Trending trends

In this post I demonstrate my template that shows linear trends in data from any given point in time to the most recent month, (which is how I determine the starting point and length of The Pause.) It can be quickly seen how trends change over time and where these changes occur so they can be investigated. This can be used for any data at all, from monthly TLT anomalies to road fatalities. In future posts I will use this with Australian surface temperatures and rainfall. It does not replace, but supplements, normal time series graphs.
 
Up to now I have used monthly UAH temperature anomalies to study The Pause, but I have recently learnt that there can still be a weak seasonal signal, so from now on I will use 12 month running means of monthly anomalies. This leads to some changes in trends and the start of The Pause in some regions, notably Australia, but overall gives similar results. Importantly it reduces the impact of outlier individual months, especially at the start of the record and as each new month is added.
 
As well, my previous Pause criterion (a linear trend of less than +0.01 degree Celsius / 100 years) has been too strict. While UAH data are to two decimal places, the uncertainty range is +/- 0.1C. Accordingly, for 2016 my Pause criterion will be a trend of less than +0.1C per 100 years. (This is still far too lenient on Global Warming Enthusiasts- compared with trends above 1C per 100 years, anything below about +0.3C is an embarrassing slowdown.) Further, it is important to be transparent. All available data should be shown, not just those that create The Pause.
 
Finally I note, thanks to Christopher Monkton, that

In 2008, NOAA’s report on the State of the Global Climate, published as a supplement to the Bulletin of the American Meteorological Society, said: “The simulations rule out (at the 95% level) zero trends for intervals of 15 yr or more, suggesting that an observed absence of warming of this duration is needed to create a discrepancy with the expected present-day warming rate.”

A look at some of the graphs shown below will show why this is a valid statement. Certainly trends of 10 to 15 years give an indication of what has been happening, but I will agree that 15 years is about the length of time needed for trend values to settle without too much undue impact from the short term fluctuations in recent values.
 
Let’s begin.
 
Fig. 1: Running linear trend values in degrees Celsius per 100 years in Global UAH TLT anomalies from December 1978 to December 2015 (12 month means)

 
Note:
The plot shows the value of the linear trend from any given month to the most recent.
It should be plainly obvious that trends constructed from less than 10 years of data are spectacularly meaningless. This is weather.
The trend for the whole data series is about +1C/ 100 years.
The trend line crosses the zero value in 1997-98, so The Pause starts there.
 
Now I reduce the scale, and demonstrate how the graph may be interpreted.
 
Fig. 2: Running trend in degrees Celsius per 100 years in Global UAH TLT anomalies from December 1978 to December 2015 (12 month means)

 
Note:
The trend for the entire record is +1.11C per 100 years.
A higher bounce in the trend indicates that earlier Temperatures were cooler relative to recent values, and a lower trend, a dip, the reverse. If recent temperatures are low enough compared with past values, the trend will reduce to zero or below, as it has above.
I have drawn a horizontal line showing +0.1 C, below which the trend cannot be distinguished from zero, unless it is below -0.1, in which case it is definitely negative.
The trend line crosses +0.1C in 1997. I have drawn in a horizontal black line from 2015 back to this point showing the length of The Pause. I can now refer to my spreadsheet table to find the exact month for the commencement of The Pause- April 1997- and graph it.
 
Fig. 3: UAH v6.0 anomalies for the Globe in blue, with data since April 1997 in orange.

 
The Pause is highly dependent on the El Nino generated 1998-99 spike. However showing the whole record makes the following plateau plainly obvious.
 
Now, what about the mysterious disappearing Northern Hemisphere Pause? In graphs of 12 month means, it’s back!
 
Fig. 4: Running trend in degrees Celsius per 100 years in Northern Hemisphere UAH TLT anomalies from December 1978 to December 2015 (12 month means)

 
Of course, this is very much dependent on values in the next few months, as it will probably disappear again!
 
You will note the series of bumps and dips in the trend values. The small upward bounces coincide with cooling events such as La Ninas or explosive volcanoes, while the dips coincide with warming events such as El Ninos.
 
So, we have a Northern Hemisphere Pause again, if only briefly, and Global Warming Enthusiasts will surely accuse me of cherry picking. But remember, values will continue to be applied to the right hand end.
 
Fig. 5: UAH v6.0 anomalies for the Northern Hemisphere with the whole series in blue, and with data since October 1997 in orange.

 
The next graph illustrates how using 12 month means can alter the Pause length. Monthly data had Australia’s Pause lasting for 18 years and 1 month, but this has shortened to 15 years and 3 months (which still meets NOAA criteria).
 
Fig. 6: Running trend in degrees Celsius per 100 years in Australian UAH TLT anomalies from December 1978 to December 2015 (12 month means)

 
As the next graph shows, the Australian Pause starts from near the bottom of a La Nina cooling. No cherry picking there.
 
Fig. 7: Australian crawl: UAH v6.0 anomalies for Australia with the whole series in blue, and with data since October 2000 in orange.

 
I’ll conclude with a warning that as each month’s data point is appended, the trend graph will change (unlike temperature graphs where all past data points are fixed.) Don’t be confused by this- we are simply re-calculating linear trends.

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Earth and Water

Graphs of The Pause are valuable as a means of confounding Global Warming Enthusiasts by showing how little temperatures have increased in the past couple of decades, but there are many other gems in monthly Temperature of the Lower Troposphere (TLT) anomalies. In this post I take a different look at monthly data using UAH v.6.0 for various regions.
 
Click on images to expand them.
 
First, here is the complete TLT record for the globe from December 1978 to December 2015.

A trend of +1.14C/ 100 years, although anomalies have definitely flattened (the Pause) since about 2002.
 
But here are the Land and Ocean data separately:
 

Due to the oceans’ greater thermal inertia, it is to be expected that land areas would warm faster than oceans in any warming scenario no matter its cause. The Pause remains as well.
 
Notice the arrow at the beginning of 1998, marking the spike of the 1997-98 El Nino.  Note that the Land data after this are flatter and slightly stepped up from the data before this. The Ocean data give no hint of this, where since June 1994 the trend has been less than +0.1C (+/- 0.1C) per 100 years. Globally, Oceans have contributed nothing to global warming for well over half the satellite era.
 
Is this step change evident in other Land regions?
 

Northern Hemisphere:

Southern Hemisphere:

There is no sign of a step change in these data.   The step change is limited to the Northern Hemisphere.
 
Tropics:

There is a flattening in the Land data from about 2001-2002, but no apparent step change.  The step change is limited to the Northern Hemisphere, but outside the Tropics.
 

North Polar:

No step change in 1998, although temperatures began changing in the mid-1990s.
 
Therefore, the 1998 step change must be in the data from the Northern Extra-Tropics (20-90 North), and specifically from 20N to 60N.
 

There’s the culprit. There is a clear discontinuity at the beginning of 1998. This graph shows it more clearly, with plots of data before and after this step change.
 

The whole record for the Northern Extra Tropics Land shows a linear trend of +2.04 degrees Celsius per 100 years. But the trend for the first half of the record (229 out of 445 months) is only +0.6C/ 100 years, and for the past 18 years only +0.36C/ 100 years. The rapid rate of warming overall is largely due to a step change in early 1998.
 
Here is the plot for the Northern Extra Tropics Ocean data:

The step change is not clearly defined, but the trend change is dramatic: +0.84C/ 100 years to zero.
 
This graph shows Land and Ocean data on the one plot, together with mean temperatures for both of them before and after the step change. The scale has been changed to highlight the differences.

Land data steps up by +0.48C and Ocean data by +0.26C.
 
What have we learnt?
 
The different behaviours of Land and Ocean data suggest that global warming trends are difficult to interpret.
 
Land TLT is warming faster than Ocean TLT.
 
North of 20S, Tropical and Northern Extra Tropical Land TLT data show warming above +2C, nearly 50% more than Southern Extra Tropical Land. (There is not much land compared with water south of 20S).
 
Global warming, by whatever cause, is dominated by Land warming, and by the Northern Hemisphere (which has most of the land area).
 
Warming in the Northern Hemisphere is dominated by a step change of nearly +0.5C at the beginning of 1998 in data for the Lower Troposphere over Land areas between 20N and 60N- by far the largest Land area on the planet, and the most heavily populated and industrialised region.
 
Significantly, this warming step change also contributed to the Pause, as temperatures since then have flattened.
 
We live in interesting times. Indeed, we are on the cusp of finding, over the next 4 to 5 years, whether the Pause has been a temporary slowdown as temperatures step up to a higher level, a longer period of levelling temperatures, or a brief plateau before a cooling phase.

The Pause: Further Update December 2015, including Northern Hemisphere

Complete UAH v6.0 data for December for all regions were released yesterday- sooner than I expected! Here are graphs for the remaining regions showing the furthest back one can go to show a zero or negative trend (less than +0.01C/ 100 years) in lower tropospheric temperatures. (See my previous post for Global, Southern Hemisphere, and Tropical regions). Note: The satellite record commences in December 1978. The entire satellite record is now 37 years 1 month long- 445 months.

[CLICK ON IMAGES TO ENLARGE]

Tropical Oceans:

One month shorter.

North Polar:

The Pause has lengthened again, by 10 months.

South Polar:

For the whole of the satellite record, the South Polar region has had a negative trend. So much for a fingerprint of warming due to the enhanced greenhouse effect being greater warming at the Poles!

Australia:

No change.

USA 49 states:

No change.

Northern Hemisphere:
Now, about the disappearance of the Pause in the Northern Hemisphere- here’s a curious thing. While there is no Pause overall, Northern Hemisphere Land data do show a Pause, albeit short:

Only 6 years 6 months- but still a pause. Northern Hemisphere Ocean data show a much more impressive Pause:

18 years and 11months. So the Pause hasn’t disappeared- it’s just hiding in the ocean!
In my next post, later today or tomorrow, I’ll compare Land and Ocean data for various other regions.

The Pause: Interim Update December 2015

UAH v6.0 data for December were released last night.  Here is an interim post with updated graphs for some regional data (Globe, Southern Hemisphere, Tropics) as released by Roy Spencer, showing the furthest back one can go to show a zero or negative trend (less than +0.01C/ 100 years) in lower tropospheric temperatures.   For the third month of the climb towards the El Nino peak, there is still NO pause in the Northern Hemisphere trend.  Note: The satellite record commences in December 1978.  The entire satellite record is now 37 years 1 month long- 445 months.

[CLICK ON IMAGES TO ENLARGE]

Globe:

The length of the Pause has remained the same, with zero trend for one month short of half the record.  While CO2 has increased by 37 ppm, energy consumption by 187 billion tons of oil equivalent, and population by 1.3 billion people, temperatures have remained flat.

Northern Hemisphere:  No Pause

Southern Hemisphere:

The Pause has shortened by four months.  For more than half the record the Southern Hemisphere has zero trend.

Tropics:

The Pause has shortened again as the El Nino peaks, but is still more than half the record.

The remaining charts will be posted when data for the remaining regions are released later in the month.