Has global warming stopped? - An examination of a fake skeptic's argument

I'm documenting here my reply I gave somewhere else to a couple of talking points that are frequently used in the fake skeptic universe. One talking point is that global warming had allegedly stopped, based on the fact that statistical significance of the temperature trend on some short time scales like 10 years has been missing. The second one is the assertion that the observed temperature trend was in contradiction to the carbon dioxide change over time. Both are common straw man arguments applied to create doubt toward the results from research in climate science that there was a global warming trend which can be distinguished from noise due to natural variability, and that an increase in the mass of carbon dioxide gas in the atmosphere causes global warming.

Fake skeptic statements are in italic.

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A clear example of this falsehood has been debated in this thread. It is a fact that there has been no statistically discernible rise in global temperature over the last 10 years. However, there was statistically discernible rise in global temperature over each of the three previous 10-year periods. Clearly, the statistically discernible rise in global temperature in each decade from 1970 to 2000 has stopped while, importantly, the rise in atmospheric CO2 has not stopped.

So, we have had arguments on this thread concerning whether a 10-year period is – or is not – meaningful. Clearly, in this case it is meaningful: i.e. it means the observable global warming since 1970 has stopped. This is an incontrovertible conclusion.

Let me repeat with my own words. The speaker asserts that each 10-year period from 1970 to 2000 showed a statistically significant warming. He also asserts, the absence of a statistically significant warming in the decade after 2000 implies the conclusion there hadn't been any global warming after the year 2000, in contrast to the previous 10-year periods. This conclusion was incontrovertible.

Now let's check the facts and then let's examine the conclusion.

First the trends for each 10-period with their 2-sigma significance threshold. I use the trend calculator at the Skeptical Science Blog: http://www.skepticalscience.com/trend.php

I split the 10-year periods as follows: 1971-1980, 1981-1990, 1991-2000, 2001-2010

Trends in K/decade.

1971-1980:

GISTEMP:   0.144+/-0.330
NOAA:      0.152+/-0.333
HADCRUT3v: 0.134+/-0.389
HADCRUT4:  0.16+/-0.359

None of the trends in the four data sets is statistically significant at 95% probability or above over the 10-year period 1971-1980.

1981-1990:

GISTEMP:   0.091+/-0.345
NOAA:      0.100+/-0.290
HADCRUT3v: 0.084+/-0.301
HADCRUT4:  0.082+/-0.291
RSS:       0.046+/-0.502
UAH:       0.058+/-0.531

None of the trends in the six data sets is statistically significant at 95% probability or above over the 10-year period 1981-1990.

1991-2000:

GISTEMP:   0.298+/-0.381
NOAA:      0.314+/-0.338
HADCRUT3v: 0.356+/-0.382
HADCRUT4:   0.301+/-0.356
RSS:        0.447+/-0.594
UAH:        0.367+/-0.640

None of the trends in the six data sets is statistically significant at 95% probability or above over the 10-year period 1991-2000.

2001-2010:

GISTEMP:   0.019+/-0.277
NOAA:      -0.021+/-0.244
HADCRUT3v: -0.069+/-0.234
HADCRUT4:   -0.012+/-0.249
RSS:        -0.161+/-0.376
UAH:         -0.065+/-0.410

None of the trends in the six data sets is statistically significant at 95% probability or above over the 10-year period 2001-2010.

So, in none of the consecutive decades 1971-1980, 1981-1990, 1991-2000, 2001-2010 had there been a statistically significant warming trend with a probability of 95% or above. According to the "logic" of the speaker, the absence of a statistically discernible warming trend implies that global warming "has stopped". Thus, no global warming at all for four decades.

Now let's do the trend analysis for all 4 decades together:

1971-2010:

GISTEMP:   0.169+/-0.038
NOAA:      0.168+/-0.035
HADCRUT3v: 0.165+/-0.038
HADCRUT4:  0.177+/-0.036

Now we get a statistically significant trend with a probability of at least 95% for all four data sets from 1971 to 2010, although, according to the "logic" of the speaker, the absence of global warming in each of the four decades was "incontrovertible" due to the absence of a statistically discernible trend in each of the four decades.

Global warming present and global warming absent. Both can't be true at the same time. It appears to be a conundrum. But it is none. the speaker has just applied the same logically fallacious argument again, which had been applied by him before. The logical fallacy is to draw the conclusion that a trend was absent in a data set from the fact that a trend was not detectable in the data set on a given time scale. This conclusion is logically fallacious, since the non-detectability of a trend in a data set does not logically exclude the possibility that the trend is only masked by noise on the time range of the analysis and only detectable when the time range is increased.

The speaker's asserted conclusion, it was incontrovertible that global warming "has stopped" after the year 2000 is scientifically not valid, since it is based on a methodologically flawed analysis.

And that conclusion is important. More than 80% of anthropogenic GHG emissions were after 1940. There was no discernible rise in global temperature from 1940 until ~1970. And the rise from 1910 to 1940 is the same as the rise from 1970 to 2000 when it stopped. This indicates that there is no discernible effect of the anthropogenic GHG emissions on global temperature.

The speaker's repeated assertion the global temperature increase before 1940 despite the fact that most of the CO2 emission has occurred after 1940, and the absence of a discernible temperature increase between 1940 to 1970 despite increasing CO2 concentration in the atmosphere were in contradiction to the explanation that increasing CO2 concentration in the atmosphere causes global warming is also false. There is no contradiction here between empirical data and physical explanation given by mainstream climate science. There would be a contradiction, if a linear relationship between CO2 and observed temperature was claimed, and if it was claimed CO2 was the only climate driver that could cause changes in the temperature. No serious climate scientist says such a thing. The temperature record is the result of a combination of forcings from various climate drivers, e.g., greenhouse gases, aerosols, solar activity, land use, plus internal variability in the system. Thus, the speaker's argument is just a straw man argument, which he has repeatedly applied.