Tierney wrong on Arctic climate change and polar bears
New York Times columnist John Tierney made several questionable and inaccurate claims about Arctic climatic change and its effect on polar bear populations. In his August 7 Times op-ed , Tierney claimed that the Arctic was as warm in the 1930s as it is now. He also suggested that recent Arctic warming may benefit polar bears, noting that polar bear populations have increased as the Arctic has grown warmer. In fact, data show that current Arctic temperatures are higher than they were in the 1930s. Also, many scientists believe that Arctic warming, rather than benefiting polar bears, will actually destroy their habitats and reduce their food supply.
In his August 7 op-ed, Tierney claimed that "[i]n the 1930's, the Arctic was as warm as it is now." But the October 2004 Arctic Climate Impact Assessment  (ACIA), "Impacts of a Warming Arctic," refutes this claim. According to the ACIA report (pdf Page 29), average Arctic near-surface air temperatures today are approximately 0.5 degrees Celsius higher than in the 1930s. The ACIA  is an "international project of the Arctic Council  and the International Arctic Science Committee  (IASC) to evaluate and synthesize knowledge on climate variability, climate change, and increased ultraviolet radiation, and their consequences."
Tierney rightly noted that the global polar bear population has increased in past decades, and that the "chief reason for the rise is probably restrictions on hunting (for which conservationists deserve credit)." But his claim that warming "could be helping bears in some places" is disputed by the Polar Bear Specialist Group  (PBSG) of the World Conservation Union  (IUCN) and the United Nations' Intergovernmental Panel on Climate Change  (IPCC), both of which found that Arctic warming is threatening polar bears' habitat and food supply. At the 14th meeting of the PBSG in June, the group concluded  that polar bears should have their status on the IUCN "Red List of Threatened Species " upgraded  from "Least Concern" to "Vulnerable." The PBSG noted that there is a "likelihood of an overall decline in the size of the total population of more than 30% within the next 35 to 50 years," and that the "principal cause of this decline is climatic warming and its consequent negative affects [sic] on the sea ice habitat of polar bears."
According to an April 2002 IPCC technical paper  on climate change and biodiversity, Arctic sea ice has "[t]hinned by 40% in recent decades," and "decreased in extent by 10-15% since the 1950s." The IPCC paper also noted the danger this reduction poses to polar bear populations:
The decrease in the extent and thickness of sea ice may lead to changes in the distribution, age structure, and size of populations of marine mammals. In the Arctic, seal species that use the ice for resting and polar bears that feed on seals are particularly at risk.
The PBSG provides greater detail on the effect warming will likely have on polar bear habitats and food supplies here .
Furthermore, Tierney's claim that warming would "increase the diversity of species in the Arctic" is highly misleading. It is reasonable to conclude that more plant and animal species would be able to live in a warmer Arctic climate. Those new species, however, would likely supplant existing Arctic species, such as the polar bear, which would likely die out or be driven to colder climates. A 1997 IPCC special report  on the regional impact of climate change concluded that "Polar warming probably will increase biological production but may lead to different species composition on land and in the sea. On land, there will be a tendency for polar shifts in major biomes such as tundra and boreal forest and associated animals, with significant impacts on species such as bear and caribou."