Guest essay by Eric Worrall
Fifteen years of satellite measurements have unexpectedly shown that parts of Greenland are getting colder. But the scientists who produced these results urge people to believe that this cooling trend is a blip, because climate models say Greenland should be warming.
Greenland’s recent temperature drop does not disprove global warming
January 29, 2018 – 09:55
Unfortunately, the planet is still getting warmer.
By: Charlotte Price Persson
Using satellite data, a group of scientists has studied the development of temperature over the past 15 years in a large part of Greenland.
More precisely, they looked at surface temperatures (the temperature close to the Earth’s surface) in a part of the country that is not covered by ice—around one fifth of the surface area of Greenland.
Intuitively, you may think that temperature throughout all of Greenland has been increasing, but that is not the case. When you look at the yearly average, the ice-free parts of Greenland show a slight drop in temperature between 2001 and 2015. With swings in temperature from year to year.
However, these results should not be interpreted as “proof” that the Earth is not warming, say the scientists behind the research, which is published in the journal Scientific Reports.
This is weather, not climate
You need to have thirty years’ worth of data before you can “talk about climate,” says Professor Bo Elberling, an environmental geochemist and senior scientist on the study.
So we should be wary of discussing these results in the context of climate change, says Elberling, who is head of the Center for Permafrost (CENPERM) at the Department of Geosciences and Natural Resource Management at the University of Copenhagen, Denmark.
“What’s interesting here is that with these new data we have a unique description of the spatial distribution of surface temperatures across the entire ice-free part of Greenland, which we couldn’t pull out of the approximately 45 weather stations that cover Greenland today,” he says.
Read More: What makes the climate change?
Global warming is real
Professor Michael Tjernström, a meteorologist from Stockholm University, Sweden, agrees with this assessment.
The time series is too short to say anything about climate trends, he writes in an email to our sister site, Videnskab.dk.
“Give me a specific location and a short time series and you could get almost any trend. Over a large area and over longer time I’m sure Greenland is warming,” writes Tjernström, who was not involved in the study.
The results should be seen as a part of the natural swings in climate. While you might find a small drop in temperature at individual locations, the overall development is in one direction, he writes.
All scientists interviewed for this article agreed that the new study does not question the inescapable reality that the planet is getting warmer.
The abstract of the study;
Contrasting temperature trends across the ice-free part of Greenland
Andreas Westergaard-Nielsen, Mojtaba Karami, Birger Ulf Hansen, Sebastian Westermann & Bo Elberling
Temperature changes in the Arctic have notable impacts on ecosystem structure and functioning, on soil carbon dynamics, and on the stability of permafrost, thus affecting ecosystem functions and putting man-built infrastructure at risk. Future warming in the Arctic could accelerate important feedbacks in permafrost degradation processes. Therefore it is important to map vulnerable areas most likely to be impacted by temperature changes and at higher risk of degradation, particularly near communities, to assist adaptation to climate change. Currently, these areas are poorly assessed, especially in Greenland. Here we quantify trends in satellite-derived land surface temperatures and modelled air temperatures, validated against observations, across the entire ice-free Greenland. Focus is on the past 30 years, to characterize significant changes and potentially vulnerable regions at a 1 km resolution. We show that recent temperature trends in Greenland vary significantly between seasons and regions and that data with resolutions down to single km2 are critical to map temperature changes for guidance of further local studies and decision-making. Only a fraction of the ice-free Greenland seems vulnerable due to warming when analyzing year 2001–2015, but the most pronounced changes are found in the most populated parts of Greenland. As Greenland represents important gradients of north/south coast/inland/distance to large ice sheets, the conclusions are also relevant in an upscaling to greater Arctic areas.
Why do the scientists who published this data seem so skittish?
One reason may be that this study potentially undermines confidence in the methodology of the NASA GISS temperature series, one of the world’s major global temperature resources.
From the NASA website;
… Handling the Arctic
There are several reasons for the small discrepancies that exist between the three records. Most important, subtleties in the way the scientists from each institution handle regions of the world where temperature-monitoring stations are scarce produce differences.
While developed areas have a dense network of weather stations, temperature monitoring equipment is sparse in some parts of the Amazon, Africa, Antarctica, and Arctic. In the Arctic, particularly, the absence of solid land means there are large areas without weather stations.
The Met Office and the NCDC leave areas of the Arctic Ocean without stations out of their analyses, while GISS approaches the problem by filling in the gaps with data from the nearest land stations, up to a distance of 1200 kilometers (746 miles) away. In this way, the GISS analysis achieves near total coverage in the Arctic.
Both approaches pose problems. By not inferring data, the Met Office assumes that areas without stations have a warming equal to that experienced by the entire Northern Hemisphere, a value that satellite and field measurements suggest is too low given the rate of Arctic sea ice loss.
On the other hand, GISS’s approach may either overestimate or underestimate Arctic warming. “There’s no doubt that estimates of Arctic warming are uncertain, and should be regarded with caution,” Hansen said. “Still, the rapid pace of Arctic ice retreat leaves little question that temperatures in the region are rising fast, perhaps faster than we assume in our analysis.” …
Infilling attempts to correct for absent temperature data in sparse regions like the Arctic. But this latest study has demonstrated … recent temperature trends in Greenland vary significantly between seasons and regions and that data with resolutions down to single km2 are critical to map temperature changes …. The NASA technique of using a single temperature station to represent up to 1200 kilometres of Arctic wilderness, then using climate models to help fill in the blanks, may be a lot less reliable than previously thought.
The world has warmed since the 1850s. But if parts of the Arctic have been cooling, when climate scientists assumed those regions were warming, the real warming trend might be less than some analysis suggest.