Warmest year

Current concentrations of GHG have already caused the mean global temperature to increase by 0.76 °C in the period from 1850 to 2005 owing to the inertia of the climate system this will lead to at least a further half-degree warming over the next few decades. Eleven of the twelve years from 1995 to 2006 rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). 

The five warmest years for which there are surface temperature records have all been since 1990 (Jones et al., 1998), with the most recent year for which there are data (at the time of writing), 1997, being the warmest in the past century (see Kerr, 1998, and references therein). Mann et al. (1998) have used a variety of indirect indicators for temperature (e.g., ice core data see later) over the past 600 years in the Northern Hemisphere and report that mean annual temperatures for three of the eight years up to and including 1995 are higher than any since 1400 A.D. 

One of the first comprehensive estimates of global mean, near-surface temperature over the earth s lands and oceans was reported in 1986 (Jones et al, 1986). The data showed a long-timescale warming trend. The three warmest years were 1980, 1981, and 1983, and five of the nine warmest years in the entire 124-year record up to 1984 were found to have occurred after 1978. It was apparent from this study that over this period, annual mean temperature increased by about 0.6 to 0.7°C, and that about 40 to 50% of this increase occurred since about 1975. According to many analysts, the warmest year on record up to 1995 is 1995, and recent years have been the warmest since 1860 despite the cooling effect of the volcanic eruption of Mt. Pinatubo in 1991... 

A trend analysis forthe investigated period reflects that the seven warmest years were observed since 1999. The positive trend in the yearly mean SSTs with an increase of 0.97K in 16 years (0.65K/decade) confirms the global observation also for the Baltic Sea. Summer and autumn temperatures mostly contribute to this positive trend. The monthly resolved trend varies between the slightly negative trends in March and the highest positive trends in July in the northern Baltic Sea. The yearly trend of the entire Baltic Sea is stronger than that of the northern hemisphere. 

FIGURE 9.4 Yearly mean SST along the transect through the Baltic Sea for all years of the investigation period with marked 15 years mean, and the coldest and warmest years. 

The 2000s was the warmest decade and 2005 was the warmest year since 1861. 

Both hemispheres show long-term warming, but it clearly has occured in two phases (1920-1944 and since about 1975, see also Table I). Spatial patterns of the changes will be considered later. For the global average, 12 of the 14 warmest years occurred between 1986 and 1999. The warmest year of the entire global series was 1998,0.57°C above the 1961-1990 average. The next four warmest years were 1997 (0.43), 1995 (0.39), 1990 (0.35), and 1999 (0.33). 

In summary, the world is in the midst of a period of unprecedented and dismptive change. This is particularly evident when examining the health of the world s ecological systems. A host of human forces impinge upon coral reefs, tropical rain forests and other critical natural systems located around the world. Half the planet s wetlands are gone. Total carbon emissions and atmospheric concentrations of carbon dioxide are both accelerating and 2004 was the fourth warmest year ever recorded. Over the course of the last 120 years, the ten warmest years have all occurred since 1990. 

Because the natural forces that control the earth s temperature are not very well understood at this point, it is difficult to decide whether the greenhouse warming has already started. But many scientists think it has. For example, the 1980s and 1990s were among the warmest years the earth has experienced since people started keeping records. 

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