Some argue the recent trends show that global warming has slowed or stopped.2007 was tied with 1998 for the second warmest year in the last 100 years, according to the NASA Goddard Institute for Space Studies.
The news is only the latest in an unbroken string of “warmest years” as measured by average global surface temperatures. The eight warmest years in the GISS records have all come since 1998 and the 14 warmest years since 1990.
According to NASA:
The greatest warming in 2007 occurred in the Arctic, and neighboring high latitude regions. Global warming has a larger affect in polar areas, as the loss of snow and ice leads to more open water, which absorbs more sunlight and warmth. Snow and ice reflect sunlight; when they disappear, so too does their ability to deflect warming rays. The large Arctic warm anomaly of 2007 is consistent with observations of record low geographic extent of Arctic sea ice in September 2007.
“As we predicted last year, 2007 was warmer than 2006, continuing the strong warming trend of the past 30 years that has been confidently attributed to the effect of increasing human-made greenhouse gases,” said James Hansen, director of NASA GISS.
But since global temperatures have leveled off a little since 2000, it has caused some people to argue that global warming has stopped.
But most climate scientists argue that the time frame is too short – only eight years – to make any statements about long-term trends. There is a long, contentious explanation of this over at RealClimate, which is my favorite climate science site.
The physics of greenhouse warming would indicate that there is no reason to believe that a lull in average warming is anything but temporary. The climate system is complex, but as more greenhouse gases are poured into the atmosphere, outstripping the natural systems of recycling those gases, the average temperature will warm in the future.
“It is unlikely that 2008 will be a year with truly exceptional global mean temperature,” said Hansen. “Barring a large volcanic eruption, a record global temperature clearly exceeding that of 2005 can be expected within the next few years, at the time of the next El Nino, because of the background warming trend attributable to continuing increases of greenhouse gases.”