Explained: Why increased rainfall in the Arctic is bad news for the whole world

Before the end of this century most of the Arctic will for the first time receive more rain than snow across a whole year Thats one of the key findings of a new study on precipitation in the Arctic which has major implications not just for the polar region but for the whole worldWhile a reduction in frozen ocean surface is one of the most widely recognised impacts of Arctic warming it has also long been anticipated that a warmer Arctic will be a wetter one too with more intense cycling of water between land atmosphere and oceanThe shift from a frozen region towards a warmer wetter Arctic is driven by the capacity of a warmer atmosphere to hold more moisture by increased rates of evaporation from icefree oceans and by the jet stream relaxingThe Arctic water cycle is expected to shift from a snowdominated one towards a raindominated one during the 21st century although the timing of this is uncertain Now a team of scientists have published a study in the journal Nature Communications which suggests that this shift will occur earlier than previously projectedThe effect will be particularly strong in autumn with most of the Arctic Ocean Siberia and the Canadian Archipelago becoming raindominated by the 2070s instead of the 2090sWarmer and wetter isnt necessarily betterSuch a profound change to the Arctic water cycle will inevitably affect ecosystems on land and in the ocean You might intuitively expect that a warmer and wetter Arctic would be very favourable for ecosystems iquest rainforests have many more species than tundra after all But the plants and animals of the Arctic have evolved for cold conditions over millions of years and their relatively simple food web is vulnerable to disturbanceFor example warmer temperatures can cause larval insects to emerge earlier before the fish species that feed upon them have hatched More rainfall means more nutrients washed into rivers which should benefit the microscopic plants at the base of the food chainHowever this also makes rivers and coastal waters more murky blocking light needed for photosynthesis and potentially clogging filterfeeding animals including some whales or sharks Brackish water typically supports fewer species than either freshwater or seawater so increasing flows of freshwater offshore may well reduce the range of animals and plants along Arctic coastsFurther into the Arctic Ocean there are more reasons to doubt the potential benefits of warmer temperatures and greater freshwater circulation The dissolved constituents of rainfall river water and melting snow and ice reduce the alkalinity of Arctic surface waters which makes it harder for marine organisms to build shells and skeletons and limits chemical neutralisation of the acidifying effects of CO2 absorbed in seawaterAt the same time rivers flowing through degrading permafrost will wash organic material into the sea that bacteria can convert to CO2 making the ocean more acidic Fresh water also essentially floats on denser seawaterThis causes the ocean to become stratified impeding exchanges of nutrients and organisms between the deep sea and the surface and restricting biological activity Therefore the likely impacts of a warmer wetter Arctic on food webs biodiversity and food security are uncertain but are unlikely to be uniformly positiveArctic change is decades ahead of global averagesTemperature increases in the Arctic have raced ahead of the global average This will only be reinforced as snowfall is reduced and rainfall increases since snow reflects the suns energy back into space As the land becomes less snowy and less reflective bare ground will absorb more solar energy and thus will warm upThe Arctic is set to continue warming faster than elsewhere further diminishing the difference in temperature between the warmest and coldest parts of the planet with complex implications for the oceans and atmosphereThe recent COP26 climate summit in Glasgow focused on efforts to iquestkeep 15degC aliveiquest It is worth remembering that the 15degC figure is a global average and that the Arctic will warm by at least twice as much as this even for modest projectionsThe new study underscores the importance of the global 15degC target for the Arctic For instance at that level of warming Greenland is expected to transition to a rainfalldominated climate for most of the year While at 3degC warming which is close to the current pathway based on existing policies rather than pledges most regions of the Arctic will transition to a rainfalldominated climate before the end of the 21stcenturyIts research that adds further weight to calls for improved monitoring of Arctic hydrological systems and to the growing awareness of the considerable impacts of even small increments of atmospheric warmingThis story has been sourced from a third party syndicated feed agencies Midday accepts no responsibility or liability for its dependability trustworthiness reliability and data of the text Midday 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