November 13, 2006

CO2 Emissions Link to Temperature Trends: A Quandary?

Filed under: Climate Forcings

Hardly a week goes by without an article appearing in the professional scientific literature with results that show shortcomings in the numerical models of climate upon which the global warming scare is based. In many cases, the problems deal with the numerical representation of some important processes, in other cases the problems deal with assumptions of growth rates in greenhouse gas concentrations, while in other cases, the problems deal with data used to initialize the models. The problems are endless and rarely reported in more popular presentations of the greenhouse-global warming story. Another recent paper has appeared with a surprising problem to be solved by the modelers.

Two scientists from the Netherlands have published a paper in the International Journal of Climatology with results not consistent with models predictions (this paper is a follow-up to an earlier paper the authors had published that we covered a few years ago). de Laat and Maurellis note that greenhouse gas (GHG) warming should be observed at the surface, and indeed, such warming appears in the surface record of the past 25 years. However, they observe that “Climate models and theory predict that enhanced GHG warming should occur throughout the troposphere” but far less warming has been observed in the free troposphere than at the surface. They write “This discrepancy between surface and free tropospheric warming is a well-documented phenomenon” and “This discrepancy opens the possibility that other anthropogenic near-surface processes may have contributed to the observed surface temperature variations.”

de Laat and Maurellis then proceed to reveal a surprising pattern in the warming trends in the data from throughout the world. As seen in the figure below, there is a clear signal in the observational records of the surface (derived from thermometer records) and troposphere (derived from satellite-based records)—places with the highest greenhouse gas emissions have the greatest warming trend. In their own words, they state “The main conclusions that can be drawn from Figure 1 are that both satellite and surface data show a significant temperature increase with increasing emissions and that this correlation is absent in the climate models’ temperature response.” Further, the state “any agreement between both types of measurements would indicate the underlying presence of an industrialization-related process that has decadal timescale effects over a vertical extent well in excess of the atmospheric boundary layer (ABL).” Whatever the cause, the pattern of increasing temperature in places with the greatest emissions of greenhouse gases shows up prominently in both the thermometer-based surface temperature measurements and in the satellite-based measurements of lower-tropospheric temperatures. No such pattern is suggested by the numerical models of climate.

Figure 1. Mean temperature trends by CO2 emission–threshold (K/decade) covering the period 1979–2001 for measurements (a and b) and two models (c and d). The additional black solid curve plotted in each panel denotes the fractional surface area of the earth for the above-threshold region (from de Laat and Maurellis, 2006)

In this current paper, the authors apply different statistical techniques to be certain the pattern is not some peculiar artifact of a particular procedure, but not matter what technique they use, the pattern shows up over and over in the empirical records. Furthermore, they find the pattern is stronger in winter than in summer and stronger at night than in the daytime. They note that “During local summer, convection will be more effective in transporting the surplus heat from the ABL to the free troposphere, reducing the near-surface warming. Thus, the seasonality in temperature trends in the measurements is quite consistent with heating from surface industrialization-related processes. Note that the same kind of process could explain the difference between daytime and nighttime surface temperature changes. During the night, a stable ABL prevails, suppressing vertical exchange of heat in the ABL. During the day, the ABL is generally thicker; hence, the surface heating could be distributed over a thicker atmospheric layer. This could result in a larger temperature increase during night compared to during the day and, thus, a reduced diurnal temperature cycle. Additionally, this would be very much in agreement with the observed reduction of the amplitude of the diurnal cycle of surface temperatures.”

The explanation is elusive at this time, but the authors conclude “Anthropogenic heat is not the only process that can or may explain the correlation between temperature trends and industrial CO2 emissions. There are a few other possible processes that may play a role: changes in land use that could change the surface albedo and also soil moisture and thus the surface energy balance and also groundwater levels; absorbing aerosols like soot, cloud cover or cloud optical properties all are potentially plausible explanations.”

The pattern the uncovered is a reminder that not all warming in a record can be ascribed to the buildup of greenhouse gases. Something is happening in areas with high CO2 emissions that is causing the surface and lower-tropospheric temperatures to rise far more quickly than other areas of the earth. Whatever the cause, it is inflating the rise in temperature observed for the planet and should be considered in any attempt to identify the temperature response to elevated concentrations of greenhouse gases.

Surprisingly, the link spatially between CO2 emissions and the rise in temperature is not consistent with model predictions!


de Laat, A.T.J., and A.N. Maurellis, 2006. Evidence for influence of anthropogenic surface processes on lower tropospheric and surface temperature trends, International Jounral of Climatology, 26, 897–913.

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