Increasing amounts of greenhouse gases are released in our environment every year. A study revealed that the amount of excessive energy produced as a result of the greenhouse gas emissions is equivalent to the energy produced through half a billion Hiroshima bomb explosions annually. Many scientists agree that this causes Earth to warm up. In the UK alone, a 0.7 Celsius increase in the last four decades was recorded.
Global Warming is Making Our Weather Wetter
A growing body of research shows that climate change not only makes our planet warmer and drier but also wetter. Observations and detailed computer simulations of the climate show large year to year fluctuations in tropical rainfall and discrepancies between simulations and measurements. These simulations indicate that drying of the drier regions continues while wet regions will experience more rainfall as the world warms in response to rising greenhouse gas concentrations.
The impacts of a wetter climate have been evident in many cities across the world. According to Green Business Watch, an online site that aims to connect people to companies providing environmentally friendly solutions to the problems of daily life, four of the wettest years in London have occurred since 2000. Statistics from the UK Met Office revealed that 2012 was the second wettest year ever as the country received 1330.7 mm of rainfall—only 6 mm less than the record set as recently as 2000. The linear increase in the amount of rainfall received has also been accompanied by irregular shifts in the pattern of precipitation. A great example of this is the increase in daily levels of rainfall since pre-industrial times.
Previous studies suggested total precipitation is likely to increase only slightly in wet regions, while dry climate regimes will see much greater increases. However, researchers from a 2019 study revealed that the situation is complicated because there are several more ways to define “wet” and “dry.” Instead of defining wet and dry regions by total annual rainfall, they defined these by local water availability. The overall finding showed that climate change is making heavy rainfall extremes in the world’s humid and arid areas more intense.
According to Physics World, the membership magazine of the Institute of Physics, one of the largest physical societies in the world, the researchers divided Earth’s land area into arid, semi-arid, sub-humid, and humid zones based on this precipitation–evaporation balance. The team then examined rainfall records going back to 1951 for each zone as well as compiling the results of 25 climate simulations out to 2100 for two representative concentration pathways: RCP8.5, where levels rise steadily throughout the century, and RCP4.5, which sees greenhouse-gas levels begin to plateau around 2060.
The findings revealed that rising global temperatures are expected to intensify the hydrological cycle by enhancing the atmosphere’s water-holding capacity, resulting in an increase in the total amount of rainfall worldwide. “More extreme precipitation may contribute to soil erosion and river flooding or flash flooding. This would also have implications for water and land-use management decisions—in particular in water-stressed regions—to make sure the precipitation that falls within a few days can be captured to be used in drier periods,” Markus Donat of Barcelona Supercomputing Center and the University of New South Wales Sydney said.
A Wetter World Can Speed Up Climate Change
Scientists have warned us about greater risks of flooding in some places, more intense and sustained droughts, and potentially lethal heatwaves in others. As temperature and precipitation increase together, climates are changing faster than the temperature trend alone would suggest.
A recent study found that the increase in rainfall is likely to intensify global warming driven by the release of carbon dioxide from tropical soils. According to Phys.org, an internet news portal that provides the latest news on science, the study was based on a detailed analysis of three sediment cores collected from the ocean floor seaward of the mouth of the Ganges and Brahmaputra rivers in Bangladesh.
The researchers managed to identify changes in soil by comparing radiocarbon dates of bulk sediment samples from these cores with samples from organic molecules known to be derived directly from land plants. Lead author Dr. Christopher Hein of William & Mary's Virginia Institute of Marine Science found that the rates of soil respiration, which refers to the release of carbon dioxide by microbes, increased while stocks of soil carbon decreased.
"This has direct implications for Earth's future, as climate change is likely to increase rainfall in tropical regions, further accelerating respiration of soil carbon, and adding even more CO2 to the atmosphere than that directly added by humans,” Hein said.
The findings published in Nature also showed a strong correlation between runoff rates and soil age. While drier, cooler epochs were linked to older soils capable of storing carbon for longer periods, wetter epochs were associated with younger, rapidly respiring soils. Using several independent lines of paleoclimatic evidence, including analysis of oxygen-isotope ratios from Chinese cave deposits and the skeletons of open-ocean phytoplankton, the team also confirmed changes in monsoon strength.
An earlier paper by the researchers also reported a threefold increase in annual rainfall in the Ganges-Brahmaputra river basin since the last Ice Age. This led to a halving of soil age due to more rapid soil turnover. “Small changes in the amount of carbon stored in soils can moreover play an outsized role in modulating atmospheric CO2 concentrations and, therefore, global climate, as soils are a primary global reservoir of this element,” Hein added.
The region has also historically experienced heavy rainfall, which fuelled accelerated erosion and sediment transport rates. Hein said that the delta and fan of the Ganges and Brahmaputra rivers are responsible for the burial of about 20% of all of the organic carbon delivered by rivers each year across the world. Unfortunately, precipitation can inspire changes across shorter time frames too.
"Other studies have shown that warming of soils can increase their carbon turnover rates, and over timescales as short as years; but these increases in soil turnover tend to be short-lived pulses. Our works suggest that increased rainfall too can increase soil turnover, and we see a change by a factor of two (soil carbon age cut in half). This effect is significant and long-lasting,” Hein said.