tirsdag 26. juli 2016

GWPF and the BEST temperatures - in retrospect

Climate contrarians often make assertions and promote theories that go against what most climate scientists argue. When assertions prove to be wrong, the contrarians make new assertions instead of acknowledging that their previous ones were wrong. It is important to focus on this behavior. In this blog post I will look at a faulty assertion about the BEST temperatures made by two conservative think tanks five years ago.

Richard Müller and his team at Berkeley released the first version of the BEST land-only temperature series in 2011. He had been sceptical about the quality of the temperature series from NASA, Met Office and NOAA 1. But the first version of the BEST temperature series confirmed the warming shown by the other land-only temperature series, and Müller stated that 'There is no reason now to be a skeptic about steadily increasing temperatures'.

Assertion made by the contrarians

Many contrarians argued that the BEST temperatures did not show steadily increasing temperatures. On the contrary they meant that the BEST temperatures showed a standstill in the global warming. Both the British GWPF and the US George Marshall Institute published a plot showing the BEST temperatures from January 2001 to May 2010 2. They argued that the plot showed a temperature standstill. The plot is similar to my Figure 1.

Figure 1: The BEST land-only surface temperatures as presented by GWPF in 2011

Was the assertion reasonable when it was made ?

The assertion was not reasonable when it was made, mainly for the two reasons outlined below.

The BEST data also include uncertainty levels for each monthly temperature. The two sigma uncertainty of the temperatures shown in Figure 1 is around 0.1 degree Celcius, except for the temperatures in April and May 2010. They have an uncertainty level of 2.8 and 2.9 degree Celcius respectively. Neither GWPF nor the George Marshall Institute informed about this. The temperature in April 2010 is obviously an outlier, and it confuses the interpretation of Figure 1.

The main objection to the assertion is that it is based on less than ten years with temperatures. Natural variations, like ENSO, dominate the trend over so short periods. Global warming is about climate change, and climate is the average weather of a longer period. The classical period is 30 years, as defined by the World Meteorological Organization WMO 3. Then natural variations tend to cancel each other, and the trend is not so sensitive to the temperatures in the start and in the end of the period.

Figure 2: The BEST land-only surface temperatures as they could have been presented in 2011.

Figure 2 shows the BEST temperatures between January 1880 and May 2010. The temperatures are as they were released in 2011. The outlier in April 2010 is intentionally included to show that the temperature series is the same as the one used by both GWPF and the George Marshall Institute. The temperature trend over the last 30 years in the plot (blue line) is a warming of 0.27 degree Celcius per decade. The 30 years moving average (green line) tells the same, i.e. that the temperature is  steadily increasing, as correctly stated by Richard Müller.

Many argued against the assertion when the contrarians made it in 2011, see eg. Tamino's blog post dated October 30, 2011 4.

Do new measurements support the assertion ?

The contrarians admitted both in 2011 and later that there was a global warming until around year 2000, but they argued that it somehow ended then. Today we have temperature measurements in more than six years after May 2010, and these measurements show that the contrarians were wrong. The global temperatures have continued to rise, as shown in Figure 3.

Figure 3: The BEST land-only surface temperatures published in 2016

Figure 3 shows the global land-only BEST temperatures as they were published in June/July 2016. The warming trend in the last 30 years has increased from 0.27 to 0.30 degrees Celcius per decade compared with the temperatures published in 2011.

More than 90 percent of the energy that causes global warming warms the oceans. Figure 4 shows the BEST global land and ocean surface temperatures. The warming is not as large as for the land-only surface temperatures due to the great thermal inertia of the ocean.

Figure 4  The BEST Global land and ocean surface temperatures published in 2016

The warming trend in the last 30 years based on the BEST global land and ocean surface temperatures is 0.19 degrees Celcius per decade, with a two sigma uncertainty of 0.05. The warming trend in the last 30 years based on a combination of the similar GISTEMP, HadCRUT4 and NOAA global temperatures is 0.17 degrees Celcius per decade, with a two sigma uncertainty of 0.05. The difference, 0.02 degrees per decade, is well within the uncertainty of the calculated trends.


Richard Müller was right when he in 2011 stated that the BEST temperatures confirmed the warming shown by the other temperature series, and that the temperatures are steadily increasing. The contrarians were wrong.


1 I download the global temperature series from these sites on the internet:
The BEST temperature series from http://berkeleyearth.org/data/ .
NASA GISTEMP from http://data.giss.nasa.gov/gistemp/
Met Office HadCRUT4 from http://www.metoffice.gov.uk/hadobs/hadcrut4/data/current/download.html
NOAA GlobalTemp from http://www.ncdc.noaa.gov/data-access/marineocean-data/noaa-global-surface-temperature-noaaglobaltemp

2 GWPF, The Global Warming Policy Forum, is a London-based think tank. In October 2011, GWPF's Science Editor Dr David Whitehouse published a plot with the BEST temperatures. See http://www.thegwpf.com/best-confirms-global-temperature-standstill/.
The US George Marshall Institute republished the same plot later the same year, see http://marshall.org/wp-content/uploads/2013/08/OKeefe-The-BEST-Is-Not-Good-Enough.pdf

3 WMO explains 'What is climate ?' at http://www.wmo.int/pages/prog/wcp/ccl/faqs.php

4 Tamino explained the weaknesses of the GWPF argumentation https://tamino.wordpress.com/2011/10/30/judith-curry-opens-mouth-inserts-foot/

Ingen kommentarer:

Legg inn en kommentar