What causes climate change?

The current global warming trend is mainly caused by human-induced emissions of greenhouse gases. The primary source of greenhouse gas emissions is the combustion of fossil fuels such as oil, coal and gas, which produces significant quantities of emissions, particularly carbon dioxide (CO2). Every year, around 36 billion tonnes of CO2 are emitted into the atmosphere. The atmospheric CO2 concentration is now higher than at any time in the past 800,000 years and is well above the pre-industrial level. In May 2013, mean daily atmospheric carbon dioxide levels reached 400 parts per million (ppm) for the first time; in the Earth’s interglacial periods, atmospheric CO2 concentrations were much lower, peaking at 280 ppm. Other greenhouse gases, such as methane and nitrous oxide from industry and agriculture, are also building up in the atmosphere.

Increased atmospheric greenhouse gas concentrations change the radiation balance. The gases prevent solar radiation and heat from escaping into space: they reflect the radiation back to the Earth, intensifying the greenhouse effect. As a result, the Earth's average surface temperature is increasing. According to the scientific assessments published by the Intergovernmental Panel on Climate Change (IPCC), a ‘business as usual’ scenario, with no changes to present policy and continued unabated greenhouse gas emissions, could increase mean global temperature at the Earth’s surface by as much as 4.5 °C. The impacts of global warming are already being felt, with climate-related droughts, extreme weather events, melting of glaciers and floods occurring in many places around the world. The international community has therefore set itself the target of limiting global warming to 2 °C above the pre-industrial level, in order to avoid major environmental impacts. Meeting this target will require more intensive efforts from industrialised and developing countries alike.

Historically, it is the developed countries that have been responsible for the major share of greenhouse gas emissions, but according to projections, the developing countries will account for around 55 per cent of global emissions by 2025. With ambitious low-emission development strategies and green growth strategies, however, it is possible for developing countries to bypass the emissions path taken by the industrialised countries and progress directly to a more sustainable, low-carbon economy.



Emissions sources – an overview

Transport: The transport sector generates more than 13 per cent of global greenhouse gas emissions, mainly from the burning of fossil fuels in road and rail transport, shipping and aviation. Cars are the main source of these emissions, but freight transport and infrastructure also contribute to this large carbon footprint. A 140 per cent increase in emissions from transport is forecast by 2050 against the 2000 baseline. The use of low-carbon fuels and improved fuel efficiency would do much to curb this trend. Good traffic management and a well-developed public transport system can also help to reduce greenhouse gas emissions.

Energy: More than 30 per cent of global emissions come from energy production, transmission and distribution, making this the sector with the largest emissions. Most electricity is generated by burning fossil fuels – oil, coal and natural gas. This produces greenhouse gas emissions, mainly carbon dioxide (CO2) and smaller quantities of methane (CH4) and nitrous oxide (N2O). These emissions can be reduced by improving energy efficiency in electricity production and consumption, by boosting the use of renewable energies and lower-carbon fuels, e.g. by replacing coal with natural gas, and by introducing systems for carbon capture and storage (CCS).

Industry: Industry produces around 10 per cent of global greenhouse gas emissions, mainly from energy generation, but also from other sources, such as cement and aluminium production. Greenhouse gases are also emitted all along every product’s value chain. That’s why economic growth in developing countries and economies in transition is generally linked to rising greenhouse gas emissions from increased resource consumption. Improving resource efficiency can support economic growth without increasing emissions. Resource efficiency means that fewer material and energy inputs are used to manufacture a product, without any loss of quality.

Agriculture: Around 14 per cent of global anthropogenic (human-induced) greenhouse gas emissions come from agriculture. Here, land degradation is the main source of CO2 emissions. Sustainable land use plays a key role in reducing greenhouse gas emissions from agriculture and in maintaining the soil’s natural function as a carbon sink. Cows and other ruminants are also major producers of methane. Meat production is a significant source of emissions compared with its nutritional value. A sow and her piglets produce the same quantity of CO2 equivalents over the course of a year as a German mid-range car. However, crop farming also produces emissions, mainly from the use of fertilisers.

Land use, land-use change and forestry (LULUCF): Deforestation accounts for 18.3 per cent of global emissions of greenhouse gases into the atmosphere. Trees and other plants remove CO2 from the atmosphere during photosynthesis and sequester it in biomass, making them one of the most important carbon sinks. If woodland is cleared, this releases the CO2 that is stored in forest biomass. Tropical forest clearance, with 13 million hectares of forest destroyed each year, thus makes a major contribution to climate change. Deforestation has various causes: often, tracts of forest are cleared to make way for agriculture, but poor management practices can also cause unintentional forest dieback. However, entire communities in developing countries are economically dependent on sustainable forest use, so promoting frameworks conducive to forest conservation, and therefore also to climate change mitigation, can help to achieve sustained improvements in local people’s quality of life.

Waste: The waste management sector accounts for a significant proportion – around 4 per cent – of global greenhouse gas emissions. Waste disposal in landfill or in informal and uncontrolled dumps or tips, such as those often found in developing countries, produces greenhouse gases, mainly methane and CO2. However, the use of landfill sites is not always associated with high emissions. With modern technology, landfill gas can be recovered and used as energy, or flared off. Nonetheless, waste prevention is always the most effective way of avoiding emissions as even the most sophisticated landfill gas technologies do not eliminate 100 per cent of landfill gas. Furthermore, recovery and recycling of waste actively contribute to resource conservation, avoiding the need to manufacture a similar product and thus avoiding emissions.

International climate policy

The United Nations Framework Convention on Climate Change (UNFCCC) forms the basis for international climate policy. Parties to the Convention commit to preventing dangerous anthropogenic interference with the climate system.


The UNFCCC: from Rio to the present day

United Nations Framework Convention on Climate Change (UNFCCC)

The United Nations Framework Convention on Climate Change (UNFCCC) was adopted, initially by 192 Parties, at the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in 1992 and entered into force in 1994. Since then, it has formed the basis for the international response to climate change. The Parties pledged to achieve stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent interference with the climate system.

In line with the target of permanently limiting global warming to a maximum of 2 °C above the pre-industrial level, the Convention requires all Parties to implement climate change mitigation measures and report on their greenhouse gas emissions. In accordance with the UNFCCC’s principle of the ‘common but differentiated responsibilities’ of developed (Annex I) and developing (non-Annex I) countries, developed countries included in Annex I have more far-reaching commitments, and as the prime contributors to climate change, have pledged to reduce their greenhouse gas emissions.

While the Convention itself does not set binding GHG reduction targets (see Kyoto Protocol), the developed countries have undertaken to assist the developing countries with climate change mitigation, adaptation and GHG reporting. Practical measures are negotiated at UN Climate Change Conferences (Climate Summits), ensuring the ongoing development and implementation of the UNFCCC on the basis of decisions adopted by the Parties – currently numbering 195 – at these yearly sessions.

Kyoto Protocol – establishing reduction commitments

To implement the UNFCCC, the 1997 Climate Change Conference in Kyoto adopted an agreement under which industrialised countries would reduce their collective emissions of greenhouse gases by 5.2% compared to 1990 within a specific period (2008-2012). With the exception of the US, all the Parties ratified this legally binding agreement and the Kyoto Protocol entered into force in 2005. Under the Kyoto Protocol, Germany undertook to reduce its greenhouse gases by 21 per cent during the first commitment period (2008-2012). No binding reduction targets were set for developing countries. The reduction targets adopted under the Kyoto Protocol for certain developed countries are not sufficient, however, to meet the international community’s target of limiting global temperature rise to a maximum of 2 °C.

To lower the cost of meeting reduction commitments, the Kyoto Protocol defines market mechanisms, known as flexibility mechanisms, to help Parties meet their targets wherever they can do so in the most cost-effective way. Via the Clean Development Mechanism (CDM; see also carbon markets), this can take place in a developing country, for example. The CDM thus enables developing countries to be indirectly involved in the implementation of the Kyoto Protocol as host countries for mitigation projects.

When the first commitment period ended in 2012, Parties met at the 2012 Climate Summit in Doha and agreed a new commitment period from 2013 to 2020. Canada formally withdrew from the Kyoto Protocol in December 2011. Japan, New Zealand and Russia are not participating in the second commitment period.

Bali Action Plan – involving the developing countries

At the Conference of the Parties in Bali in 2007, the international community agreed to launch a process for a comprehensive climate treaty for the post-2012 period, in order to enhance international action on climate change. The Bali Action Plan adopted at the Summit is the basis for negotiations on a new agreement. It defines four main fields of action: mitigation of climate change (including reducing emissions from deforestation and forest degradation), adaptation, technology development and transfer, and provision of financial resources and investment. In Bali, developing countries and economies in transition, for the first time, agreed to mitigate emissions by voluntarily adopting ‘nationally appropriate mitigation actions’ (NAMAs) in accordance with their capacities, supported by technology, financing and capacity building from developed countries.

Copenhagen Accord and Cancún Agreements: a 2 °C target and voluntary reduction commitments

A new post-2012 climate treaty was originally to be negotiated at the15th session of the Conference of the Parties in Copenhagen in 2009. However, the Copenhagen meeting failed to produce a new treaty; instead, the outcome was merely a political agreement, known as the Copenhagen Accord, which included the target of holding the increase in global temperature below a manageable 2 °C. The 2 °C target was included in a COP decision for the first time the following year, in the Cancún Agreements. It is regarded as the limit that would prevent dangerous anthropogenic interference with the climate system. The Cancún Agreements also include voluntary reduction commitments for industrialised and developing countries.

A new post-2020 treaty

At the UN Climate Change Conference in Durban in 2011, Parties pledged to negotiate a new international climate treaty, to be adopted in 2015 and to enter into force in 2020. The UNFCCC’s Ad Hoc Working Group on the Durban Platform for Enhanced Action (ADP) is tasked with negotiating this new climate treaty. It will also develop and implement a plan of work to cover the period to 2020, when the new treaty enters into force. The new treaty will intensify the international response to climate change and close the ambition gap with a view to ensuring the highest possible mitigation efforts by all Parties.


Dr. Jörg Linke