It will come as slim consolation to western Canadians currently enduring a cold snap frosty enough to prompt warnings to stay indoors by civic health and safety agencies. But Alberta, Saskatchewan, the Yukon Territory and Alaska are North America’s hotbeds of global warming, according to a new climate change report on continental temperature trends by the United States Geological Survey.

The study ‑ titled Attribution of the Causes of Climate Change Variations and Trends over North America during the Modern Reanalysis Period ‑ reports uncovering a notable trend in the three chilly Canadian jurisdictions and the coldest U.S. state.

That “reanalysis period” is 1951-2006, or a half century that defines itself as the limited time best suited for studies by the availability of detailed and reliable enough weather records for scientific use. Among the USGS findings: “Observed surface temperature change has been largest over northern and western North America, with up to +2 degrees Celcius (3.6 degrees Fahrenheit) warming in 56 years over Alaska, the Yukon, Alberta and Saskatchewan.”

Other, more thickly populated areas may think they have heated up. But perception is not the same as measured reality. “Observed surface temperature change has been smallest over the southern United States and eastern Canada, where no significant trends have occurred,” the USGS reports.

In the northwestern reaches of the continent, the American scientists suspect two climate mechanisms are behind the warming. There have been documented increases in surface temperatures on the nearest oceans. There have been related changes in winter wind patterns, with warm air pouring ashore into the northwestern interior of the continent.

This is a professional report by a responsible agency. The scientists do not claim to be absolutely right or certain. The USGS experts say “there is very high confidence that changes in atmospheric wind patterns have occurred.” The connection between land and ocean temperature change is “very likely.”

A press release that accompanied the report emphasized that it concludes abrupt changes are possible in the 21st century ‑ at least by the standards of climate trends ‑ due to the interaction of ocean surfaces, winds and northwestern inland regions.

But as always, scientists professionally bound to stick to the evidence are considerably less assertive than the publicity material. There is much hesitation about concluding that the available records finally prove global warming is an entrenched trend, and that it is caused by greenhouse-gas emissions of waste byproducts from making and using fossil fuels.

To scientists, each step in this popular chain of reasoning remains a big one with a tendency to go beyond the available evidence. The USGS report observes that the 1930s Dust Bowl appears to have been related to a rise in ocean temperatures and shifts in wind patterns, much like the observed trends since 1951 and especially since the mid-1970s. However, the 1930s disaster appears to have been part of a natural cycle. “It is reasonable to wonder whether the current warmth will also revert to colder conditions in coming decades akin to events following the 1930s peak.”

Says the USGS report: “It is reasonable to ask whether such a 56-year assessment period adequately samples the principal features of climate variability. Does it, for example, capture the major climate events, such as droughts, that may be of particular concern to decision makers? Is it a sufficiently long period to permit the distinction between fluctuations in climate conditions that are transient , or cyclical, from trends that are related to a changing climate? How well do scientists understand the climate conditions prior to 1951 and what insight does analysis of those conditions provide toward explaining post-1950 conditions?”

That is, climate change science is still studded with questions. Recommendation number one of the USGS report is to “improve the quality and consistency of the observational data.” The agency urges development of “new national capabilities” to examine “variables that are of high relevance to policy and decision support. Such variables include those required to monitor changes in the carbon cycle and to understand interactions among Earth system components ‑ atmosphere, ocean, land, cryosphere and biosphere ‑ that may lead to accelerated or diminished rates of climate change.”

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