A Skeptic’s Guide To Global Temperatures

Climate change may well turn out to be a benign problem rather than the severe problem or “emergency” it is claimed to be.

This will eventually depend on just how much the Earth’s climate is warming due to our transient but relatively large increase in atmospheric CO2 levels.

This is why it is so important to accurately and impartially measure the Earth’s average temperature rise since 1850. It turns out that such a measurement is neither straightforward, independent, nor easy.

For some climate scientists, there sometimes appears to be a slight temptation to exaggerate recent warming,  perhaps because their careers and status improve the higher temperatures rise.

They are human like the rest of us. Similarly, the green energy lobby welcomes each scarier temperature increase to push ever more funding for their unproven solutions, without ever really explaining how they could possibly work better than a rapid expansion in nuclear energy instead.

Despite over 30 years of strident warnings and the fairly successful efforts of G7 countries to actually reduce emissions, CO2 levels in the atmosphere are still stubbornly accelerating upwards.

This is because simultaneously the developing world has strived to raise the wellbeing and living standards of their large populations through the use of ever more coal and oil, exactly as we did.

This is our current dilemma. Should they somehow be stopped from burning fossil fuels, or maybe compensated financially to ‘transition’ to so-called renewable energy instead?

All this again depends on the speed of climate change, which simply translates to the slope of the temperature record.

The good news is that once global emissions start reducing, as they inevitably will, so the climate will rather quickly stabilize. Yet it may still take a thousand years or more for the Earth to fully return to a supposedly “normal” pre-industrial climate.

But is this actually what we want? This idyllic normal climate also includes regular Ice Ages, the last one of which reduced the human population to just a few thousands of individuals struggling to survive outside of Africa.

The Earth’s climate has anyway been cooling by ~4C over the last 5 million years mainly due to land uplift caused by plate tectonics, which initiated violent natural swings in climate.

Human civilization only developed within the current Holocene interglacial (last 10,000 years).  Therefore it is in all our interests for the Holocene to continue for as long as possible.

Once we get through this temporary climate “transition” we will soon realize that controlling the climate through some enhanced CO2 levels is a far better outcome for humanity than returning to a pre-industrial climate. A 2C colder climate is far worse than a 2C warmer climate.

So how accurately do we really know what the Earth’s temperature really is? The answer would appear to be not very well at all since it has been constantly changing since the last IPCC report.

The most notable of these changes since 2012 is a  dramatic increase in what experts now say the global temperatures are compared to what those same experts said it was 10 years ago.

The hiatus as reported in the latest IPCC report has now completely vanished.  How is this possible?

The Paris agreement proposed limiting temperature increases to 1.5C since pre-industrial times, but if you believe the most recent temperature results this limit was already breached in 2016, and will surely be exceeded with another major El Nino event.

In this report, I hope to explain how a combination of new temperature data, further adjustments to those data, and changes in the methods used for calculating global averages can explain why temperatures ended up being ~0.25C warmer than they were originally reported in 2012.

Somehow each new version of any temperature series essentially rewrites climate history. Global warming always turns out to be far worse than we feared it was a year previously. This ratcheting up of alarm is continuous.

Recent temperatures now apparently show a ~0.25C warming simply due to a continuous process of adding, merging and adjusting multiple short temperature records.

But how is that possible? To really answer that question we first need to understand what the term “global temperature” really means.

Temperatures have traditionally been measured by national weather stations around the world since the early 19th century.

Traditionally these used mercury thermometers inside a Stevenson screen designed to shield them from direct sunlight and allow ambient air to mix inside.

For this reason, the slats of the Stevenson screen are painted white to reflect sunlight. This is because the aim is to measure the ambient air temperature at about 1.5-2m above the ground and not any localized effects.

The siting of weather stations should, therefore, be away from buildings and any other artificial source of heat.

Weather stations were always read manually by an operator until about the early 1990s. Large stations would be read 8 or more times per day, while smaller ones readjust twice a day usually at 9 am and 4 pm.

In addition to real-time thermometers, nearly all stations also contained a max/min thermometer. This is a linked dual glass bulb thermometer where the mercury on one side could only move up and not down and vice versa on the other side.

These thermometers measure the maximum and minimum temperatures reached between each reading whereupon they were reset by shaking the mercury back down/up again. These max/min thermometers were read and reset once a day.

The time of observation (TOBS) was important because if they were read at 9 am then the minimum temperature would be for today (early morning) but the maximum temperature would be for yesterday eg. 3 pm.

However, if they were instead read at say 6 pm then both maximum and minimum would be for today. The readings were then written in logbooks, which have since been digitized.

Typically then, each station produces three values each day. Tmax, Tmin, and Tav.

Tav is defined as (Tmax-Tmin)/2, but this is really an approximation to the average daily temperature because the shape of the diurnal variation changes every day.

A better estimate would be to use the hourly temperature values and integrate them over a 24 hour period.

However since these don’t exist for the early data, it is common practice to simply use Tav = (Tmax+Tmin)/2 instead. Note that Tav also increases if just Tmax increases or just Tmin increases.

Corrections for TOBS have become notorious especially for the US stations because the corrections are time-dependent as operating practices evolved in time.

The TOBS corrections alone produce US warming, although on paper these corrections seem correct. However, I discovered that is probably just as good to use the twice-per-day measurements at fixed times to calculate temperature anomalies.

Automated weather stations began to be introduced in the 1980s and essentially replaced all manual weather stations by the late 1990s. These log temperatures automatically every hour. This eventually removed any TOBS effects.

Spatial Coverage

The historical record shows a large increase in the spatial coverage of weather stations globally with time. In the 18th-century weather stations mainly existed only in Europe, the US and a few colonial outposts. Even today large parts of Africa and South America still have no coverage of weather stations.

An archive of the daily temperatures and rainfall back to the 18th century has been collected at NCDC and is updated regularly. The data has been subjected to quality control but should otherwise be as close to the original measured values as possible.

Monthly temperature averages predate GHCN-Daily and are processed and published by GHCN-Monthly, and CRUTEM. Berkeley Earth used a collection of archives to maximize station coverage, but today you can do almost the same by using GHCN-Daily.

Recently NCDC has released version 4 of GHCN-Monthly which is 75% the monthly averages of GHCN-Daily and 25% of national archives.

There are 24,000 stations in total but 17,000 with data between the standard 30y period 1961-1990. V4 has been subject to quality control features and in the adjusted version has homogenization applied.

Read rest at Clive Best