Separating signal and noise in climate warming

Nov 17, 2011 by Anne M Stark
A National Oceanic and Atmospheric Administration (NOAA) weather satellite. Image courtesy of NASA.

(PhysOrg.com) -- In order to separate human-caused global warming from the "noise" of purely natural climate fluctuations, temperature records must be at least 17 years long, according to climate scientists.

To address criticism of the reliability of thermometer records of surface warming, Lawrence Livermore National Laboratory scientists analyzed of the temperature of the lower troposphere (the region of the atmosphere from the surface to roughly five miles above) and saw a clear signal of human-induced warming of the planet.

Satellite measurements of are made with microwave radiometers, and are completely independent of surface thermometer measurements. The satellite data indicate that the lower troposphere has warmed by roughly 0.9 degrees Fahrenheit since the beginning of satellite temperature records in 1979. This increase is entirely consistent with the warming of Earth's surface estimated from thermometer records.

Recently, a number of global warming critics have focused attention on the behavior of Earth's temperature since 1998. They have argued that there has been little or no warming over the last 10 to 12 years, and that computer models of the are not capable of simulating such short "hiatus periods" when models are run with human-caused changes in greenhouse gases.

"Looking at a single, noisy 10-year period is cherry picking, and does not provide reliable information about the presence or absence of human effects on climate said Benjamin Santer, a climate scientist and lead author on an article in the Nov. 17 online edition of the Journal of Geophysical Research (Atmospheres).

Many scientific studies have identified a human "fingerprint" in observations of surface and lower tropospheric temperature changes. These detection and attribution studies look at long, multi-decade observational temperature records. Shorter periods generally have small signal to noise ratios, making it difficult to identify an anthropogenic signal with high statistical confidence, Santer said.

"In fingerprinting, we analyze longer, multi-decadal temperature records, and we beat down the large year-to-year temperature variability caused by purely natural phenomena (like El Niños and La Niñas). This makes it easier to identify a slowly-emerging signal arising from gradual, human-caused changes in atmospheric levels of greenhouse gases," Santer said.

The LLNL-led research shows that climate models can and do simulate short, 10- to 12-year "hiatus periods" with minimal warming, even when the models are run with historical increases in and sulfate aerosol particles. They find that tropospheric temperature records must be at least 17 years long to discriminate between internal climate noise and the signal of human-caused changes in the chemical composition of the atmosphere.

"One individual short-term trend doesn't tell you much about long-term climate change," Santer said. "A single decade of observational temperature data is inadequate for identifying a slowly evolving human-caused warming signal. In both the satellite observations and in computer models, short, 10-year tropospheric temperature trends are strongly influenced by the large noise of year-to-year variability."

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User comments : 7

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3432682
1.3 / 5 (13) Nov 17, 2011
Since 1998 it is clear that there has been no warming. Satellite and ARGO ocean surveys agree. Inconvenient.
hush1
1 / 5 (6) Nov 17, 2011
Big picture:
All planets with atmospheres have one signal to noise ratio.

The 'noise' is atmosphere-less. Zero. The signal starts at zero and ends at zero. What is periodic or cyclic about a single signal? Nothing. The signal is an impulse of energy. And the climate is an energy distribution and dissipation scenario. You start with zero atmosphere and end with zero atmosphere. No exceptions.

The only point of interest for a single signal is the signal's shape during the signal's duration.

What is the shape of earth's single climate signal?
What shape of the signal will give you the time span of the signal - when an atmosphere and climate starts and stops?
The Fourier components nails the boundary conditions - the duration of the signal - the beginning and end of climate.

If you defy entropy, then we can talk of periodicity and cycle.
If you don't defy entropy, then we can talk about rise and decay of a single signal and the shape of the signal during the signal's duration.
hush1
1 / 5 (6) Nov 17, 2011
The simplification above assumes a constant star outlasting the single signals of all climates of all planets in the universe.
Vendicar_Decarian
4.5 / 5 (10) Nov 17, 2011
"Since 1998 it is clear that there has been no warming." - Liar

That is odd because your fellow Denialists the Koch brothers just spent a whack of money funding the "BEST" study of global climate and it found that over the last decade, global temperatures have risen by 0.14'C.

BEST also found concluded that the science of the IPCC, NOAA, NASA, CRU, etc. were all excellent, and the BEST results very closely matched their conclusions.

Are the Koch brothers lying to you Tard Boy?

Or are you the one who is lying?

rubberman
5 / 5 (1) Nov 18, 2011
Wasn't 1998 the warmest year on record since modern record keeping began? Saying it hasn't warmed since 1998 is the same as picking the year the most precipitation fell in recorded history and saying annual rainfall hasn't increased since that year.....can't even say nice try on that one.
MarkyMark
not rated yet Nov 22, 2011
Since 1998 it is clear that there has been no warming. Satellite and ARGO ocean surveys agree. Inconvenient.

Moron! This myth is a truely stupid one, as its pretty obviouse to those with a mind and free will ( i.e. not a tea party Drone\cultst).
PinkElephant
5 / 5 (2) Nov 22, 2011
@3432682,
"Since 1998 it is clear that there has been no warming." - Liar
Normally, VD's infantile name-calling merely irritates. This time, however, it's quite accurate.

Here's some summary graphs from ARGO:

http://www.argo.u...sis.html

Scroll down to "Ocean temperature and heat content". What do you see? What do you refuse to see?

Here's a graph of satellite and radiosonde data:

http://en.wikiped...ture.svg

(Note: 1998 had a monster El Nino as an excuse; what is 2010's excuse?)

Will you now apologize for spouting blatant falsehoods? Or are you, in fact, a congenital liar?