During more than 15 years of reporting on climate change science and policy, I have watched climatology become increasingly politicized. Most headlines and publicized scientific reports confirm that humanity is heating up the planet by burning fossil fuels that load the atmosphere with heat-trapping carbon dioxide.
Take just two reports from the last week. The Arctic Climate Impact Assessment report from the Arctic Council found that Arctic warming is increasing twice as fast as elsewhere on the planet. This finding corresponds nicely with predictions made by various computer climate models that forecast that the poles should be warming faster than the rest of the planet.
Another new study from the journal Nature that seems to confirm this prediction finds that krill are declining in the frigid oceans around Antarctica. Why? Evidently because the sea ice is declining, and krill live on the algae that live and grow on the underside of the sea ice.
These reports are confirming what the majority of climate scientists have been saying—that man-made global warming is occurring at a rapid rate.
Well, maybe. Once a particular notion becomes conventional wisdom, evidence and stories confirming that conventional wisdom are easily accepted and published—and reported in the media. Those that contradict the prevailing views have a much harder time getting a hearing. Either global warming has hardened into conventional wisdom in the climatological community, or mounting scientific evidence shows that humanity is in fact warming the world at a dangerous pace.
Which is it and how can one tell?
To show how hard answering that question can be, let's take a little closer look at the two reports mentioned above. The Arctic Council report is based on the observations and deliberations of 300 scientists from eight countries and six groups of indigenous people over the past four years. They find that the Arctic region is warming at twice the rate of the rest of the world. They further find that the sea ice that covers the Arctic Ocean is thinning, and could almost disappear in the summer months by 2100.
But University of Alabama at Huntsville climatologist John Christy, a climate expert on whom I have relied for years, makes some interesting observations about the Arctic Council's report. "If you look at the long term records, the Arctic has been as warm or warmer than it is today," says Christy. He cites temperature data from the Hadley Centre in the UK showing that from 70 degrees north latitude to the pole, the warmest years on record in the Arctic were 1937 and 1938. This area is just slightly above the Arctic Circle.
Furthermore, those same records show that the Arctic warmed twice as fast between 1917 and 1937 as it has in the past 20 years. After 1940, the Arctic saw a big cool-down and climatologists noted sea ice expanding in the northern Atlantic. Christy argues that what he calls the Great Climate Shift occurred in the late 1970s and caused another sudden warming in the Arctic. Since the late 1970s there has not been much additional warming in the region at all. In fact, on page 23, the Arctic Council Assessment offers very similar data for Arctic temperature trends from 60 degrees north latitude—the area that includes most of Alaska and essentially all of Greenland, most of Norway and Sweden, and the bulk of Russia.
Interestingly, the recent increase in temperatures in Alaska and Siberia seem to have coincided almost simultaneously with a shift in the Pacific Decadal Oscillation (PDO) in the late 1970s. Could this be part of Christy's Great Climate Shift? Swings in the PDO occur on 30 to 40 year time frames, and the most recent one brought warmer currents flowing north to the coast of Alaska. The Assessment does note that "several important natural modes of variability that especially affect the Arctic have been identified, including the Arctic Oscillation, the Pacific Decadal Oscillation, and the North Atlantic Oscillation. Each of these can affect the regional patterns of such features as the intensity and tracks of storm systems, the direction of prevailing winds, the amount of snow, and the extent of sea ice."
The Arctic Council report states that satellite measurements find the area over which ice melts in the summer in Greenland increased 16 percent between 1979 and 2002. Should the ice cap in Greenland completely melt away, sea levels would rise seven meters or so, inundating Florida, New York City, London, and Bangladesh. Not an immediate worry, since this process even with extreme warming would take centuries.
But what to make of the report earlier this year in the scientific journal Climate Change by Petr Chylek and his colleagues from the Los Alamos Laboratory, which found that average temperatures in Greenland have been falling at the rather steep rate of 2.2 degrees Celsius since 1987?
In addition, the study found "summer temperatures, which are most relevant to Greenland ice sheet melting rates, do not show any persistent increase during the last fifty years." Strangely, when I searched the Assessment I could not find any reference to the Chylek team's study of Greenland temperature trends.
What about the report on the Antarctic krill? The shrimp-like krill are the foundation of the food chain in the oceans around Antarctica, being dined upon by whales, seals, fish, and penguins. The report finds that krill populations off the Antarctic Peninsula have declined by 80 to 90 percent in recent years. The study in Nature notes that the extent of winter sea ice has been declining near the Antarctic Peninsula, where temperatures have increased by 2.5 degrees Celsius over the past 50 years.
But again, the picture is complicated. Overall winter sea ice around Antarctica has been increasing since 1979. However, Antarctica experienced a very rapid decline in winter sea ice in the early 1970s and the area covered today is not quite as large as it was before the decline in the 1970s.