Facts: Carbon Dioxide – The exhaust gas that changed the world


Transport, electricity, food: Carbon dioxide is in everything that makes modern life easier. But the greenhouse gas is something we can neither see nor smell nor taste. Unnoticed by large parts of the population, it accumulates in the atmosphere and is heating up the Earth.

Humankind has released more than 2,200 billion tonnes of carbon dioxide (CO2) into the atmosphere since the start of the industrial age some 270 years ago. That figure does little to raise people’s awareness to the problems involved. The green house gas can’t be seen, tasted or smelled. That is why most people find the topic easy to ignore. Whether indoors at work or out in the open, no one notices how atmospheric CO2 concentrations increase.

Even so, the impacts of ongoing CO2 emissions are becoming increasingly evident. The gas accumulates in the atmosphere and slows down the Earth’s cooling mechanisms. The Earth’s surface can no longer as easily as it once could, radiate infrared energy back into space. Instead, the heat becomes captured in the Earth system. The global mean surface temperature has consequently risen by 1 °C over the past 100 years. In Germany, warming was even stronger: In the period 1881 to 2014, annual average temperatures rose by 1.3 °C. Climate change has had visible impacts on Germany’s North Sea and Baltic Sea coasts. In the past century, sea levels in both these areas have risen by between 10 and 20 centimetres because glaciers and ice sheets are melting, and the increasingly warmer waters expand.

Change in temperature (green) and CO2 concentration (blue), with additional business-as-usual temperature scenarios (dashed red lines)

Challenge on a global scale

The picture is similar all over the world. In Alaska, people on islands and in coastal villages like Shishmaref and Newtok plan to relocate their communities because the Arctic permafrost on which their homes are built is melting and being washed away by the sea. After a long drought in 2018, the Cape Town metropolitan area almost ran out of drinking water. The Gulf Stream is weakening, glaciers in polar regions and on the highest mountain peaks are melting, and in Australia’s Great Barrier Reef – the largest coral reef on Earth – almost half of the corals died due to heat stress following two consecutively warm summers in 2016 and 2017. Low-lying island states such as Kiribati and Tovalu are currently struggling with the effects of sea-level rise. In these regions mentioned or elsewhere, it is obvious: Climate change does not stop at borders. It is a global problem whose consequences affect different countries to different degrees, but its causes and impacts can only be addressed if countries join forces and work together.

For this reason, since the 1990s, the international community has sought to negotiate an international policy framework to limit greenhouse gas emissions. A key breakthrough was achieved in December 2015 at the 21st Climate Change Conference in Paris, when government representatives from 175 nations agreed to limit global warming to well below 2 °C and to pursue efforts to limit the temperature increase to 1.5 °C. In other words, the Parties agreed to drastically reduce greenhouse gas emissions. After the Paris summit, almost all countries defined national emission reduction targets. Whether the international community will actually succeed in implementing this agreement in policy form depends on individual states translating their words into action and introducing effective measures to reduce their emissions.

Even if all possibilities for reducing CO2 emissions are used, it is highly probable that the 2 °C target will stay out of reach. A certain amount of warming remains, indicated by the orange area in the chart.

Carbon-neutral lifestyles: The only solution

Carbon dioxide is a very long-lived greenhouse gas which is produced as an undesired waste product in almost everything that simplifies our lives – in air, road and rail transport, in burning coal, oil and gas, in agriculture, in building and construction, and in the production of most consumer goods. Once released, CO2 can drive the Earth’s temperature curve upwards for centuries to come. By way of example: 1,000 billion tonnes of CO2 in the atmosphere have the potential to increase the Earth’s temperature by as much as 0.7 °C. Climate researchers are thus trying to determine the quantities of greenhouse gases that have already been emitted to date, so they can then calculate how much CO2 can still be emitted before a given temperature level is reached.

To achieve the 1.5 °C goal, the Intergovernmental Panel on Climate Change (IPCC) says that around 420 billion tonnes of CO2 can be emitted after 2018. That figure would increase to 1,200 billion tonnes if the temperature is not supposed to rise by more than 2 °C. At present, some 40 billion tonnes of CO2 are globally emitted every year. This means that at the current rate the budget available for the 1.5 °C goal would be exhausted before 2030, and the budget for the 2 °C goal by 2050. Some scientific studies give humanity slightly more time, others slight less, but their core message is the same: If global warming is to be halted, CO2 emissions must be reduced to zero – even if science is not able to exactly quantify how much time remains before specific temperature targets are met.

Equitable burden sharing

One important question is how this can be done without endangering economic and social development worldwide. The fact is, that the Earth is not warming up at the same rate everywhere and that climate change affects different countries to different degrees. For example, many emerging and developing economies near the equator are already feeling the effects of global warming to a far greater extent than many industrialised nations in the North. Long periods of drought, poor harvests and hunger are just three of many negative impacts of climate change. But there are regions that actually benefit when temperatures rise. For example, fishermen in Greenland profit from climate change. Many popular food fish are now caught in their nets after having migrated in the Atlantic Ocean from mid-latitudes to waters further north as a result of rising water temperatures. However, the losers will outnumber the winners.

As climate change continues, large regions of the world might become uninhabitable for humans. The changing climate threatens crop growing in many areas around the globe and hence world peace. The international community thus does not only face the challenge of finding fast-track paths to a carbon-neutral future. It must also find ways to equitably distribute the burden and the costs of developing emission-free societies, as well as the costs for adapting to climate change. Otherwise, the UN Sustainable Development Goals (SDGs) will not be met. Those goals include combating poverty and securing access to sufficient supplies of food and water, as well as to sustainable, reliable energy for all people on the planet. Climate action and sustainable development are inextricably linked.

Can 0.5 °C make a difference?

Given the political debate surrounding the Paris Agreement, the question arises as to what difference it will make if global warming is limited to 1.5 °C rather than 2 °C. Does it really make sense to pursue such an ambitious goal?

The IPCC set out the differences in impacts regarding the 1.5 °C goal in its 2018 Special Report. In a world that warms by only 1.5 °C by 2100, the ice sheets in the Arctic Ocean would less frequently completely melt in summer than in a 2 °C world. Sea levels would rise to a much lesser extent at 1.5 °C compared to 2 °C. This would increase the chances for adaptation for both people and ecosystems in coastal areas and on small islands. Ocean acidification would increase at a lesser rate at 1.5 °C and marine communities would be less severely affected. For example, in a 1.5 °C warmer world, up to 30 percent of the world’s coral reefs would survive, while at 2 °C, there is a far greater chance of them disappearing altogether. The difference of 0.5 °C would also be relevant for conserving terrestrial habitats and the extent of species loss. Over land, daily maximum temperatures would rise less dramatically, the risk of weather extremes such as heavy rain and heat waves would be lower, and the world would be spared tremendous economic impacts. At the moment, however, we are even far from limiting global warming to 2 °C, and unless concrete measures are taken that go beyond the existing pledges of individual states, we are heading for a world that is more than 3 °C warmer. ◆



Since the beginning of industrialisation, levels of CO2 in the Earth’s atmosphere have been rising continuously and have intensified global warming. The global surface temperature rose by 1 °C over the course of the 20th century, a trend that continues today.

  • The effects of global warming are now being felt in all parts of the world and are leading, among other things, to an increase in extreme weather events and sea-level rise. The impacts of global warming threaten millions of people worldwide.
  • At the Climate Change Conference in Paris, 175 countries agreed on the goal of limiting global warming to well below 2 °C by 2100, and in the best case even to 1.5 °C. To achieve this, by the second half of the century at the latest, global annual CO2 emissions must be reduced from the current
    40 billion tonnes to zero.

  • The effects and subsequent costs of climate change will be less drastic if global warming can be limited to 1.5 °C rather than 2 °C.

  • To promote sustainable development and social peace (for example avoiding major refugee flows), the costs and burdens of the needed adaptation and social change must be shared equitably.


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