Global warming

The evidence that global warming is a reality is compelling. Our planet’s climate is increasingly prone to extreme weather events, and there is a steady trend towards higher temperatures.

This is triggered by the excessive concentration of carbon dioxide (CO2) in the atmosphere. CO2 is the by-product of burning fossil fuels. Deforestation has also diminished the planet’s capacity to recapture CO2 from the atmosphere.

The largest share of these emissions is from energy generation, especially coal-fired power stations. Other greenhouse gases, such as methane and nitrous oxide, also contribute to the overall effect.

Our planet has its own greenhouse balance. After all, water vapour is the most abundant and important greenhouse gas. In the atmosphere it increases the temperature by about 30 °C, without which there would be no life. The cycle of water in our planet strikes a balance between the incoming heat and that which is dissipated into outer space. The heat that is trapped in our atmosphere generates weather patterns, ocean currents, and is absorbed by vegetation.

The net balance in this heat equation is zero, otherwise our planet would either warm up or cool down. Geological cycles of warmer or cooler global temperatures correspond to periods of time when the Sun’s variability altered this balance. Opacity due to volcanic eruptions is another factor too. If the Sun is going through a warmer or cooler cycle, so is our planet. As a result, there have been past periods of global warming and global cooling as part of a recurring cycle and in sync with the Sun’s temperature variations.

The excess of CO2 disturbs this balance in a way that is not cyclical. The excess heat that is trapped by CO2 is not dissipated or consumed by weather systems in the atmosphere, so it leads to a rise in global temperatures (see “predictions”). The heat excess simply accrues indefinitely.

Global warming caused by CO2 is eventually a runaway process, with warm phases are followed by warmer ones.

There are secondary effects in the process. CO2 emitted by human activity stays at a low altitude in the atmosphere for a long time. Therefore the greenhouse effect is most active at lower altitudes. The immediate consequence of this is that the atmosphere is becoming warmer at lower altitudes and cooler at higher. This gradient is the cause of a greater occurrence of extreme weather patterns.

Global warming also suffers from “feedback” effects, i.e. self-enhancing processes that reinforce it still further. One such effect is that with rising temperatures the planet’s vegetation absorbs less CO2 and therefore the greenhouse effect becomes still stronger, in turn accelerating temperature rises.


Global warming is a fast and dramatic process, as discussed above. Our best chance to mitigate its effects, and ultimately to reverse them, is by curbing our CO2 emissions drastically. In any case, global warming will continue its course for some time, for as long as the concentration of CO2 and other greenhouse gases remain too high. The reason is because, even if we were able to bring all our CO2 emissions to zero immediately, the excess concentration of CO2 already present in the atmosphere will continue to trap large amounts of heat from the Sun. This heat has a cumulative effect and it is what ultimately leads to an increase in global temperature. Unless we had a means to dissipate the extra heat, the increase in temperature remains with us permanently.

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Our mission

Emission cuts

The reality of modern life is that reducing CO2 emissions in any significant way is an immense challenge. In the next decades, it will be possible, with international goodwill and consensus of the highest CO2-emitting nations to head towards a low-carbon economy and cut CO2 emissions as much as possible. However, the key question is whether emissions can be ultimately brought down to such a low level as to reach a sustainable phase. In actual terms, this would entail cutting down emissions to below 80% their actual level. The goal would be that ultimately our planet’s capacity for carbon capture should be able to absorb all our annual emissions. If such a phase can be achieved, CO2 concentrations in the atmosphere would reach a plateau and remain constant.

At present, the CO2 concentration in the atmosphere is 430 ppm (in CO2 equivalent, if we take into account the combined effect of all greenhouse gases). As we discussed in the earlier sections, this is very close to the threshold of 450 ppm, where global warming enters a more serious and possibly irreversible phase. We are therefore at the threshold of this situation. The annual increase in concentration is about 2.5 ppm, which corresponds to our annual emissions of about 42 giga-tonnes of CO2 (1 giga-tonne equals 1 billion tonnes). In order to achieve a stable concentration of CO2 at around the level of 450 ppm, we must within the next 10 years take steps to decrease our annual emissions by about 1.5 giga-tonnes each year, for about 30 years until 2050, when the total emissions should be below 12 giga-tonnes per annum, or in other words, less than 70% the present level.

This is an immensely challenging undertaking. Unless we turned to nuclear energy to generate 100% of our electricity and drastically restructured our economies to turn away from fossil fuels in the shortest time possible, we would have no hope of meeting such a target. Even a more realistic target of cutting down CO2 emissions by 50% (with respect to the current levels) by 2050, as suggested in the G8 summit in July 2008, will prove very elusive without very specific year-by-year targets and an immediate reduction of high-emitting sources such as coal-fired power stations, that are currently proliferating in developing countries.

In reality, supposing that a reduction of 70% of our emissions were feasible by 2050, we would be only half-way to our objective. Having stabilised the concentration of CO2 at 450 ppm, this will continue to create a year-by-year steady trend to global warming. Between the present time and 2050, this concentration is likely to have increased the average global temperature by as much as 2-5°C, and if it remained at that level thereafter, the temperature increase by the end of the century may exceed 10 °C. With this increase of temperatures, the feedback effects kick in and the planet’s natural ability to capture carbon is also weakened. As a result, the stability of CO2 concentration in the atmosphere will be undermined by these effects. With increased warming, the release of large amounts of CO2 stored in peat deposits will in all likelihood make it impossible to maintain stability in the concentration of CO2.

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Carbon sinks

Therefore, all good efforts to cut emissions drastically in the next few decades will not achieve the desired result if CO2 concentrations in the atmosphere remain high. The additional ingredient that is required is carbon capture from the atmosphere in order to decrease the concentration of CO2. This in itself will be at least a difficult a challenge as implementing drastic emission cuts. The excess concentration must be removed over the next few decades and returned to a safe level, somewhere between pre-industrial concentrations (280 ppm — the ideal level) and approximately 350 ppm (a more realistic objective). The sooner this is done the better, because the excess heat accrued every year will keep pushing temperatures up. The ideal timescale to readjust the CO2 concentration to prevent dramatic global warming is about 100 years.

Mitigation is indeed possible in theory but it can only be effective if the reduction of our annual CO2 emissions runs in parallel with CO2 capture on quite a colossal and completely unprecedented scale. We need to put these general principles in numbers to see if this is realistic. The general principle is that reforestation on a very large scale will increase the planet’s natural capacity to absorb carbon, and will therefore offset part of our CO2 emissions. Over time, as CO2 emissions decrease and the capacity to absorb them increases, there will be a stage where both will equal and this is when the CO2 concentration in the atmosphere peaks. Beyond that, the excess capacity to absorb carbon will decrease the CO2 concentration, and eventually restore it to the chosen level. This has to be fine-tuned to finally reach an equilibrium, because if one was to overshoot and increase the CO2 capture excessively, then we would transform this problem into its diametrical opposite, creating a situation of CO2 depletion.

Mitigation model

The magnitude of the CO2 sequestration from the atmosphere must be such that it will make a significant impact on the total CO2 concentration on an annual basis, and the decrease must be rapid enough to avoid irreversible global warming. Let us take for example the scenario of aiming to reduce CO2 emissions by 70% in 2050. The present emissions are 42 giga-tonnes of CO2 per annum, and if one brings this down gradually over the next 40 years to 12 giga-tonnes in 2050 we reach stability at 450 ppm. At the same time, we offset 2.5 giga-tonnes per annum, by planting of the order of 3 billion fast-growing trees at tropical latitudes. This is an annual rate of reforestation equivalent to one tenth of the surface area of the United Kingdom. The scale of this undertaking is a significant challenge, but by no means beyond our technological abilities. This level of offset allows us to reach stability in the CO2 concentration at 450 ppm 10 years earlier than before, at around 2040. From then on, the CO2 concentration will decrease every year by just under 1 ppm. At this rate of reforestation, it will take of the order of 100 years to restore a CO2 concentration of about 350 ppm, having completed a reforestation of an area equal to ten times that of the UK (or approximately one quarter of that of the US).

By the end of that period, global warming will have increased the average temperature by a few degrees, but continuation of this process for a long time will eventually permit our atmosphere to dissipate this excess heat. One must bear in mind also that the process of reforestation must be managed to be effective, replacing trees after their natural life cycle of about 50 years, in order to sustain the capacity of carbon capture. After an additional 100 years, the CO2 concentration will in all likelihood fall below pre-industrial levels, and our planet will be able to undergo a phase of mild global cooling and dissipate the extra heat accumulated during the period of global warming.

This illustration summarises a mitigation model where the CO2 emission cuts and the increase of capacity of carbon capture are probably optimistic. But one must bear in mind that both factors are needed in the equation to combat global warming and restore the planet’s natural balance. If emissions are cut by 50% by the middle of the century, instead of 70% as discussed in the example, then the rate of reforestation will have to exceed the rate we have discussed above, otherwise the CO2 concentration in the atmosphere will not decrease at a quick enough rate to prevent excessive global warming. On the other hand, if a reforestation rate higher than what is described above can be achieved, then it will allow some leeway to decrease emissions at a slower rate. Mitigation relies on the right balance between these two competing processes.

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myths about global warming

The belief that global warming is a myth or somehow open to debate has been discredited by all the available scientific data. The evidence for climate change and global warming is everywhere and it comes from many sources. Global warming is a reality that will remain with us for as long as the concentration of CO2 in the atmosphere is high. Our actions to mitigate global warming will not have an effect for at least a few decades, so global warming will continue for the best part of this century.

Research shows that the public perception is that climate change is a confusing subject, and people don’t know how it relates to them. One reason could be that climate change awareness has not been part of the mainstream debate for long. People want to know how this is going to affect them personally and whether this is just a problem for the future and not so much for the present.

A commonly held view is that the problem is so huge that there is nothing an individual can do to change it. This is obviously not true, we can all do our bit to combat climate change. An individual’s lifestyle choices can contribute to decrease our net CO2 emissions, whether it is through small things such as using low-energy light bulbs or with more significant decisions like fitting a wind-turbine to generate the household’s electricity.

The problem is big but so is the force of public opinion. One individual cannot on his own change the way electricity is generated by big companies that supply to entire countries. If these companies generate electricity by burning fossil fuels, then an individual’s choices alone will have little impact in reducing CO2 emissions. But the collective awareness and the force of public opinion can change the way power companies operate, not only in one country but globally. This is after all a global issue, and a single country’s mitigation policies would go nowhere if we don’t engage in an international effort to combat climate change.

There are many myths surrounding the causes of global warming, and here is a discussion of two common misconceptions.

1. “Global warming is caused by the Sun

The Sun’s output of heat and light is not exactly constant, it has a small variability. It experiences cycles of higher and lower intensity (“warmer” and “cooler” cycles). These variations can have an impact on our planet’s climate but on their own they cannot explain the level of warming that our planet has experienced in the last decades.

Four billion years ago, the Sun emitted about one third less heat and radiation than it does today, and has been steadily getting hotter and brighter since. However, our planet has experienced higher global temperatures in the past than it does today. The reason for this is that during our planet’s early years there was an abundance of greenhouse gases that trapped much of the Sun’s heat.

Our planet’s cooling during the ice ages was far greater than can be explained by the small variations in the Sun’s activity. In the same way, the warmer interglacial periods cannot be explained by the Sun alone. All this shows that the correlation between changes in solar activity and our planet’s climate during its lifetime is far from simple and it cannot be understood without taking into account other effects.

During its warmer periods, the Sun shows a high incidence of sunspots on its surface. This indicates periods of greater activity, when the Sun emits more light and heat. In the early part of the 20th century, there was direct link between solar activity and rising global temperatures, and satellite measurements show that during the second half of the century, solar activity went actually into a decline whilst global temperatures have been rising steadily. Therefore, during the last decades other effects have played a more active role than the solar activity, which on its own, would have indicated a decrease in global temperatures.

It is likely that during the first half of the 20th century the warmer Sun cycle compounded the human contribution to CO2 emissions and both effects contributed to rising temperatures. In the later part of the second half of the century, the cooler cycle of the Sun in all likelihood offset the rising temperatures caused by escalating CO2 emissions and the resulting global temperature increase is likely to have been mitigated with respect to what it would have otherwise been the case if the Sun continued in a warm cycle.

In addition to the human effect, there are other natural effects that contribute to complicate the relationship between the Sun’s cycles and our planet’s climate.

Volcanic eruptions have a significant cooling effect in our planet’s atmosphere by releasing significant amounts of ash, which has the effect of increasing the opacity and preventing that the Sun’s radiation from reaching the surface. Another cooling effect is the presence of sulphate aerosols, a by-product of burning of fossil fuels. Oddly, the contributions of fossil fuels to global warming is made up of two competing forces: on the one hand it produces CO2 emissions, and on the other hand sulphate aerosols.

The figures for global temperatures prior to 1940 show that rising temperatures can be explained by an increase in CO2 concentrations, enhanced by an increase of solar activity. Between 1940 and 1970, global temperatures declined slightly, which is explained by strong volcanic activity and an abundance of sulphate aerosols from a sudden increase in the use of fossil fuels. However, from 1970 onwards, in spite of a decline in the solar activity, global temperatures rose above the pre-1940 levels, which can only be explained by the fact that the concentration of CO2 in the atmosphere has reached such a high level that it is now the dominant factor in determining the global temperature changes.

2. “Global warming is not caused by humans: the Earth has experienced global warming in the past

It is true that our planet’s climate is constantly changing. It has experienced warmer and cooler periods in the past, so our planet is not a stranger to “natural” forms of global warming and global cooling. It is only very recently in the Earth’s long life that humans have the ability to make a global impact on the environment. Even within human history, the post-industrial age that is responsible for escalating CO2 concentrations in the atmosphere is a tiny fraction of time. It is therefore difficult to believe that our planet’s long-spanning natural cycles do not prevail and that they would be disturbed by such a brief recent episode in our history.

Different parts of the world also experienced regional cycles of warmer or colder weather. The medieval warm weather in the UK, when vines were widely cultivated in the south of England is one such example, or the “little ice age” during which the Thames and other rivers in the UK regularly froze during winter.

Having said that, there are significant differences between the kind of rapidly evolving global warming that we are seeing now and the cycles of warm and cold global temperatures in the past. Some of these phases of global warming and cooling were a combination of factors: changes in our planet’s orbit in relation to the Sun, variability of the intensity of heat emitted from the Sun, and periods of increased volcanic activity. The combination of all three is responsible for the global cooling that led to the ice ages. Global warming of the magnitude that has been detected during the last century cannot be explained by any combination of these natural effects.

In the last century, the global temperature has risen by about 0.75°C, a rather abrupt increase compared to the very slow increases over very long periods of time that has been the characteristic of past warm cycles. The temperature increase is in fact getting bigger, and during the next 4 decades the increase could be up to 7 times what has been experienced in the past century. An immediate consequence of this is that the incidence of the years with the highest temperatures on record will be higher in the most recent past. This pattern has been observed already. These indicators suggest that global warming is in fact accelerating. This can only be explained by the high concentration of CO2 in the atmosphere, and it is consistent with the fact that the excess heat trapped has a cumulative effect in increasing the global temperature. It is the equivalent of compound interest of your money in the bank: the interest adds to the capital and the increased capital generates yet more interest. The growth is exponential. The temperature increase behaves in an identical way: it weakens the Earth’s ability to capture carbon, releases more CO2 from peat deposits and on the whole contributes to increase the CO2 concentration which in turn leads to a yet higher temperature increase.

The excess of CO2 in the atmosphere is mainly man-made and very recent in our planet’s history. It has reached and crossed a level at which it has a key role in driving climate change over all other factors. Pre-industrial CO2 concentrations were about 60% of present levels and the excess is almost entirely due to the burning of fossil fuels. Another important cause is deforestation. By diminishing the planet’s natural ability to capture carbon, we have increased its concentration in the atmosphere. Natural contributors such as volcanic activity contribute less than a few percent of our industrial emissions, so their relative impact is negligible.

The scientific evidence shows that global warming today is a different process entirely and not comparable to past cycles of warm weather. It is exclusively man-made and not part of a cycle. Global warming will continue for as long as CO2 concentrations are high. By contrast, natural warm and cold cycles in our planet have spanned long geological periods and have been caused by natural variations in physical processes. It is very possible that the decline of solar activity indicates the slow onset of a cooler period in our planet’s life, which has probably offset part of the man-made global warming during the 20th century. However, the present global warming is a more dominant process and it will prevail over any of the planet’s natural cycles in the future.

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Our planet will warm up considerably during this century. The increase in the average global temperature will depend on the amount of CO2 emissions during the next decades. Most conservative estimates predict that if our emissions remain at the present level, the world’s average temperature will increase by about 2-5°C in 2050 and by 5-10°C by the end of the century.

This dramatic increase in temperature is unprecedented, and it is hard to envisage the enormity of its impact on our planet’s ecosystems.

Several studies point out that there is a 20% chance that global warming could still be greater, exceeding 10°C, and in addition compounded by feedback effects which enhance the process by a further 2°C, by the end of the century. A 20% likelihood of having a temperature increase greater than 12°C by the end of this century is a not a negligible probability.

The Intergovernmental Panel on Climate Change (IPCC) published in 2007 its fourth assessment of the science of global warming. This remains the most influential study on the subject, and we derive all our data from this report. The Stern Review on the economic impact of global warming (also derived from the IPCC data) is another influential and important work.

The reality of the scientific basis is that weather models are very uncertain, owing to the chaotic processes in climatology. Even if we knew the exact amount of CO2 that will be emitted in future, the key question that needs to be successfully addressed is how sensitive is the average global temperature to the increase of CO2 concentrations. This is subject of a lot of debate but the answers are still unclear and the models can only give us predictions on the basis of likelihoods and confidence levels.

The IPCC assessment on global warming is the work of a large number of scientists, and a work of consensus. Given that there is so much uncertainty in the predictions, what is the accepted paradigm by the IPCC is a conservative view of the extent of global warming within the highest confidence levels; these are the predictions that we can assume as a bottom-line of the changes that can be expected with almost unfailing certainty. These already make a grim reading, but beyond this, more dramatic increases are permitted by the models with significant likelihood, because, it is perfectly possible, within a high probability, that our planet is more sensitive to the impact of greenhouse gases than previously thought.

The naturally occurring concentration of CO2 in the atmosphere is 280 ppm (parts per million). This is often referred to as the “pre-industrial” (or pre-1750) level. Today, the measured concentration of CO2 stands at 385 ppm, so we have increased the naturally occurring concentration by just under 40%. It is widely accepted that a CO2 concentration of 350 ppm is the area where the excess of industrially-generated CO2 in the atmosphere begins to become problematic and cause measurable global warming. We already crossed that threshold in the mid-80s. Furthermore, if we also take into account the impact of the other main greenhouse gases, such as methane, nitrous oxide, PFCs, HFCs, etc, their combined contribution to global warming together with CO2 is equivalent to a total concentration of CO2 of 430 ppm. The contribution of these greenhouse gases adds 45 ppm to the net effect of CO2 in our atmosphere. Therefore, if we consider that CO2 was the only contribution to global warming, the weather models must take into account that the reality is a CO2 concentration of 430 ppm, or in other words, a 60.7% increase over pre-industrial levels (and not merely 385 ppm).

It is acknowledged that a level of CO2 of 450 ppm marks a grey area where global warming enters a dramatic and perhaps irreversible phase. This area is in an ill-defined boundary of unchartered waters from the scientific point of view, and it is little known when an irreversible process may begin. However, the compound effect of all man-made contributions to global warming already adds to a balance of 430 ppm in CO2 equivalent, and this places us on the threshold of the 450 ppm mark. Therefore it is likely that if the current level of emissions is maintained (even without projecting an increase), the CO2 concentration in the atmosphere will cross the 450 ppm mark within the next decades, reaching 550 ppm by as early as 2035.

If the projected growth in CO2 emissions takes place (rather than curbing our emissions), we will reach a CO2 concentration of 1,000 ppm by 2100. The increase of global temperatures will be well above 10 °C, and the planet’s warming will be well into an irreversible phase.

The immediate implication of the rise of CO2 concentration in the atmosphere is a change in the energy balance in our planet. As more heat from the Sun is trapped in our planet, the atmosphere’s temperature rises, and so does the average temperature of the oceans. Ultimately there is a gradual melting of ice sheets, sea ice and glaciers, and in parallel a rise of sea levels. The cycle of water will change completely in the atmosphere, with greater rainfall concentrations at higher latitudes and a greater incidence of drought at subtropical latitudes, and in particular the Mediterranean. It will also become more extreme, with stronger hurricanes, more floods and drought events.

Global warming is an uneven phenomenon. It affects different regions of the planet in very different ways. It is least pronounced over oceans and coastal regions, and the temperature increases are more accentuated at higher and mid-latitudes. Heat-waves will be a regular occurrence in continental climates, and they will be amplified in cities, owing to the “heat island” effect of urban areas. The predicted collapse of the Gulf Stream and the North Atlantic drift (probably by the end of the century) will make Europe cooler, but this effect will be offset by global warming.

There are on the other hand “feedback effects” which worsen the problem of global warming, but have not been scientifically quantified. It is well known that global warming weakens the ability of vegetation to capture carbon. With an additional projected deforestation of the tropical rainforests, in particular in the Amazon, the ability of the planet’s “carbon sinks” to capture CO2 from the atmosphere, will be diminished, adding a further complication to the problem. The increase of CO2 concentration in the atmosphere will also increase the acidity of oceans and damage the CO2 absorbing organisms, thus weakening the “ocean sink”, which is also another natural mechanism of CO2 capture that the planet relies on to maintain its natural carbon cycle.

Perhaps the most significant contribution to global warming from “feedback effects” will come from the warming of peat deposits on the Earth’s surface, where large amounts of CO2 and methane are stored. With rising temperatures, CO2 and methane in peat deposits, wetlands and thawing permafrost will be gradually released into the atmosphere. The estimated total release (over a period of time) may amount to as much as double the cumulative emissions resulting from fossil fuels. This will add further to the temperature increases that we have discussed above.

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German Chancellor's call for reform of ETS is relevant and timely

The Emissions Trading Scheme (ETS) has demonstrated to be inherently flawed and over the years has not delivered the desired results to create a framework to reduce emissions in real terms. The surplus of CO2 certificates and low prices mean the motivation to implement emission reduction strategies is no longer there for the largest emitters, and in some cases utilities have increased their emissions even though their operations have been reduced as a cause of the economic downturn.

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