GISS Surface Temperature Analysis
Global Temperature Trends: 2004 Summation
The 2004 meteorological year was the fourth warmest year in the period of accurate instrumental data (since the late 1800s). The annual-mean global surface temperature is 0.48°C above the climatological mean (1951-1980 average) in the GISS analysis, which uses meteorological station measurements over land and satellite measurements of sea surface temperature over the ocean.
In Figure 1 above, the left-hand panel shows that globally the warmest temperature occurred in 1998, while the second and third warmest years were 2002 and 2003, respectively. As the figure shows, there has been a strong warming trend over the past 30 years, a trend that has been shown to be due primarily to increasing greenhouse gases in the atmosphere.
Figure 1 illustrates substantial year-to-year variability of global temperature, as well as coherent long-term change. Some of the variability is associated with known climate forcings, notably large volcanoes that injected sulfuric acid aerosols into the stratosphere in 1963, 1982, and 1991. However, much of the variability consists of chaotic fluctuations, including El Ninos, when warm water spreads over much of the tropical Pacific Ocean. The large spike in global temperature in 1998 was associated with one of the strongest El Ninos of recent centuries, and a weak El Nino contributed to the 2002-2003 global temperature.
Despite the chaotic aspect of climate, the increasing role of human-made climate forcing agents makes it possible to hazard predictions of likely global climate trends even on time scales as short as a few years or less. This is because of the recognition that the Earth is now out of energy balance, with 0.85±0.15 W/m2 more solar energy coming in than terrestrial heat radiation going out to space (Hansen et al., The Earth'Energy Imbalance: Confirmation and Implications, to be submitted to Science, 2005). One result of this imbalance is that it makes it likely that global temperature in 2005, aided also by a weak El Nino, will exceed those of 2003 and 2004 and perhaps even the temperature of 1998, which had stood out far above the temperature of any year in the preceding century.
The right-hand panel of Figure 1 compares the global, national (United States), and local (New York City) annual mean temperature anomalies (relative to their 1951-1980 means) since 1950. This figure illustrates that the global warming of about 0.5ºC (0.9ºF) over that period is smaller than year-to-year fluctuations of even annual mean local temperature. Even the average temperature for the United States fluctuates more than the global warming. However, global warming is large enough that it is beginning to affect the frequency of warmer than normal seasons, as we have shown elsewhere.
A global map of surface temperature anomalies in 2004, in the left-hand panel of Figure 2, shows that the largest warm anomalies compared to the 1951-1980 baseline were in Alaska, near the Caspian Sea, and over the Antarctic Peninsula. But compared to the previous five years, the United States was quite cool, as shown in the right-hand panel Figure 2.
Figure 3, at right, shows global maps to surface temperature anomalies for each month of meteorological 2004 (Dec. 2003 through Nov. 2004). Natural variability is evident from month to month during the year. Most of the United States was unusually cool during the summer of 2004.
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Further Information
Related webpages on the GISS website include:
- GISS Surface Temperature Analysis (GISTEMP)
- Global Temperature Annual Summations: 2005, 2003, 2002, 2001.
References
Please see the GISTEMP references page for citations to publications related to this research.