119: Greenland - temperature trends COOLING before 1990

Climate catastrophe is generally thought of as occurring in two ways: rising temperatures and rising sea levels. Greenland is fairly unique in that it is claimed by climate science to be indicative of both. The only problem is that in reality things aren't that simple. In fact Greenland is currently colder than it was 100 years ago.

The significance of Greenland is two-fold. Firstly it is the largest landmass in the Arctic Circle. As such it is one of the best indicators of climate change near the North Pole given that, as I showed in the previous post, there is no reliable temperature data within 840 km of the North Pole. But secondly, Greenland, like Antarctica, is a large store of frozen fresh water. Its ice sheet is second only in size to that of Antarctica, and has an average thickness of 1,500 m, rising to over 3,700 m above sea level at some points. If it were to melt completely it would raise global sea levels by more than seven metres. Yet between 1930 and 1990 the climate of Greenland actually cooled by almost 2°C, and while the mean temperature has risen quite sharply by a similar amount since 1990, mean temperatures are still below their 1930 levels (see Fig. 119.1 below).

Fig. 119.1: The mean temperature change for Greenland since 1920 relative to the 1976-2005 monthly averages. The best fit is applied to the monthly mean data from 1931 to 1990 and has a negative gradient of -2.81 ± 0.35 °C per century.

In order to quantify the changes to the climate of Greenland the temperature anomalies for each of the 39 stations with the most data (over 300 months) were determined and averaged. This was done using the usual method as outlined in Post 47 and involved first calculating the temperature anomaly each month for each station, and then averaging those anomalies to determine the mean temperature anomaly (MTA) for the region. The MTA since 1920 is shown as a time series in Fig. 119.1 above and clearly shows that temperatures declined continuously from 1930 to 1990 before rebounding.

The process of determining the MTA in Fig. 119.1 involved first determining the monthly reference temperatures (MRTs) for each station using a set reference period, in this case from 1976 to 2005, and then subtracting the MRTs from the raw temperature data to deliver the anomalies. If a station had at least twelve valid temperatures per month within the MRT interval (1976-2005) then its anomalies were included in the calculation of the mean temperature anomaly (MTA). The total number of stations included in the MTA in Fig. 119.1 each month is indicated in Fig. 119.2 below. The peak in the frequency after 1980 suggests that the 1976-2005 interval was indeed the most appropriate to use for the MRTs.

Fig. 119.2: The number of station records included each month in the mean temperature anomaly (MTA) trend for Greenland in Fig. 119.1.

The data in Fig. 119.2 above indicates that after 1960 there were up to 39 active stations, but before 1890 there were less than about five. As five is generally too low a number to produce a reliable trend, particularly over a large region like Greenland, the MTA data in Fig. 119.1 was truncated with only data post-1920 being shown. However, if all the data is considered, the MTA trend will have data extending back to 1863 as shown in Fig. 119.3 below. Note also that the low number of stations before 1940 results in a much higher variance of points in Fig. 119.3 about the mean (yellow line). This is more evidence of the greater unreliability of this earlier data, which is why the plot shown in Fig. 119.1 is more statistically reliable.

Fig. 119.3: The mean temperature change for Greenland since 1860 relative to the 1976-2005 monthly averages. The best fit is applied to the monthly mean data from 1871 to 2010 and has a positive gradient of +0.93 ± 0.12 °C per century.

The locations of the 39 stations used to determine the MTA in Fig. 119.3 are shown in the map in Fig. 119.4 below. This appears to show that the stations are all located on the coast, with none in the interior or at altitude, and a majority on the south-west coast. Of these 39 stations, five are long stations with over 1200 months of data before 2014, and a further eighteen are medium stations with over 480 months of data. What is more remarkable is how many stations Greenland has despite its low population. This may be because it has historically been part of the Kingdom of Denmark. The result is it has a similar amount of temperature data as Denmark (see Fig. 48.4 and Fig. 48.5 in Post 48) yet its population is only 1% of that of Denmark.

Fig. 119.4: The (approximate) locations of the 32 longest weather station records in Greenland. Those stations with a high warming trend between 1911 and 2010 are marked in red while those with a cooling or stable trend are marked in blue. Those denoted with squares are long stations with over 1200 months of data, while diamonds denote stations with more than 300 months of data.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data shown in Fig. 119.5 below. This again was determined by averaging each monthly anomaly from the 39 longest stations in Greenland. The mean temperature follows a similar trajectory to that of the unadjusted data in Fig. 119.3 with temperatures fluctuating by over 1°C and a large peak occurring around 1930. However the BE adjustments appear to have lowered this peak relative to temperatures in 2010 by over 0.5°C compared to the raw data in Fig. 119.3.

Fig. 119.5: Temperature trends for Greenland based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1876-2010 and has a positive gradient of +1.43 ± 0.07°C/century.

Comparing the curves in Fig. 119.5 with the published Berkeley Earth (BE) version for Greenland in Fig. 119.6 below shows that there is good agreement between the two sets of data. This indicates that the simple averaging of anomalies used to generate the BE MTA in Fig. 119.5 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 119.6. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 119.1 even though the geographical distribution of stations is far from homogeneous, as was shown in Fig. 119.4.

Fig. 119.6: The temperature trend for Greenland since 1820 according to Berkeley Earth.

Most of the differences between the MTA in Fig. 119.3 and the BE versions using adjusted data in Fig. 119.6  are mainly due to the data processing procedures used by Berkeley Earth. These include homogenization, gridding, Kriging and most significantly breakpoint adjustments. These lead to changes to the original temperature data, the magnitude of these adjustments being the difference in the MTA values seen in Fig. 119.3 and Fig. 119.5. 

The magnitudes of these adjustments are shown graphically in Fig. 119.7 below. The blue curve is the difference in MTA values between adjusted (Fig. 119.5) and unadjusted data (Fig. 119.1), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Both are considerable after 1920 with the former leading to an additional warming since 1930 of up to 0.5°C. These adjustments are, however, much smaller in total than the natural variation of 2°C seen in the raw data in Fig. 119.3, so while they change the overall magnitude of the climate changes slightly, the general form of the temperature trends in Fig. 119.5 and Fig. 119.3 look broadly similar.

Fig. 119.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 119.5 after smoothing with a 12-month moving average. The blue curve represents the total BE adjustments including those from homogenization. The linear best fit (red line) to these adjustments for the period 1921-2000 has a positive gradient of +0.56 ± 0.02 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

Summary

According to the raw unadjusted temperature data, the climate of Greenland has cooled from 1930 to 1990 by about 2°C. It then warmed by a similar but slightly smaller amount until 2005 (see Fig. 119.1).

Over the same period adjusted temperature data from Berkeley Earth appears to show that the climate of Greenland has warmed by over 0.5°C since 1930 and up to 3.5°C since the 1880s (see Fig. 119.5).

The reliability of the temperature data before 1930 is debatable due to the low number of stations and the large jumps in temperature that occur repeatedly. The origin of these jumps is uncertain but cannot solely be the result of greenhouse gas emissions when those emissions increased the atmospheric carbon dioxide concentration by so little compared to today. However, similar patterns are seen in the temperature data of nearby islands of Iceland and Jan Mayen (from 1920 only), so these features seen in the data before 1930 may be real changes to the climate and not localized data errors.

Acronyms

BE = Berkeley Earth.

MRT = monthly reference temperature (see Post 47).

MTA = mean temperature anomaly.

Link to list of all stations in Greenland and their raw data files.

16. The story so far

 

The main purpose of this blog has been to analyse the physics behind climate change, and then to compare what the basic physics and raw data are indicating with what the climate scientists are saying. These are the results so far.

Post 7 looked at the temperature trend in New Zealand and found that the overall mean temperature actually declined until 1940 before increasing slightly up to the present day. The overall temperature change was a slight rise, but only amounting to about 0.25 °C since the mid 19th century. This is much less than the 1 °C rise climate scientists claim.

Post 8 examined the temperature trend in New Zealand in more detail and found that the breakpoint adjustments made to the data by Berkeley Earth, that were intended to correct for data flaws, actually added more warming to the trend than was in the original data.

Post 9 looked at the noise spectrum of the New Zealand data and found evidence of self-similarity and scaling behaviour with a fractal dimension of about 0.25. This implies that long-term temperature records over several thousands of years should still see fluctuations between the average temperature each century of over 0.5 °C, even without human intervention. In other words, a temperature rise (or fall) of at least up to 1 °C over a century is likely to be fairly common over time, and perfectly natural.

Post 10 looked at the impact of Berkeley Earth's breakpoint adjustments on the scaling behaviour of the temperature records and found that they had a negative impact. In other words the integrity of the data appeared to decline rather than improve after the adjustments were made.

Post 11 looked at the degree of correlation between pairs of temperature records in New Zealand as a function of their distance apart. For the original data a strong linear negative trend was observed for the maximum possible correlation between station pairs over distances up to 3000 km. But again the effect of Berkeley Earth's breakpoint adjustments to the data was a negative one. This trend became less detectable after the adjustments had been made. The one-year and five-year moving average smoothed data did become more highly correlated though.

After analysing the physics that dictate how the Sun and the Earth's atmosphere interact to set the Earth's surface temperature in Post 13, I then explored the implications of direct heating or energy liberation by humans at the Earth's surface in Post 14. Calculations of this direct anthropogenic surface heating (DASH) showed that while human energy use only contributed an average increase of 0.013 °C to the current overall global temperature, this energy use was highly concentrated. It is practically zero over the oceans and the poles, but in the USA it leads to an average increase of almost 0.2 °C. This rises to 0.3 °C in Texas and 0.5 °C in Pennsylvania. Yet in Europe the increases are typically even greater. In England the increase is almost 0.7 °C, and in the Benelux countries almost 1.0 °C. Perhaps more significantly for our understanding of retreating glaciers, the mean temperature rise from this effect for all the alpine countries is at least 0.3 °C.

Finally in Post 15 I looked at the energy requirements for sea level rise (SLR). Recent papers have claimed that sea levels are rising by up to 3.5 mm per year while NOAA/NASA satellite data puts the rise at 3.1 mm per year. These values are non-trivial but are still a long way short of the rate needed to cause serious environmental problems over the next 100 years.

In upcoming posts I will examine more of the global temperature data. But given what I have discovered so far, it would be a surprise if the results were found to be as clear cut as climate scientists claim. Contrary to what many claim, the science is not settled, and the data is open to many interpretations. That is not to say that everything is hunky dory though. Far from it.

15. The truth about sea level rise

One of the most emotive and alarmist claims made by climate scientists is that global warming will lead to a catastrophic sea level rise (SLR) that will submerge major cities and lead to an unprecedented humanitarian crisis and global extinction event.

Fig. 15.1: Britain's favourite polar bear - Peppy.

On the face of it this seems quite plausible, even likely. We see images of collapsing ice shelves and retreating glaciers on an almost daily basis. We see icebergs the size of cities being calved off from Antarctica and then polar bears looking forlorn on icebergs the size of a lifeboat, like something from a Fox’s glacier mint advert. So what is the reality?

Fig. 15.2: Life imitating art.

There are two principal ways that sea levels might change: either the amount of water in the sea changes, or the existing sea water changes its density. The former can happen if ice caps on Greenland or Antarctica melt. It cannot happen through the melting of sea ice because of Archimedes' Principle as I explained in Post 2, nor for the same reason can an increase in sea ice change the sea level. One alternatively mechanism is through increased evaporation of condensation, but that requires the humidity of the atmosphere to change. As for density changes, these are governed mainly by changes in the temperature of the sea water.


Scenario 1: Thermal Expansion

In the case of rising sea temperatures it is not the current global temperature that is important per se, but the temperature history and the thermal budget of the Earth. Global temperature rises can only raise sea levels directly (excluding from ice melting) by thermal expansion of the sea water. As I pointed out in Post 2, the coefficient of thermal expansion by volume for water is 0.000207 per degree Celsius or 207 ppm/°C. So a column of water 1000 metres or 1 km high will increase in height by only 20.7 cm if its temperature increases by 1 °C (or 1 K where K is the unit of absolute thermodynamic temperature - the kelvin).

But there is another factor we need to consider - the total heat or thermal energy required to do this. This is because this energy needs to come from somewhere, and once used it remains trapped in the water. It is, therefore, energy that has been sequestrated, the effect of which is to create an imbalance between the amount of energy the Earth receives from the Sun, and the amount it emits back out into space. This difference can only come from the net energy imbalance of the Earth’s energy budget.

In the last post we saw that this imbalance is currently estimated to be as much as (and no-one is saying it is more than) 0.9 W/m². If this figure is true (and as I pointed out, there is enormous uncertainty over its accuracy), and if it had been constant over the last 100 years (which is very unlikely), it would imply that the Earth has absorbed a total of 4.591x10¹⁴ joules of energy every second in that time period, or 1.45 x 10²⁴ J in total. Of course that is the upper limit of what is likely. No-one seriously thinks the Earth’s energy imbalance has always been 0.9 W/m². So the average over the last 100 years must be considerably less, and probably less than half.

Whatever the value, though, this heat will increase the temperature of the oceans. The question is, by how much, or to what depth?

As the specific heat capacity of water is 4200 Jkg^-1K^-1, the amount of energy required to heat 1 kg of water by 1 K (or 1 °C as these temperature changes are the same) will be 4200 J. If our 1 km high water column has a cross-section of 1 m², then it will contain 1000 tonnes of waters. Therefore, the total energy required to raise the temperature of the entire column by 1 °C will be 1,000,000 times greater than 4200 J, in other words 4.2 x 10⁹ J. As 70.8% of the Earth’s surface is covered by the oceans, the total volume of water down to a depth of 1 km will be 3.61 x 10¹⁷ m³. The total mass will be 3.61 x 10²⁰ kg, and the total heat capacity will be 4200 times higher still at 1.52 x 10²⁴ J/°C. So the mean temperature rise of the oceans down to a depth of 1 km over then last 100 years will be (at the absolute maximum) 1.45 x 10²⁴ ÷ (1.52 x 10²⁴) = 0.95 °C.

So, if we assume that the Earth’s energy imbalance over the last 100 years has been 0.9 W/m² everywhere and at all times, and if we assume that this heat has all ended up in the ocean, and it has heated the top 1000 m only, then the temperature rise of that top layer of water will be 0.95 °C. Some may find this number suspiciously close to the value claimed for global warming of about 1 °C per century. In other words, that climate scientists have worked backwards. They have assumed that the oceans must heat up by the same amount as the land over the same period, and to a depth of up to 1000 m, and worked out the amount of heat required to do this. From this they have inferred an imbalance in the Earth’s thermal budget rather than measured it.

Whatever the sequence of events, the resulting sea level rise (SLR) will be 197 mm (i.e. 0.95 x 207). If the warming layer of the ocean is thinner (say 500 m) but the surface energy imbalance is still 0.9 W/m², its mean temperature rise will be greater (an unlikely 1.90 °C for a 500 m thick layer), but the SLR will be the same, in other words a massive 1.97 mm per year. So what is clear is that the maximum sea level rise that can occur depends on the energy imbalance and not the water depth. In reality, the surface energy imbalance may be less than 0.9 W/m² (G. L. Stephens et al., Nature Geoscience 5, 691–696 (2012) suggest 0.6 W/m² as I pointed out in Post 13) and has in all likelihood got worse over time. So while it may be 0.9 W/m² now, it has probably averaged less than half of 0.9 W/m² over the last 100 years as global temperatures have risen. In which case the SLR has probably been less than 100 mm over the last century (or less than 66 mm if Stephens et al. are correct). But what about the future?

Assuming that the surface energy imbalance remains at 0.9 W/m² for the foreseeable future, and if we now assume that only that portion of the surface energy imbalance over the oceans is actually absorbed by the oceans, then the heat absorbed by the oceans each year will be 28.4 MJ/m². If this were absorbed by a column of water 1000 m deep it would result in a temperature rise of 6.76 mK. If it were instead absorbed by a column of water only 100 m deep it would result in a temperature rise of 67.6 mK. Either way, the resulting thermal expansion would be 1.40 mm per year. Even over 100 years this is a long way short of the 10 m rise some doom-mongers are projecting, and on its own is unlikely to pose a major threat to human civilization or the planet.

But thermal expansion is just one component of the overall problem, because not all the 0.9 W/m² (or 0.6 W/m²) need end up in the oceans. Some may instead end up melting the ice caps.


Scenario 2: Melting Ice Caps

In this scenario there are a number of factors that we need to identify and address. Firstly, where is the ice? If it is floating on the ocean surface then it cannot add to the sea level increase when it melts, despite 9% of the ice being above the water line. This is because of Archimedes’ principle as I explained in Post 2. It can, though, sequestrate energy and actually reduce warming elsewhere. The only ice that can increase sea levels when it melts is ice that is on land. This is found mainly on Greenland (3 million cubic kilometres) and Antarctica (30 million cubic kilometres).

Then there is the question of the ice temperature. Before it can melt it needs to be heated to 0 °C, yet the mean temperature of the ice on Antarctica is about -50 °C. In order to raise the ice temperature to melting point would require 3.20 x 10²⁴ J of energy (the specific heat capacity of ice is 2108 Jkg^-1K^-1 and its relative density is 0.92).

Next, you need to melt the ice. This will require an energy input of 1.01 x 10²⁵ J (the specific latent heat of ice is 332 kJ/kg); and then you need to heat it to the ambient temperature of the Earth, about 15 °C, otherwise it will cool the oceans and your global temperatures will go down. This requires another 1.91 x 10²⁴ J of energy. So the total energy required is 1.52 x 10²⁵ J. Given that the amount of power available to achieve this is at most only 0.9 W/m², that means it would take at least 1100 years to occur. But even that assumes that all the power from the Earth’s energy imbalance could be channelled somehow into melting the ice caps and nothing else.

In reality most will initially go into the oceans. As Antarctica and Greenland comprise only 3% of the Earth’s surface area, a more realistic estimate is that it would take up to 30,000 years, by which time we would be in the next ice age. Recent studies of Greenland appear to confirm this as they show Greenland has lost less that 0.05% of its ice in the last 10 years, but this may just be cyclical. 

One final point of note: while the total volume of ice on Antarctica is 30 million cubic kilometres, almost a third of this is below sea level. The net result is that if all the ice on Antarctica and Greenland were to melt, sea levels would rise by 65 metres not 91 metres. Yet over 30,000 years this will amount to a rise of only about 2 mm per year.


Scenario 3: Evaporation

The final possibility is that the sea water might just evaporate into the atmosphere leading to a loss of volume in the sea rather than a gain. Approximately 0.4% of the atmosphere by volume is water vapour. But if all this water were to suddenly condense out of the atmosphere it would only add 3.6 cm to the depth of the oceans. Given that the ambient temperature at the surface of the Earth is 15 °C, while the humidity at 0 °C would be expected to drop to near zero, this suggests that an increase of 1 °C in the surface temperature of the air would lead to a decrease in sea levels of around 2.4 mm. That is a pretty crude estimate, though, and assumes that the vapour pressure of water increases proportionately with temperature from its freezing point. A more accurate estimate can be made using the Clausius-Clapeyron equation.

Fig. 15.3: Schematic of phase boundaries on a P-T diagram.

This equation (see Eq. 15.1) relates the the slope of a phase boundary in a pressure-temperature diagram to the thermodynamic temperature, T, the molar latent heat for the phase change, L, and the change in molar volume across the boundary ∆V. An example of a phase diagram is shown in Fig. 15.3 above.

(15.1)

For a change from liquid to gas (as in evaporation) the term ∆V should be the difference in molar volumes between the water in the liquid phase and the vapour in the gas phase. However, as the volume of the vapour at the relevant pressures we are likely to encounter (i.e. around atmospheric pressure) is so much greater than it is for water (in fact by more than a factor of 1000) we can use the ideal gas law in Eq. 15.2 to substitute the molar volume of water vapour V for ∆V on the basis that the molar volume of the liquid is negligible.

(15.2)

In Eq. 15.2 the term V is the volume of one mole of water vapour at a pressure P and a temperature T. The term R is the molar gas constant where R = 8.314 Jmol^-1K^-1 and n is the molar density in mol/m³. The approximation of V for ∆V allows us to make a substitution from Eq. 15.2 into Eq. 15.1 to generate Eq. 15.3 which is now a function of only two variables, P and T.

(15.3)

This allows us to relate fractional changes in the pressure of the gaseous phase to fractional changes in temperature along the phase boundary. The differential in Eq. 15.3 implies that for small changes in P and T the following relation holds

(15.4)

while Eq. 15.2 yields the following relation between P, T and n.

(15.5)

Equating Eq. 15.4 with Eq. 15.5 gives the result for the fractional change in molar concentration of the vapour that will occur due to  evaporation across the phase boundary for a temperature change ∆T.

(15.6)

The relation in Eq. 15.6 allows us to estimate the change in water vapour concentration n as the temperature T changes. So for example, if the temperature T = 288 K and the latent heat of evaporation of water is 40.8 kJmol^-1K^-1, then a temperature rise of ∆T = 1 K will yield a fractional change of water vapour concentration of 0.0557. That in turn implies a total fall in sea level over the period of the temperature rise (which is about 100 years) of 2.0 mm (= 0.0557x36). Reassuringly, this is not that dissimilar to our original estimate of 2.4 mm, thus demonstrating two important points. Firstly, that the result is robust and consistent. Secondly, that our original back-of-the-envelope approximation, much loved by physicists everywhere, did not let us down.

The advantage of calculating the fractional change in n using Eq. 15.6 rather than calculating ∆n directly is that it means that we can avoid the complication of working out the relative humidity. The Clausius-Clapeyron equation, strictly speaking, only applies to closed systems in equilibrium, i.e. at 100% relative humidity. In open systems, such as the Earth's atmosphere above large oceans, the humidity is always less than the maximum. But Eq. 15.6 effectively removes the issue of relative humidity as it just introduces an additional scaling term that applies more or less equally to n and ∆n. Therefore it cancels out in Eq. 15.6. All of this may be somewhat pedantic, however, as the sea level fall due to evaporation is a full two orders of magnitude less than the previous two effects considered.


So the conclusion is this: prophesies of apocalyptic rising sea levels and submerging cities are still just alarmist nonsense. The physics proves that there is currently not enough energy available to achieve this on the timescale that some climate scientists predict, at least not yet. Thermal expansion and melting ice caps will each add not much more than 2 mm per year to sea levels. A recent paper by Anny Cazenave et al. (Advances in Space Research 62(7) 1639-1653 (2018) ) puts the sea level rise (SLR) from all sources at about 3.5 mm per year for the period 2005-2015  (see Fig. 15.4 below). These numbers do appear to be more consistent with the surface energy imbalance of 0.9 W/m² reported by Trenberth and co-workers rather than the 0.6 W/m² of Stephens et al., particularly the thermal expansion component.

Fig. 15.4: Possible breakdown of different contributions to sea level rise (1993-2015) from Cazenave et al.

One of the striking features of Fig. 15.4 in my view is the low contribution to sea level rise from ice melt in Antarctica compared to that from glaciers. Three explanations spring to mind. Firstly, there is probably more warming in the Northern Hemisphere because that is where the heat is being generated. Secondly, the glaciers in Europe are very close to the source of that heating. And thirdly, the ice in Antarctica is much colder than that in alpine glaciers, and so requires more heat to melt it. So, as I pointed out in the last post, this could mean that alpine glaciers will continue to recede, not because of CO₂ emissions, but because of local human industrial activity that leads to surface heating of the local environment, and thus a temperature rise of more than 0.3 °C above pre-industrial levels.

2. Is climate change real?

Well, first there is the nature of the temperature rise itself. Below is the graph of the global temperature rise since 1880 (as postulated by climate scientists) which shows the generally accepted rise in temperature of about 0.9 °C. There are a number of problems with it, not least regarding how it is constructed. This I will discuss at length in later posts. But more immediately there is the question of why this temperature curve doesn’t look like most real temperature data.

Fig. 2.1: Global temperature rise since 1880.

Actual temperature records don’t look anything like the one above: they look like the one below.

Fig. 2.2: Temperature anomaly at Berlin-Templehof (1701-2013).

This is the temperature record from Berlin showing average monthly temperatures from month to month. It is probably the longest temperature record we have and extends back to 1701, which is doubly remarkable since Daniel Fahrenheit only invented the thermometer and the temperature scale that bears his name in 1714. But there you go.

The first point to note is that the data in the Berlin-Templehof record consists of fluctuations of up to ±5 °C. These are changes to the monthly mean and are not the result of seasonal variations. I suspect the size of these fluctuations is far greater than what most people would imagine them to be if asked to speculate. Was February 1929 really almost 13 °C colder on average than the previous February? Well apparently it was, and we are not talking about the odd cold day here or there, we mean all 28 of them, or most of them at least. But not only that, the average yearly temperatures fluctuated by over two degrees over the period 1701-2013, and the average temperature for each decade by more than one degree. In which case, why are climate scientists getting so worked up about a temperature rise of 0.9 °C over 125 years?

It is a rhetorical question that the Norwegian Nobel Laureate in physicist, Ivar Giaever posed when he resigned from the American Physical Society (APS) in 2011, principally over its stated position that global warming was happening and the “The evidence is incontrovertible”. He pointed out that a rise of the mean temperature on Earth from 288.0 K to 288.8 K (which is also 0.8 °C) in 150 years seems remarkably stable. This represents a change of less than 0.3% per century, which most people (including most physicists) would consider an example of extreme systemic stability.

Then there is the issue of carbon dioxide. The graph below is the plot of CO₂ concentration in parts per million (ppm) in the atmosphere as measured near the top of Mauna Loa in Hawaii at an altitude of 3397 m. In climate science this data is one of the few pieces of hard evidence that is undisputed (except perhaps by a few cranks).

Fig. 2.3: The concentration of carbon dioxide in the atmosphere since 1959.

By 2005 the CO₂ concentration had risen to just over 370 pp, up from 280 ppm in pre-industrial times. This coincides with a temperature rise of about 0.9 °C. Yet if you look at when these changes happened there are striking differences. Two-thirds of the rise in CO₂ levels occurred before 1980, but two-thirds of the temperature rise is after 1980. That is not a strong positive correlation.

Then there is the plateau in temperatures between 1940 and 1980 in Fig 2.1 above. What caused this? We don’t know for sure, but one suggestion is that it may be due to the cooling effect of particles in the air due to industrial pollution, and that this increased as dirty heavy industry expanded after World War II, thus offsetting the temperature rise. This means, though, that up until 1980 there was virtually no noticeable increase in global temperatures. But this raises a much bigger question that rarely gets asked and is never answered, at least not by climate scientists. If temperatures before 1980 had not yet increased, why was it that in the 1980s this whole global warming hysteria suddenly took off? Are climate scientists also clairvoyants? How could their claims be based on evidence if the evidence wasn’t there (yet)?

Part of the reason why I think the global warming debate will not go away is that the whole subject is based on two facts that are undoubtedly true, but which has led many to a conclusion, via bad physics or bad logic, which may not be. The fact that CO₂ levels in the atmosphere are increasing is true, as is the assertion that CO₂ is a greenhouse gas. But this does not mean that increasing CO₂ levels must lead to an increase in temperatures. The greenhouse effect is not linear, as I will probably discuss further at a later date.

What is particularly worrying about climate science is that the things that are controversial now were just as controversial back in the 1980s. Back in 1990, Channel 4 in the UK broadcast a documentary entitled “The Greenhouse Conspiracy” (try getting that commissioned on Channel 4 now). What is particularly striking about the programme is how many of criticisms of global warming it made at the time still remain valid today. Equally striking is how apocalyptic claims made 30 years ago still haven’t come true but are still being touted by climate scientists to justify current policy.

One such issue is extreme weather. We are led to believe that global warming will lead to more extreme weather events such as droughts, storms, floods etc., except of course when it doesn’t. Then the explanation is that warming at the poles reduces the temperature gradient, thus reducing extreme weather. Talk about having your cake and eating it. Except that there is no evidence of warming at the poles. The temperature at the South Pole has gone down since 1956 (when the first measurements were taken) not up, and there is no weather data within 1000 miles of the North Pole and never has been. As for extreme weather, well the USA has some of the longest weather records on the planet, including records of extreme weather. These show that over the last 170 years there has been no increase in the number of hurricanes hitting the USA (see Fig. 2.4), nor was there any change in their average strength.

Fig 2.4: Number of hurricanes hitting the USA by decade (1850-2019).

Over the last 70 years the number of tornadoes has also been stable (see Fig. 2.5) but might actually be going down (2018 was the first year on record where no violent EF4 or EF5 tornadoes were recorded).

 Fig. 2.5: Annual frequency of tornadoes (EF1-EF5) in the USA (1954-2014).

There has been no increase in drought, flooding or wildfires, or in the number of fatalities due to extreme events. And while most of these events are difficult to record accurately, their insurance costs can be measured and these have also remained stable as a proportion of GDP. And before anybody cries foul about the use of %GDP as a valid measure rather than real value in pounds or dollars, I will point out that insurance costs are invariably linked to the value of property, and property values are inextricably linked to increases in GDP.

Then there is the issue of melting polar ice-caps and rising sea levels. The problem here is that very little of this is true either. While glaciers in the Northern Hemisphere may be shrinking, some of those in the Southern Hemisphere have been growing. In New Zealand since 1980 many glaciers have expanded in size after large declines prior to 1960 (see below). Both of these changes are uncorrelated with either the local or the global temperature records.

Fig. 2.6: Length of selected New Zealand glaciers since 1900.

But it is really the claims regarding rising sea levels that need to be addressed. One frequent claim is that melting sea ice will raise sea levels. It won’t. Anyone who understands Archimedes’ principle should understand that. If a floating iceberg melts, then the sea level must remain the same. That is basic physics. The iceberg floats because it displaces a volume of water equal to its own mass: 10% of the iceberg is above the waterline because the density of ice is 10% less than water. When it melts it contracts and exactly fills the hole in the sea that it had previously created. There is no rise in sea level and never can be.

Nor can warming oceans be a significant factor in sea level rise either. The thermal coefficient of expansion of water is 207 ppm/°C. As the average ocean depth is 3688m, a 1 °C rise in all ocean temperatures at all depths would result in a rise of less than 77 cm. However, as it is extremely unlikely that any heating of the ocean surface could extend down beyond more than about 500 m from the surface (remember, warm water is less dense and so rises to the surface), a more likely sea level rise would be a mere 10 cm or 1 mm per year. That is unnoticeable, and un-measureable.

Finally, there is one last philosophical question to consider. If the temperature of our planet is changing, and mankind is responsible, and if it is in our power to set that temperature to one of our choosing, what temperature should we choose? In short, what is the optimum surface temperature of Planet Earth, and what should be the optimum level of CO₂ to ensure that our plant is the greenest, and most beneficial for life and diversity that it can possibly be? These are the questions that no environmentalists will answer, partly because before they got hysterical about global warming, they got equally hysterical about global cooling. And at the centre of both was one man: Stephen Schneider.