It was two years ago in 2013 that I last posted on the difference between climate scientists’ expectations and reality, so in this series of posts I bring these points up to date, and add a couple of related points.
What the climate scientists tell us:
Dr Karl Braganza in The Conversation on 14/06/2011 lists the “fingerprints” of climate change (my bold).
These fingerprints show the entire climate system has changed in ways that are consistent with increasing greenhouse gases and an enhanced greenhouse effect. They also show that recent, long term changes are inconsistent with a range of natural causes…..
…Patterns of temperature change that are uniquely associated with the enhanced greenhouse effect, and which have been observed in the real world include:
• greater warming in polar regions than tropical regions
• greater warming over the continents than the oceans
• greater warming of night time temperatures than daytime temperatures
• greater warming in winter compared with summer
• a pattern of cooling in the high atmosphere (stratosphere) with simultaneous warming in the lower atmosphere (tropopause).
Similarly, greater global warming at night and during winter is more typical of increased greenhouse gases, rather than an increase in solar radiation.
This post will examine “greater global warming at night” and whether it can be attributed to increased greenhouse gases.
If night time temperatures (minima) increase faster than day time temperatures (maxima), then the difference between these, the Diurnal Temperature Range (DTR) will decrease.
I use BEST global land temperature data,
and annual CO2 concentration data from NOAA.
Fig. 1: Global DTR (derived from BEST Land Tmax and Tmin)
Yes, the long term linear trend shows globally DTR has decreased, at a rate of more than half a degree Celsius per century.
Case closed! That is, if you ignore the sudden turnaround in the early 1980s. Since then DTR has been increasing at +1.1C per 100 years.
The plot showing the relationship with CO2 concentration is even more revealing:
Fig. 2: Global DTR vs CO2 concentration
If we break the series in two at the dogleg, we get the following plots:
Fig. 3: Global DTR vs CO2 concentration to 1982
Fig. 4: Global DTR vs CO2 concentration 1982 to 2015
Calling Global Warming Enthusiasts! I am puzzled:
Is DTR decreasing at 1.14 C/ 100 ppm CO2 or increasing at 0.61 C/ 100 ppm?
Can there be any logical explanation for this distinct turnaround?
Is there a problem with (a) the CO2 concentration data? (b) BEST data? (c) the theory behind decreasing DTR being an indicator of enhanced greenhouse warming? (d) all of these?
I now turn to the Australian context, with Australian surface data.
Fig. 5: Annual DTR Australia (from ACORN)
While averaged across Australia, DTR has decreased since 1910, there has been a marked increase recently. As well, the pattern is different in different regions.
Fig. 6: DTR North Australia
Fig. 7: DTR Southwest Australia
Fig. 8: DTR South Australia
Fig. 9: DTR Victoria
Fig. 10: DTR Tasmania
The effect is strongest in the tropical northwest and northeast, and weakest in the southwest and South Australia, Victoria, and Tasmania.
Moreover, the dominant influence on DTR is rainfall:
Fig. 11: DTR vs Rainfall
Definitely not CO2!
Fig. 12: DTR vs CO2 concentration
Assessment of decreased DTR as evidence for the enhanced greenhouse effect: Fail.
Other factors- especially rainfall- overwhelm the enhanced greenhouse effect.
Perhaps I should be more blunt: If Global Warming Enthusiasts stick to decreasing DTR as an indicator of greenhouse warming, then this shows BEST and ACORN surface data are completely unreliable. If they stick to claiming ACORN and BEST are “world’s best practice” then they must accept that DTR as an indicator of greenhouse warming is a dead duck.