February 5, 2007

Arctic Lessons from the Last Interglacial (Polar bears survived)

Filed under: Arctic, Extinctions, Polar

In recent years, much has been made of the warming in the northern high latitude region of Earth over the last two decades of the 20th century. Data on glacial and sea ice recession and frightening computer simulations of rising sea levels underscore the doom and gloom of the warmth in the Arctic. On top of this, global climate models are predicting that this region will continue to be a “hotspot” of greatest warming during the 21st century. And, in an effort to drive the impact of all of this home (because who would otherwise really care if the coldest places on earth warmed up a bit), a small, but vocal band of climate alarmists have attempted to convince us that as a result of Arctic warming, everyone’s favorite bear (with the exception of perhaps Teddy and/or Yogi), ursus maritimus—the polar bear—will be pushed to extinction.

The contention of climate alarmists that the late-20th century warming is unprecedented over the past two millennia has been contested with contrary scientific evidence over and over, especially in the high latitudes. As the geologic timeline that is available to the global warming crusade gets spottier, one thing is clear – they can only shorten their sights. Going back to Earth’s last interglaciation is not an option for building their argument that much of the recent warmth is unnatural—because back during the last interglacial warm period, temperatures in the Arctic were higher, and polar bears survived (obviously).

Circum-Arctic PaleoEnvironments (CAPE) is an activity within the International Geosphere-Biosphere Program that aims to facilitate international syntheses of Arctic records of past environments. A 25-member CAPE-Last Interglacial Project Members team recently published an article that further characterizes the Arctic warmth during the time of the last interglaciation (LIG). The work “Last interglacial Arctic warmth confirms polar amplification of climate change” was published earlier this year in Quaternary Science Reviews. Many previous works indicate that Earth was warmer during the LIG than for any other period within the past 250,000 years. However, few detailed quantitative reconstructions of the period exist. The CAPE research group quantitatively estimated circum-Arctic summer air and sea surface temperatures for the LIG as reconstructed from terrestrial- and marine-based proxy records detailed in previous research conducted by a large body of scientists. The group emphasized temperatures in summer because they “exert the dominant control on glacier mass balance” and summer temperature is “the most effective predictor for most biological processes.”

The group found evidence that the LIG persisted for 10,000-12,000 years and that Arctic summer air temperatures during the LIG were 4-5ºC (Figure 1) above present for much of the region, which was well above the LIG average temperature for the rest of Earth. The warming seems to have occurred rapidly, peaking in the early portion of the LIG. The group contends that Arctic summer temperatures were warm enough “to melt all glaciers below 5 km elevation, except the Greenland ice sheet, which was reduced by ca 20-50%.” In regard to Arctic Ocean sea ice, the group states that the margins of the permanent ice “retracted well into the Arctic Ocean basin” and the ice was of an extent that was smaller than during the highly publicized ice retreat of the Holocene. When examining evidence of vegetation changes, the group concluded that “boreal forests advanced to the Arctic Ocean Coast across vast regions of the Arctic currently occupied by tundra.” In fact, across most of northern Russia, they report that forests were displaced northward by as much as 400 to 1000 km.

Figure 1. Regional maximum LIG summer Arctic temperature anomalies (ºC) relative to present. Taken from Cape Project Members (2006).

The CAPE researchers explain that the dramatic surface changes in the Arctic during the LIG would have reduced the albedo (reflectivity to solar radiation) and altered the transfer of energy among the land, atmosphere, and oceans. The changes in the general energy budget seemed to amplify the incoming solar radiation-driven warmth of the LIG through positive feedback. The researchers conclude that the feedback in the Arctic accounts for the greater LIG summer warming (5ºC above today) in the Arctic than across the rest of the Northern Hemisphere (0-2ºC above today). So, the idea of modern polar warming in excess of that of the rest of Earth is not new or unnatural – it clearly defined the climate of the LIG those many years ago. The amount of Arctic warming today relative to the remainder of Earth is much less than with the LIG. As the CAPE researchers note, “During the 20th century, the planetary temperature increased 0.7ºC, whereas most regions of the Arctic record warming of 1–3ºC over the same interval.” The global climate models that produce 21st century climate change scenarios upon which alarmists hang their hats have trouble replicating the Arctic warming. The Cape researchers explain that most of the 20th century warming in the Arctic occurred in summer months, as with the LIG, but model projections indicate winter warming should dominate. The LIG did not experience the increase in greenhouse gases that is projected for the remainder of the 21st century, but still, the model-reality discrepancy is troublesome.

The next time that you see Al Gore’s photo collection of decaying glaciers and polar bears drowning as the distance between icebergs and the shore is too far to swim, think of the LIG – a natural period in Earth’s history when hippopotamus and the water tortoise were widespread as far north as Great Britain and birch forests reached the shores of the Arctic Ocean. Remember that then, as now, the Arctic naturally warmed more dramatically than the rest of the world, and also keep in mind that our modern global climate models – those that sit next to the panic button – are stumbling around that reality.


CAPE Project Members, 2006. Last interglacial Arctic warmth confirms polar
amplification of climate change. Quaternary Science Reviews, 25, 1383-1400.

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