Most people are unaware that the bulk of anthropogenic (man-made) global warming theory (AGW) is built on the concept of atmospheric water vapor feedback—not rising carbon dioxide (CO2) levels. Plenty of climate critics have questioned the soundness of this assumption, however, and evidence of its flaws may be more obvious than we realize.
Here’s the essence of AGW theory: CO2 is something of a limited greenhouse gas, in that it rapidly becomes saturated in the atmosphere. CO2’s limitations stem from the fact that, even in minute concentrations, it quickly renders the atmosphere opaque to a certain spectrum band of infrared radiation. And past that saturation point, additional concentrations of CO2 can offer only a minuscule and ever-diminishing amount of further heat-trapping function.
However, climate alarmists propose that the small amount of additional heat that CO2 traps in the atmosphere (before it becomes saturated) can sustain a corresponding rise in atmospheric water vapor content. Notably, water vapor is the primary “greenhouse” gas in the atmosphere and accounts for the overwhelming majority of atmospheric “greenhouse” function.
This additional quantity of atmospheric water vapor is expected to trap more heat, leading to a positive feedback “loop” of further heat-trapping, which will sustain yet more atmospheric water vapor, further raising temperatures, etc.
The obvious question mark in all of this is the issue of cloud formation. Atmospheric water vapor inevitably condenses into clouds, and transitions to rainfall that exercises some of this trapped energy. And cumulus clouds in the troposphere also reflect sunlight back into space.
Thus, the only way for water vapor to succeed as a positive feedback is for relative humidity to remain constant—that is, for the proportion of moisture forming into clouds to remain perpetually constant, no matter the increase in temperature—and not yield additional cloud cover.
The need for relative humidity to remain constant puts climate scientists in a bit of a quandary, however, since cloud formation is an inevitable result of atmospheric humidity.
Suppose, though, that we could look at an example of a massive injection of heat and humidity into the atmosphere, and then study the results. What might we find?
Fortunately, it’s not hard to conduct such an experiment, since El Nino weather patterns offer exactly the sort of warming needed to consider the impacts of added heat and humidity.
In 1998, the planet experienced a major El Nino, with temperatures spiking by several tenths of a degree for almost a year. A 2010 El Nino was more muted. But the recent 2015-2016 El Nino was a massive occurrence, with temperatures soaring globally to potentially record heights.
It’s important to consider that El Ninos are not simply ephemeral, and they are not random occurrences. They do in fact represent a profound shift in Pacific Ocean circulation patterns.
Typically, equatorial winds blow east to west in the Pacific. These winds continually push warm surface water toward the western Pacific. Over time, a large surplus of this warm water accumulates in the west. When this pile of warmer water begins to leak back eastward it can shift rising convection patterns, helping to shut down the prevailing east-to-west winds.
Once that happens, the warm, trapped water in the west comes spilling back, unfurling a massive surface area of trapped heat—which rises upward, carrying tremendous amounts of heat (and humidity) into the atmosphere. This huge, added volume of heat content not only raises global temperatures but also succeeds in shifting weather patterns worldwide. (The recent El Nino yielded such strange occurrences as the Northeast United States experiencing balmy winter days at the same time that the Southwest was plunged into unusually cold weather.)
Significantly, the injection of such a whopping amount of heat into the atmosphere, along with far more atmospheric humidity, duplicates some of the presumptions of AGW theory. Not only did global temperatures rise, but the added humidity helped to trap additional heat at the same time—further spiking temperatures. And the overall process took months to build, with temperatures progressively rising during that time.
But as was seen with even the most recent El Nino, these higher temperatures inevitably wash out. There are obvious weather disturbances during an El Nino, but cycles of rainfall help to gradually equalize conditions, eventually leading to a sharp drop off, as global temperatures fall back to their “starting point.”
Meteorologists often watch for a post-El Nino transition to a “La Nina,” wherein east-to-west winds reinitiate, drawing up colder, underlying waters in the Eastern Pacific Ocean. La Nina activity can drive an accompanying drop in global temperatures as these colder, upwelling waters absorb surface heat.
While no apparent La Nina has yet developed after the most recent El Nino, global temperatures still dropped precipitously at the end.
What’s interesting to ponder in watching this El Nino cycle is how clearly the additional heat and humidity failed to sustain itself, or drive a concurrent, longer-term rise in temperatures. Some of the elements of projected water vapor feedback (as expressed by AGW theory) were indeed present, yet atmospheric processes inevitably countervailed, and temperatures eventually fell.
If AGW theory trusts that an ongoing rise in atmospheric heat content will support an accompanying rise in evaporated water content, and thus lead to positive feedback for further warming, the El Nino cycle demonstrates that the mechanism to do so is more tenuous than presumed. Indeed, the global weather cycle readily demonstrates that evaporation and rain cycles innately tend to “wash out” such added humidity.
Overall, the water vapor feedback of AGW theory assumes a very high climate “sensitivity” to CO2. But just as the issue of cloud formation makes the issue more problematic, El Nino cycles show that water vapor feedback has obvious limits. And so, we see another reason to scrutinize man-made global warming theory, and to question its overall plausibility.