There’s an interesting paper in the latest issue of Geophysical Research Letters.

Walters, J. T., R. T. McNider, X. Shi, W. B. Norris, and J. R. Christy (2007), Positive surface temperature feedback in the stable nocturnal boundary layer, Geophys. Res. Lett., 34, L12709, doi:10.1029/2007GL029505. [PDF - requires subscription]

Abstract: The techniques of nonlinear analysis are used to examine the behavior of the stable nocturnal boundary layer (SNBL) when it is subjected to changes in incoming radiation or in surface characteristics. A single-column model and nonlinear bifurcation techniques are used to demonstrate that any atmospheric forcing, such as weak radiative forcing from greenhouse gases or cloud cover, can trigger a potentially significant positive feedback. Multiple solutions occur in some parameter spaces. This analysis shows that any forcing that decreases the stability, whether by increasing greenhouse gases or surface heat capacity, can cause large increases in surface temperature as the SNBL shifts from a weak turbulent regime, which allows the surface to cool, to a turbulent regime, which mixes warm air from aloft. Positive feedback may be a key factor in interpreting the long-term observed nocturnal warming trend in the SNBL.

There has been an observed decrease in the surface diurnal temperature range - the difference between the high and low temperature during a 24-hour period. This is been postulated to be caused by the increase in greenhouse gases. And it is widely acknowledged that greenhouse gases have contributed to this changed. However, climate models are unable to accurately reproduce the observed changes. Models have underestimated the observed changes.

This paper uses non-linear techniques (that I’ll admit I don’t totally understand) in an attempt to elucidate this discrepancy. They found that the geostrophic wind can cause a bifurcation and lead to regime changes.

They conclude that “[t]he amount of warming depends on the turbulent regime, being greater in the non-turbulent boundary layer (cold solution) and less in the turbulent boundary layer (warm solution). Of most interest is the fact that increased GHG forcing or increased cloud cover, even if slight, can cause the system to transition from the non-turbulent to the turbulent state and produce large changes in surface temperature. This is the essence of a positive temperature feedback and may be a contributing factor to the observed decrease in DTR.”

Taken from How Can We Avert Dangerous Climate Change?, arXiv:0706.3720v1 [physics.ao-ph].

Abstract: Recent analyses indicate that the amount of atmospheric CO2 required to cause dangerous climate change is at most 450 ppm, and likely less than that. Reductions of non-CO2 climate forcings can provide only moderate, albeit important, adjustments to the CO2 limit. Realization of how close the planet is to “tipping points” with unacceptable consequences, especially ice sheet disintegration with sea level rise out of humanity’s control, has a bright side. It implies an imperative: we must find a way to keep the CO2 amount so low that it will also avert other detrimental effects that had begun to seem inevitable, e.g., ocean acidification, loss of most alpine glaciers and thus the water supply for millions of people, and shifting of climatic zones with consequent extermination of species.

Here I outline from a scientific perspective actions needed to achieve low limits on CO2 and global warming. These changes are technically feasible and have ancillary benefits. Achievement of needed changes requires overcoming the spurious argument that developed and developing countries have equivalent responsibilities, as well as overcoming special interests advocating minimalist or counterproductive actions such as corn-based ethanol and liquid-fuel-from-coal programs.

This paper is almost entirely composed of testimony given before the Select Committee on Energy Independence and Global Warming, United States House of Representatives on 26 April 2007. There is a very good sections on sea level rise, and its consequences. Also, I was pleasently surprised to see a section on “sky islands” and how they are affected by global warming. He also put forth a four point plan on how to reduce the effects of global warming:

• First, we must phase out the use of coal and unconventional fossil fuels except where the CO2 is captured and sequestered. There should be a moratorium on construction of old-technology coal-fired power plants.
• Second, there must be a rising price (tax) on carbon emissions, as well as effective energy efficiency standards, and removal of barriers to efficiency. These actions are needed to spur innovation in energy efficiency and renewable energies, and thus to stretch oil and gas supplies to cover the need for mobile fuels during the transition to the next phase of the industrial revolution ‘beyond petroleum’.
• Third, there should be focused efforts to reduce non-CO2 human-made climate forcings, especially methane, ozone and black carbon.
• Fourth, steps must be taken to ‘draw down’ atmospheric CO2 via improved farming and forestry practices, including burning of biofuels in power plants with CO2 sequestration.

There’s a new paper on arXiv about climate change.

Abstract: The sun’s role in the earth’s recent warming remains controversial even though there is a good deal of evidence to support the thesis that solar variations are a very significant factor in driving climate change both currently and in the past. This precis lays out the background and data needed to understand the basic scientific argument behind the contention that variations in solar output have a significant impact on current changes in climate. It also offers a simple, phenomenological approach for estimating the actual-as opposed to model dependent-magnitude of the sun’s influence on climate.

Let’s look at a few of the figures, since that’s where most of the interesting stuff happens. Figure 1 (below) is a variety of reconstructions of the total solar irradiance (TSI). Also plotted in grey (without an axis) is the sunspot numbers. He says “[n]ote the correlation between sunspot number and total solar irradiance.”

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Chen, W.-T., H. Liao, and J. H. Seinfeld, (In Press). Future climate impacts of direct radiative forcing of anthropogenic aerosols, tropospheric ozone, and longlived greenhouse gases, J. Geophys. Res. [Abstract free, full text requires subscription.]

Abstract: Long-lived greenhouse gases (GHG) are the most important driver of climate change over the next century. Aerosols and tropospheric ozone are expected to induce significant perturbations to the GHG-forced climate. To distinguish the equilibrium climate responses to changes in direct radiative forcing of anthropogenic aerosols, tropospheric ozone, and GHG between present day and year 2100, four 80-year equilibrium climates are simulated using a unified tropospheric chemistry-aerosol model within the Goddard Institute for Space Studies General Circulation Model II’. Concentrations of sulfate, nitrate, primary organic carbon, secondary organic carbon, black carbon aerosols, and tropospheric ozone for present day and year 2100 are obtained a priori by coupled chemistry-aerosol GCM simulations, with emissions of aerosols, ozone and precursors based on the Intergovernmental Panel on Climate Change Special Report on Emissions Scenario A2. Changing anthropogenic aerosols, tropospheric ozone, and GHG from present day to year 2100 is predicted to perturb the global annual mean radiative forcing by +0.18 (considering aerosol direct effects only), +0.65, and +6.54 W m-2 at the tropopause, and to induce an equilibrium global annual mean surface temperature change of +0.14, +0.32, and +5.31 K, respectively, with the largest temperature response occurring at northern high latitudes. Anthropogenic aerosols, through their direct effect, are predicted to alter the Hadley circulation owing to an increasing inter-hemispheric temperature gradient, leading to changes in tropical precipitation. When changes in both aerosols and tropospheric ozone are considered, the predicted patterns of change in global circulation and the hydrological cycle are similar to those induced by aerosols alone. GHG-induced climate changes, such as amplified warming over high latitudes, weakened Hadley circulation, and increasing precipitation over the Tropics and high latitudes, are consistent with predictions of a number of previous GCM studies. Finally, direct radiative forcing of anthropogenic aerosols is predicted to induce strong regional cooling over East and South Asia. Wintertime rainfall over southeastern China and the Indian subcontinent is predicted to decrease because of the increased atmospheric stability and decreased surface evaporation, while the geographic distribution of precipitation is also predicted to be altered as a result of aerosol-induced changes in wind flow.