The dry regions of the Earth are affecting CO2 concentrations more than previously thought. When it rains at the end of the dry season on dried-out soils, large amounts of CO2 are released. According to data from the National Oceanic and Atmospheric Administration (NOAA), the CO2 concentration in the Earth’s atmosphere has reached its highest level in a million years. While the concentration of CO2 fluctuates significantly throughout the year, it is believed to be less variable on the southern hemisphere due to the smaller land area. However, Australia is an exception, with up to 60% of the annual anomalies of global terrestrial CO2 sinks attributed to the continent.
Researchers from the University of Heidelberg analyzed data from the Greenhouse Gases Observing Satellite (GOSAT) between 2009 and 2018 to understand why Australia has such a significant impact on the annual carbon cycle. They found that the seasonal patterns of CO2 emissions over Australia are much more dynamic than previously thought. Detailed analysis of the data showed that the Australian Outback emits a lot of CO2 when strong rains occur at the end of the summer dry season. The water reactivates microorganisms that were inactive during the summer months, leading to high CO2 emissions.
This reaction, known as the Birch effect, occurs when microbial respiration is reactivated by rehydration. The strong CO2 emissions in Australia occur because the rehydration happens before the start of the vegetation period, so the photosynthesis from strong plant growth does not occur simultaneously. This leads to the carbon dioxide from the soil not being bound and instead being released into the atmosphere. The study sheds light on a blind spot in previous approaches to quantifying and attributing CO2 fluctuations and has implications for other semi-arid regions of the world that likely have a stronger impact on the global carbon cycle than previously thought. The findings can contribute to a better understanding of global climate-carbon feedbacks and can be incorporated into climate models.
