You already know that the amount of greenhouse gases in the atmosphere has been increasing rapidly in recent years leading to increases of its concentration in the atmosphere (Fig. 3.1.1). The natural content of carbon dioxide in the atmosphere has varied in the last few hundred thousand years (which have included periods of interglacial warming and glacial cooling) between 180 and 300 particles of CO2 per million other particles.
In 2013, the level of CO2 in the atmosphere exceeded 400 parts per million for the first time in at least 800,000 years. This concentration continues to grow rapidly, reaching levels of 421 parts per million in 2022. The reason is that globally, net greenhouse gas (GHG) emissions from human activity, defined as a difference between the gross emissions minus removals, for example by forests, have continued to grow. Between 2010 and 2022 the level of GHG emissions was higher than at any previous time in human history. Their concentration in the atmosphere will continue to grow until annual emissions are reduced sufficiently to be balanced by removals.
Figure 3.1.1 Growth of Co2 concentrations in the atmosphere since 1960

Everyone on the planet contributes to climate change by emitting greenhouse gases into the atmosphere year after year. We are the end users of goods and services, the production of which requires energy, and energy comes mostly from non-renewable fossil fuels (oil, coal, and natural gas). The production of goods and services accounts for 75% of all greenhouse gas emissions associated with human activities.
We already discussed the devastating impacts of climate change on the health of our society and the planet. Scientists confirmed that the recent changes in climate are widespread, rapid, intensifying, and unprecedented in thousands of years. Such changes are expected to continue, as under all emissions scenarios outlined in the IPCC AR6 report, the Earth’s surface warming is projected to reach 1.5⁰C in the next two decades. Unless there are immediate, rapid, and large-scale reductions in greenhouse gas emissions, limiting warming to 1.5°C or even 2°C will be soon beyond reach.
To decrease the concentration of greenhouse gases in the atmosphere and limit global warming, strong, rapid, and sustained reductions in CO2, methane, and other greenhouse gases in this decade and reaching net zero emissions by 2050 are critical. Together with reductions of the ‘short-lived climate forces’ such as aerosols and particulate matter, these would not only reduce the consequences of climate change but also improve air quality, reduce health impacts, and bring other sustainable development benefits. Such reductions need to follow a nature-positive approach, which can help to enrich biodiversity, store carbon, purify water and reduce pandemic risk. In short, reducing greenhouse gas emissions in the atmosphere should also enhance the resilience of our planet and our societies.
Many countries have taken action to reduce emissions. As of 2022, most industrialized countries have steadily reduced greenhouse gas emissions for more than ten years and many developing countries have taken measures to slow down emissions growth. However, scientists have shown us that this is not enough, and we need a system transformation in all countries and in all sectors of economy and society towards net zero emissions by mid-century.
What does this mean in practice and how can we reduce the concentration of greenhouse gases in the atmosphere? There are several ways of doing this.
The first is by switching to climate-friendly sources of energy. If we compare the different types of fossil fuel, the most polluting is coal, followed by oil and oil products, and the least polluting is natural gas.
But it is possible to produce energy without using fossil fuels at all. Since ancient times, people have used the heat of the sun, the power of wind and running water, and biomass. These are all renewable energy sources. Modern technologies make it possible to use them more widely. A rapid increase in the use of renewable sources of energy should go hand in hand with the phasing out of fossil fuel energy. Other carbon-free sources of energy, such as nuclear energy, can also help to reduce emissions in many countries, provided that all necessary safety measures are in place.
The second way of lowering greenhouse gas emissions is to reduce our daily energy consumption, by developing more energy-efficient machines and household appliances, improving the energy efficiency of buildings, and increasing electrification and energy storage. Current industrial processes, such as iron and steel, and cement, need to be replaced by carbon-free ones, and electrification in transport needs to go faster. We must also change our own habits to save energy and water.
The third way is to get plants to help us or use technologies that remove CO2 from the atmosphere. Plants and trees absorb CO2, so by reducing deforestation and by planting trees, people can reduce the amount of greenhouse gases in the atmosphere. Using environmentally friendly agricultural practices and restoring and protecting natural ecosystems can help soils absorb more carbon and bring other sustainable development benefits. New technologies that remove CO2 from the atmosphere, such as carbon capture and storage or CO2 removal, are at early stages of development and demonstration. They hold the promise that some emissions that cannot be avoided, e.g., some residual emissions from agriculture, will be captured by such emerging technologies soon.
Lastly, climate change is a complex global problem that can be solved only with cooperation among all governments, and an “all-of-society-approach” that especially involves business in efforts to manage the climate risk and disclose such risk as part of their business practices.