October 16, 2007

Greenland Climate: Now vs. Then, Part I. Temperatures

Filed under: Arctic, Polar

We at World Climate Report have been spending some time over at the local library digging through some old journals looking for information about climate conditions in Greenland during the early-to-mid 20th century—a time when it pretty well established that much of Greenland was as warm, or warmer, than it is presently. This fact, however, seems largely ignored by alarmist scientists and the media who continue to turn up the volume on rhetoric claiming that Greenland is experiencing events that have not been experienced there for time immemorial. Knowing what we do about the climate history of Greenland, we can’t help to wonder whether time immemorial only extends back about 50 years or so.

We will present what we uncover through a multi-part series of World Climate Reports under the general title, “Greenland Climate: Now vs. Then.”

In our first installment, we’ll briefly review the temperature history of Greenland over the course of the 20th century, setting the stage for future articles in which we’ll visit topics that have been in the news recently such as record levels of surface melt extent, rapidly retreating glaciers, surface mass balance estimates, and “warming islands.”

First things first, Figure 1 is a map of Greenland depicting the locations of some coastal locations where temperature measurements have been historically made, along with the general surface contours of its ice sheet.


Figure 1. Contours depicting the elevation of Greenland’s ice map (meters) and the locations where historical temperature measurements have been recorded; Gothab Nuuk (GN), Angmassalik (AM), Upernavik (UP), Jakobshavn (JH), Ivigtut (IV), Egedesminde (EG), Prins Christi (PC) and Dansmarkhavn (DH) (from Chylek, 2006).

You’ll see that the surface of a good portion of Greenland’s ice sheet lies at or above 2000m (6560ft) with some areas of the inland ice sheet exceeding 2750m (9020 ft) in elevation. The vastness of the inland ice sheet explains why all towns lie along the coast.

Now let’s look at the temperature histories from some of these coastal locations. Godthab Nuuk, in the southwestern part of the country, and Angmagssalik, along the southeastern coast have the longest period of continual observations, with data stretching back into the late 19th century. Both show a similar pattern of the trace of annual temperatures. At Godthab Nuuk (Figure 2), observations show that in a matter of a few years in the early 1920s, the typical average temperature rose by about 2ºC and then gradually cooled off through the late 1980s. Since then, during the past 15-20 years, annual temperatures have risen to about mid-20th century levels. At Angmagssalik (Figure 3), the record shows generally the same thing—rising temperatures from the late 1800s to the early 1920s, a quick jump of a couple of degrees, a prolonged, gradual cooling from the 1940s through the mid-1980s, and a recent rise. With the exception of the record warmth observed in 2003, recent temperatures there are only at about mid-20th century levels.


Figure 2. Historical record of average annual temperatures records at the Greenland station of Godthab Nuuk (data source: Goddard Institute of Space Studies, http://data.giss.nasa.gov/gistemp/)


Figure 3. Historical record of average annual temperatures records at the Greenland station of Angmagssalik (data source: Goddard Institute of Space Studies, http://data.giss.nasa.gov/gistemp/)

A more or less similar behavior can be pieced together from temperature observations made from other stations further north along the coasts. On the western shores, the temperature records at Jakobshavn (Figure 4) and Upernavik (Figure 5) begin the late-1800s and extend up until about 1980, while the observations at Egedesminde (Figure 6) begin in the 1950s and continue until present. Together, the observations of these stations suggest that the temperatures there have behaved similarly to those continuously observed at Godthab Nuuk.


Figure 4. Historical record of average annual temperatures records at the Greenland station of Jakobshavn (data source: Goddard Institute of Space Studies, http://data.giss.nasa.gov/gistemp/)


Figure 5. Historical record of average annual temperatures records at the Greenland station of Upernavik (data source: Goddard Institute of Space Studies, http://data.giss.nasa.gov/gistemp/)


Figure 6. Historical record of average annual temperatures records at the Greenland station of Egedesminde (data source: Goddard Institute of Space Studies, http://data.giss.nasa.gov/gistemp/)

On the eastern side of the island, the temperature record at Danmarkshavn (Figure 7), along the central coast, only picks up in the 1950s. It shows that there, recent temperatures have exceeded the ones observed in the 1950s, but can’t tell us how they relate to the conditions of the 1930s—a period which was warmer than the 1950s elsewhere on Greenland.


Figure 7. Historical record of average annual temperatures records at the Greenland station of Danmarkshavn (data source: Goddard Institute of Space Studies, http://data.giss.nasa.gov/gistemp/)

A recent study by Peter Chylek et al. (2006) put all of these Greenland temperature records together in one place (Figure 8 ), and commented:

Although there has been a considerable temperature increase during the last decade (1995 to 2005) a similar increase and at a faster rate occurred during the early part of the 20th century (1920 to 1930) when carbon dioxide or other greenhouse gases could not be a cause. The Greenland warming of 1920 to 1930 demonstrates that a high concentration of carbon dioxide and other greenhouse gases is not a necessary condition for period of warming to arise. The observed 1995–2005 temperature increase seems to be within a natural variability of Greenland climate.


Figure 8. The 1995–2005 and 1920–1930 warming periods at Greenland stations show a similar behavior (source: Chylek et al., 2006).

Chylek and colleagues went on to comment as to how the impacts of these recent warm temperatures on glacier movements likely compared to impacts that probably resulted in the past from similarly warm (or warmer) conditions:

The glacier acceleration observed during the 1996–2005 period has probably occurred previously. There should have been the same or more extensive acceleration during the 1920–1930 warming as well as during the Medieval Warm period in Greenland when Greenland temperatures were generally higher than today.

In articles to come in our series “Greenland Climate: Now vs. Then,” we will show that not only have aspects of the recent behavior of glaciers been similar to those in the past, but also that other recent ice observations in Greenland are a repeat of conditions of the early-to-mid 20th century.

And if they happened last time it was as warm or warmer than conditions there are now, then undoubtedly they happened the time before that—a span of at least a thousand years about 8,000 years ago, as Figure 9, taken from the latest report of the Intergovernmental Panel on Climate Change, shows.


Figure 9. Timing and intensity of temperature deviations from pre-industrial levels during the past 12,000 years. Note that Greenland and most of the high latitudes in the Northern Hemisphere were likely as warm, or warmer, than present for multi-millennial periods since the end of the last Ice Age (source: IPCC, AR4, Chapter 6, p. 462).

There are copious indications that recent conditions in Greenland do not represent an aberrant fluctuation in the region’s climate. Instead, conditions currently lie within the known limits of natural variations.

Reference:

Chylek, P., et al., 2006. Greenland warming of 1920-1930 and 1995-2005. Geophysical Research Letters, 33, L11707, doi:10.1029/2006GL026510.




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