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Chapter Two - What Is Climate Change?

I'm writing this as the latest climate-changed induced heatwave grips Europe (The World Meteorological Organisation has said the high temperatures are "absolutely consistent" with anthropogenic increases in greenhouse gases).  The mercury hit 45C in Montpellier, France, yesterday - a record high for June - as high as August in Death Valley.

Climate and Weather

Yet it is important to make a distinction between climate and weather.  According to, simple climate definitions include:

1. The composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years; and

2. A region or area characterized by a given climate: to move to a warm climate.

Weather is defined as:

1. The state of the atmosphere with respect to wind, temperature, cloudiness, moisture, pressure, etc.; and

2. A strong wind or storm or strong winds and storms collectively.

Simplistically, weather characterizes a particular day or season whereas climate concerns regional or protracted trends.  Thus, climate change summates long-term climatic (and, therefore, daily weather) patterns.  One simple analogy is that the weather determines daily dress whereas climate determines wardrobe content.


Natural variability is a prevalent factor.  In periods of history the world has both warmed and cooled. School Ice Age geography lessons often take precedent over atypical warm periods.  For the past 6,000 years the climate has been relatively benign with very little major fluctuation.  Small variations have, however, been recorded.  In the Middle Ages, for example. Europe experienced the so-called Medieval Warm Period while the 17th Century was marked by a period known as the Little Ice Age.

Solar radiation plays an important role in this natural variation, as does changes to the Earth's tilt (albeit over millions of years).  Since the 1970s, however, natural variation has been replaced by progressive warming, which cannot be explained by these natural factors alone.  By 2018, global average temperatures exceeded their 1900 equivalents by 1C (+/-0.2C) (IPCC, 2018) and the upward trend continues (estimated antropogenic global warming is currently increasing at 0.2C per decade due to past and ongoing emissions (IPCC, 2018).

Elevated Temperature

Although 1C is comparable to daily temperature fluctuations, and may not sound like much, even small increases impact negatively on ecosystems on which we all depend.  It is a truism that humans have adapted to live in most corners of the globe in widely different temperature zones so will lifestyles adapt to counter global warming?  Temperature increases could militate global dislocation and local ecosystem failure.  For example, biodiversity loss may pre-empt rising sea levels accompanied by heat waves and droughts, severe flooding, and more intense storms, all of which must be countered.

Since the 1970s much reasearch has focused on global warming with the consensus that human activity is the most likely principal protagonist.  The IPCC, which was formed in 1988 to study the problem, predicted that likelihood as greater than 90% in its 4th Assessment Report (IPCC AR4, 2007).  The factors responsible are now well documented with the Industrial Revolution the genesis due to rural to urban migration, the indtroduction and adoption of coal-fired steam engines and the concomitant release of CO2, whose atmospheric longevity equates to more than 100 years.  Following the West's lead, similar events are now taking place in modern day China (together with India and the African continent) where massive rural to urban migration is leading to industrialization on an unprecedented scale.

The Greenhouse Effect and its Causes

Svante Arrhenius (1896) was the first to use the basics of chemistry to estimate the effect of increases in CO2 on surface temperatures, and this led Charles David Keeling (1958) to conclude that human-caused CO2 emissions (F in the Kaya Identity) are high enough to cause global warming.  The physical science basis of this is well established and has been documented for many years.  Carbon dioxide acts like an atmospheric blanket to minimize solar radiation exit to the outer atmosphere, and so the planet warms with the result that an average surface temperature of 17C has resulted.  Since the Industrial Revolution, atmospheric CO2 concentrations have increased progressively from around 280 parts per million (ppm) to some 415ppm as recorded this year, 2019.  With a time lag between concentration and temperature, scientists have predicted that a further 0.5C warming is imminent - so we must prepare for a warmer world.

One thing to bear in mind, however, is that recent pollution - in particular from aerosols caused by China, India and North Africa - has a colling effect on temperatures.  Hopefully, as these countries and regions develop further, environmental regulations will be promulgated and pollutants (and concomitant aerosols) reduced.  However, this will mean more warming is in store.

Unfortunately, as mentioned above, CO2 is not the sole 'greenhouse gas' and coal is not the only pollutant.  Six gases: CO2; CH4; N2O; CFC-11; HFC-134a; and CF4 have been identified with 'global warming potential', which is simply a calculation of the greenhouse effect caused by the release of a kilogram of gas, relative to that produced by an equivalent volume of CO2.

Methane (CH4) is perhaps the next focus and, in terms of warming, is up to 30 times more potent than CO2. Methane comes from a variety of source including humans and ruminants, landfill sites and paddy fields, all of which are increasing as the global population rises.

Since the beginning of the 20th Century, oil has been consumed on an ever-increasing scale, and this too, together with other fossil fuels, such as coal and natural gas, contributes to global warming.

Finally, deforestation and agricultural land use also play important roles. Around 20% of human-induced CO2 emissions are now attributed to deforestation with countries such as Brazil and Indonesia providing the principal outputs.  Paddy fields and the increasing demand for rice are also adding to the problem.  Despite these, in terms of scale and impact, coal still presents the biggest problem and, as the largest global energy source, is an increasing problem.  So, while coal is the major culprit here, we should also not ignore the contributions of oil and gas to global emissions either.


The time frame for impacts does not look good.  We already witness more frequent freak weather conditions with a 1C rise in temperature recorded since 1900.

Unchecked, global temperatures will continue to increase in parallel with CO2 emissions since oceans and biospheres absorb as little as 50%.  In any case, oceans are set to become more acidic and there is concern that absorption will decrease with time.  This global warming will then effect climate change step-changes and 'tipping points' will result.  These tipping points occur when temperatures reach critical points that trigger further releases of inimical gases.  There is concern that rising temperatures, for example, could mediate trapped methane release from permafrost or beneath the oceans.  Since our knowledge of this area is lacking, further study is warranted urgently.


Warming is amplified or ameloirated by positive and negative feedbacks, respectively.  Positive feedbacks include: the ice-albedo feedback where, when ice melts, darker exposed ocean surfaces absorb more radiation; and the water-vapour feedback where warmer atmosphere holds more water vapour, which is itself a greenhouse gas and leads to further warming.  One native feedback is the lapse-rate feedback where a warmer atmosphere radiates more solar power to space.  Therefore, as the atmosphere warms, the enhanced radiation offsets some of the initial warming.  Feedbacks such as cloud feedback are the summation of two opposing effects.  While reflected sunlight reduces energy input, surface emitted absorbed infrared radiation decreases energy loss and the temperature increases.

A complicating factor is time with both rapid and protracted feedbacks apparent.  Most are relatively rapid but carbon cycle feedback is a long-term possibility.  This is characterized by an initial warming, which effects release of frozen CO2 and CH4 which, in turn, contributes to warming and further gas release.

Climate Sensitivity

Quantifying temperature increase in relation to CO2 volume depends on 'climate sensitivity'.  Commonly, this refers to temperature increase resulting from CO2 doubling since the pre-industrial times atmospheric baseline of 280ppm to approx. 550ppm.  The IPCC models predict a range of 2C to 4.5C, with a best estimate of 3C.

Although both temperature and atmosphere water vapour will continue to increase, specific impacts will depend on geographical location.  For example, higher latutudes together with mid-continental locations are expected to warm sooner and faster.  Also, high rainfall areas should get wetter contrasting drier drought-prone regions.  Much modelling is in progross to predict thse regional impacts in greater detail.  The challenge of climate change, particularly dangerous climate change, cannot be understated with magnitude the principal variable.

Evidence for rising temperatures includes:

  • Actual reduction is Artctic and Antarctic ice shelves;
  • Shrinking of glaciers in the Alps, Greenland, South America, Himalayas, etc;
  • Shrinking snowcap of Mt Kilimanjaro;
  • Rising sea levels as witnessed by Fiji Islands and Bangladesh.
Current Trends

World population, which exceeded 7.5 billion in 2017, is expected to reach 9.7 billion by 2050 (UN: The median estimate for future growth projects the world population reaching 9.7 billion in 2050 and 11.2 billion in 2100 assuming a continuing decrease in the average fertility rate from 2.5 in 2015 to 2.25 in 2050 and 2.0 in 2100).  Compounding this, growth forecasts anticipate that world economic output will double in size by 2050, assuming Business-As-Usual practices.  If this growth continues to be fossil fuel powered global temperatures will increase in parallel during the course of the 21st Century.

Predicting the Future

To address this, the IPCC, in its 5th Assessment Report (IPCC AR5, 2014) stated that "antropogenic greenhouse gas emissions are mainly driven by population size, economic activity, lifetsyle, energy use, land use patterns, technology and climate policy". They then set out four Representative Concentration Pathways of greenhouse gas emissions and atmospheric concentrations, air pollutant emissions and land use.  It was worth noting, however, that one pathway, RCP2.6, known as the Stringent Mitigation Scenario, was the only option that aimed to keep global warming below 2C above pre-industrial temperatures (by 2100) since it saw net carbon emissions falling to zero by 2050.  This is required absolutely.  

Now, of course, we also have at our disposal the IPCC report of 2018 which aims for 1.5C rather than 2C given increasing scientific concerns than climate change is happening faster than earlier models had predicted.  It is sharper and less compromising than anything the IPCC has ever put out previously.

Beyond 2100

Temperature will not simply stop rising in 2100.  Since the onset of the Industrial Revolution a total of 375 GtC has been emitted  (with a significant amount being since 2000) while the estimates of the remaining fossil deposits range from 1,500 to 5,000 GtC.  Our remaining 'carbon budget' consistent with a 2C temperature rise is roughly 500GtC.  It is clear that we must move to a clean energy future ASAP where the majority of fossil fuels are left in situ as continued use will result in catastrophic temperature increases.


Since increasingly volatile and violent climate change will come to define the lives of this and future generations, we must act NOW to reduce its severity over the next century.  The definitive challenge is how to best use our existing carbon resources to re-invest in clean carbon-free technologies within a time frame to obviate 'dangerous' temperature and potential tipping points.  That time frame appears to be rough 10 years at most, and also requires that we get on a "downward slope" in total global emissions around 2020 - the turn of the next decade.

Finally, do not be thrown by arguments that say that there are also variations in temperature that are not man-made, such as sun intensity and large-scale volcanic eruptions.  These are true.  But it does not negate the fact that CO2 and other greenhouse gases are also warming the planet!

In the next chapter, due out 1 August, I will discuss what is meant by "dangerous" climate change.  Come the Autumn (Fall for American readers), we will then return to the Kaya Identity with an initial discussion about economic growth.


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Chapter One - The Kaya Identity & IPAT

Carbon dioxide is a greenhouse gas that is contributing to climate change by trapping solar infra-red rays within the atmosphere and, in turn, heating up the ocean and land temperatures.  Although other gases play a role, since 2000 the dominant gas is CO2.  CO2 is the biggest headache and therefore the focus in this blog.

The 'problem' of climate change is immensely complicated but, at the same time, the solution is very simple - we need to stop emissions.  Without getting too involved in the contradictions surrounding the subject (and often hypocritical actions), resolution can be simplified into one equation, the Kaya Identity, which was developed by a Japanese energy economist of the same name, Yoichi Kaya (1993):

           F = P * (G/P) * (E/G) * (F/E) = P * g * e * f


F is global CO2 emissions from human sources;

P is the global population;

G is world GDP (Gross Domestic Product) and g = (G/P) the global per-capita GDP;

E is global primary energy consumption and …