What a wonderful year, 1998! Global temperatures reached their highest value recorded in all three available records -- surface, satellite, and weather balloon. Sayers of doom had pronounced dire and immediate consequences -- so for once it was possible to check their models of misery against what actually happened when it really got warm.
El Niño vs. Greenhouse Warming
Judging from the conflation of El Niño andhuman-induced global warming, you mightthink the two were one and the same, or maybeeven, as Vice President Al Gore intimated, thatone caused the other.
Like many of his reaches, there was a bit oftruth in the stretch, but only a bit. Global warmingdidn't cause El Niño in any appreciablesense, but the two were related: It was a verygood El Niño year, and it was a very, verywarm year.
El Niño is natural. Just because scientists discoversomething, or because we, as taxpayers,shell out tens of millions of dollars to researchsomething, does not mean that something newhas happened. Chemicals existed beforechemists, DNA existed before its discovery wona Nobel Prize, and El Niño ebbed and flowedlong before the first climatologist was born.
| El Niño is a commonly occurring slowing (or even reversal) of the northeasterly and southeasterly trade winds that dominate the tropical Pacific Ocean (Figure 1). When the trades are blowing, they move vast amounts of oceanic water northwestward and then westward from the coast of South America. In doing so they drag the warm water off the surface, and much colder water "upwells" in replacement. So the eastern equatorial Pacific Ocean is relatively cool for a tropical ocean.
No one knows why the trades suddenly slowor even reverse, piling warm water up againstSouth America. Reid Bryson, the modernfounder of the very true notion that climatedoes change in ways that are important to people,believes this reversal is mainly an effect ofsome other large-scale physical fluctuation.During an El Niño, a large portion of the tropicalPacific is much warmer than average -- asmuch as 8oC (14.4oF) -- and this heat eventuallydisperses through the atmosphere.
|Figure 1. Schematic representation of the conditions that occur during an El Niño event as compared with a La Niña event.|
Heat is energy, and an El Niño shows upboth as warming and as motion. Its reachextends into the tropical Atlantic, where itsuppresses -- yes, suppresses -- hurricanes. Rain,often absent for years, falls in the ultradesertsof Peru and Argentina. And the global temperaturewarms.
When the trade winds return, the coldupwelling reappears. This is La Niña. It stands toreason that the more the cold water is suppressed,the greater the amount that eventually bubblesup, so a big El Niño warm spike may mean a bigtemperature fall in the months thereafter.
| As our daily satellite data show (Figure 2), the lower atmospheric temperature peaked around April, and was in rapid decline through the rest of the year. As of this writing (mid-March 1999) it continues to head south faster than an Internet stock with a bad earnings report.
We're totally confident that 1998's big warmingspike was a result of El Niño, and not dreaded"global warming" -- that is, a human product. Weknow because the stratosphere tells us so.
The human version of global warming iscaused by increasing amounts of "greenhouse"gases in the lower atmosphere. These compoundsabsorb the heating radiation that resultsfrom the sun's warming of the earth's surface,and reemit that radiation either downward,resulting in additional atmospheric warming, orout to space. If these compounds weren't there,the radiation would pass directly outward.
|Figure 2. Daily measurements of the global temperature anomalies as observed by satellites show that the anomalies peaked in the month of April 1998 and have been declining ever since.|
| Increasing the greenhouse effect, then, warms the lower atmosphere but, by virtue of the "recycling" of warming radiation in the lower atmosphere, cools the stratosphere that lies above. The heat from El Niño, on the other hand, burbles up through it all.
So what we should see from the increasing greenhouseeffect is a lowering trend for stratospherictemperature. And El Niño should temporarilystop that trend, at least for a year or so.Figure 3 shows that 1998 was indeed one of thewarmest years in the stratosphere in the lasttwo decades and is testimony to El Niño asthe cause.
|Figure 3. The rather steady decline in stratospheric temperatures was abruptly interrupted in 1998 -- a strong sign of El Niño.|
We were besieged with news reports abouthow El Niño (and, by not-so-subtle extension,global warming) would cause terrible agriculturaldisasters. Who can forget the miles of CNNfootage showing tractors mired in the Georgiamud, or network reels of browned corn in Texas?
Well, some folks did poorly, and some folksdid well. That happens every year. About thebest way we know of to settle the overall scoreis in the wheat, corn, and soybean markets.When there's a big supply, the price goes down.Demand fluctuates some too, but a perpetuallyincreasing population has a way of ensuringmore mouths to feed.
By late 1998, the price of U.S. wheat stood,after adjusting for inflation, at its lowest levelsince reliable records began in 1915. Fluctuationsin America's massive supply of agricultural products,more than anything, dictate the global price.
| Turns out all that rain in the winter -- so ugly on television -- was quite salutary for the major food and feed crops, especially wheat. Figure 4 shows the U.S. historical wheat yields, and there's little doubt that 1998 gets the prize.
Many agricultural economists and a few climatologistshave made careers of studying theinfluence of global weather patterns on cropyields. Moisture at planting time and in the winter before harvest is the major determinant -- by far -- of winter wheat yield. Winterwheat is planted in the early fall, requiresmoisture to germinate, and then, when springsprings, is really poised to take advantageof wet soil. In addition, yields are positivelyinfluenced by above-normal wintertemperatures.
|Figure 4. Historical yields of wheat in the United States (inset: since 1970). The El Niño year of 1998 holds the record. Notice that yields were also very high during the last great El Niño year, 1983.|
Undoubtedly, the climate of 1998 led tothe record yields. But there was another factoras well: Increased carbon dioxide in the airincreases yields and makes crops much moreefficient in their use of moisture. As SylvanWittwer, former head of the Board onAgriculture of the U.S. National ResearchCouncil wrote,"Overall, it has been conservativelyestimated that global crop productivityhas risen by approximately 2.5 to 10 percent,and possibly as high as 14 percent from thecurrent increase in atmospheric CO2 over pre-industriallevels."
We've Seen Fire and We've Seen Rain
Two other prominent newsmakers this year included the spate of overland fires in Florida during the early summer, and Mitch, a real son-of-a-gun of a flood, but really not much of a hurricane by the time it hit land.
| We were tempted to say,"Now there you go again, Al," about Florida, when he said the fires offered a "glimpse of what global warming may mean to families across America." In fact, the natural Florida ecosystem (something pretty hard to find with all the Disney Worlds, Homosassa Springs and Kissimmees dotting the landscape) is attuned to fire. Judging from their writings, the early Florida explorers found the burning of the peninsula perhaps its most impressive aspect.
That didn't stop everyone from blaming allthis on El Niño and global warming, but the factis that, in general, there is no relationshipbetween summer dryness in Florida and the existenceof an El Niño during the previous winter.That's because El Niño makes it rain during thewinter greening season. In the summer, there'sprecious little documentation that El Niño doesanything at all to Florida weather. Of course, wecould blame Florida's high temperatures thisyear on global warming, but that would meanignoring the fact that changing the greenhouseeffect warms up the coldest air masses a lot morethan it heats up the warmer tropical ones.
|Figure 5. The history of the Palmer Drought Severity Index for central Florida during summer. The filled circles indicate those years with a strong El Niño in the preceeding winter. There is no relation between El Niño and summer droughts in Florida.|
|Hurricane Mitch was a tragedy, but unfortunately, not a singularity. Mitch started as a Category 5 (that's the worst kind) hurricane in the western Caribbean. These are not all that uncommon in that part of the world. Edith (1971) and Janet (1955), for example, come to mind (Figure 6). Because it was a slow mover, as Mitch interacted with the mountains of Central America, the winds dropped to Category 2 status, but the rains were extreme. Precipitation totals of more than 50 inches brought tremendous flooding and loss of life. Although the actual number of deaths remains quite elusive, it was clearly in the ten-thousand range. Speaking in Argentina at a meeting designed to strengthen the United Nations climate treaty, State Department Spokesman J. Brian Atwood told U.S. networks that Mitch was a "typical greenhouse effect."||Figure 6. Six Category 4 or 5 hurricanes have occurred in the same vicinity as Mitch since 1950. That's about one every eight years.|
That was inflammatory nonsense. A 1974hurricane named Fifi, which was also aCategory 2 at landfall, took much the same trackand killed 7,500. Janet and Edith had muchmore powerful winds and wreaked tremendoushavoc. Perhaps the most interesting comparativeaspect with Mitch is that a tropical stormnamed Claudette, in 1979, also produced 50inches of rain and resulted in nine deaths (that'sabout 9,990 fewer than Mitch caused) when ithit Texas. Perhaps infrastructure and poverty,not global warming, created the tragedy namedMitch. Maybe, just maybe, allowing us to saveour money for investment in developing nationslike Honduras and El Salvador is a better ideathan taking it away in an attempt to stop somethingthat would happen anyway.
El Niño and hurricanes do share at least onecommon trait. They have been around for a longtime and the biota of the world, thanks to thenature of evolution, likely take advantage ofthem. In California, rains of the magnitude thatassociate with El Niño are required to make thedesert bloom. Just any old storm isn't enough,even though the ground gets wet. In that environment,many seeds have to be scarred by themotion of overland movement of water beforethey'll even germinate.
Long before banging the climate-disaster gong became the key to career advancement, federal climatologist George Cry calculated the percentage of normal rainfall that comes from all tropical cyclones, including tropical depressions, storms, and hurricanes in the eastern United States. Figure 7 shows the result for September.
In most of the areas with high values,American agriculture has adopted a double-cropsystem that plants one early, fast-maturingcrop, and then replaces it with an October harvestcrop, mainly soybeans. Late August andSeptember rain can be very important determinantsof final yield. It's pretty clear that years inwhich amounts are below normal because oflack of tropical cyclones are those in whichyields are in jeopardy.
|Figure 7. The percentage of September rainfall in the eastern United States that comes from tropical systems. The regions that normally receive more than 15 percent are shaded.|
People adapt to their climatic environment.The biota of the world take advantage ofchange, and so does our agriculture: One of thebiggest El Niños in recent centuries produced aglut of food. That's the lesson of 1998.
But the climate hype of 1998 also has portents.If this past year is any guide, when global warming becomes a major focus of the Y2K presidentialcampaign, the amount of distortion, exaggeration,scare stories and fear-mongering we're sure towitness will be a real climate disaster.
Cry, G.W., 1967. Effects of tropical cyclone rainfall on the distribution of precipitation over the eastern and southern United States. ESSA Professional Paper, 1, U.S. Dept. of Commerce. Washington, D.C.
Michaels, P.J., 1979. Atmospheric anomalies and crop yields inNorth America. Ph.D. Dissertation. University of Wisconsin.
Wittwer, S., 1995. Food Climate and Carbon Dioxide.CRC Press, Boca Raton, Fla., pp. 236.