--by Horatio Algeranon
It oft is claimed by warming "skeptics,"
"Global warming stopped in '98.
The temperature change is downward, you see.
It's clear we're in a cooling state".
The problem with this "rationale",
Is that greenhouse gases are not alone
In affecting air temps from year to year,
But only set the long-term "tone."
The short-term "noise" includes such things,
As changes in sea-surface temperature,
And volcanic erruptions that block the sun.
Which swamp the "signal", that's for sure.
CO2-emissions each year have small impact,
But accrued over decades, nonetheless,
Produce a long-term warming trend,
"3 C per doubling" is the scientists' guess.
The issue here is "signal to noise",
Which tends to increase as more time passes,
Except among warming "skeptics", that is,
Who endlessly emit their own hot gases.
Though there have not been any major volcanic eruptions over the past decade, 1998 marked the height of an exceedingly strong El Niño (high sea surface temperatures in the Pacific), which led to a significantly heightened global mean temperature in 1998. One can see this effect as well as the effect of a volcanic eruption (Mt. Pinatubo, in 1991) on the global average temperature (annotations for El Niño and Pinatubo were added).
Over the long term (decades), the noise "washes out" (the "ups" balance the "downs") and what remains is the overall trend (the "signal"). Over the past 30 years, that trend is pretty obvious: warming of about 0.2 deg. C per decade, most of which has been attributed by climate scientists to human influence (see IPCC 4th Assessment Report summary) .
Over the short term, the noise overwhelms (dominates) the temperature signal. The temperature effect of yearly greenhouse gas emissions (about 0.02 deg C) is only 1/10th the effect of a strong El Niño. Even over ten years, the cumulative effect of the emissions just barely equals the (transient) effect of the El Niño (which usually only lasts a year or two, followed by a drop in temperature) .
In other words, a statement like "Global warming stopped in 1998" -- with the implication that yearly CO2 increases do not really increase the temperature -- is actually quite empty.
Think of it this way: the scientific consensus on global warming -- that it's real and that greenhouse gases are causing it -- is the "signal" and statements like "Global warming stopped in 1998" are the background "noise."
Unfortunately, the noise can (and often does) completely swamp the signal (small "signal to noise ratio"), making it exceedingly difficult for the non-scientific public to even find the signal -- a state of affairs that is all too often the very objective of those making the most noise.
*****
"Global warming stopped in '98.
The temperature change is downward, you see.
It's clear we're in a cooling state".
The problem with this "rationale",
Is that greenhouse gases are not alone
In affecting air temps from year to year,
But only set the long-term "tone."
The short-term "noise" includes such things,
As changes in sea-surface temperature,
And volcanic erruptions that block the sun.
Which swamp the "signal", that's for sure.
CO2-emissions each year have small impact,
But accrued over decades, nonetheless,
Produce a long-term warming trend,
"3 C per doubling" is the scientists' guess.
The issue here is "signal to noise",
Which tends to increase as more time passes,
Except among warming "skeptics", that is,
Who endlessly emit their own hot gases.
"Signal to Noise" or more precisely, the "Signal to Noise Ratio", "compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is." -- from Wikipedia article
The "ups" and "downs" from year to year about the solid line (5 year average) in the NASA graphic below essentially represent the "noise" in the global temperature due to things like El Niño, La Niña and volcanic eruptions.
The "ups" and "downs" from year to year about the solid line (5 year average) in the NASA graphic below essentially represent the "noise" in the global temperature due to things like El Niño, La Niña and volcanic eruptions.
Though there have not been any major volcanic eruptions over the past decade, 1998 marked the height of an exceedingly strong El Niño (high sea surface temperatures in the Pacific), which led to a significantly heightened global mean temperature in 1998. One can see this effect as well as the effect of a volcanic eruption (Mt. Pinatubo, in 1991) on the global average temperature (annotations for El Niño and Pinatubo were added).
Over the long term (decades), the noise "washes out" (the "ups" balance the "downs") and what remains is the overall trend (the "signal"). Over the past 30 years, that trend is pretty obvious: warming of about 0.2 deg. C per decade, most of which has been attributed by climate scientists to human influence (see IPCC 4th Assessment Report summary) .
Over the short term, the noise overwhelms (dominates) the temperature signal. The temperature effect of yearly greenhouse gas emissions (about 0.02 deg C) is only 1/10th the effect of a strong El Niño. Even over ten years, the cumulative effect of the emissions just barely equals the (transient) effect of the El Niño (which usually only lasts a year or two, followed by a drop in temperature) .
In other words, a statement like "Global warming stopped in 1998" -- with the implication that yearly CO2 increases do not really increase the temperature -- is actually quite empty.
Think of it this way: the scientific consensus on global warming -- that it's real and that greenhouse gases are causing it -- is the "signal" and statements like "Global warming stopped in 1998" are the background "noise."
Unfortunately, the noise can (and often does) completely swamp the signal (small "signal to noise ratio"), making it exceedingly difficult for the non-scientific public to even find the signal -- a state of affairs that is all too often the very objective of those making the most noise.
The above ditty was inspired by a comment by a warming "skeptic" who posted on Real Climate. The response by NASA climate scientist Gavin Schmidt is one of the best (clearest, most concise) explanations that I have seen of the "signal to noise" issue as it relates to climate science. It explains in very simple terms what is so utterly wrong with the claim that "Global warming stopped in 1998" (or variations on that theme).
