Temperature basically partitions water into the liquid, gas and ice phases. Yet temperature, itself, depends on the amount, distribution and state of water. The dialectic causes trouble for scientists attempting to predict climate change. Global warming’s threat has brought increasingly more attention to the earth’s hydrological cycle. Many scientists believe that the cycle’s strength has grown as a byproduct of global warming, ultimately due to obese anthropogenic production of greenhouse gases. If such a theory holds water, so to speak, recent Science articles reporting alleged tell-tale signs are very important. Decreased air-borne dust particles, increased sea surface temperatures and increased tropical precipitation are key results, some scientists say, of an enhanced hydrological cycle.P> In their Feb., 1996 Science article, Dust: A Diagnostic of the Hydrologic cycle During the Last Glacial Maximum, Yuk L. Yung, et. al. reported that polar ice cores show a dramatic decrease of airborne dust particles since the last glacial maximum, (LGM). Studying the Greenland ice shelf, researchers found that the amount of glacial ice dust present at the LGM was 30 times that of our present atmospheric concentrations. Also, there were four times more marine aerosols present in the ice cores.

Using a 2D general circulation model based on modern deposits and conditions, Yung, et. al. studied the travel time of dust particles from a consistent dust source in South America, (45 degrees S. latitude), to Antarctica, (85 degrees S. latitude).

Little of the model’s dust made it to the Antarctic continent: “The reason was that although the mean transport time was on the order of several months, the washout lifetime of the dust particles was on the order of a week,” (Yung, et. al., 1996). The results agreed with another 3D general circulation model.

In contrast, a model based on 1/2 the washout rate, (hydrological cycle intensity), yielded five times the rates of deposition. The latter set-up imitated the levels of deposition present in the LGM.

Yung, et. al.’s article also highlighted a rise in sea surface temperatures since the LGM. Measurements of strontium and calcium in tropical corals showed a leap of five degrees Celsius since the LGM in equatorial waters. Polar waters appear to have risen eight to nine degrees Celsius since the LGM. The polar waters appear to be more sensitive to climate change.

Another article, presented in the June, 1996 issue of the Bulletin of the American Meteorological Society by Mark Morrissey, et. al., Recent Trends in Rain Gauge Precipitation Measurements from the Tropical Pacific: Evidence for an Enhanced Hydrologic Cycle, also supports the enhanced hydrological cycle theory. Morrissey, et. al. claim that increased oceanic precipitation in the tropics during the years 1971-1990 are consistent with suggestions that: “...an enhancement of the tropical hydrologic cycle has been responsible for the increases in globally averaged tropospheric temperatures during the past two decades,” (Morrissey, et. al., 1996).

This article also cites increased tropical sea surface temperatures as the stimulants for more evaporation and precipitation. Morrissey, et. al., refer to radiosonde measurements which found increases in tropical tropospheric moisture content on the order of 5 percent. Radiosonde readings from the lower troposphere during the years 1973-1986 showed an increase of 5 to 10 percent moisture content.

Rain gauge data, (showing a definite upward trend in tropospheric water content), taken during the 1971-1990 period corroborate with previous results based on satellite measurements, estimates of oceanic evaporation by shipboard meteorological observations and results from global circulation models, according to the article.

Although the latter article’s suggestions are backed by a plethora of supporting evidence, the idea that such dynamic patterns in rainfall actually occurred has been cautiously approached. The problem with unyielding acceptance so far has been that complete and quality-controlled in situ rain gauge measurements have only recently been available. Previously, the precipitation changes were inferred primarily from satellite proxies, diagnostics based on observed winds and sea surface temperatures. Such proxies, diagnostics, and, of course, model results are always subject to considerable error and uncertainty.

But the corroboration of evidence presented in these two articles seems to prove beyond the shadow of a doubt that increased sea surface temperatures exist, have lead to more moisture in the troposphere and an enhanced hydrological cycle. These scientists gingerly approached the obvious implications of their discoveries on the global warming question. Yung, et. al., however, hinted at the possibility of a link: “This, then, raises a difficult question: Can the much lower sea surface temperature deduced from the corals be accounted for by the observed decrease in CO2 and the associated reduction in greenhouse forcing? [decreases in the sense of a retro-span of the LGM],” (Yung, et. al., 1996).