, urban expansion, and landscape fragmentation. Such changes alter biophysical properties that are key determinants of land-atmosphere interactions (water, energy, and carbon exchanges). To understand the potential implications of these land use transformations, we developed and analyzed 20-km land cover and biophysical parameter data sets for the eastern United States at 1650, 1850, 1920, and 1992 time slices. Our approach combined potential vegetation, county-level census data, soils data, resource statistics, a Landsat-derived land cover classification, and published historical information on land cover and land use. We reconstructed land use intensity maps for each time slice and characterized the land cover condition. We combined these land use data with a mutually consistent set of biophysical parameter classes, to characterize the historical diversity and distribution of land surface properties. Time series maps of land surface albedo, leaf area index, a deciduousness index, canopy height, surface roughness, and potential saturated soils in 1650, 1850, 1920, and 1992 illustrate the profound effects of land use change on biophysical properties of the land surface. Although much of the eastern forest has returned, the average biophysical parameters for recent landscapes remain markedly different from those of earlier periods. Understanding the consequences of these historical changes will require land-atmosphere interactions modeling experiments. “

 The conclusion has the text

“The eastern half of the United States has experienced extensive land cover transformations over the past 350 years. Land use change has fundamentally altered the land cover of entire vegetation regions (e.g., wetland forests in the lower Great Lakes region and lower Mississippi River floodplain, tallgrass prairie, and southeastern pine savannas and open woodlands). Forest management practices, pests, and disease have modified forest composition and structure. Wetlands have been converted by intensive agriculture, plantation forestry, flood control, navigable waterway development, and urban development. Few areas of the eastern United States have escaped considerable alteration by human land management. (Even these have been exposed to increases in the average partial pressure of atmospheric CO2, enhanced nitrogen deposition, and changing distributions of anthropogenic aerosols, as well as numerous human-introduced pests, pathogens, and invasive exotic competitors.) Although seminatural vegetation reestablished on many former cutover or agricultural lands during the 20th century, it typically persists in landscapes fragmented by transportation corridors, residential-urban development, agriculture, industrial forestry, and other intensive land uses. Recent land cover provides an insufficient basis for understanding the functional responses and feedbacks of historical land cover. Modeling experiments and sensitivity tests incorporating coupled land-atmosphere interactions are needed to understand and quantify the feedbacks, interregional connections, and integrated consequences of these land cover and land use changes.”

Two figures from their paper dramatically illustrate the substantial amount that land surface climate forcings have changed. To illustrate the magnitude of this effect, if the value of solar radiation received at the ground were 600 Watts per meter squared,  a change in albedo of 12% to 16%, translates to a 24 Watt per meter squared increase in solar energy absorbed at the surface.

 steyeart-fig-7.jpg

 steyaert-fig11.jpg

This paper, therefore, represents a landmark study for the use of the climate modeling community in order to quantify the role of human land management effects on the climate system, relative to other human climate forcings.

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Additional Research Articles On the 2003 European Heat Wave

In 2006 we published a paper on the 2003 European heat wave titled

 Chase, T.N., K. Wolter, R.A. Pielke Sr., and Ichtiaque Rasool, 2006: Was the 2003 European summer heat wave unusual in a global context? Geophys. Res. Lett., 33, L23709, doi:10.1029/2006GL027470.

William W. Connolley questioned our results and decided to investigate this issue himself (we need more such open-minded climate scientists!).  He has confirmed our results in his article

Connolley W. M. (2008), Comment on “Was the 2003 European summer heat wave unusual in a global context?” by Thomas N. Chase et al., Geophys. Res. Lett., 35, L02703, doi:10.1029/2007GL031171,

where he wrote

“Figure 1  largely replicates Figure 2 of CO6 [CO6 is the Chase et al paper].

 He wrote that the shallowness of the extreme temperature values.

“….. may well indicate a strong role for surface drying in causing the 2003 event [Ferranti and Viterbo, 2006]; though Black et al. [2004]  have suggested a role for large-scale anomalies leading to the surface drying.”

Our reply to his comment was published at the same time as his comment;

Chase T. N., K. Wolter, R. A. Pielke Sr., I. Rasool (2008), Reply to comment by W. M. Connolley on “Was the 2003 European summer heat wave unusual in a global context?”, Geophys. Res. Lett., 35, L02704, doi:10.1029/2007GL031574.

Our main conclusion from our 2006 paper has been independently confirmed by William Connolley. We wrote in our 2008 Chase et al Reply;

“Assuming the near-surface temperature measurements are spatially representative, the conclusion that the heat wave was a shallow phenomenon in terms of its unusualness argues against the point of view that it was a direct manifestation of the effects of increased atmospheric CO2..…. we … conclude that land surface conditions (low soil moisture) are the likely direct cause for such an “unusual” event near the surface.”

Thus, those who claim that the 2003 European heat wave is evidence of global warming are, therefore, ignoring peer reviewed literature on this subject. Instead, it appears that land surface forcing, as has been so repeatedly emphasized on Climate Science, is the main reason for the extreme heat right near the surface. Attempting to mitigate such heat waves by focusing only on CO2 emission reductions will not reduce the risk from these weather events. Clearly, adaptation must also play a major role through deliberate land management practices to reduce the threats from heat waves.

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Comment By Chris Colose On Water Vapor Feedback

There is a posting  on the weblog Climate Change An Analysis of Key Questions entitled “How not to discuss the Water Vapor feedback” by Chris Colose with respect to the Climate Science set of weblogs on the subject  Climate Metric Reality Check #3 – Evidence For A Lack Of Water Vapor Feedback On The Regional Scale.

Chris Colose has the following issues with the Climate Science weblog:

1.  He states that the roughly constant relative humidity of the atmosphere “is an emergent property in models, not a built-in assumption“.

This is certainly true (the models do predict this response), but the models themselves are hypothesis, constructed with parametrization of physical processes. Thus, the emergence of a roughly constant relative humidity in a model needs to compared (tested) with real world data, and this is where the assumption of a nearly constant relative humidity does not appear to be occurring recently, at least for regions where the data is available to compare.

2. He concludes, with citations of two papers (see and see)  that a nearly constant relative humidity with an increase in temperature is “confirmed by real world observations..”

However, these two papers do not confirm this. The first paper only deals with surface humidity (which as shown on Climate Science is very significantly altered by land use ; e.g. see), while the second paper shows no trend in absolute humidity since 1998 (see their Figure 1) despite ssurface temperature increasing since then! Indeed, plotting the model data since 1900 is disingenuous, since there is no data to compare with. 

3.  He reports that “[t] he point about relative humidity remaining constant applies mainly to global scale averages.”

This is an important admission, and he needs to elaborate on this statement.  The second paper that he lists as supporting his conclusion on a roughly constant relative humidity is for the oceans from 50N to 50S, so that already conflicts with his statement about applying mainly to global scale averages. In fact, to construct a global average, we need to obtain the data and regional and smaller scales, which is what we have done in our paper

Wang, J.-W., K. Wang, R.A. Pielke, J.C. Lin, and T. Matsui, 2007: Does an atmospheric warming trend lead to a moistening trend over North America?Geophys. Res. Letts., in revision.

4.  He states that it is the “upper levels  [of the atmosphere] which are radiatively significant”. He also writes “[i]n fact, as specific humidity changes in a warming climate, around 90% of the radiative response is dominated by the mid to upper atmosphere (above 800 millibars), with more effect in tropical latitudes.”

It is true that the upper levels are radiatively important. However, so are the lower levels, as Chris acknowledged where he wrote “[s]urface radiative fluxes are most sensitive to specific humidity variations in the lower troposphere”.

Climate Science Conclusion

Thus, while we agree that it is important to monitor the changes in water vapor  in the upper atmosphere, it is also as  important to monitor the depth-integrated water vapor (precipitable water).  Our weblogs on the subject of regional trends in precipitable water are a part of this discussion, and we welcome Chris Colose joining  in this important scientific debate.

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Modeling the impact of historical land cover change on Australia’s regional climate

There is a very important new paper that highlights the role of land surface processes, including its human management, as an integral component of climate variability and change. The paper is

  McAlpine C. A., J. Syktus, R. C. Deo, P. J. Lawrence, H. A. McGowan, I. G. Watterson, S. R. Phinn (2007), Modeling the impact of historical land cover change on Australia’s regional climate, Geophys. Res. Lett., 34, L22711, doi:10.1029/2007GL031524. 

The abstract reads

“The Australian landscape has been transformed extensively since European settlement. However, the potential impact of historical land cover change (LCC) on regional climate has been a secondary consideration in the climate change projections. In this study, we analyzed data from a pair of ensembles (10 members each) for the period 1951–2003 to quantify changes in regional climate by comparing results from pre-European and modern-day land cover characteristics. The results of the sensitivity simulations showed the following: a statistically significant warming of the surface temperature, especially for summer in eastern Australia (0.4–2C) and southwest Western Australia (0.4–0.8C); a statistically significant decrease in summer rainfall in southeast Australia; and increased surface temperature in eastern regions during the 2002/ 2003 El Nino drought event. The simulated magnitude and pattern of change indicates that LCC has potentially been an important contributing factor to the observed changes in regional climate of Australia.”

The conclusions read,

“The findings of our sensitivity experiment indicate that replacing the native woody vegetation with crops and grazing in southwest Western Australia and eastern Australia has resulted in significant changes in regional climate, with a shift to warmer and drier conditions,  especially in southeast Australia, the nation’s major agricultural region. The simulated changes in Australia’s regional climate suggest that LCC is likely a contributing factor to the observed trends in surface temperature and rainfall at the regional scale. While formal attribution studies are required, the outcomes raise important questions about the impact of LCC on Australia’s regional climate, and highlight a strong feedback effect between LCC and the severity of recent droughts impacting on Australia’s already stressed natural resources and agriculture.”

This a very important paper, and yet another example of an issue concering climate change that was mostly ignored by the IPCC assessment.

 

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Comment on Andy Revkin’s New York Times Weblog “Dot Earth”

Andy Revkin has started a dialog on the policy statements of professional organizations with respect to the role of humans within the climate system on his weblo Dot Earth.

 Please enter this discussion if you are a credentialed climate scientist. My comment that I have submitted is

 “Andy – Thank you for bring this issue up. There is actually considerable diversity of views on the role of humans within the climate system. The AGU (and AMS) policy statements are actually written by just a few individuals.  While this captures their views, it is incorrect and inaccurate to present these policy statements as a consensus of these professional organizations. These policy statements certainly do not represent my views on this issue.

Readers of your weblog should also visit my Climate Science weblog [http://climatesci.org/], where other viewpoints are presented, including that of a 2005 National Research Council report entitled

Radiative forcing of climate change: Expanding the concept and addressing uncertainties [http://www.nap.edu/openbook/0309095069/html/].”

I also urge you, for completeness, to post the policy statement of the AGU Natural Hazards Committee.

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