The 2-Degree Limit I

The Business As Usual Trajectory

Today we’re going to be discussing more specifically about a particular target that we have already mentioned, the objective of limiting the temperature increase to less than 2 degrees Celsius compared to the pre-industrial level, the target that was adopted by the world government in 2010 in Cancun.

We have already discussed in the previous lectures the basic elements of the climate science. We have also shown what are the key milestones on the road to Paris in 2015 when an ambitious agreement on climate change need to be reached but I’m want to start this lecture by describing what are some of the possible consequences of climate change if we don’t control the greenhouse gases emissions that we need to.

I want to be discussing where the business as usual trajectory leads us so if we continue with the current trends of rising emissions because we’ve seen already some of the impacts of climate change that are already occurring because climate change is real and is already happening in many parts of the world but if greenhouse gases concentrations continue to rise the way they’re currently doing these impacts would be really getting more and more severe overtime so let’s start this first chapter of lecture 3 by discussing where the business as usual trajectory, the continuation of the current trends, would lead us and what would be the consequences.


As we’ve said several times now the United Nations Framework Convention on Climate Change or the UNFCCC was adopted in 1992 and entered into force two years later in 1994 and by now you should all almost know by heart what is the ultimate objective of the UNFCCC, that is stated in its Article 2, which is to stabilize greenhouse gases concentrations at a level that prevents dangerous anthropogenic interference with the climate system in order to enable economic development to proceed in a sustainable manner.


The last part of the sentence is very important because it shows very well that we’re not aiming only for an environmental objective were not only aiming to protect the planet we’re aiming to protect planet in order to let economic development proceed in the future so this commitment to  stabilize greenhouse gases concentrations was re-iterated at basically each and every conference of the parties or COP of the UNFCCC since 1992 and in 2010 as we’re going to discuss in more detail today, the parties to the UNFCCC even adopted a quantified target for the first time to operationalize the objective of the UNFCCC, as I said, they agreed to limit the rise in mean surface temperature below two degrees Celsius compared to pre-industrial level and in this lecture we’re going to explain why they chose this particular target and why it is so important for sustainable development going forward but the truth is that in spite of these repeated commitments each and every year to stabilize greenhouse gases concentrations, also in spite of the growing awareness of the potentially catastrophic impacts of uncontrolled climate change and in spite of a growing number of climate change mitigation policies the anthropogenic greenhouse gases emissions, the greenhouse gases emissions that are human-induced are fall from stabilizing as opposed to the goal the UNFCCC quite the country in fact, they continue to increase, continue to increase steadily, and they even continue to increase very rapidly.312

In fact the average annual growth rate of anthropogenic greenhouse gases emissions has been even higher during the last ten years than during the previous thirty years. From the year 2000 to the year 2010 we have added approximately 1 billion tonnes or one gigatonnes as we’re going to say of CO2 equivalent for year on average in the atmosphere so remember we use the unit of CO2 equivalent to find a common metric to add together all of the different greenhouse gases of which carbon dioxide CO2 is only one. So this rise, this addition of one billion ton of Co2 in the atmosphere per year from the year 2000 to the year 2010 represents on average a 2.2 annual rate increase and so my point is that this is even more than the 0.4 billion tonnes of CO2 equivalent per year on average that we added in the atmosphere in the previous thirty years from the year 1972 to the year 2000 which represented of course an increase but an increase of only 1.3 percent per year as opposed to the 2.2 percent of the last ten years and so as a consequence of this continued and accelerated in fact increase, the anthropogenic greenhouse gas emissions reached their highest level in  human history in 2010 which is the latest data that we have available so to put a number on these emissions and one you need to remember because it’s going to be important going forward in 2010 the annual anthropogenic greenhouse gases emissions stood at 49 billion tonnes of CO2 equivalent that’s the level of the emissions per year today or in 2010 and this is what you show on this graph and you show the increase in the total greenhouse gases emissions from the year 1970 to today to 2010 and you show that divided by the main types of greenhouse gases so in particular CO2 coming both from the burning of fossil fuels and from industrial processes, the CO2 coming from a different source of human activities, the deforestation and agriculture and also methane emissions and nitrous oxide emissions.

313So the bottom line looking at this graph is that since 1970 all major sources of greenhouse gases emissions have increased. As I said, the CO2 emissions but also all the other greenhouse guess but what I want you look at in particular is to the increase in CO2 emissions from the burning of fossil fuels and from other industrial processes because this rise in particular was spectacular and is going to be the main focus of this course. It contributed to about 78 percent of the total greenhouse gases emissions increase since 1970 so today the fossil fuel related CO2 emissions are the single largest source of  greenhouse gases emissions in 2010, it reached 32 billion homes per year and represented approximately 65 percent of the total greenhouse gases emissions and since 2010 these emissions still grew further by about 3 percent between 2010 and 2011 and again by something in between 1 and 2 percent in between 2011 and 2012 and so where did these emissions come from? Which are the sectors that are responsible for these rising CO2 emissions?

Well first they came from the energy supply directly for 47 percent, then they came from the industry sector for about 30 percent. After that from the transport sector for 11 percent and the remaining CO2 energy emissions came from the building sector for 3 percent. So what are the drivers of these rapidly-growing greenhouse gases emissions? Well since 1970 economic growth and population growth were the most important drivers of this increase in emissions.


The contribution of the population growth to the increase in emissions during the past 10 years remain roughly the same compared to the previous three decades but the contribution to economic growth to the increase in emissions has risen very sharply in the past 10 years compared to the previous three decades and as we already pointed out in some of the previews lectures this is in part the result of good news and that is the very strong catch-up economic growth in the middle-income countries and in particular in China but of course that came with side effects and in particular rising levels of greenhouse gases emissions so these are the two most important factors that explain the rise in emissions in the recent past: the population rose and the economy grows.

On the other side since 1970 the energy efficiency of economic growth has pretty significantly improved. It means that progressively we were able to manage to consume less energy per unit of GDP which is the good news in a way from the climate change mitigation perspective because it means that we were also adding less unit of greenhouse gas emissions per unit of GDP produced but the bad news on the other side is that this improvement of energy efficiency was too small compared to the other driving force going in the other direction:the population and the economic growth, in particular the increase in income per capita.315

Since 1970 the carbon intensity of energy also decreased. What does that mean? Well it means, progressively we were emitting less CO2 per unit of energy consumed which again was the good news from the climate change mitigation perspective but here too this improvement in the carbon intensity of energy was much too small compared to be the necessary emission reductions to avoid dangerous climate change but what I want to point out here and what is in a fact very worrying is that during the past ten years the increased use of fossil fuels but in particular of coal relative to the other energy sources has reversed the long-standing trend of gradual decarbonization of the world energy supply.

It means that the carbon content of energy is increasing during the past ten years we emitted more carbon emissions per unit of energy we consume when instead this trend should be decreasing and it should be decreasing very strongly and very quickly. So the current trends are clearly going in the wrong direction but the question is where do they lead us? What would be the global warming consequence of these rising emissions going forward so let’s do the math.317

I mean let’s look at where we are today and and let’s look at where we would be if the current trends were continued in the coming years so where are we today? In 2011, the CO2 equivalent concentration was estimated to be at approximately 430 parts per million remember parts per million is the unit we use to measure the concentration of greenhouse gases in the atmosphere.

If the current trends continued then the concentration of these greenhouse gases in the atmosphere would exceed 450 parts per million of CO2 equivalent as soon as 2030. I am stressing this particular number of 450 parts per million because we’re going to see when we discuss two-degree limit that this is the concentration of greenhouse gases emissions that corresponds to the two-degree limit in the temperature increase but it wouldn’t stop at 450 parts per million in 2030; it would be somewhere in between 750 and perhaps even more than 1300 parts per million of CO2 equivalent by the end of the century so what would be the consequence of that amount of greenhouse gases emissions in the atmosphere?

Well that would be very dangerous because it would result in global mean surface temperature increase by the end of the century from somewhere in between 4 and 5 degrees Celsius compared to  pre-industrial level and the truth is that if you build into the analysis all the uncertainty regarding the reaction of the climate to the greenhouse gas emissions then this range could expand potentially up to 8 degrees Celsius of warming before the end of the century and the consequences of such an increase in temperature would be really catastrophic.

Pedro Pereira Leite

Researcher and professor. He had his PhD. on museology in 2011, with the title “Muss-amb-ike Homeland: The commitment on musicological process”, that was published in 2011. In 2012 he finishes a Post-PhD Research on "Biographical Glances: The intersubjectivity poetry on museology, at Lusófona University (Lisbon). Presently he is working in his Post PhD. Research about: “Global Heritages" with the aims to build a network on local cognizance and memory manager has a tool to build the will of action in 3 different communities, linked by past communed heritages.” He works at CES. He participates on different Research network, presented papers in national and international conferences, and had published books on research subjects.

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