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Global
Temperatures
2008 Global Temperature
Calendar
year 2008 was the coolest year since 2000, according to the NASA Goddard
Institute for Space Studies (GISS) analysis of worldwide temperature
measurements, but it was still in the top ten warmest years since the start of
record-keeping in 1880. Given the range of uncertainty in the measurements, the
GISS team concluded that 2008 was somewhere between the seventh and the tenth
warmest year on record. (The 10 warmest years have all occurred within the
12-year period from 1997-2008.)
The map above shows global temperature anomalies in 2008 compared to the
1950-1980 baseline period. Below-average temperatures are shown in blue, average
temperatures are white, and above-average temperatures are red. (Gray indicates
no data.) Most of the world was either near normal or warmer than normal.
Eastern Europe, Russia, the Arctic, and the Antarctic Peninsula were
exceptionally warm (1.5 to 3.5 degrees Celsius above average). The temperature
in the United States in 2008 was not much different than the 1951-1980 mean,
which makes 2008 cooler than all of the previous years this decade. Large areas
of the central and eastern Pacific Ocean were cooler than the long-term average,
linked to a La Nina episode that began in 2007.
The graph shows the long-term trend in surface temperatures since 1880. The
annual average temperatures are shown in light orange, and the jaggedness of the
line indicates how much the average global surface temperature varies from year
to year. Because climate is so variable form year to year, it can be easier to
spot long-term trends through multi-year averages. The dark red line shows the
five-year running average, which is an average of five years of annual
temperatures centered on a given year. Even this five-year average shows that
climate has ups and downs, but the long-term increase in global average surface
temperatures is obvious. The gray "barbells" indicate the range of
uncertainty. Not surprisingly, the uncertainty is larger for older measurements
than for more recent ones.
In their report on 2008 temperature trends, the scientists at NASA GISS, led by
James Hansen, attribute the relative coolness of 2008 to the persistent La Nina,
which continued as of late 2008/early 2009. The summary also describes how the
delay in the start of the next solar sunspot cycle, volcanic activity from
Aleutian Island volcanoes (both Okmok and Kasatochi erupted in August), and
emission rates of greenhouse gases could influence average global temperatures
in the next few years.
Credit:NASA
Goddard Institute for Space Studies NASA image by Robert Simmon, based on GISS
surface temperature analysis data. Caption by Rebecca Lindsey, adapted from
Global Temperature Trends: 2008 Annual
The global
January-December temperature for combined land and ocean surfaces was 0.49°C
(0.88°F) above the 20th century average, tying with 2001 as the eighth warmest
since records began in 1880. Globally averaged land temperatures were 0.81°C
(1.46°F) above average, while the ocean temperatures were 0.37°C (0.67°F)
above average, ranking as the sixth warmest and tenth warmest, respectively.
Eight of the ten warmest years on record have occurred since 2001, part of a
rise in temperatures of 0.5°C (0.9°F) since 1880.
The year began with
a cold phase (La Nina) El Nino-Southern Oscillation (ENSO) which developed
during late 2007, transitioned to a neutral phase in June 2008, and remained
neutral through the end of the year. The presence of a strong La Nina dampened
ocean sea surface temperatures (SSTs) and contributed to a February global
average temperature that was the coolest since the La Nina episode of
2000-2001. During March, sea surface temperature (SST) anomalies were
cooler-than-average in all Nino regions, with the exception of the Nino 1+2
region where the monthly temperature anomaly rose to +0.82°C (+1.48°F).
Temperatures across Nino 3.4 and Nino 4 regions increased slightly but the
anomalies remained below average. These conditions indicated the first signs of
weakening of the cold event (La Nina), however a moderate La Nina remained
across the equatorial Pacific Ocean. By June, temperatures across the Nino 3.4
and Nino 4 regions continued to warm and the Oceanic Nino Index threshold
[3-month (April-June) running mean] was -0.50°C (-0.90°F), indicating a
transition into a neutral phase. By the end of December, neutral phase ENSO
conditions persisted across the equatorial Pacific Ocean, although
characteristics of a developing La Nina were present. According to the latest
information from NOAA's Climate Prediction Center, La Nina conditions could
develop into early 2009.
Temperature Trends
During the past century, global
surface temperatures have increased at a rate near 0.05°C/decade
(0.09°F/decade), but this trend has increased to a rate of approximately
0.16°C/decade (0.29°F/decade) during the past 30 years. There have been two
sustained periods of warming, one beginning around 1910 and ending around 1945,
and the most recent beginning about 1976. Temperatures during the latter period
of warming have increased at a rate comparable to the rates of warming projected
to occur during the next century with continued increases of anthropogenic
greenhouse gases.
Temperature measurements have
also been made above the Earth's surface over the past 51 years using
balloon-borne instruments (radiosondes) and for the past 30 years using
satellites. These measurements support the analyses of trends and variability in
the troposphere (surface to 10-16 km) and stratosphere (10-50 km above the
earth's surface).
Credit: NASA
Goddard Institute for Space Studies , NOAA
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