CURIOUS: Why do people who express so much skepticism at the daily weather forecast readily panic at one for 50 years from now?

The latest version, presented to a Senate committee last week by NASA, left the impression after the media got through with it of unqualified gloom and doom by the year 2030.

It's one thing to say this disastrous global warming could happen. But no computer model, as noted by the National Aeronautics and Space Administration, is sophisticated enough to predict that it's certain. Doubly so when you consider that for all the carbon dioxide, methane and chloroflourocarbons we've pumped into the atmosphere since the Industrial Revolution, temperatures in the United States and northern latitudes have actually declined over the last half-century.

The menace in question is called the "greenhouse effect," in which man-made pollutants rise into the atmosphere and prevent heat from escaping into space. NASA's Washington forecast for 2050 calls for a 1,000 percent increase in 100-degree days and a 70 percent chance that the polar ice cap will melt, swamping Ocean City's condos.

Certainly, there's hardly a sane scientist, weatherwise or otherwise, who doubts that an increase in carbon dioxide will warm up an idealized, simplified Earth -- the kind that exists in the computer's memory. The more CO2, the warmer it gets. And there's no doubt that the amount of C02 in the atmosphere is going up.

Compounding the effect of CO2 is the fact that a thin ice cap sits precariously atop our hemisphere, reflecting much of the sun's radiation. Melt it and, as you descend a bit from the pole, you have an ocean that absorbs a lot more radiation than it used to. Thus the earth's surface warms, the Greenland ice sheets begin to melt, and the bottom falls out of the condo market in Ocean City.

From reading the newspaper accounts, one gets the impression that disaster has already begun. But, buried in the bowels of most expert testimony concerning the issue are more than the usual number of caveats. As NASA's Robert Watson told the Senate, "It's only a question of magnitude and time."

Indeed. Here's the problem: in spite of the current increase in C02, and despite the headlines, there's precious little evidence that the Northern Hemisphere has warmed up significantly over the last 50 years. Moreover, when we look to the medium-high latitudes of our hemisphere, generally conceded to be most prone to climatic change, the warming simply isn't there. That includes the critical polar margin.

A look at the temperature curves from the National Research Council's 1983 report "Changing Climate" sums up the problem. The Northern latitudes, from 24 through 90 degrees, have actually cooled off since 1930. The tropics warmed up slowly from 1880 to 1920, and then stopped. The Southern Hemisphere, as noted below, has warmed steadily throughout the period.

There is not one graphic in the entire 496-page report that indicates a statistically significant warming of the northern latitudes of our hemisphere since 1930. One figure shows two warm years at the end of the record, but to say that is a significant indicator of the great warmup would be exactly akin to saying that the three consecutive very cold years in the late 1970s indicated imminent glaciation -- which some people thought.

As far as the United States is concerned, the state-of-the-art temperature history remains Henry Diaz' and Robert Quale's 1981 article in the journal "Monthly Weather Review." Although the last data in that article is from 1979, it is clear that mean United States temperatures have actually dropped in the last 30 years.

The most recent major article to detail the Northern Hemisphere temperature history appeared in the February, 1986 edition of the "Journal of Climate and Applied Meteorology." Even though the data from the last few years are slightly biased towards warmer urban locations, a plot of the raw data does not support the conclusion that the big warmup has begun. While two very warm years highlight the end of the 135-year record, I challenge readers to find a statistician -- even in Washington -- who will say these indicate significant change.

While words such as "inescapable" and "undeniable" get bandied about in the news, it is sobering to read one of the conclusions of the National Research Council in "Changing Climate" (1983):

"In view of the relatively large and inadequately explained fluctuations over the last century, we do not believe that the overall pattern of variations in hemispheric or global mean temperature or associated changes in other climatic variables yet confirms theoccurrence of temperature changes attributable to increasing atmospheric C02 concentration."

The conclusions of the 1985 self-proclaimed "state-of-the-art" report by the Department of Energy aren't much different, although couched in the peculiarly Washingtonian neither-confirm-nor-deny mode:

"The findings from each of the lines of inquiry taken individually are, by themselves, insufficient to constitute convincing evidence that the climate models are correctly projecting the effects of the increasing C02 concentration on climate. However, to varying degrees, the evidence is generally consistent with, or at least not contradictory to, model projections of such effect."

The real bad actors in the warmup scenario have been the Northern Hemisphere's oceans. They refuse to go to along with the program, showing nothing but a slow, significant cooling since World War II. With oceanic, as opposed to land, temperatures, short-term fluctuations are damped, although long-term changes take longer to appear.

So why isn't the Northern Hemisphere warming, if the amount of CO2 in its atmosphere is increasing? The best explanation is that other factors, unknown or currently unexplainable, are interfering.

Example: Francis Bretherton (recognized by the atmospheric science community with numerous research awards and prizes) and James Coakley of the National Center for Atmospheric Research recently looked again at satellite images to see if there has been an increase in the Northern Hemisphere's high cloudiness. According to John Botzum's Washington-based "Weather and Climate Report," "Coakley said that an increase of 4 percent to 7 percent in cover by certain types of clouds could offset a doubling of carbon dioxide."

Cirrus clouds aren't the only unknown. Most of the computer models contain major limitations in their geography and oceanic heat transfer, and no global climate model has accurately simulated changes in regional rainfall since the beginning of the increase in C02.

Meanwhile, the Southern Hemisphere has been much with the program, warming up in a fashion that no one doubts.

So what's the difference between hemispheres?

Perhaps some type of atmospheric turbidity -- volcanic or man-made -- has so far countered the effect of carbon dioxide in our hemisphere. The fact is that C02 stays in the atmosphere a lot longer than the stuff that goes into the air alongside it. While both are primarily produced in the Northern Hemisphere, only C02 resides long enough to diffuse into the Southern Hemisphere. Thus the Southern Hemisphere's clearer atmosphere receives and traps more radiation.

Sooner or later the C02 effect should predominate in our hemisphere, but probably not soon enough to turn Washington into beachfront property for a while. As NASA's Watson said, the magnitude and the timing are unclear.

Further, if such a thing can be said to be reassuring, Cassandra's Law of predicted atmospheric disasters says the first forecasts are usually the worst. Remember how we worried at first about the SST in 1970, and chloroflourocarbons in 1972, the coming Ice Age in 1974, and the weather forecast in Dennis Meadows' "The Limits to Growth"? Even the nuclear winter scenario has softened up a bit during the last year.

So, until we understand why the Northern Hemisphere has been so slow to warm, please pass the research funding -- and don't sell the condo.