More Water Vapor Woes For Climate Modelers
Using satellite infrared spectroscopy to provide an almost global perspective on the near-surface distribution of water vapor, a new report in Science has identified more water vapor inaccuracies in current general circulation models (GCM), the computer programs used by climate scientists to predict future climate trends. The researchers uncovered anomalies in the Hadley circulation and its misrepresentation in GCM. Looks like climate theory and the IPCC's error ridden models are in for another round of corrections.
Following hot on the heals of my last column that reviewed a study on water vapor latent heat transfer and climate modeling modeling (see “Climate Models Blown Away By Water Vapor”), a new report has identified even more places where current climate models get atmospheric circulation and the hydrological cycle wrong. Christian Frankenberg of the SRON-Netherlands Institute for Space Research, et al., in a paper entitled “Dynamic Processes Governing Lower-Tropospheric HDO/H2O Ratios as Observed from Space and Ground,” used a previously overlooked technique to obtain global information with high sensitivity near ground level. This part of the lower troposphere, the bottom 1-2 km of the atmosphere, has previously been missed because earlier satellites used thermal infrared frequencies lacking sensitivity in that area. At the start of the report the authors explain the motivation for their work:
Water vapor is the most important greenhouse gas in the atmosphere. As saturation vapor pressure increases exponentially with temperature, a positive feedback effect with respect to the current global warming trend is expected and confirmed by satellite measurements over the ocean. However, highly complex interactions via cloud formation and the release of latent heat, impacting convection, complicate matters and seem not to be well represented in climate models, especially in the tropics. Land-atmosphere coupling adds further uncertainties. An accurate knowledge of hydrological cycles and feedback mechanisms is therefore indispensable for reliable weather and climate predictions.
Evaporation, precipitation and atmospheric circulation are all part of the hydrological or water cycle that constantly recirculates water throughout the biosphere. People have kept rainfall records on land for centuries, but there are many isolated regions and vast expanses of ocean for which no records are available. Isotope measurements of water vapor can give important information regarding precipitation and evaporation. Using remote sensing from satellites, proxy readings from even Earth's remotest regions can be gathered. Atmospheric applications have traditionally focus on isotopes as a proxy for exchange processes in the upper troposphere and lower stratosphere and few models incorporated any water vapor components for other factors. The results of this report, which extends observations to the lower atmosphere, will hopefully allow current models to be corrected.
The water cycle is complex and not fully understood.
The trick here is that part of the water vapor in Earth's atmosphere has, as one of its molecule's two hydrogen atoms, an isotope of hydrogen called deuterium or D. Such isotropic water molecules are referred to as Hydrogen Deuterium Oxide, or HDO for short. Owing to the large spectral displacement of the rotational and vibrational modes of HDO, it has spectroscopic absorption lines distinctly different from those of H2O. This allows simultaneous measurements of the relative abundance of HDO and normal H2O by the SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) instrument aboard the European Space Agency (ESA)’s environmental research satellite ENVISAT.
For the first time a global picture of near surface HDO/H2O levels can be constructed. The HDO abundance relative to standard mean ocean water (SMOW) in delta-notation (δD) is shown below. Figure 1A from the Sciencereport shows the global δD distribution as derived from 3 years of SCIAMACHY spectra. From these data, the isotopic fractionation of water provides deeper insight into the global hydrological cycle as evaporation and condensation processes deplete heavy water in the gas phase.
Figure 1A from Frankenberg st al., Science, Sept. 11, 2009.
Over the large ocean basins, where few surface stations are located, the high δD values typical for the tropics extend farther north than over land. This is most striking in the north Atlantic, where zonal symmetry is broken and δD iso-lines point northeast (see the arrow). This feature can be attributed to the warm Gulf Stream and strong evaporation, associated with storm tracks efficiently transporting vapor northeastward.
Strong continental gradients were observed in North America and, to a lesser extent, in Eurasia. The smaller gradient in Eurasia can be explained by the relatively efficient transport of Atlantic water vapor into the continent. In North America, by comparison, the Rocky Mountains and their associated precipitation obstruct the propagation of oceanic moisture further inland.
There is more evaporation up north than suspected.
Some of the most interesting data are from comparisons of direct measurements with model results for several northern locations. The researchers suggest that the contrast of sea surface temperature against air temperature in the lower troposphere results in maximum ocean evaporation and more local moisture origin of precipitation in winter. Particularly at Ny Ålesund, in the Norwegian high arctic (78.9°N 11.9°E), where the monthly predictions of the IsoGSM model underestimate the amplitude of seasonal change. Quoting from the report:
In the Ny Ålesund area, δD seasonality is, compared with other models, best represented by IsoGSM. Although data are only available for a coastal station, this indicates that moisture transport largely influences high-arctic isotopic variability and that its misrepresentation in general circulation models (possibly due to differences in storm track activity between reanalysis data and general circulation models) can be critical.
The researchers also observed an unexpectedly high seasonal change in the HDO/H2O ratio in the inner Sahel region of Africa. Such seasonal δD variations provide important insights into dynamic changes in evaporation, precipitation, and general atmospheric circulation. Conditions similar to the “continental effect” appear in tropical regions such as the Amazon basin or central Africa, where continental water vapor is least depleted.
Figure S12: Comparison of modeled monthly precipitable water content (left panel) and isotopic composition (right panel) in the southern Saharan region.
In addition to comparing measured results with the IsoGSM model other models were run. These included ECHAM-4 and GISS-E, a favorite of the IPCC. In simulations of the Sahara region, the GISS-E model captured the large isotopic seasonal changes well but was too moist during the Northern Hemisphere summer. ECHAM-4 also missed the mark on summer moisture content. This can be seen in Figure S12, taken from the report's online supplement.
So to sum up, here is yet another scientific report identifying the shortcomings of current GCM programs. In this case better empirical data has shown things in the lowest parts of the atmosphere to not behave as the models describe. Evaporation rates are higher up north and precipitation predictions inaccurate in many regions. These are not minor factors, the report's authors termed them “critical” to correctly modeling the atmosphere and hydrological cycle.
Tie these findings to the new revelations regarding latent heat, insolation effects and aerosols and you have to ask why mainstream climate science has bet its reputation on climate modeling. The siren call of easy grant money and media acclaim has lured many otherwise sensible scientists onto the rocks of politically motivated consensus science. They have forgotten that science demands they adhere to the truth as dictated by nature, and nature cannot be negotiated with or ignored. We can expect the clamor from global warming true believers to rise during the run-up to Copenhagen, the last shrill outcries defending a discredited theory.
Be safe, enjoy the interglacial and stay skeptical.