Jan. 17, 2008
2007 Was Earth's Second Warmest Year in a Century
Climatologists at the NASA Goddard Institute for Space Studies (GISS) at Columbia University have found that 2007 tied with 1998 for Earth's
second warmest year in a century.
Temperature changes in 2007 from the previous year
Goddard Institute researchers used temperature data from weather stations on land, satellite measurements of sea ice temperature since 1982 and data
from ships for earlier years.
The greatest warming in 2007 occurred in the Arctic and neighboring high-latitude regions. Global warming has a larger effect 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 warming anomaly of
2007 is consistent with observations of record-low levels 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.
"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
The eight warmest years in the GISS record have all occurred since 1998,
and the 14 warmest years in the record have all occurred since 1990.
A minor data processing error found in the GISS temperature analysis in
early 2007 does not affect the present analysis. The data processing flaw
was the result of a failure to apply NOAA adjustments to U. S. Historical
Climatology Network stations in 2000-2006, as the records for those years
were taken from a different database (Global Historical Climatology
Network). This flaw affected only 1.6% of the Earth's surface (the contiguous
48 states) and only the last several years in the 21st century. The data
processing flaw did not alter the ordering of the warmest years on record
and the global ranks were unaffected. In the contiguous 48 states, the
statistical tie among 1934, 1998 and 2005 as the warmest year(s) was
unchanged. In the current analysis, in the flawed analysis, and in the
published GISS analysis, 1934 is the warmest year in the contiguous states
(but not globally) by an amount (magnitude on the order of 0.01°C) that is
an order of magnitude smaller than the certainty.
The NASA Goddard Institute for Space Studies, at Columbia University in New York City, is a laboratory of the Earth Sciences Division of NASA's Goddard Space Flight Center and a unit of the Columbia University Earth Institute.
- Image courtesy of NASA