Cites Natural Causes
It’s wrong to blame our warming climate on human pollution alone, says a major analysis by U. S. climate scientists who say North America’s warming and drying trend also has important natural causes.
Natural shifts in ocean currents have caused much of the warming in recent decades, and almost all of the droughts, says the U. S. National Oceanic and Atmospheric Administration (NOAA).
Most climate researchers today deal exclusively with man-made “greenhouse” gases, and often dismiss suggestions of naturally caused warming as unscientific.
Yet NOAA says Western Canada has warmed by two degrees and Eastern Canada hasn’t warmed at all because flows of air from naturally shifting Pacific currents have affected the West most.
The lengthy re-analysis of climate data doesn’t dispute that greenhouse gases from fossil fuels cause a warmer climate. But it raises questions about the details: How much warming? How many causes? And why isn’t it the same every-where?
It also stresses that we don’t understand climate as well as we like to think, because scientists only have good data from about 1948 onward.
“Most of the warming [worldwide] is the consequence of human influences,” said Martin Hoerling, a NOAA climate scientist. But he said the question remains, “What does that mean for my backyard?”
Policy-makers need to know whether natural changes or pollution is causing local conditions such as the current drought from California across to Texas, the report notes.
“All regions are not participating [in warming] at the same rate as the global temperature is changing,” Mr. Hoerling said. Some in the West are warming rapidly, and some not at all (the southeastern United States and Atlantic Canada).
Oceans carry vast amounts of heat, releasing heat and moisture into air, which then travels inland. The re-analysis focused on this fact.
Some of the changes in North America’s warming trend of the past half-century have been due to shifting ocean currents, the NOAA team found. It estimates the “natural” change is substantial and could be close to half of all warming in North America (though it is still less than the amount caused by greenhouse gases.)
The study found:
- The 56-year trend of annual surface temperature showed a rise of 0.9C, plus or minus one-tenth of a degree.
- The greatest warming — up two degrees — has taken place across Alberta, Saskatchewan, Yukon and Alaska. Quebec and Atlantic Canada stayed cool.
That East-West difference “is not what we would expect from the effect of greenhouse gases alone,” Mr. Hoerling said. Greenhouses gases should have influenced both. However, NOAA believes Western Canada is receiving more warm air due to shifting patterns of the Pacific Ocean currents.
- Variations within North America “are very likely influenced by variations in global sea surface temperatures through the effects of the latter on atmospheric circulation, especially during winter.” The term “very likely” is defined as a chance of 90% or more.
- It’s “unlikely” that patterns of drought have changed due to global warming caused by human pollution. Rather, natural shifts in ocean currents are probably to blame. For instance, the current drought in Texas and the southwest are due to La Nina, a Pacific Ocean current that starts and stops periodically (such as El Nino), and cuts off the movement of moist air inland. Warmer temperatures from greenhouse gases, however, would worsen the basic drought.
- Seven of the warmest 10 years since 1951 occurred in the decade from 1997 to 2006. The data in the study cover only to the end of 2007.
The study, Reanalysis of Historical Climate Data for Key Atmospheric Features, was completed in December but hasn’t been widely publicized.
(Read the report here, PDF 8 MB)
Meanwhile, a study published in the research journal Science last week raises further questions about our under-standing of global warming. It disputes the theory that global warming is causing more major hurricanes.
NOAA and the University of Wisconsin at Madison blame, instead, a reduction in the number of volcanic eruptions and dust storms near the equator. When there’s less airborne dust and ash, more sunshine reaches the planet’s surface, which warms the tropical oceans and spawns strong hurricanes.