Aerosol Pollutants, Dust and Soot Partly Responsible for Warming at Higher Elevations

An international team of scientists is calling for urgent and rigorous monitoring of temperature patterns in mountain regions after finding evidence that high elevations could be warming faster than previously thought.

The research team says that without substantially better information, we risk underestimating the severity of a number of already looming problems, including water shortages and the possible extinction of some alpine flora and fauna.

The research is published in the journal Nature Climate Change.

Lead author, Dr Nick Pepin of the University of Portsmouth, said: “Most current predictions are based on incomplete and imperfect data, but if we are right and mountains are warming more rapidly than other environments, the social and economic consequences could be serious, and we could see much more dramatic changes much sooner than previously thought.”

The most striking evidence that mountain regions are warming more rapidly than surrounding regions comes from the Tibetan plateau. Here temperatures have risen steadily over the past 50 years and the rate of change is speeding up. But masked by this general climate warming are pronounced differences at different elevations. For example, over the past 20 years temperatures above 4,000 m have warmed nearly 75 per cent faster than temperatures in areas below 2,000 m.  

The team of scientists came together as part of the Mountain Research Initiative, a mountain global change research effort funded by the Swiss National Foundation. The team includes scientists from the UK, US, Switzerland, Canada, Ecuador, Pakistan, China, Italy, Austria and Kazakhstan. Between them, they have studied data on mountain temperatures worldwide collected over the past 60-70 years.

Dr Pepin said: “There is growing evidence that high mountain regions are warming faster than lower elevations and such warming can accelerate many other environmental changes such as glacial melt and vegetation change, but scientists urgently need more and better data to confirm this.

“It’s understandable that the information collected so far is somewhat piecemeal. Mountains are difficult to study, they are remote and often inaccessible, and it is expensive and often challenging to find ways of effectively monitoring what is happening. Mountains are also very complicated landscapes, and have a wide variety of microclimates which makes it hard to see the overall picture.”

Improved observations, satellite-based remote sensing and climate model simulations are all needed to gain a true picture of warming in mountain regions, the researchers say. Much of that requires international agreement and collaboration – and funding.

World-leading climatologist Professor Raymond Bradley, of the University of Massachusetts, is one of the report’s co-authors.

He said: “We are calling for special efforts to be made to extend scientific observations upwards to the highest summits to capture richer data on what is happening across the world’s mountains.

“We also need a strong effort to find, collate and evaluate observational data that already exists wherever it is in the world. This requires international collaboration.”

Among the reasons the researchers examined for faster rates of temperature increase in mountain regions are:

-     Loss of snow and ice, leading to more exposed land surface at high elevation warming up faster in the sun;

-     Increasing release of heat in the high atmosphere. A warmer atmosphere holds more moisture, which, when condensing as clouds at high elevation, releases more heat to the mountain environment;

-     Aerosol pollutants at low elevations, including haze, dust and smoke, reduces  warming at those elevations, thus increasing the difference in rates of warming between low and high elevations;

-     Dust and soot deposited on the surface at high elevations causes more incoming sunlight to be converted to heat;

-     The complex combination of any or all of the above factors in different regions and at different times of the year.

Records of weather patterns at high altitudes are ‘extremely sparse’, the researchers found. The density of weather stations above 4,500 m is roughly one-tenth that in areas below that elevation. Long-term data, crucial for detecting patterns, doesn’t yet exist above 5,000 m anywhere in the world. The longest observations above this elevation are 10 years on the summit of Kilimanjaro.

The world’s highest mountain, Mt Everest, stands at 8,848 m. More than 250 other mountains, including Mt Elbrus in Russia, Mt Denali in Alaska, Mt Aconcagua in Argentina and Mt Kilimanjaro in Africa also all top the 5,000 m mark.

Ben Nevis, in Scotland, is the UK’s highest mountain, standing at 1,344 m.