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Tuesday, January 6, 2015

Land of the Midnight Sun Warms Fastest in World

Over the past nearly two centuries, Finland's average temperatures have increased by more than 2 degrees Celsius

by Niina Heikkinen and ClimateWire, Scientific American, January 5, 2015

Finland's temperatures have risen at roughly double the rate of the planet as a whole, a new study suggests. 
Credit: josef.stuefer/Flickr
Finland's temperatures have risen at roughly double the rate of the planet as a whole, a new study suggests.
A team of researchers from the University of Eastern Finland and the Finnish Meteorological Society found that over the past 166 years, the country's average monthly temperatures have increased by more than 2 degrees Celsius (3.6 degrees Fahrenheit), a 0.14 C change per decade.
For the planet as a whole, the average temperature had increased by 0.8 C over the same period.
Although extensive previous research had shown that countries at high latitudes were warming at a faster rate than the rest of the world, this was the first time that researchers had recorded such a high increase in average temperature, according to Ari Laaksonen, a professor in the Department of Applied Physics at the University of Eastern Finland and a co-author of the study.
"You would expect that the temperatures in the north would be rising faster than the global average," Laaksonen said. "But [researchers] expected a rate that was 50 percent faster; Finland's temperature is rising by almost 100 percent."
The study was published in the journalStochastic Environmental Research and Risk Assessment last month.
Laaksonen and his colleagues did not try to predict how Finland's temperatures will change in the coming decades, but according to the U.N. Intergovernmental Panel on Climate Change's latest report, Arctic temperatures are likely to continue rising faster than the global average through the end of the 21st century.
Better data, bigger temperature jumps?
In Finland, the rate of warming increased to 0.2 to 0.4 C per decade after the 1960s, providing further proof of the human influence on global warming, according to the Finnish researchers. The increase in average monthly temperature was most noticeable over the months of November, December and January. Temperatures were also warmer than the annual average from March through May.
Determining the rate of temperature change is more difficult at a local and regional level because researchers have less data to average, so trends are not as evident because of "statistical noise." To find out how average monthly temperatures had changed from 1847 to 2013, the researchers used an advanced statistical time series approach to figure out what changes in temperature were due to natural variability and what changes represented a long-term trend.
Because there were much fewer weather stations collecting temperature data in Finland for the earlier portion of the time series, the researchers also used temperature data from neighboring Sweden, Norway and Russia.
The study's results are consistent with temperature research based on data from the past 135 years at NASA's Goddard Institute for Space Studies (GISS).
NASA researchers found that countries in the Northern Hemisphere had an average temperature increase of 0.93 C, and latitudes around 60 degrees north or above had an average temperature increase of 1.8 C, according to Gavin Schmidt, director of GISS and principal investigator for the GISS Model E Earth System Model.
"It is indeed expected that land will warm more than the ocean, the Northern Hemisphere will warm more than the South, and high latitudes more than the tropics. Details of the pattern are a little random, but the basic structure is robust," he wrote in an email.
The higher average change in the Finnish study could be because of more detailed data than what was included in the NASA study, Schmidt said.
Other researchers have recorded less dramatic warming trends in Norway and Sweden.
'This thing is real'
A temperature series study recently published in the International Journal of Climatology found that over 175 years (1838 to 2012), the annual average temperature in Oslo, Norway, has gone up 1.5 C. The most noticeable changes occurred in the last 50 years and in the early 20th century until the 1930s.
The Swedish Meteorological and Hydrological Institute found that average national temperatures between 1991 and 2013 were 1.6 C higher than the average of temperatures between 1861 and 1890, according to Markku Rummukainen, a professor at the Centre for Environment and Climate Research at Lund University in Sweden.
Causes of warming trends at higher latitudes have gained more widespread attention from researchers in the past few decades, but the idea that the Arctic would warm faster than the rest of the planet has been around for more than 100 years. In 1896, the Swedish chemist Svante August Arrhenius proposed that changing concentrations of CO2 in the atmosphere would lead to more temperature variability in the poles.
While Arrhenius appears to have been wrong about the temperature effect on the Antarctic, scientists today have found strong evidence for what they now call Arctic amplification in the North Pole, said Mark Serreze, the director of the National Snow and Ice Data Center at the University of Colorado, Boulder.
"If you look at the overall rise in temperature across the globe ... the polar region is warming at twice the rate," Serreze said. "So this thing is real, absolutely."
Scientists hypothesize that a loss of sea ice is a main reason for the warming.
"When you remove sea ice cover, you remove insulation, so all the ocean heat can be released into the atmosphere above," Serreze said.
Lumber, ice roads and reindeer at risk
During the summer months, the newly ice-free parts of the ocean take in much more heat than they used to. That heat is then released in the autumn and winter as air temperatures fall. The higher atmospheric temperatures lead to even more ice melt and prevent new ice from forming, creating a feedback loop. Changes in cloud cover and ocean currents also contribute to temperature changes. The Atlantic Multidecadal Oscillation, which causes natural variability in the north Atlantic Ocean, may also be preventing ice from forming in parts of the Arctic, according to Serreze.
"In part Arctic amplification is linked to global warming, and part is natural climate variability, and the challenge for researchers is to separate out the two," he said.
In Finland, interpreting temperature data is made more difficult because of its naturally highly variable temperatures. Low-pressure air currents off the Atlantic Ocean make for mild winters and cool wet summers. High-pressure air currents from over Siberia tend to have the opposite effect: cold winters and hot, dry summers, according to Laaksonen.
The effects of rising temperatures in Finland and other countries at higher latitudes are mixed. There is some evidence that trees are budding earlier than they used to in Finland, and growing seasons could be extended for agricultural crops.
Warmer winters could also affect the country's forestry industry. Lumber is harvested during the winter months when the ground is frozen, but higher temperatures could make it harder for heavy equipment to navigate on soft ground, said Santtu Mikkonen, the lead author of the study and statistician at the University of Eastern Finland.
In Finland and other high-latitude countries, warmer winters could also mean the disappearance of ice roads, which help connect areas difficult to reach on regular routes. According to the latest IPCC report, Finland could lose 41 percent of its area accessible by winter roads by the middle of the century, while Iceland could lose as much as 82 percent.
The Saami people, who live in northern Finland, Sweden and Norway, have also raised concerns about the health of their reindeer herds. Highly variable temperatures and precipitation could have a negative impact on their ability to find food.
The negative impacts of warmer winters may be less evident in Nordic countries than in places like Alaska, where people and animals like polar bears and seals are more dependent on the presence of sea ice, according to Serreze.

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