“Every additional tonne of carbon dioxide increases the rate of climate change”
Interview with Sönke Zaehle from the Max Planck Institute for Biogeochemistry on the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC)
Sönke Zaehle from the Max Planck Institute for Biogeochemistry in Jena has been dealing with global carbon sinks, among other things, for the report of the IPCC. He is also looking into how important the methane and nitrous oxide cycles are for calculating the remaining carbon budget in order to limit climate change to a certain level.
Dr Zaehle, what do you think are the most important findings of the new report of the IPCC?
Zaehle: We can now clearly say that human-induced greenhouse gas emissions are the main cause of both past and future global warming. Based on significantly improved data, the report clearly points out that this human contribution is causing extreme weather events such as heat waves, droughts, and heavy rainfall to become more frequent and more severe. However, the report also shows that climate protection and better air quality can be reconciled if we quickly reduce greenhouse gas emissions and implement air pollution control measures.
Oceans and terrestrial ecosystems – for example wetlands and tropical rainforests – are always referred to as natural carbon sinks. Why can they store so much carbon?
Over the past 60 years, oceans and terrestrial ecosystems have absorbed about half of the carbon dioxide from fossil fuel combustion and land use, thereby slowing the increase in greenhouse gas. The oceans absorb carbon dioxide from the atmosphere and dissolve it in the form of carbonic acid. In rural areas, plants and soils act as carbon reservoirs. In forests, for example the tropical rainforests, plants can convert the carbon dioxide into biomass and thus remove large amounts from the atmosphere. Mosses also use carbon dioxide to grow in wetlands. Because the plants do not rot well in the wet, acidic environment, the carbon can be stored in the soil as peat for thousands of years.
How do these natural carbon sinks respond to climate change?
The increasing acidification of the oceans and warming because of climate change reduce the absorption capacity of the oceans. The sink of terrestrial ecosystems also responds to environmental changes. Although wetlands and rainforests are currently suffering more from human destruction than from climate change per se, drought and heat can also reduce their storage capacity. In addition, soil respiration is faster at higher temperatures. The soil microbes thus produce more carbon dioxide. In addition, fire and droughts further limit the ability of these ecosystems to store carbon.
All this means that as emissions progress, natural sinks will absorb a smaller proportion of our emissions, and the carbon dioxide content in the atmosphere will continue to increase.
Is carbon dioxide the sole offender in climate change?
No. Other greenhouse gases such as methane and nitrous oxide as well as aerosols – microscopic particles in the atmosphere – also play a considerable role. In addition to the use of fossil energy sources, methane is primarily produced in animal husbandry and agriculture. Nitrous oxide emissions are also linked to food production through intensive fertilization and livestock farming. As is the case with carbon dioxide, we can also directly influence the emission of these two gases. This report deals, in particular, with the reduction of methane emissions.
What is the most important conclusion for you from your research and the IPCC report?
The window of opportunity to limit climate change to 1.5 or 2 degrees is rapidly shrinking. Without a rapid and significant reduction in the emissions of carbon dioxide, methane, and nitrous oxide, we will not be able to achieve the 1.5 degree target. “Every additional tonne of carbon dioxide increases climate change”
Protecting natural carbon reservoirs such as wetlands and rainforests is also important. This would also be in the interest of protecting biodiversity – because the worldwide extinction of species is just as big a threat as climate change.
Interview: Harald Rösch