Climate Science: Roger Pielke Sr. Research Group News

There is an important new research paper

Mahmood, R., K.G. Hubbard, R.D. Leeper, and S.A. Foster, 2008: Increase in Near-Surface Atmospheric Moisture Content due to Land Use Changes: Evidence from the Observed Dewpoint Temperature Data. Mon. Wea. Rev., 136, 1554–1561.

The abstract reads

“Land use change can significantly affect root zone soil moisture, surface energy balance, and near-surface atmospheric temperature and moisture content. During the second half of the twentieth century, portions of the North American Great Plains have experienced extensive introduction of irrigated agriculture. It is expected that land use change from natural grass to irrigated land use would significantly increase near-surface atmospheric moisture content. Modeling studies have already shown an enhanced rate of evapotranspiration from the irrigated areas. The present study analyzes observed dewpoint temperature (T_d ) to assess the affect of irrigated land use on near-surface atmospheric moisture content. This investigation provides a unique opportunity to use long-term (1982–2003) mesoscale T_d  data from the Automated Weather Data Network of the high plains. Long-term daily T_d   data from 6 nonirrigated and 11 irrigated locations have been analyzed. Daily time series were developed from the hourly data. The length of time series was the primary factor in selection of these stations. Results suggest increase in growing-season T_d  over irrigated areas. For example, average growing-season T_d due to irrigation can be up to 1.56°C higher relative to nonirrigated land uses. It is also found that T_d  for individual growing-season month at irrigated locations can be increased up to 2.17°C by irrigation. Based on the results, it is concluded that the land use change in the Great Plains has modified near-surface moistness.”

This is yet another paper that documents a major role of landscape change on weather and climate.

It also closely relates to our papers

Davey, C.A., R.A. Pielke Sr., and K.P. Gallo, 2006: Differences between near-surface equivalent temperature and temperature trends for the eastern United States - Equivalent temperature as an alternative measure of heat content. Global and Planetary Change, 54, 19–32.

Pielke Sr., R.A., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content. Eos, 85, No. 21, 210-211

where we show that the inclusion of variations in time of dew point temperatures is an essential component of diagnosing variations in surface air heat content.

The Mahmood et al. paper concludes with the statement (which Climate Science endorses also), that

“It is proposed that the climate change framework should be inclusive of the land use change issue in context of its impacts on the atmospheric system.”

In the weblog Three Climate Change Hypotheses - Only One Of Which Can Be True the conclusion is presented that the correct scientific hypothesis is

While natural variations are important, the human influence is significant and involves a diverse range of first-order climate forcings (including, but not limited to the human input of CO₂).

There is a new paper that further bolsters this perspective. It is

Andreae and Rosenfeld, 2008: Aerosol–cloud–precipitation interactions. Part 1. The nature and sources of cloud-active aerosols. Earth System Reviews.

The abstract reads

“Atmospheric aerosol particles serve as condensation nuclei for the formation of both, cloud droplets and atmospheric ice particles. As a result, they exert a substantial influence on the microphysical properties of water and ice clouds, which in turn affect the processes that lead to the formation of rain, snow, hail, and other forms of precipitation. In recent years, considerable progress has been made in understanding the chemical composition of aerosols, their microphysical properties, and the factors that enable them to act as cloud condensation nuclei (CCN) and ice nuclei (IN).

The first part of this review article will focus on the nature and sources of CCN and IN. We discuss the fundamentals of the cloud droplet and ice nucleation processes, and the role that the chemical composition and particle size play in this process.We show that, in many instances, the influence of chemical composition can be represented by a simple parameterization, which leaves particle size as the main variable controlling CCN efficiency.

Aerosol particles are produced either directly by anthropogenic and natural sources (dust, sea salt, soot, biological particles, etc.), or they are formed in the atmosphere by condensation of low-volatility compounds (e.g., sulfuric acid or oxidized organic compounds). We discuss the magnitude of these sources, and the CCN and IN characteristics of the particles they produce. In contrast to previous assessments, which focused on the aerosol mass, we are emphasizing the number of particles being produced, as this is the key variable in cloud microphysics. Large uncertainties still exist for many aerosol sources, e.g., the submicron part of the seaspray aerosol, the particles produced by the biosphere, and the secondary organic aerosol. We conclude with a discussion on what particle concentrations may have been in the pristine atmosphere, before the onset on anthropogenic pollution. Model calculations and observations in remote continental regions consistently suggest that CCN concentrations over the pristine continents were similar to those now prevailing over the remote oceans, suggesting that human activities have modified cloud microphysics more than what is reflected in conventional wisdom. The second part of this review will address the effects of changing CCN and IN abundances on precipitation processes, the water cycle, and climate.”

The authors start their paper with the statement

“There is now clear and rapidly growing evidence that atmospheric aerosols have profound impacts on the thermodynamic and radiative energy budgets of the Earth…”

The importance of aerosols, that are input into the atmosphere as a result of human activities, also provide evidence to answer the question listed on Tuesday on Climate Science (see);

“How much climate change is natural, how much is attributable to anthropogenic non-CO₂ sources, and how much results from the accumulation of CO₂?”

There clearly are very significant non-CO₂ human climate forcings.

An important paper has been published that further documents the increasing recognition of the role of land surface processes in environmental variability and change, including issues with the climate system. This new paper is

Turner, B.L. II, Eric F. Lambin, and Anette Reenberg, 2007: The emergence of land change science for global environmental change and sustainability, PNAS, vol. 104. no. 52, 20666-20671, 10.1073/pnas.0704119104.

where the abstract reads

“Land change science has emerged as a fundamental component of global environmental change and sustainability research. This interdisciplinary field seeks to understand the dynamics of land cover and land use as a coupled human–environment system to address theory, concepts, models, and applications relevant to environmental and societal problems, including the intersection of the two. The major components and advances in land change are addressed: observation and monitoring; understanding the coupled system—causes, impacts, and consequences; modeling; and synthesis issues. The six articles of the special feature are introduced and situated within these components of study. ”

The article states that

“Changes in land and ecosystems and their implications for global environmental change and sustainability are a major research challenge for the human-environmental sciences.”

In the context of mitigating and adapting to the effects of climate variability and change on society and the environment, it is clear that actions which do not include this first order environmental forcing and feedback are doomed to be inadequate as stated in the Climate Science weblog

Roger A. Pielke Sr.’s Perspective On Adaptation and Mitigation.

The Turner et al. paper also provides refutation of the third hypothesis listed on the Climate Science weblog (and reproduced below)

Three Climate Change Hypotheses - Only One Of Which Can Be True

The three hypotheses are

There is a very important paper, published in 2005, that demonstrates the important role of heterogeneous climate forcings on weather thousands of kilometers removed from the forcing. This paper concerns SST anomalies but the same spatial forcing due to aerosols and land-use change would apply.

This issue of “teleconnection” was one of the findings in the National Research Council report:

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.

On page 5 of that Report, it is written

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

The paper is

Katsafados P., A. Papadopoulos, and G. Kallos, 2005: Regional atmospheric response to tropical Pacific SST perturbations,Geophys. Res. Lett., 32, L04806, doi:10.1029/2004GL021828.

The abstract reads,

“ An extended domain limited area model was implemented for seasonal-range simulations to assess the effect of tropical Pacific SST perturbations on weather patterns over Europe and Mediterranean. The experimental method consisted of Skiron/Eta model integrations with coarse and fine grid increment using artificially-modified as well as analysis SST forcing. The selected period was August–October 1997. Model simulations with coarse grid increment produced a weak signal in the precipitation pattern and the synoptic scale circulation over Europe, implying a damping of the North Atlantic atmospheric response to the tropical Pacific SST perturbation. Fine resolution experiments suggested an amplified dynamic response providing a direct link between tropical Pacific SST and North Atlantic synoptic circulation. The output signal is mainly attributed to the effective representation of the regional/ mesoscale atmospheric features due to the model implementation with a fine mesh grid.”

In the conclusion, the authors write,

“…the results obtained from this study suggest that the tropical ocean does indeed influence the atmospheric patterns over Europe and the Mediterranean.”

The framework of this study provides an excellent approach to assess the importance of teleconnections due to human alterations in regional diabatic heating such as 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.

We have another paper on the role of historical landscape change on the near-surface atmosphere

 Beltrán-Przekurat, A., R.A. Pielke Sr., D.P.C. Peters, K.A. Snyder, and A. Rango, 2008:Modelling the effects of historical vegetation change on near surface atmosphere in the northern Chihuahuan Desert. J. Arid Environments, accepted.

 The abstract reads

“Our goal was to evaluate effects of broad-scale changes in vegetation from grasslands to shrublands over the past 150 years on near-surface atmosphere over the Jornada Experimental Range in the northern Chihuahuan Desert, using a regional climate model. Simulations were conducted using 1858 and 1998 vegetation maps, and data collected in the field. Overall, the vegetation shift led to small changes in sensible heat (SH) and an increase in latent heat (LH). The impacts of shrub encroachment depended on shrubland type: conversion from grass to mesquite cools the near-surface atmosphere and from grass to creosotebush warms it. Higher albedo of mesquite relative to grasses reduced available energy, which was dissipated mainly as LH due to the deeper root system in mesquite. In creosotebush-dominated areas, a decrease in albedo, an increase in roughness length and displacement height contributed to the SH increase and warmer temperatures. Sensitivity simulations showed that an increase in soil moisture content enhanced shrub LH and a reduction in mesquite cover enhanced the temperature differences. The observed shift in vegetation led to complex interactions between land and surface fluxes, demonstrating that vegetation itself is a weather and climate variable as it significantly influences temperature and humidity.”

The evidence that landscape alteration, both deliberate and inadvertant, is a first-order climate forcing should be a priority when setting climate policy. However, the current United States Senate debate on a “climate bill” ignores the major role of land surface processes on climate.

If the  Senate were serious about climate policy, they would include landscape issues. Of course, the Senate is actually debating an energy bill in the guise of climate policy (see for a summary of the Climate Science Perspective on this issue).

We have completed a new review chapter on the role of landscape processes within the climate system, as well as added to our discussion of the need for bottom-up, resource based vulnerability assessments. The information on this contribution is in

Pielke Sr. R.A., and D. Niyogi, 2008: The role of landscape processes within the climate system. In: Otto, J.C. and R. Dikaum, Eds., Landform - Structure, Evolution, Process Control: Proceedings of the International Symposium on Landforms organised by the Research Training Group 437. Lecture Notes in Earth Sciences, Springer, Vol. 115, in press.

The Introduction starts with

“Land-surface processes form a dynamic boundary interface within the earth system (Fig. 1). The multiscale impacts of land-surface processes in modifying regional weather and climate is noted from both the analysis of observations, as well as systematic experiments involving nonlinear, coupled modeling systems. Landscape processes and their interactions with the atmosphere are critical at different micro, regional, and global scales for weather, hydrological and other broad range environmental modeling studies (Alpert et al. 2006).

The land-surface characteristics determine the surface energy partitioning by assigning the distribution of incoming solar radiative energy (insolation) into sensible, latent, and ground heat fluxes. The change in the surface radiative energy affects regional- and larger-scale moisture and temperature. Modifications in the surface fluxes and the thermodynamic parameters lead to changes in regional wind fields and localized circulation patterns. The changes in the wind and regional thermodynamic variables alter convective potential and interact with large-scale processes to affect the amount and distribution of clouds and rainfall (Pielke et al. 2007a). At a larger scale, the systematic transformation of the land surface can alter regional flow patterns associated with developing persistent zones of moisture convergence, and localized pockets that lead to long-term regional warming or cooling.

The role of landscape process within the climate assessments however has been mostly ignored except in terms of how carbon assimilation is affected. As summarized in National Research Council (2005), the role of vegetation and soils is much more than that and includes effects on water and heat storage and fluxes, as well as on a variety of other gases and aerosols. The climate system is an integration of physical, biological, and chemical effects associated with land, atmosphere, ocean, and continental ice interactions. The current IPCC (2007) focus on the radiative forcing of the well-mixed greenhouse gases is too limiting; a broadening in its perspective is overdue. The current view, unfortunately, does not properly address the diverse effect of the human disturbance of the climate system. The role of land-surface forcing and feedbacks within the climate system, as one important example of this need for broadening, provides a dynamical feedback that is required if regional-scale climate assessments are to become skillful.”

Later in the chapter, we emphasize the need for the further development of assessments of vulnerability, and that this should be the starting point for the information provided to policymakers rather than information created at the end of a chain of downscaling from the multi-decadal global climate models. 

Section 2.d of the Chapter starts with the text

“Within the climate system, the need to consider the broader role of land-surface feedback becomes important not only for assessing the impacts but also for developing regional vulnerability and mitigation strategies.
 

The IPCC fourth assessment second and third working groups deal with a range of issues targeted to these topics (Schneider et al. 2007). The IPCC identifies seven criteria for ‘key’ vulnerabilities. They are: magnitude of impacts, timing of impacts, persistence and reversibility of impacts, likelihood (estimates of uncertainty) of impacts and vulnerabilities and confidence in those estimates, potential for adaptation, distributional aspects of impacts and vulnerabilities, and the importance of the system(s) at risk. While a number of potential vulnerabilities and uncertainties are considered (such as irreversible change in urbanization), the resulting feedback on the atmospheric processes due to such changes is still poorly understood or unaccounted for in these assessments. Indeed the UNFCCC Article 1 states: “’Adverse effects of climate change’ means changes in the physical environment or biota resulting from climate change which have significant deleterious effects on the composition, resilience or productivity of natural and managed ecosystems or on the operation of socio-economic systems or on human health and welfare.” Thus, while the role of landscape is inherent within the UNFCCC framework, the corresponding translation for the assessments still remains largely greenhouse gas driven.

Further, while the climate change projections have largely been at coarser resolution, the impacts and potential mitigation policies are often at local to regional scales. For example, climate models often project increasing drought at a regional scale. The resilience to such increased occurrence as well as changes in the intensity of droughts is, however, dependent on the local scale environmental conditions (such as moisture storage, and convective rainfall), and farming approaches (access to irrigation, timing of rain or stress, etc). As summarized in Adger (1996), an important issue for IPCC-like global assessments is to assess if the top-down approach can incorporate the “aggregation of individual decision-making in a realistic way, so that results of the modelling are applicable and policy relevant.”

We conclude the chapter with the paragraph

“Finally, unless there is a broadening of the current IPCC focus it will only lead to promote energy policy changes, and not provide an effective climate policy, which necessarily needs to include how humans are altering the climate system through land surface processes. Policymakers need to be informed of this very important distinction where a separation of climate policy from energy policy is essential.”

Thanks to Major Robb Randall for alerting us to the paper by M. Susan Lozier, Susan Leadbetter, Richard G. Williams, Vassil Roussenov, Mark S. C. Reed, and Nathan J. Moore entitled “The Spatial Pattern and Mechanisms of Heat-Content Change in the North Atlantic” originally published in Science Express on 3 January 2008, Science 8 February 2008, Vol. 319., no. 5864, pp. 800 - 803, DOI: 10.1126/science.1146436

The abstract reads

“The total heat gained by the North Atlantic Ocean over the past 50 years is equivalent to a basinwide increase in the flux of heat across the ocean surface of 0.4 ± 0.05 watts per square meter. We show, however, that this basin has not warmed uniformly: Although the tropics and subtropics have warmed, the subpolar ocean has cooled. These regional differences require local surface heat flux changes (±4 watts per square meter) much larger than the basinwide average. Model investigations show that these regional differences can be explained by large-scale, decadal variability in wind and buoyancy forcing as measured by the North Atlantic Oscillation index. Whether the overall heat gain is due to anthropogenic warming is difficult to confirm because strong natural variability in this ocean basin is potentially masking such input at the present time.”

The authors conclude with the text,

“Lastly, the positive trend in the winter NAO index in the 1990s has been attributed to anthropogenic forcing (Hurrell 1995), implying that the NAO could be the route by which anthropogenic warming is imprinted on the ocean. However, although most climate models show a slight strengthening of the NAO index with anthropogenic forcing, the climate models also underestimate the strength of the recent decadal trend in the NAO, raising doubts as to the viability of the connection between the NAO and anthropogenic forcing in climate models (Gillett et al. 2003; Stephenson et al. 2006). Hence, although the change in ocean heat content over the North Atlantic can be connected to the decadal trend in the NAO, it is premature to conclusively attribute these regional patterns of heat gain to greenhouse warming. Continued long-term monitoring of North Atlantic temperatures is needed to answer the question of whether the basin-average warming is reflecting anthropogenic forcing and/or natural variability. ^“

This paper illustrates yet another shortcoming of the global climate models that are used to predict the climate system in the coming decades. They cannot accurately simulate the important climate feature of the North Atlantic Oscillation (the NAO). As the authors, themselves write “it is premature to conclusively attribute these regional patterns of heat gain to greenhouse warming.”  This shortcoming of the multi-decadal global models applies to other low frequency climate variations, such as ENSO and  the North Pacific Decadal Oscillation, which are major factors in the climate that we experience.

I would like to thank Dr. Peter Lawrence from CIRES, CU Boulder and Gordon Bonan from NCAR in Boulder for alerting us to the following paper:

Zaitchik, B.F., A.K. Macaldy, L.R. Bonneau, and R.B. Smith, 2006: Europe’s 2003 heat wave: A satellite view of impacts and land atmosphere feedbacks. Int. J. Climatol. 26: 743–769.

The abstract reads
 

“A combination of satellite imagery, meteorological station data, and the NCEP/NCAR reanalysis has been used to explore the spatial and temporal evolution of the 2003 heat wave in France, with focus on understanding the impacts and feedbacks at the land surface. Vegetation was severely affected across the study area, especially in a swath across central France that corresponds to the Western European Broadleaf (WEB) Forests ecological zone. The remotely sensed surface temperature anomaly was also greatest in this zone, peaking at +15.4°C in August. On a finer spatial scale, both the vegetation and surface temperature anomalies were greater for crops and pastures than for forested lands. The heat wave was also associated with an anomalous surface forcing of air temperature. Relative to other years in record, satellite-derived estimates of surface-sensible heat flux indicate an enhancement of 48–61% (24.0–30.5 W m⁻²) in WEB during the August heat wave maximum. Longwave radiative heating of the planetary boundary layer (PBL) was enhanced by 10.5 W m⁻² in WEB for the same period. The magnitude and spatial structure of this local heating is consistent with models of the late twenty-first century climate in France, which predict a transitional climate zone that will become increasingly affected by summertime drought. Models of future climate also suggest that a soil-moisture feedback on the surface energy balance might exacerbate summertime drought, and these proposed feedback mechanisms were tested using satellite-derived heat budgets.”

The authors conclude with the text,

“This study further suggests that extreme heat waves have implications for ecology and land management. A number of studies focused on trends in NDVI across the higher latitudes, for example, have documented an increase in mean NDVI associated with the warming of recent decades (Zhou et al., 2001; Zhou et al., 2003; Stöckli and Vidale, 2004). For Europe specifically, Stöckli and Vidale (2004) document a 0.96 day year⁻¹lengthening of the growing season (mostly due to earlier green-up) and a corresponding 0.78% increase in NDVI. In their German subdomain (closest to the present study region), the increase is even greater. The present results are not inconsistent with this finding, as the 2003 anomaly in NDVI was positive during spring green-up. In 2003, however, the negative impacts of late-summer drought overwhelmed the positive effects of a warmer spring, leading to a net reduction in NDVI integrated over the growing season. If heat waves like that of 2003 become typical in the future European climate, then it is possible that ‘extreme’ events may change the observed trend in NDVI in some portions of Europe, with implications for regional hydrology, agricultural and forestry outlooks, and terrestrial carbon sequestration.”

While the paper, unfortunately, includes text on what could occur in late 21st century France based on the multi-decadal global model predictions (which are not skillful prediction tools), it does provide further confirmation on the important role of landscape in this heat wave, as we discussed in our paper

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

There is  a very important new weblog on water vapor and cloud feedbacks within the climate system as represented by the models used to project multi-decadal climate change. The paper is

Sun, D.-Z., Y. Yu, and T. Zhang, 2007: Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations. J. Climate, Submitted. [a powerpoint talk of this research was completed for my class last spring (see Validating and Understanding Feedbacks in Climate Models).

The abstract reads,

By comparing the response of clouds and water vapor to ENSO forcing in nature with that in AMIP simulations by some leading climate models, an earlier evaluation of tropical cloud and water vapor feedbacks has revealed two common biases in the models: (1) an underestimate of the strength of the negative cloud albedo feedback and (2) an overestimate of the positive feedback from the greenhouse effect of water vapor. Extending the same analysis to the fully coupled simulations of these models as well as to other IPCC coupled models, we find that these two common biases persist. Relative to the earlier estimates, the overestimate of the positive feedback from water vapor is alleviated somewhat for most of the models. Improvements in the simulation of the cloud albedo feedback are only found in the models whose AMIP runs suggest a positive or nearly positive cloud albedo feedback. The strength of the negative cloud albedo feedback in all other models is found to be substantially weaker than that estimated from the corresponding AMIP simulations. Consequently, all models analyzed in this study are found to have a weaker negative feedback from the net surface heating over the ocean than that indicated in observations. The weakening in the cloud albedo feedback is linked to a reduced response of deep convection over the equatorial Pacific which is in turn linked to the excessive cold-tongue in the mean climate of these models. The results highlight that the feedbacks of water vapor and clouds—the cloud albedo feedback in particular—depend on the mean intensity of the hydrological cycle. We have also examined whether the variations among models of the feedback from cloud albedo (water vapor) in the ENSO variability are correlated with the variations among models of the feedback from cloud albedo (water vapor) in global warming. While we find a weak positive correlation between the variations among models in the feedback of water vapor during ENSO and the variations among models in the water vapor feedback during global warming, we find no significant correlation between the variations among models in the cloud albedo feedback during ENSO and the variations among models in the cloud albedo feedback during global warming. We thereby suggest that the two common biases revealed in the simulated ENSO variability may not be carried over to the simulated global warming, though these biases highlight the continuing difficulty that models have to simulate accurately the feedbacks of water vapor and clouds on a time-scale we have observations.

The conclusion the paper has the text,

“The extended calculation using coupled runs confirms the earlier inference from the AMIP runs that underestimating the negative feedback from cloud albedo and overestimating the positive feedback from the greenhouse effect of water vapor over the tropical Pacific during ENSO is a prevalent problem of climate models. The estimates from the coupled simulations of both the cloud albedo feedback and the water vapor feedback differ from the estimates from the corresponding AMIP simulations. The changes in the cloud albedo feedback are particularly significant. The previous analysis of Sun et al. (2006) has suggested that the GFDL CM2 may have a cloud albedo feedback that is as strong as observations. The new estimate with the coupled runs puts this suggestion in doubt as the new estimate is significantly weaker than the previous estimate. All models we have examined in this analysis are found to have a weaker negative feedback from the net surface heating than that from observations, indicating that deep convection over the equatorial Pacific in the models has a weaker regulatory effect over the SST in that region. The differences between the values estimated from the coupled runs and the values estimated from the corresponding AMIP runs are shown to be linked to the excessive cold-tongue in the climatology in the coupled models.

The two common biases, shown in the ENSO cycle, however, do not appear to be carried over the global warming simulations. The variations in the cloud albedo feedback among different models are not correlated with the variations in the same feedback in the global warming simulations among different models. The variations in the water vapor feedback among different models during ENSO over the cold-tongue are positively correlated with the variations in the water vapor feedback during global warming, but the correlation is weak. There is no correlation between the feedbacks over the cold-tongue region during ENSO and the globally averaged feedbacks during global warming. Therefore, the overestimate of the water vapor feedback and the underestimate of the cloud albedo feedback during the ENSO cycle in the models do not necessarily imply that the sensitivity of the mean tropical climate to anthropogenic forcing is overestimated by the models. On the other hand, we are not suggesting that the prevalence of these two biases in the models during ENSO should not be of concern for the accuracy of global warming simulated by the models. This is because the lack of correlation in the models between the feedbacks on these two time-scales could be due to error cancellations in the models. In any case, the present results highlight the continuing difficulty that models have in simulating accurately the water vapor and cloud feedbacks in the deep tropics on the time-scale over which we have observations to compare with model simulations. The results should also be of value to the diagnosis of the causes of the biases in the ENSO amplitude in the models.”

An important conclusion from the Sun et al study is that “all models analyzed in this study are found to have a weaker negative feedback from the net surface heating over the ocean than that indicated in observations.”

The authors further state that

“We thereby suggest that the two common biases revealed in the simulated ENSO variability may not be carried over to the simulated global warming, though these biases highlight the continuing difficulty that models have to simulate accurately the feedbacks of water vapor and clouds on a time-scale we have observations”.

However it is not clear how such a bias could be removed when the models are applied in longer term model projections. Indeed, what is the data which says that the biases are removed?

FOLLOW UP

In order to obtain an answer to the above question, I contacted Dr. Sun with the following
“I have set for your paper to be weblogged on in a couple of weeks. However, I have a question on your conclusion that ‘We thereby suggest that the two common biases revealed in the simulated ENSO variability may not be carried over to the simulated global warming, though these biases highlight the continuing difficulty that models have to simulate accurately the feedbacks of water vapor and clouds on a time-scale we have observations’, however it is not clear how such a bias could be removed when the models are applied in longer term model projections. Indeed, what is the data which says that the biases are removed?

Please clarify and I can add to the weblog.”

REPLY FROM DR. SUN

“You are right that no data have shown that those biases will not be removed. We are just mentioning the possibility that there could be error cancellation as global warming may involve more processes that those in ENSO, and the errors may cancel in such a way that prediction of global warming by these models that have these errors may actually get the answer right.  It is just a possibility worth mentioning.”

The message from the Sun et al. study, therefore, is that the models used to make the multi-decadal global climate projections that are reported in the IPCC report are “…that underestimating the negative feedback from cloud albedo and overestimating the positive feedback from the greenhouse effect of water vapor over the tropical Pacific during ENSO is a prevalent problem of climate models.” 

This study indicates that the IPCC models are overpredicting global warming in response to positive radiative forcing.

There is an important new paper on the role of landscape processes within the climate system [and thanks to Tobis Rothenberger at the University of St. Gallen for alerting us to it!].  The article is

Barnes, C. A., and D. P. Roy (2008), Radiative forcing over the conterminous United States due to contemporary land cover land use albedo change, Geophys. Res. Lett., 35, L09706, doi:10.1029/2008GL033567.

The abstract reads

“Recently available satellite land cover land use (LCLU) and albedo data are used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 36 ecoregions covering 43% of the conterminous United States (CONUS). Moderate Resolution Imaging Spectroradiometer (MODIS) snow-free broadband albedo values are derived from Landsat LCLU classification maps located using a stratified random sampling methodology to estimate ecoregion estimates of LCLU induced albedo change and surface radiative forcing. The results illustrate that radiative forcing due to LCLU change may be disguised when spatially and temporally explicit data sets are not used. The radiative forcing due to contemporary LCLU albedo change varies geographically in sign and magnitude, with the most positive forcings (up to 0.284 Wm⁻²) due to conversion of agriculture to other LCLU types, and the most negative forcings (as low as −0.247 Wm⁻²) due to forest loss. For the 36 ecoregions considered a small net positive forcing (i.e., warming) of 0.012 Wm⁻² is estimated.”

The conclusion includes the text

“ Loss of agricultural and forested lands were observed to be the LCLU changes that caused the greatest absolute albedo induced forcing. Across the CONUS however there is no single profile of LCLU change, rather, there are varying pulses affected by clusters of change agents [Loveland et al., 2002]. This argues strongly for the ecoregion based analysis we have described, as continental averages may mask regional differences; indeed, because of the variability in magnitude and sign of forcing, we estimate only a small, 0.012 Wm⁻², net CONUS forcing due to contemporary LCLU albedo change. This work did not consider snow, which may have a significant land cover dependent albedo effect [Jin et al., 2002] and so may impact the forcing associated with actual albedo change [Betts, 2000]; however, only about one eighth of the CONUS ecoregions considered in this study have significant annual snow cover. Further research will be undertaken to address these impacts for a larger number of ecoregions as more LCLU change data become available.”

This study is yet another example of why we need to include the assessment of landscape on the regional scale, as altered by humans, in terms of how our climate is being changed.