Monthly Archives: August 2006

New Papers on the Importance of Land Use/Land Cover Change on Climate

Thanks to Timo Hämeranta, several new papers on the important role of land surface processes in the climate system are listed below. These are

1) Kleidon, Axel, 2006. The climate sensitivity to human appropriation of vegetation productivity and its thermodynamic characterization. Global and Planetary Change, in press, corrected proof available online 26 July 2006. The abstract reads,

” Humans appropriate terrestrial productivity to meet their food supply, their primary source of free energy. Removal of productivity from terrestrial vegetation has its direct impacts in that less energy is available for vegetation growth. Since vegetation strongly shapes the physical exchange of energy, water and momentum at the land surface, a lower ability for vegetation growth should affect this surface exchange, the overlying atmosphere, and therefore climate. Here I attempt to quantify the climate sensitivity to different intensities of human appropriation of vegetation productivity. I use sensitivity simulations with a coupled dynamic vegetation–climate system model of intermediate complexity in which I artificially remove different fractions of the simulated net primary productivity to implement human appropriation, thus reducing vegetation growth in the model. The simulations show noticeable differences in the surface energy- and water balance, with a consistent reduction in the amount of absorbed solar radiation and latent heat flux of up to 10 W m− 2 and 27 W m− 2 respectively and a reduction in continental precipitation by up to 30% in the global land mean when compared to the “Controlâ€? climate. However, the study also shows that mean land surface temperature is insensitive at the global scale despite pronounced regional patterns and is therefore not well suited to characterize the climatic sensitivity to land cover change at the global scale. I motivate the use of entropy production to characterize climate sensitivity. Entropy production is a thermodynamic measure of the strength of dissipative processes which perform physical work. With this measure, I show that the climate sensitivity is reflected as a clear trend towards less entropy production over land with increased intensity of human appropriation of NPP in general, and less entropy production by biotic activity in particular. I conclude that large-scale land cover changes are likely to lead to a noticeably different climate which is less favorable to biotic productivity and that this climate sensitivity is well captured by differences in entropy production as a meaningful, thermodynamic measure. “

An important conclusion of this paper, which has also been one of the conclusions of Climate Science (e.g. see), is that

“However, the study also shows that mean land surface temperature is insensitive at the global scale despite pronounced regional patterns and is therefore not well suited to characterize the climatic sensitivity to land cover change at the global scale.”

2) Mahmood, Rezaul, Stuart A. Foster, Travis Keeling, Kenneth G. Hubbard,
Christy Carlson, and Ronnie Leeper, 2006. Impacts of irrigation on 20th century temperature in the northern Great Plains. Global and Planetary Change, in press, corrected proof available online 28 July 2006. The abstract of this paper reads,

“Land use change can modify root zone moisture distribution, energy partitioning and subsequently, near surface energy balance. Various modeling studies provided evidence of these changes. For example, land use change from natural grass land to irrigated land use would significantly increase and decrease latent and sensible energy flux, respectively. This type of long-term modification of energy balance would in turn change near surface temperatures. The Great Plains of North America experienced significant overturning of land from natural grass land to irrigated land use during the 20th century. This study provides assessment on the changes in the historical near surface temperature records in Nebraska, USA. Long-term mean monthly maximum, minimum, and monthly mean air temperature data from 5 irrigated and 5 non-irrigated sites were analyzed. Length and homogeneity of time series and stability of stations were primary determinants in selection of these stations. The time series include Cooperative Weather Observation Network (COOP) and Historical Climate Network (HCN) data sets. Pairwise comparisons of temperatures between irrigated and non-irrigated locations for pre- and post-1945, -1950, and -1955 periods were completed for both data sets. These breakdowns of time series helped to identify periods of widespread land use change. Results show notably cooler temperatures over irrigated areas. For example, mean maximum growing season temperature at irrigated Alliance was 0.64 °C and 1.65 °C cooler compared to non-irrigated Halsey during pre- and post-1945 period, respectively. Hence, there was a 1.01 °C cooling during post-1945 years. Moreover, there has been a greater cooling during the second half of 20th century. The bootstrap re-sampling method was applied and trend analyses were completed for further verification of results. These assessments largely show a decreasing trend in mean maximum growing season temperatures over irrigated areas. To further verify the results and to determine the impacts of extreme values (including extremely cool temperatures), the 20% trimmed mean approach was applied. The impacts of extreme values have been minimal and based on the results obtained we conclude that land use change in the northern Great Plains has modified near surface temperature records. “

An important conclusion from this paper, that has also been concluded for a wide range of geographic regions on Climate Science (e.g.see), is that

“…….we conclude that land use change in the northern Great Plains has modified near surface temperature records.”

3) Ramankutty, Navin, Christine Delire, and Peter Snyder, 2006. Feedbacks between agriculture and climate: An illustration of the potential unintended consequences of human land use activities. Global and Planetary Change, in press, corrected proof available online 11 July 2006. The abstract reads,

“Agriculture has significantly transformed the face of the planet. In particular, croplands have replaced natural vegetation over large areas of the global land surface, covering around 18 million km2 of the land surface today. To grow crops, humans have taken advantage of the resource provided by climate — optimum temperature and precipitation. However, the clearing of land for establishing croplands might have resulted in an inadvertent change in the climate. This feedback might, in turn, have altered the suitability of land for growing crops. In this sensitivity study, we used a combination of land cover data sets, numerical models, and cropland suitability analysis, to estimate the degree to which the replacement of natural vegetation by croplands might have altered the land suitability for cultivation. We found that the global changes in cropland suitability are likely to have been fairly small, however large regional changes in cropland suitability might have occurred. Our theoretical study showed that major changes in suitability occurred in Canada, Eastern Europe, the Former Soviet Union, northern India, and China. Although the magnitude, sign, and spatial patterns of change indicated by this study may be an artifact of our particular model and experimental design, our study is illustrative of the potential inadvertent consequences of human activities on the land. Moreover, it offers a methodology for evaluating how climate changes due to human activities on the land may alter the multiple services offered by ecosystems to human beings. .”

Among the conclusions of this paper, is that their research methodology,

“….offers a methodology for evaluating how climate changes due to human activities on the land may alter the multiple services offered by ecosystems to human beings.”

This perspective fits with the framework that has been advocated on Climate Science of seeking to assess the vulnerability of important societal resources to the spectrum of social and environmental risk, including inadvertent land use change effects on climate (e.g. see).

These three papers add to an already overwhelming conclusion of the first-order climate effect of human alteration of the landscape. The drafts of the current IPCC Report that I have seen, as well as the first CCSP Report (see), have failed so far to adequately consider the importance of this climate forcing.

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Mismatch Between Multi-decadal Global Climate Models Predictions And The Global Radiative Imbalance

There is a clear mismatch between the model predictions reported in the 2005 Science article by Hansen, J., L. Nazarenko, R. Ruedy, Mki. Sato, J. Willis, A. Del Genio, D. Koch, A. Lacis, K. Lo, S. Menon, T. Novakov, Ju. Perlwitz, G. Russell, G.A. Schmidt, and N. Tausnev 2005. “Earth’s energy imbalance: Confirmation and implications” , and the observational results in the Geophysical Research Letters paper by John M. Lyman, Josh K. Willis, and Gregory C. Johnson entitled “Recent Cooling of the Upper Oceanâ€?.

The abstract of the Hansen et al article reads,

“Our climate model, driven mainly by increasing human-made greenhouse gases and aerosols among other forcings, calculates that Earth is now absorbing 0.85±0.15 W/m2 more energy from the Sun than it is emitting to space. This imbalance is confirmed by precise measurements of increasing ocean heat content over the past 10 years. Implications include: (i) expectation of additional global warming of about 0.6°C without further change of atmospheric composition; (ii) confirmation of the climate system’s lag in responding to forcings, implying the need for anticipatory actions to avoid any specified level of climate change; and (iii) likelihood of acceleration of ice sheet disintegration and sea level rise.”

However, the new Lyman et al 2006 study which also is based on the same “precise measurements of increasing ocean heat content” report that the global radiative imbalance for 1993 through 2005, for the entire 13-year period, was an average warming rate of 0.33 ± 0.23 W/m2 , as a result of the 2003 to 2005 period which has a diagnosed radiative imbalance of -1.0 (+/- 0.3) W/meter squared.

The Comments on the Climate Science weblog with respect to earlier weblogs on the Lyman et al 2006 paper (see and see) include raising the issue on the relationship of this recent cooling to the reported continuing rise in the global average sea level. This is an appropriate scientific question.

However, if the upper ocean heat content data was considered precise in the Hansen et al 2005 study, and was used in that paper to bolster the confidence in their ability to model global climate process, then the same confidence should be placed on the recent diagnosis of observed cooling. The mismatch between the data and the model predictions, however, raises serious questions on the ability of the multi-decadal global climate models to accurately predict even the global average variability and long term trend of the radiative imbalance of the climate system.

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Coupled Ocean-Atmosphere Response to Seasonal Modulation of Ocean Color: Impact on Interannual Climate Cimulations in the Tropical Pacific by Raghu Murtugudde

State of the art climate models continue to be plagued by some standard biases especially in the crucial regions such as the tropical Pacific (http://www.usclivar.org/Meeting_Files/SSC 11/Bias_worskhop_summary.pdf) which has a global reach through El Nino-Southern Oscillation (ENSO). One such bias is the so-called ‘cold bias’ where the model sea surface temperatures are typically colder than observed leading to a stronger east-west gradient, stronger winds, and the related cascades into annual cycle errors and thus ENSO and its teleconnections.

It has been known for decades that microscopic algae in the ocean convert light to heat during photosythesis and other suspended solids in the ocean also affect light attenuation in the water column. Satellites like SeaWiFS now provide global maps of pigments and other materials which affect light absorption in the ocean. With this global information, we can now specify the e-folding depth for light-attenuation in ocean general circulation models and represent the conversion of light to heat by the photosynthesizing critters (http://essic.umd.edu/~ragu/biofeedbacks/murtuguddeqpen.pdf).

The eastern equatorial Pacific is a really unique place with the mixed layer variability interacting closely with the location of the maximum chlorophyll concentrations. During the boreal spring months when the mixed layer is shallow due to weak winds and maximum surface heating, the chlorophyll maximum is just below the mixed layer since the thermo/nutricline are just below the mixed layer, i.e., in the euphotic zone. This provides a heat source of about 5-20 W/m2 depending on the strength of the chlorophyll maximum and this heat restratifies the water column leading to a deeper mixed layer and momentum penetration, thus weaker surface divergence and subsurface upwelling. Much of the ‘cold-bias’ is thus alleviated if this bio-climate feedback is represented appropriately (http://essic.umd.edu/~ragu/biofeedbacks/quimfeedback.pdf).

A hybrid coupled model and physical-biological models confirm that improving the annual cycle in this way is a natural solution to improving the annual phase-locking of the ENSO events in the model (http://essic.umd.edu/~ragu/biofeedbacks/coupledfeedbacks.pdf). The assumption that annual biases do not impact ENSO simulations and predictions thus appears not to be very robust since improving the annual cycle of the coupled system also improves the ENSO cycle by improved mixed layer-thermocline or Bjerknes feedbacks (http://essic.umd.edu/~ragu/biofeedbacks/marzeion.pdf).

Models tend to produce ENSO-like behavior that is surface-trapped and quasibienniel (http://www.grida.no/climate/ipcc_tar/wg1/024.htm) whereas improved Bjerknes feedback due to accurate biological feedbacks provides a more accurate representation of the recharge-discharge processes thus improving the ENSO amplitude and frequencies. As we continue to increase the complexity of our coupled climate models, these processes have to be represented appropriately since bio-climate feedbacks also occur in other regions of the World Ocean and also over land (http://www.gfdl.noaa.gov/~jpd/esmdt.html).

Raghu Murtugudde, Assoc. Professor, ESSIC/DAOS, Univ of MD, College Park, MD 20742
http://essic.umd.edu/~ragu

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Information on the Argo Ocean Monitoring Network

In order to let readers of Climate Science have a clear idea of the spatial distribution of the upper ocean temperature distributions that were used so effectively in the Lyman et al 2006 study “Recent Cooling of the Upper Oceanâ€? [see and see ] information on the Argo monitoring network is provided below.

A summary of Argo is available (see). Excerpts from the Argo webiste are,

“Argo is a global array of 3,000 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection.”

The objectives of Argo are:

“It will provide a quantitative description of the changing state of the upper ocean and the patterns of ocean climate variability from months to decades, including heat and freshwater storage and transport.

The data will enhance the value of the Jason altimeter through measurement of subsurface temperature, salinity, and velocity, with sufficient coverage and resolution to permit interpretation of altimetric sea surface height variability.

Argo data will be used for initializing ocean and coupled ocean-atmosphere forecast models, for data assimilation and for model testing.

A primary focus of Argo is to document seasonal to decadal climate variability and to aid our understanding of its predictability. A wide range of applications for high-quality global ocean analyses is anticipated. “

The data density of the Argo network can be viewed here.

The Lyman et al 2006 GRL paper demonstrates the value of this data, including the demonstration that when multi-decadal climate predictions are compared with real-world data, the models can fail to explain observed climate variability and change.

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Max Mayfield, Director of the National Hurricane Center Announces His Retirement

The weather and climate community will lose a valuable public servant whose work has saved lives. Max Mayfield, Director of the National Hurricane Center is retiring at the end of this season (see). We wish him continued success in whatever he chooses to do, as well as look forward to his continued involvement in weather and climate science.

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Research Papers On The Accuracy Of Weather and Climate Modeling Simulation and Prediction Of The Stable Atmospheric Boundary Layer

A set of excellent papers has appeared in Boundary Layer Meteorology on the stable atmospheric boundary layer. This research is led by Professor Bert Holtslag of Wageningen University, and is part of the GEWEX Atmospheric Boundary-layer Study (GABLS) on Stable Boundary Layers program. The stable boundary layer occurs on most nights, and persists for months at high latitudes over land and sea ice in the winter.

An important research question is whether global and regional climate models can accurately simulate the stable boundary layer, including long term near surface temperature variability and trends that result from natural- and human-climate forcings and feedbacks. The research papers presented in the Boundary Layer Meteorology document that major issues remain on the ability of the climate (and weather) models to skillfully simulate stable boundary layer processes, including near surface temperatures.

Excerpts from two of the papers (subscriptions required) read,

[from "Modeling the arctic stable boundary layer and its coupling to the surface" by Steeneveld et al],

“The impact of coupling the atmosphere to the surface energy balance is examined for the stable boundary layer, as an extension of the first GABLS (GEWEX Atmospheric Boundary-Layer Study) one-dimensional model intercomparison. This coupling is of major importance for the stable boundary-layer structure and its development because coupling enables a realistic physical description of the interdependence of the surface temperature and the surface sensible heat flux. In the present case, the incorporation of a surface energy budget results in stronger cooling (surface decoupling), and a more stable and less deep boundary layer. The proper representation of this is a problematic feature in large scale numerical weather prediction and climate models…..”

and from ["Preface: GEWEX Atmospheric Boundary-layer Study (GABLS) on Stable Boundary Layers" by Bert Holtslag],

“Unfortunately regional and global climate models show great sensitivity to the model formulation of mixing in stratified conditions. As an example, Viterbo et al. (1999) studied the vertical mixing in the ECMWF model in stable conditions. From two model runs with the same forcing conditions, but with (slightly) different stability functions in the mixing scheme, they noticed that differences in the mean winter temperatures at a height of 2m between the two model runs can be as large as 10 K over continental areas.

In addition, King et al. (2001) found similar results between model runs for the winter climate over Antarctica. Also over Europe, it was found that significant differences are present between the 2-m temperatures of a 30- year regional climate simulation with observations for present day winter climate (e.g., Lenderink et al., 2003). It also appears that the magnitude of the diurnal temperature cycle is typically underestimated over land….”

“Within GABLS, a rather simple case was selected as a benchmark to review the state of the art and to compare the skills of single column (1D) models (Cuxart et al., 2006) and large-eddy simulation (LES) models (Beare et al., 2006). The papers in this special volume report on these findings. The case studied is based on the results originally presented by Kosovic and Curry (2000). As such the stable boundary layer is driven by an imposed, uniform geostrophic wind, with a specified surface-cooling rate over (homogeneous) ice. Overall it turns out that, with the same initial conditions and model forcings, the results of the LES models are surprisingly consistent (Beare et al., 2006). As such the LES outputs can serve as suitable reference for the 1D models. Moreover, the results of the LES models are consistent with field observations and local scaling ideas (Nieuwstadt, 1984), at least for the case studied here.

In contrast, the 1D models indicate a large range of results for the mean temperature and wind profiles as well as for the heat and momentum flux profiles (Cuxart et al., 2006). As expected the models in use at operational weather forecast and climate centres typically allow for enhanced mixing, while typical research models show less mixing, more in agreement with the LES results for this case. Because of the enhanced mixing in weather and climate models, these models tend to show too strong surface drag, a too deep boundary layer, and an underestimation of the wind turning in the lower atmosphere. However, by decreasing the mixing and surface drag, a direct impact on the atmospheric dynamics (‘Ekman pumping’) is noted (e.g., Beljaars and Viterbo, 1998). Consequently, cyclones may become too active, corresponding with too high an extremes for wind speed and for precipitation. When the models with enhanced mixing are coupled to a surface energy balance, they also produce a too high surface temperature (e.g., Steeneveld et al., 2006). Given the latter arguments and the current GABLS findings, there is still a clear need for a better understanding and a more general description of the atmospheric boundary layer under stably stratified conditions in atmospheric models for weather and climate.”

Since the 1D models are the type used in the parameterization of the stable boundary layer in multi-decadal climate model projections, this is yet another reason to question their use as accurate predictive models, including their use to forecast the long term trends in near surface air temperature over land and sea ice.

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December 2006 American Geophysical Union meeting “Aerosol Cloud-Precipitation

What promises to be an informative climate science meeting is scheduled for December 2006 at the American Geophysical Union meeting in San Francisco. The Session is entitled “Aerosol Cloud-Precipitation Interaction: Facts and Fiction“. The announcement for the meeting reads,

“This session, which was initiated by the recently deceased Dr. Yoram Kaufman, recognizes his contributions to studies of aerosol, cloud and precipitation interactions. Aerosol interaction with clouds and precipitation is one of the most complex yet most important array of processes in the climate system. Aerosols affect clouds through determining their microstructure, and through affecting atmospheric and surface temperatures. Clouds process aerosols and their precursors, changing the aerosol size distributions and CCN concentrations that feed back on the clouds. Aerosols were shown to induce changes in cloudiness, in precipitation patterns, in regional circulations and in cloud-mediated forcing of climate. We are in the early stages of research and our knowledge may be faulty and lacking. Therefore we seek contributions that untangle these effects, distinguish facts from fiction using in situ and remote observations and model analysis, and discuss regional implications. The session is designed to foster stronger links between measurements, models and regional assessments.

We are looking forward to your participation and contributions to this exciting and controversial topic.”

The summary of this meeting accentuates how much more we need to learn about the climate system, including the role of humans. An obvious interpretation from this meeting announcement is that accurate multi-decadal climate predictions are not possible since we inadequately understand the diverse roles of aerosols in the climate system. This has been a message that has been repeatedly emphasized on Climate Science, and this AGU meeting summary reinforces this view.

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