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climate impacts
Climate-Intensified Mountain Rain Could Affect Billions of People: Study
"This increase in rainfall extremes is not only something that is going to happen from now until the end of the 21st century—we're already seeing it," said the lead author.
Jun 28, 2023
Researchers from a U.S. national laboratory warned Wednesday that rising temperatures are shifting snow to rain in mountainous regions, increasing the risk of dangers such as floods, landslides, and soil erosion for up to a quarter of the world's population.
Scientists have previously determined that a warmer climate will mean more intense extreme precipitation events, but this "is the first time researchers have looked at whether that extreme precipitation comes as rain or snow," according to the Department of Energy's Lawrence Berkeley National Laboratory.
The new study, published in the peer-reviewed journal Nature, connects every 1°C rise in the global temperature to an average of 15% more rain at high elevations, particularly in certain "hot spots" around the world.
Lead author Mohammed Ombadi said in a statement that "our findings revealed a linear relationship between the level of warming and the increase in extreme rainfall: For instance, 1°C of warming causes 15% more rain, while 3°C leads to a 45% increase in rainfall."
"This increase in rainfall extremes is not only something that is going to happen from now until the end of the 21st century—we're already seeing it," he noted. "That same rate was also evident in the data from 1950 to 2019. Rainfall extremes in mountains have already been increasing, and will continue to change with that 15% rate."
"One-quarter of the global population lives in or downstream from mountainous regions... They are going to be directly affected by this risk."
"One-quarter of the global population lives in or downstream from mountainous regions," he highlighted. "They are going to be directly affected by this risk."
The researchers found the shift from snow to rain is occurring in all Northern Hemisphere mountain ranges, but those at greatest risk of extreme events are the Cascades, Himalayas, Sierra Nevada, and coastal ranges from Southern California to Canada.
While further study is needed to determine why certain areas face greater potential danger, Ombadi said that "we think that North American Pacific mountain ranges are more susceptible to the risk of rainfall extremes than other mountain ranges because a significant portion of snowfall in this region typically occurs at temperatures just below 0°C."
"The slightest change in air temperature will shift this snowfall to rainfall. This is unlike other mountain ranges where snowfall may occur at very low temperatures below 0°C," he explained.
Ombadi expressed hope that the study will assist not only scientists conducting future research but also civil engineers and policymakers trying to mitigate and prepare for the worsening climate emergency.
"We need to factor these results into how we design and build the infrastructure in these mountainous regions, so that they can withstand the negative consequences of increases in rainfall extremes," Ombadi asserted.
"There are many technologies in progress that could help us reduce greenhouse gas emissions and how much the planet warms," he added. "To me, this study shows the need to invest in those clean solutions, and also start preparing for the consequences of warming now."
The study came a day after Ian Fry, the United Nations special rapporteur on human rights in the context of climate change, said the number of people displaced by climate impacts "is rapidly increasing" and the global community "must realize its responsibility" to protect them.
World leaders are set to meet in the United Arab Emirates later this year for COP28, the next U.N. climate summit. Previous conferences have led campaigners and scientists to argue that countries' pledges and plans to reduce planet-heating emissions—particularly from fossil fuels, which made up 82% of global energy consumption last year—are wildly inadequate.
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The Hottest Years
The past decade, from 2010 to 2019, has almost certainly been the warmest in records dating back to the 19th century.
Dec 02, 2019
This year has been one of the hottest on record, as the world comes to the end of a decade of "exceptional" heat, the World Meteorological Organisation has said.
The past decade, from 2010 to 2019, has almost certainly been the warmest in records dating back to the 19th century, and the past five years from 2015 have also been the hottest on record, the UN body said.
This year temperatures have been 1.1C above pre-industrial levels, putting 2019 on course to be the second or third hottest year on record, data from January to October shows.
Extreme
The WMO provisional statement on the state of the global climate also warns that sea levels are rising ever faster, ice is melting and "once in a century" heatwaves and floods are now becoming more regular occurrences.
Millions of people were forced from their homes as a result of extreme events such as cyclones, hurricanes and flooding.
The past year has also seen droughts in many parts of the world and two major heatwaves in Europe in late June and late July - with a new temperature record of 38.7C set in the UK.
WMO Secretary-General Petteri Taalas: "If we do not take urgent climate action now, then we are heading for a temperature increase of more than 3C by the end of the century, with ever more harmful impacts on human well-being.
"On a day-to-day basis, the impacts of climate change play out through extreme and "abnormal" weather.
Melting
And he warned: "One of the main impacts of climate change is more erratic rainfall patterns.
"This poses a threat to crop yields and, combined with population increase, will mean considerable food security challenges for vulnerable countries in the future."
The report is released as countries meet in Madrid for the latest round of UN climate negotiations, known as "Cop25", amid pressure to increase their ambitions to cut the greenhouse gas emissions driving climate change.
The assessment warns concentrations of greenhouse gases in the atmosphere have reached new record levels in 2019.
And the rate at which sea levels are rising has increased as a result of melting ice sheets in Greenland and Antarctica, reaching new highs this year.
Temperature
The world's oceans take in much of the extra heat and carbon dioxide caused by human activity, but it has serious impacts for the marine environment.
Ocean heat is at record levels, there have been widespread marine heatwaves and sea water is increasingly acidic, damaging wildlife.
At the poles, Arctic sea ice is in long term decline and has been a relatively low levels in Antarctica since a sudden drop in late 2016.
The year 2016, which began with an exceptional "El Nino" weather phenomenon in the Pacific that pushes up global temperatures, remains the hottest year on record.
The report draws on information from other UN bodies and three major global temperature datasets, including from the Met Office Hadley Centre and the University of East Anglia's Climatic Research Unit
Warmest
Colin Morice, of the Met Office Hadley Centre, said: "Our global temperature figures are in agreement with other centres around the world that 2019 is set to join each of the years from 2015 as the five warmest years on record.
"Each decade from the 1980s has been warmer than the previous decade. 2019 will conclude the warmest decade in records that stretch back to the mid-19th century."
Prof Tim Osborn, from UEA's Climatic Research Unit, said: "The five warmest years for average global surface temperature since records began in 1850 have all occurred in the last five years; by contrast the five coldest years all occurred before 1912.
"This is climate change and not a coincidence."
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