Monthly Archives: February 2006

The Need to Broaden the IPCC Perspective

The IPCC has used a figure of estimated radiative forcing since preindustrial times to present its overview of the human impact on the climate system. This figure was reproduced in the 2005 National Research report as Figures ES-1 and Figure 2-1.

As stated in the 2005 NRC report starting on page 28,

“According to the IPCC definition, applied to the data in Figure 2-1, ‘The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent is the change in net irradiance at the tropopause after allowing for stratospheric temperatures to readjust to radiative equilibrium, but with the surface and tropospheric temperatures and state held fixed at the unperturbed values.’ This definition of forcing is restricted to changes in the radiation balance of the Earth-troposphere system imposed by external factors, with no changes in stratospheric dynamics, without any surface and tropospheric feedbacks in operation, and with no dynamically induced changes in the amount and distribution of atmospheric water. A somewhat broader perspective is applied in this chapter to include, in particular, volcanic aerosols, the effects of land-use changes and aerosols on precipitation, and the radiative forcing due to changes in ocean color.”

The figure caption to the IPCC figure in the 2005 NRC Report states,

“FIGURE 2-1 Estimated radiative forcings since preindustrial times for the Earth and troposphere system (TOA radiative forcing with adjusted stratospheric temperatures). The height of the rectangular bar denotes a central or best estimate of the forcing, while each vertical line is an estimate of the uncertainty range associated with the forcing, guided by the spread in the published record and physical understanding, and with no statistical connotation. Each forcing agent is associated with a level of scientific understanding, which is based on an assessment of the nature of assumptions involved, the uncertainties prevailing about the processes that govern the forcing, and the resulting confidence in the numerical values of the estimate. On the vertical axis, the direction of expected surface temperature change due to each radiative forcing is indicated by the labels ‘warming’ and ‘cooling.’ SOURCE: IPCC (2001).”

The first comment on the IPCC figure is that the magnitude of the warming and cooling terms listed on the left-hand vertical axis are not the current radiative forcing. The magnitudes plotted are the difference of the estimated fluxes between the preindustrial times and 2000. For example, some of the radiative forcing of the well-mixed greenhouse gases presumably resulted in an adjustment in the Earth’s radiative budget before the 20th century. This is the reason for the last sentence in the NRC figure caption with respect to the IPCC figure where the Committee elected to clarify that the terms “warming” and “cooling” do not refer to the current magnitudes of radiative forcing. The current radiative forcing of the well-mixed greenhouse gases is not 2.4 Watts per meter squared.

Secondly, the IPCC figure recognizes the ” very low” level of scientific understanding of a number of the radiative forcings. This uncertainty should have immediately raised concerns about using the climate models as skillful projections. Recently, even the radiative forcings of the well-mixed greenhouse gases have seen a new uncertainty (with respect to methane), as discussed on this weblog (More Complications on Quantifying the Radiative Effects of Well-mixed Greenhouse Gases“).

On page 30, the 2005 NRC report summarized the perspective on this figure as follows,

“Figure 2-1 has been an effective way to portray the relative magnitudes of different radiative forcings, the associated scientific uncertainties, and an assessment of the current level of understanding. It has been used widely in the scientific and policy communities. However, it has some important limitations, including the following:

The figure does not provide information about the timescales over which each of the forcings is active. For example, the greenhouse gases in the first bar (CO2, CH4, N2O, and halocarbons) remain in the atmosphere for decades or longer, whereas the various aerosols persist for days to weeks.

The figure shows globally-averaged forcings and therefore does not provide information about regional variation in forcing or vertical partitioning of forcing.

The figure does not provide information about other climate effects of each forcing agent, such as impacts on the hydrological cycle.

The figure gives the impression that one can simply sum the bars to determine an overall or net radiative forcing; however, such a calculation does not give a reasonable description of the cumulative effect of all the forcings.

The uncertainty ranges are generally estimated from the range of published values and cannot be readily combined to determine a cumulative uncertainty.

The figure does not consistently indicate the forcing associated with specific sources (e.g., coal, gas, agricultural practices).

The figure omits nonradiative forcings as discussed in this report.

Although it would be unrealistic to expect a single figure to fully portray all of these aspects of radiative forcings, there are clearly opportunities to improve upon Figure 2-1 and to introduce new figures that address these limitations in the next IPCC report.”

Clearly, there is a National Research Council recommendation that the new IPCC Report address these issues. My reading of the IPCC Report so far, however, (see the post entitled “Overlooked Issues in Prior IPCC Reports and the Current IPCC Report Process: Is There a Change From the Past?“) indicates that the IPCC is ignoring the National Research Council’s report. This is very disappointing, if we want to advance our scientific understanding of climate, rather than use the IPCC process as political advocacy.

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Cross-scale Interactions, Nonlinearities, and Forecasting Catastrophic Events

In the context of our weblog posting of December 26, 2005 “More on Sudden Climate Transitions – A Book by John D. Cox“, the paper we published in the Proceedings of the National Academy (PNAS) in 2004 is relevant.

Our paper by Peters et al, 2004 entitled “Cross-scale interactions, nonlinearities, and forecasting catastrophic events discussed the issue of nonlinear scale interactions. In terms of the climate system, a nonlinear perspective of this type is certainly needed, but has been lacking in assessments. The vulnerability framework that we have proposed (see and see ) is much more inclusive with communicating to policymakers the environmental and societal threats associated with the nonlinearity of the climate system.

The abstract of our PNAS paper states,

“Catastrophic events share characteristic nonlinear behaviors that are often generated by cross-scale interactions and feedbacks among system elements. These events result in surprises that cannot easily be predicted based on information obtained at a single scale. Progress on catastrophic events has focused on one of the following two areas: nonlinear dynamics through time without an explicit consideration of spatial connectivity [Holling, C. S. (1992) Ecol. Monogr. 62, 447–502] or spatial connectivity and the spread of contagious processes without a consideration of cross-scale interactions and feedbacks [Zeng, N., Neeling, J. D., Lau, L. M. & Tucker, C. J. (1999) Science 286, 1537–1540]. These approaches rarely have ventured beyond traditional disciplinary boundaries. We provide an interdisciplinary, conceptual, and general mathematical framework for understanding and forecasting nonlinear dynamics through time and across space. We illustrate the generality and usefulness of our approach by using new data and recasting published data from ecology (wildfires and desertification), epidemiology (infectious diseases), and engineering (structural failures). We show that decisions that minimize the likelihood of catastrophic events must be based on cross-scale interactions, and such decisions will often be counterintuitive. Given the continuing challenges associated with global change, approaches that cross disciplinary boundaries to include interactions and feedbacks at multiple scales are needed to increase our ability to predict catastrophic events and develop strategies for minimizing their occurrence and impacts. Our framework is an important step in developing predictive tools and designing experiments to examine cross-scale interactions. ”

Edited excerpts from the paper include,

“Nonlinear interactions and feedbacks across spatial scales and their associated thresholds are common features of biological, physical, and materials systems …..These spatial nonlinearities and emergent behaviors challenge the ability of scientists and engineers to understand and predict system behavior at one scale based on information obtained at finer or broader scales ….Cross-scale interactions often result in “surprises” with severe consequences for the environment and human welfare. ”

“Our ability to forecast future system dynamics is severely constrained unless we can account for spatial nonlinearities, threshold behavior, and cascading effects …. Even then, skillful predictions may not be possible ….although we can identify vulnerabilities of systems to thresholds. Research will need to adopt approaches that cross traditional disciplinary boundaries to address system dynamics. Collaborative efforts among ecosystem ecologists and atmospheric scientists have made considerable progress in explaining broad-scale patterns and dynamics in the Earth System …., and human behaviors are increasingly being recognized by ecologists as integral to explaining system dynamics…..More intensive cross-disciplinary studies that identify the pervasive role of cross-scale interactions are essential to understanding and forecasting changes in the various components of the Earth System. Our framework represents an initial step in seeking generalities among disciplines. ”

A key conclusion of our paper is that,

“These events result in surprises that cannot easily be predicted based on information obtained at a single scale”.

This again illustrates the very limited value of using a global averaged surface temperature linear trend as the primary climate metric to determine the consequences of human- and natural-climate change, even if we could accurately diagnose such a quantity.

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Uncertainties in Modeling Cloud and Precipitation Processes Within Global Climate Models

A recent BBC news article by Richard Black entitled “Experiment probes climate riddle” , which was brought to my attention by Timo Hämeranta has some interesting text and quotes in it (Timo has been very effective at alerting the community to research papers and studies that otherwise might be missed – or ignored). The BBC article was written with respect to the Tropical Warm Pool – International Cloud Experiment (TWP-ICE).

These include

“Tropical clouds carry heat and moisture from the Earth’s surface high up in the atmosphere, a key process in driving heat around the globe.

‘You have these ‘hot towers’, tropical storm clouds acting like chimneys to carry heat to the upper atmosphere,’ said Peter May from the Australian Bureau of Meteorology Research Centre, co-chair of the project’s organising committee.

Scientists need to learn how climate change affects storm activity
‘Also, you’ve got large areas of cirrus clouds which are reflecting a lot of incoming sunlight back away from the Earth; but they’re also absorbing infra-red radiation coming back from below,’ he told the BBC News website.

‘So you’ve got competing processes going on; and that balance depends on how big the ice crystals are and what the density is, how high they are and so on.’

Existing computer models did not reflect these processes accurately, said Tom Ackerman of the University of Washington in Seattle, US, because they typically treated convection and cloud formation as separate processes.

‘We’re working now to develop a more integrated approach to the convection where these processes are all tied together, and the convection leads directly to the clouds,’ he told the BBC News website.

‘But in order to do that you need to understand this total life cycle of air going into the clouds, condensation, vertical lifting and then cloud being dumped out at other levels.’

All of which provides a mandate for a comprehensive and intensive new research programme. ”

This research program is important. However, a critical message lost in the BBC news article is how can skillful multi-decadal predictions be made if we do not yet adequately understand cloud processes? How can international climate protocols, such as Kyoto, be established when the climate response to human climate forcings (and even natuaral forcings) is not adequately understood. That the global climate models that have been used to justify an international treaty have serious uncertainties when applied as forecast models should have been the headline to this news article.

Even with respect to cloud and precipitation processes (which are just one aspect of the climate system), there are major uncertainties. Several of these issues are discussed on the Climate Science web site ( see Workshop Summary of the Indirect effects of Aerosol on Climate , Added Significance of the Climate Forcing of Aerosols and Ignored Consequences of Their Study with Respect to Human-caused Climate Change, Atmospheric Chemistry Within the Climate System, and More Evidence On The Spatial Complexity Of Climate Forcings) . There are a diverse spectrum of cloud and precipitation processes, and thus radiative fluxes, that are affected by aerosols.

The Tropical Warm Pool – International Cloud Experiment is an excellent step to better understand the role of clouds in the climate system. However, we need to also recognize that such observational programs are needed because of serious deficiencies in the physics that are modeled by multi-decadal global climate prediction models. This means we should be much more critical of the forecast skill of these models than is typically seen in the media and in many published papers.

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What is the Current Understanding of Solar Forcing of Climate Change

The solar focing of the climate system was discussed in the 2005 NRC Report entitled “Radiative forcing of climate change: Expanding the concept and addressing uncertainties.

One of the authors of the NRC Report was Judith Lean of the Naval Research Laboratory.

Volume 11 No 1 of Past Global Changes News publication has a valuable summary of the current understanding of solar forcing of the climate system by Judith Lean. Her short article on pages 13-15 entitled “Solar forcing of climate change: current statusâ€? concludes that the

“…total solar irradiance increases ~ 0.5 W per meter squared from the Maunder Minimum to the present-day quiet Sun.â€?

This is a smaller value than earlier reconstructions of long-term solar irradiance.

The article also discusses mechanisms of climate response to solar variability, i.e.

“Distinctly different mechanisms are surmised for climate’s response to solar radiative forcing. Direct ‘short-wave’ heating of the surface, ocean and troposphere generates geographical and seasonal inhomogeneities that may alter land-atmosphere-ocean interactions. Climate may respond indirectly to stratospheric ozone changes driven by varying solar ultraviolet radiation. The altered altitudinal temperature gradient (from the troposphere to the stratosphere) and latitudinal gradient in the stratosphere (from the equator to the poles) couples the stratosphere to the troposphere radiatively and dynamically (Rind, 2002). A result of both direct and indirect solar forcing is thought to be the alteration of atmospheric circulation patterns, including the Hadley, Walker and Ferrel cells, with subsequent effects on, for example, rainfall patterns in tropical regions. A third mechanism involves modulation of the frequency and occurrence of internal modes of climate variability. Pacific sea surface temperature gradients arising from the deeper thermocline in the west Pacific Ocean relative to the east can affect ENSO. Solar UV irradiance changes may alter the high latitude stratosphere and the polar vortex, thereby affecting the NAO, which is observed to expand longitudinally to the Arctic annual oscillation during solar maxima. Furthermore, since the climate system exhibits significant ‘noise’, the forcing may be amplified by stochastic resonance. Also possible are non-linear interactions of the forcing with existing cyclic modes.â€?

Dr. Lean also concludes that,

“Drought and rainfall seem particularly sensitive to solar variability, especially in vulnerable geographical regions such as those in the vicinity of the ITCZ.â€?

There are implications from her summary:

1) There are significant regional effects from the observed variability of solar forcing.

As discussed on the Climate Science weblog of July 28, 2005, spatially heterogeneous changes in tropospheric temperatures are more important in terms of weather pattern changes than a change in the global average. The temporal global averaged variations in total solar irradiance that Dr. Lean documents in Figure 1 of her paper will have dispproportinate effects on different regions of the Earth.

2) The magnitude of the global averaged solar forcing could realistically vary by as much as 0.5 Watts per meter squared over multi-decadal time periods in this century.

Even between 1979 and 2004 an increase of the global averaged radiative forcing at the time of solar cycle maxima of 0.2 Watts per meter squared was observed. The magnitude of this temporal variation in forcing is a function of latitude and time of year, and regionally is larger than 0.2 Watts per meter squared. Spatial maps of the solar fluxes received at the top of the atmosphere, in the atmosphere, and at the surface should show regions of increased diabatic heating during the time of the solar cycle maxima, which would alter tropospheric temperature patterns. Retrospective global atmosphere-ocean-land-continental ice sheet model runs which include the temporal variation in solar irradiance that was observed since 1979, but no other climate forcing, should be performed as sensitivity experiments to determine if his magnitude of solar forcing is important in regional weather patterns.

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Workshop Summary of the Indirect effects of Aerosol on Climate

The November 2005 International Global Atmospheric Chemistry (IGAC) Newsletter had an excellent summary of a January 2005 workshop entitled “The Indirect Effects of Aerosols on Climateâ€? by D. Cziczo and colleagues. The write up provides a succinct and updated report on this component of the climate system.

The summary provides a concise list of the recognized indirect effects:

“ 1) The First Indirect Aerosol Effect: In clouds with fixed water amount, more particles lead to more numerous but smaller cloud drops that reflect more solar radiation. Also known as the cloud albedo or Twomey effect.

2) The Second Indirect Aerosol Effect: Smaller cloud drops can lower precipitation efficiency and prolong cloud lifetime. Also known as the cloud lifetime or Albrecht effect.

3) The Semi-Direct Effect: Absorption by particles such as soot leads to cloud evaporation. Also known as cloud burning or the Hansen effect.

4) Glaciation Effects: An increase in ice nuclei (IN) number lead to an increase in precipitation efficiency.

5) Thermodynamic Effects: In convective clouds, smaller cloud droplets lead to a delay in homogeneous freezing and latent heat release.

6) Surface Energy Budget: Increased aerosol and cloud optical thickness decreases net surface radiation.�

This listing mirrors the conclusion in Table 2-2 of the 2005 NRC Report entitled ” Radiative forcing of climate change: Expanding the concept and addressing uncertainties. ”

As stated in the summary of the workshop,

“One common thread that ran through the many presentations at the workshop was the number of complicated interactions between the ways aerosols affect clouds and the clouds themselves…â€?

Figure 1 in the workshop summary, prepared by G. Feingold, very effectively summarizes the nonlinear coupling between dynamics, cloud microphyics, aerosols, and gas phase processes.

While the workshop focused on the radiative effects of the six indirect aerosol effects, the workshop provides a basis in which to improve our understanding of the diverse non-radiative climate effects of these spatially heterogenous climate forcings. This includes their effect on tropospheric temperature patterns, and thus, on weather and precipitation patterns.

The importance of spatially heterogeneous climate forcing was discussed in the July 28, 2005 weblog entitled “What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?” The concept of “global warming” fails to capture the more significant effect of spatially heterogeneous climate forcings on the Earth’s climate system.

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Further Evidence of the Role of Nitrogen Deposition as a First-Order Climate Forcing

In the October 10, 2005 weblog entitled “Is Nitrogen Deposition a First-Order Climate Forcing?, we concluded that it certainly is a first order forcing. The paper

Lamarque J.-F., et al. (2005), Assessing future nitrogen deposition
and carbon cycle feedback using a multimodel approach: Analysis of
nitrogen deposition, J. Geophys. Res., 110, D19303, doi:
10.1029/2005JD005825

demonstrates the very important role of this climate process that will continue into the rest of the 21st century. Their paper concludes that

“In 2100 the nitrogen deposition changes from changes in the climate account for much less than the changes from increased nitrogen emissions.â€?

The Lamarque et al paper further demonstrates the role of the human disturbance of the climate system that extends beyond the IPCC focus on the global average radiative forcing of the well-mixed greenhouse gases. As illustrated in Figure ES-1 in the 2005 National Research Council report, the result of increased nitrogen deposition will be changes in the other components of the climate system.

Controls on the emissions of carbon dioxide, by itself, will not significantly influence climate perturbations caused by nitrogen deposition, unless nitrogen emissions were also reduced. Nitrogen deposition increases will also alter the amount of carbon that is sequestered within vegetation through its fertilization effect.

As with the Feddema et al Science paper “The Importance of Land-Cover Change in Simulating Future Climatesâ€? , that was discussed in our December 7, 2005 weblog entitled “New Science paper Confirms Land Cover Change as a First Order Climate Forcing on the Global Scale” , the climate forcing of nitrogen deposition is spatially heterogeneous.

The full abstract of the Lamarque et al paper reads,

“In this study, we present the results of nitrogen deposition on land from a set of 29 simulations from six different tropospheric chemistry models pertaining to present-day and 2100 conditions. Nitrogen deposition refers here to the deposition (wet and dry) of all nitrogen-containing gas phase chemical species resulting from NOx (NO + NO2) emissions. We show that under the assumed IPCC SRES A2 scenario the global annual average nitrogen deposition over land is expected to increase by a factor of 2.5, mostly because of the increase in nitrogen emissions. This will significantly expand the areas with annual average deposition exceeding 1 gN/m2/year. Using the results from all models, we have documented the strong linear relationship between models on the fraction of the nitrogen emissions that is deposited, regardless of the emissions (present day or 2100). On average, approximately 70% of the emitted nitrogen is deposited over the landmasses. For present-day conditions the results from this study suggest that the deposition over land ranges between 25 and 40 Tg(N)/year. By 2100, under the A2 scenario, the deposition over the continents is expected to range between 60 and 100 Tg(N)/year. Over forests the deposition is expected to increase from 10 Tg(N)/year to 20 Tg(N)/year. In 2100 the nitrogen deposition changes from changes in the climate account for much less than the changes from increased nitrogen emissions.

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Readers of the weblog know that I resigned from this Committee in August 2005 and have documented as a Public Comment the concerns regarding a biased assessment process, which includes dismissing important climate science issues that are within the charge to the Committee. A summary of the weblog on the Public Comment is available as is the entire Public Comment.

A Public Comment period and meeting of the Climate Change Science Program (CCSP) Product Development Committee for Synthesis and Assessment Product 1.1 (CPDC-S &A 1.1) will be held February 8-9, 2006 at the Chicago O’Hare Airport Hilton, Hotel, Chicago, IL (see this link and this link).

When the Committee releases their response to my Public Comment, I will post on the Climate Science weblog, along with my reply.

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