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Towards the end of the 19th century, the Swedish scientist Svante Arrhenius showed that if the concentration of CO2 in the atmosphere increases, the temperature of the earth will also increase. A doubling of the CO2 concentration could increase the temperature by 5 oC, he wrote. But he believed that it would take between 2,000 and 3,000 years before the concentration had become so high. According to COMPUTERMINUS, the UN Climate Panel, with more than 2,500 climate scientists behind it, presented a gloomy report. It shows that climate change is coming to us far faster than Arrhenius could predict.

• What happens to the CO2 concentration in the atmosphere?
• How does man affect the carbon cycle?
• What kind of connection is there between increased greenhouse gas emissions and temperature week?
• What could be the consequences of climate change?

Arrhenius’ calculation turned out to be surprisingly correct, but he was completely wrong on one point: When he had to calculate how long it would take before the concentration of CO2 was doubled, he took as his starting point the consumption of coal in his own time. He could not imagine how quickly the consumption of coal, oil and gas – non-renewable fuels – which emit CO2, would increase. Today we expect a doubling in the middle of the 2000s – only about 200 years after Arrhenius wrote his article.

2: The carbon cycle

Energy consumption is one of the most important sources of greenhouse gas emissions (greenhouse gases). Energy consumption also leads to many other environmental problems, but these can be avoided by implementing reindeer husbandry measures . CO2 emissions, on the other hand, cannot be significantly reduced without reducing the use of fossil fuels, because carbon is what we use to burn. It does not disappear, but is just moved from one city to another.

Carbon is found in almost everything that surrounds us – in the air, in the sea, in plants and wood and in the soil. Carbon is constantly exchanged between these elements. This is called the carbon cycle (the carbon cycle). Trees and plants absorb carbon from the air. When the plants rot, some goes back into the air, some becomes soil and some eventually becomes coal, oil and gas.

Extraction and use of fossil fuels disrupts this natural cycle: We “extract” carbon in the form of oil and gas from the earth, burn it and send it into the atmosphere in the form of CO2. The “natural” amount of carbon in the earth then becomes smaller and the amount in the air becomes larger than it would have been without human intervention. It also means that one can regulate the concentration of carbon in the air by speeding up the exchange of carbon between the other elements. It is thus possible to reduce the concentration in the air by increasing the uptake of carbon in wood and plants, among other things. by planting forests. If we manage to capture CO2 emissions, they can also be stored in underground landfills, such as oil and gas reservoirs or in the sea. But doing this on a large scale to compensate for emissions to air is very expensive.

3: Climate change underway?

In Svante Arrhenius’ time, the concentration of CO2 in the atmosphere was just slightly above its natural level of about 285 ppmv (number of CO2 molecules per million air molecules), which is what the concentration is measured in. Since then, it has increased to the current 390 ppmv. It was long discussed whether this increase was due to emissions from human activity or whether it had natural causes. The natural variations can be large if we look back many thousands of years.

Today, this discussion has subsided. The correlation between increased man-made emissions and increased CO2 concentration is too strong. The United Nations Intergovernmental Panel on Climate Change (IPCC) has recently reported that it is very likely that CO2 concentrations will increase due to man-made emissions. Compared with the previous report, human responsibility has thus been made considerably more probable.

So has the temperature increased in step with the increased concentrations of greenhouse gases? The figure on page 2 shows estimates of the earth’s average temperature over the last 1000 years. It shows that the temperature increased noticeably in the 20th century, despite a reduction from 1950 to 1970. In the year 2000, the temperature was 0.5–0.7 ºC higher than the average for the period 1000–1900.

Uncertainty in these measurements is shown as a gray belt around the temperature curve. So there is great uncertainty, especially before 1600. If we go even further back in time, we find traces of large and rapid climate change. We can therefore imagine that at least part of the temperature week since 1900 has a natural explanation, without us fully knowing it. It has therefore taken longer to acknowledge that the observed temperature increase (not just the increased CO2 concentration) was also created by humans. In the last 10 years, however, the doubt has been removed. It may be uncommon for humans to have contributed 0.4 ºC or 0.8 ºC to global warming, but there is no longer any doubt that the effects of human activity on Earth have all led to global warming.