07/25/2002
Alaska's surface pitches and yaws as the temperature bubbles above and below, freezing and thawing as it has been for millennia. The land, ice and ecosystem respond to those temperature swings.
In 1976-77, Alaska's average surface temperature jumped up and as a result glaciers melted, pavements buckled and utility poles toppled. Both pink and sockeye salmon became established in the Alaskan waters. All these signs pointed to warming.
Thermometer readings from various locations around Alaska indicate that a warming occurred during the last five decades. But can this Alaska warming be connected to the air's increased carbon dioxide concentration from human activities like fossil fuel consumption?
The short answer -- despite the media hype courtesy of vivid images that convey impending disasters -- is, no. And that is at odds with the analysis from the United States National Assessment (USNA).
Back in 1990, Congress enacted a law requesting a report describing the potential consequences of climate change in the 21st century across the U.S -- thus the USNA was born. The 2001 USNA futurecast includes an estimate of "humanity's influence on the global climate, [which] will grow in the 21st century." The report concludes, "It is very likely that the U.S. will get substantially warmer [in the 21st century]," owing to industrialization.
According to the computer simulations of man-made global warming, as the air's carbon dioxide content rises, the polar regions should warm faster than the global average. The reason is that sea and land ice should begin to melt as local temperature increases. For example, because ice is very reflective of sunlight and the exposed sea -- after ice melts -- is not, the sea begins to absorb more sunlight and further warm. This "sea-ice and sunlight feedback" explains why the computer simulations predict rapid warming at the high latitudes.
The USNA says that Alaska should warm between 5 and 18 degrees F by the year 2100. That means Alaska should have already shown a systematic warming trend of a few degrees Fahrenheit over the last fifty years. And the USNA shows a merged annually averaged temperature record for Alaska, whose linear trend is numerically a "4 F warming since the 1950s." More worrisome is the reported winter warming trend of 7 F for the interior of Alaska.
So do these trends -- ominous as they sound -- vindicate the projections of human-made global warming? Alas, no.
One immediate concern is the ability of the global computer simulations to explore the impact of changing sea ice conditions on the model results. So, for example, researchers associated with a program at the University of Alaska-Fairbanks recently wrote, "Unfortunately, most global climate models are not capable of sufficiently reproducing the climatological state of the Arctic Ocean, sea ice and atmosphere...as [an] example, the simulated sea ice thickness is overestimated, and its overall pattern is in error, with the thickest ice located in the Siberian instead of the Canadian sector of the Arctic Ocean."
Another concern is the mismatch between the predicted warming trend and the trend present in the actual temperature measurements. The computer simulations expect gradual warming over decades as the carbon dioxide and its trapped energy smoothly accumulates over decades. But the Alaska temperature records definitely do not show similar smoothness.
The USNA report remarks, "Much of the recent warming occurred suddenly around 1977, coincident with the most recent of the large-scale Arctic atmosphere and ocean regime shifts..." But the report forgets to explain that such a sudden shift is completely uncharacteristic of the forecast global warming results, and so the sudden warming is unrelated to the air's buildup of carbon dioxide.
If not human-caused, what is the origin of the sudden jump in temperature in 1977, and what is its consequence for estimating the carbon-dioxide-influenced warming in the Alaskan temperature record?
The northern Pacific Ocean temperature strongly affects the temperatures of Alaska. The Pacific Ocean temperature changes naturally on multiple time scales. The major pattern in the northern Pacific Ocean is for it to hold at a low average temperature for roughly 20 to 30 years, and then to suddenly shift upward, where it remains for some decades. Then it shifts back down again.
This pattern has been observed over one hundred years, further back than the period of recent and substantial increase in the air's carbon dioxide content, and so the pattern must be natural. In 1976-1977, the northern Pacific Ocean shifted naturally to a state that produces the observed rapid rise in Alaska's land temperatures. Alaska's ecology responded to this natural, rapid warming, too.
How significant is the Great Pacific Climate Shift? In the USNA record merged across Alaska's interior and coastal locations, the warming over 1976 - 1977 from the Great Shift is about + 3 F, or nearly the full magnitude of the computed, linear 50-year warming trend. In other words, the long-term warming trend seems largely a mathematical artifact owing to the presence of the sharp warmth. The most dramatic impact of the Great Shift is felt in the west-coast locations. For example, in Nome the temperature jumped around 8 F over the period 1976 - 1977.
But to make a case supporting the climate simulations and their predictions of a large, human-induced, fifty-year warming trend in Alaska, the dramatic warmth introduced by the Great Pacific Climate Shift of 1976 - 1977 must be subtracted. One way to assess the human-made warming trend is to look at the temperature records after 1977, and calculate the linear trend during the period when the carbon dioxide concentration in the air increased most rapidly.
Twenty-two of the thirty individual locations defining Alaska's temperature history show either no warming trend or a significant cooling trend after 1977. Nor does the USNA's Alaska record show a meaningful man-made warming trend in the period beyond the Great Pacific Climate Shift of 1976 - 1977. Those facts contradict the predictions from the climate simulations.
As for the future, University of Washington researchers find that the northern Pacific Ocean temperatures dropped back to a state of cold around 1998 - 1999. That should mean sharply colder temperatures in Alaska for the next twenty to thirty years.
Once again, the reality of the climate records, even in the sensitive bellwether regions like Alaska, undercuts the alarmism that Alaska is overheating owing to the build-up of the concentration of man-made carbon dioxide in the air.