Global Temperature Update

Nearly everyone with any interest in the global warming issue is tuning in to the monthly updates of the NASA satellite-measured temperatures to see if they are ever going to drop back down to the 1982–1991 mean value. The temperatures the satellite measure (an aggregate value of the air between about 5,000 feet and 30,000 feet) had been hovering around the mean value (with short-term digressions) since records began in 1979 until December 1997 (Figure 1). The overall global trend up until that point was a minuscule –0.03°C per decade, compared with the surface trend of +0.15°C per decade and a model forecast trend of 0.18°C.

Figure 1. Global satellite-measured temperatures, 1979 to present.

But in January of this year, the temperatures began a sharp rise to record (or near-record) values. They have remained at those levels ever since. This increase has prompted some skeptics of the moderate and largely beneficial warming paradigm to declare the satellites were now showing signs of an apocalyptic warmup.

We pointed out that a global temperature rise is typically associated with El Niņo conditions (WCR, Vol. 3, No. 19) and that the coming La Niņa would quickly return temperatures to normal.

We are still waiting.

Perhaps we were a little premature in our forecast of a temperature drop. A closer look at the temperatures following the 1982–1983 El Niņo would probably have set us straight. No two El Niņos are alike, but these two have proven to be similar.

During 1982–1983’s major El Niņo, global temperatures were depressed because of spring 1982’s large eruption of the El Chicon volcano, so the temperature rise doesn’t stand out as much as the one associated with the 1997–98 El Niņo.

Nevertheless, it is present. The interesting thing is that even though the El Niņo conditions had disappeared by the summer of 1983, temperatures did not drop again until the fall of 1983.

Why isn’t the cooling more in step with the degradation of El Niņo? Perhaps it has to do with the nature of the earth’s seasons. In winter, atmospheric circulation patterns (e.g., the jet stream) play a large role in establishing global temperatures; but during summer, as the jet stream weakens, other processes dominate. Therefore, changes in El Niņo, which can cause changes in the jet stream, are not felt globally until wintertime.

The same scenario that occurred in 1983 is likely occurring this year. Figure 2 shows the progression of the 1982–1983 El Niņo compared with one in 1997–1998. Both peaked at nearly the same value, during winter, and rapidly deteriorated during spring and summer.

Figure 2. A comparison of the 1982–1983 and 1997–1998 El Niņos.

The temperatures during these two El Niņos have also behaved similarly so far—sharply rising in winter and then remaining at the elevated levels throughout the spring and summer. In the fall of 1983, temperatures began to drop; by winter, they had fallen back to the levels that preceded the El Niņo event. If similarities persist, look for 1998 to end with temperatures close to those that ended 1997.