TCS Daily


What's Going on with the Arctic?

By George Taylor - November 22, 2004 12:00 AM

Recently the Arctic Climate Impact Assessment (ACIA) report was recently released by the Arctic Council, a self-described "high-level intergovernmental forum that provides a mechanism to address the common concerns and challenges faced by the Arctic governments and the people of the Arctic." The report received significant press attention (New York Times "As the Arctic Warms", Washington Post "Study Says Polar Bears Could Face Extinction"). The report documents significant ecosystem response to surface temperature warming trends that occurred in some areas since the mid-19th century and in the last thirty years. Among the conclusions of the report are:

  • Annual average temperature in the Arctic has increased at almost twice the rate of the rest of the world.
  • Winter temperatures in Alaska and western Canada have increased about 3-4 deg C over the past half century, with larger increases projected in the next 100 years.
  • There has been widespread melting of sea ice and glaciers. The average extent of sea-ice cover has declined by 15-20% over the past 30 years.
  • There has been increased precipitation, shorter and warmer winters, and decreases in snow cover.
  • The area of the Greenland Ice Sheet that experiences some melting has increased about 16% since 1979.

These are just a few of dozens of conclusions, some of which involve effects on plant and animal populations, others which describe consequences to humans (some beneficial, but most detrimental). Because the ACIA is so lengthy, I have not yet had a chance to thoroughly examine it. But based on a review of the Executive Summary (26 pages in length) and Conclusions (29 pages), I have been able to compare the ACIA statements with the conclusions of scientists studying the Arctic, from peer-reviewed journal publications. One of these days I'll get through the much longer Overview Report and perhaps update this analysis.

Is the ACIA a breakthrough climate assessment? Does it faithfully capture the essence of climate change in the Arctic? Or is it just another doom-and-gloom report from the international climate community? Let's examine climate behavior in the Arctic over the last couple centuries (and beyond) and see what we find.

Arctic Air Temperatures

Naurzbaev, et al (2002) created a proxy temperature data set spanning nearly 2,500 years for the Taimyr Peninsula of northern Russia, all of which is poleward of 70° N. The authors studied tree rings-widths of living and deceased larch trees. They reported that "the warmest periods over the last two millennia in this region were clearly in the third, tenth to twelfth and during the twentieth centuries." The first two, they claim, were warmer than those of the last century. Twentieth century temperatures appeared to peak around 1940.

Chylek, et al (2004) analyzed Greenland air temperatures over the last 100 years. At coastal stations, "summer temperatures, which are most relevant to Greenland ice sheet melting rates, do not show any persistent increase during the last fifty years." The peak coastal temperatures occurred in the 1930s, followed by significant cooling, followed by warming; but current temperatures "are about 1°C below their 1940 values." In the highest elevations of Greenland's ice sheet, "the summer average temperature has decreased at the rate of 2.2°C per decade since the beginning of the measurements in 1987."

The warm period in the first half of the twentieth century, prior to the big increases in greenhouse gases, saw very rapid warming -- even though CO2, reputed by many to be the most significant driver of temperature change, rose very little. In fact, during the decade of the 1920s at the coastal stations, "average annual temperature rose between 2 and 4°C [and by as much as 6°C in the winter] in less than ten years." The authors conclude that conclude that "since there was no significant increase in the atmospheric greenhouse gas concentration during that time, the Greenland warming of the 1920s demonstrates that a large and rapid temperature increase can occur over Greenland, and perhaps in other regions of the Arctic, due to internal climate variability such as the NAM/NAO [Northern Annular Mode/North Atlantic Oscillation], without a significant anthropogenic influence." Further, "the NAO may play a crucial role in determining local Greenland climate during the 21st century, resulting in a local climate that may defy the global climate change." Contrary to the ACIA statements, CO2 increases would seem to have little or no effect on Greenland climate.

The instrumental record demonstrates a consistent trend as well. Polyakov et al. (2002, 2003b) studied a large area in the Arctic and created a history of temperature from 1875. They report that temperature peaked in the late 1930s, with 1937 the warmest single year. Since that time, there was a cooling, then a recent warming, but current temperatures have yet to reach the levels observed 65 years ago.

I decided to create some temperature plots myself. Using data from the Global Historical Climate Network (GHCN) data base, I created graphs displaying annual average temperatures for all stations north of 70°N. Figure 1 shows trends from 1970 through 2003, a period with significant warming -- about 1.5°C in 33 years, the equivalent of 4.5°C per century, which fits right in with the ACIA's projections.

Figure 1. Annual average temperature at all GHCN stations above 70 deg N, 1970-2003

Now take a look at Figure 2, showing the trend from 1934 to 2003. Significant cooling occurred through about 1964, followed by a leveling off and then a slow rise, but temperatures remain cooler than they were in the 1930s.

Figure 2. Annual average temperature at all GHCN stations above 70 deg N, 1934-2003

Finally, in Figure 3 we see the entire period, back to 1880. Overall, there is about a 2°C warming, but this is because the record starts with a very cold period and ends on a warm one. Fitting a linear trend (as shown) to such an oscillatory time series strikes one as highly inappropriate!

Figure 3. Annual average temperature at all GHCN stations above 70 deg N, 1880-2003

These results are nearly the same as those of Polyakov, et al (2002):

Figure 4. Surface air temperature anomalies in the Arctic, from Polyakov, et al (2002); graphic obtained from http://www.greeningearthsociety.org/wca/2004/wca_27b.html.

Conclusion: while temperatures appear to have warmed in the last 40 years, a longer viewpoint shows much warmer temperatures in the 1930s and 1940s, apparently even warmer than those today.

Sea Ice in the Arctic

Grumet et al. (2001) created a record of sea ice conditions in the Baffin Bay region of the Canadian Artic going back 1,000 years. They concluded that the 11th through 14th centuries saw reduced sea ice, but that ice extent was greater over the next six centuries. The last century has shown that "sea-ice conditions in the Baffin Bay/Labrador Sea region, at least during the last 50 years, are within 'Little Ice Age' variability," despite several periods of warmer temperatures. The authors added an interesting statement, as well, stating that the sea ice cover history of the Arctic "can be viewed out of context because their brevity does not account for interdecadal variability, nor are the records sufficiently long to clearly establish a climate trend."

For an area in the Greenland Sea, Comiso et al. (2001), used satellite images to assess the size and character of the Odden ice tongue, a 1,300 km long feature, from 1979 to 1998. They were also able to infer its character back to the early 1920s using temperature measurements. The authors stated that there has been no statistically significant change in any of the parameters studied over the past 20 years. However, the proxy record several decades further into the past reveals that the ice tongue was "a relatively smaller feature several decades ago," apparently as a result of warmer temperatures.

Omstedt and Chen (2001) identified a proxy record of the annual maximum coverage of Baltic sea from 1720 through 1997. They stated that there was a sharp decline in sea ice in about 1877. There was also greater variability in sea ice extent in the first 150 years of the record, which was colder, than in the warmer period of the last 100 years.

Jevrejeva (2001) reported on a longer Baltic sea ice data set from 1529 to 1990 for the port of Riga, Latvia. The time series included four climate eras: (1) 1530-1640, with warming accompanied by earlier ice break-up (by 9 days/century); (2) 1640-1770, a cooler period with later ice break-up (5 days/century); (3) 1770-1920, with warming and a tendency toward earlier ice break-up (15 days/century); and (4) 1920-1990, a cooling period with later ice breakup (by 12 days/century).

Conclusion: Arctic sea ice has undergone significant changes in the last 1,000 years, even before the mid-20th century "greenhouse enhancement." Current conditions appear to be well within historical variability.

Ocean conditions

Polyakov, et al (2003a) were anxious to assess reports of "extraordinary change in the Arctic Ocean observed in recent decades" made by various parties. To investigate these claims, they used temperature and salinity measurements in made winter in the central Arctic Ocean near Russia in 1973-79. They also employed 40 years of summer and winter observations in the Laptev Sea.

The authors concluded that earlier reports of rapid Arctic warming "considerably underestimates variability." Their new analyses "place strong constraints on our ability to define long-term means, and hence the magnitudes of [air and sea temperature] anomalies computed using synoptic measurements from the 1990s referenced to means from [earlier] climatologies."

Conclusion: ocean temperature histories, like those of air temperature and sea ice, display marked variability. We are in danger of oversimplifying the historical trends and misrepresenting the future if we simply assume "the Artic Ocean is warming up and will continue to do so."

Discussion

Oddly, the ACIA does a very poor job of documenting its sources of information. For such an ambitious document (it is hundreds of pages long, with stunning graphics and a very professional appearance) its science consists primarily of blanket statements without any sort of reference or citation. Were any of the references listed above considered by the ACIA team? It's hard to say - one can only guess "no."

The ACIA appears to be guilty of selective use of data. Many of the trends described in the document begin in the 1960s or 1970s -- cool decades in much of the world -- and end in the warmer 1990s or early 2000s. So, for example, temperatures have warmed in the last 40 years, and the implication, "if present trends continue," is that massive warming will occur in the next century. Yet data are readily available for the 1930s and early 1940s, when temperatures were comparable to (and probably higher than) those observed today. Why not start the trend there? Because there is no net warming over the last 65 years?

For that matter, can't we dispense with the use of linear trends for cyclical time series which have a cyclical nature? My college statistics prof would have been very upset at this practice, because the character of a trend line in a data set like the one shown in Figure 3 is largely a function of the starting and ending points selected.

I also looked closely at many of the charts and saw misleading information. For example, the chart on global sea level rise goes back only 10 years but shows a steep increase. Then I read the y-axis -- a total rise of about one inch! Since we don't know where the data originated (the caption says "from a satellite launched in 1992") we can only wonder whether the measurement accuracy is sufficient to even measure a one inch change (or whether such a change even matters!).

Conclusions

Recently National Geographic devoted an issue to "Global Warming." Reading the ACIA brought back memories of the NG publication, and brought to mind the overall comment I made upon reviewing it: slick and beautiful but very one-sided. That pretty much sums up my feelings about the ACIA, based on what I have seen so far: nice graphics but bad science.

References

Arctic Climate Assessment (ACIA), 2004. Impacts of a warming Arctic. Cambridge University Press, Cambridge, UK

Chylek, P., Box, J.E. and Lesins, G. 2004. Global warming and the Greenland ice sheet. Climatic Change 63: 201-221.

Comiso, J.C., Wadhams, P., Pedersen, L.T. and Gersten, R.A. 2001. Seasonal and interannual variability of the Odden ice tongue and a study of environmental effects. Journal of Geophysical Research 106: 9093-9116.

Grumet, N.S., Wake, C.P., Mayewski, P.A., Zielinski, G.A., Whitlow, S.L., Koerner, R.M., Fisher, D.A. and Woollett, J.M. 2001. Variability of sea-ice extent in Baffin Bay over the last millennium. Climatic Change 49: 129-145.

Jevrejeva, S. 2001. Severity of winter seasons in the northern Baltic Sea between 1529 and 1990: reconstruction and analysis. Climate Research 17: 55-62.

Omstedt, A. and Chen, D. 2001. Influence of atmospheric circulation on the maximum ice extent in the Baltic Sea. Journal of Geophysical Research 106: 4493-4500.

Naurzbaev, M.M., Vaganov, E.A., Sidorova, O.V. and Schweingruber, F.H. 2002. Summer temperatures in eastern Taimyr inferred from a 2427-year late-Holocene tree-ring chronology and earlier floating series. The Holocene 12: 727-736.

Polyakov, I., et al., 2002. Trends and Variations in Arctic Climate Systems. EOS, Transactions, American Geophysical Union, 83, 547-548.

Polyakov, I., Walsh, D., Dmitrenko, I., Colony, R.L. and Timokhov, L.A. 2003a. Arctic Ocean variability derived from historical observations. Geophysical Research Letters 30: 10.1029/2002GL016441.

Polyakov, I.V., Alekseev, G.V., Bekryaev, R.V., Bhatt, U.S., Colony, R., Johnson, M.A., Karklin, V.P., Walsh, D. and Yulin, A.V. 2003b. Long-term ice variability in Arctic marginal seas. Journal of Climate 16: 2078-2085.

Pryzbylak, R., 2000. Temporal and spatial variation of surface air temperature over the period of instrumental observations in the Arctic. International Journal of Climatology, 20, 587-614.

Acknowledgments: many of the journal citations were obtained from www.co2science.org, which has a treasure-trove of journal reviews and listings (listed under Subject Index)

The author is a Certified Consulting Meteorologist and State Climatologist, Oregon.


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