Global Temperature

Based on the National Oceanic and Atmospheric Administration (NOAA) and the U.S. National Climate Data Center records, the rise in global surface temperatures since 1900 is 0.66°C, when calculated as a linear trend. The year 2005 was notable for its global warmth, both at the surface and throughout the troposphere. Globally, surface temperatures remained above average in all 12 months and reached a record high value for the year. This anomalous warmth

FIGURE 1.2 Global temperature since 1850.

is part of a long-term warming trend of approximately 0.7°C per century since 1900 and a rate of increase almost three times as great since 1976.

Generally, the globally averaged annual mean surface temperature in 2005 was the warmest since the inception of consistent temperature observations in 1880. Unlike the previous record, the positive anomaly of 1998 (+0.50°C), the 2005 global anomaly of 0.53°C above the 1961-1990 mean occurred in the absence of a strong El Niño signal. However, statistically, the 2005 global temperature anomaly could not be differentiated from either 1998 or any of the previous four years. The majority of the top 10 warmest years on record have occurred in the past decade, and 2005 continues a marked upward trend in globally averaged temperature since the mid-1970s. The global temperature from 1850 until 2006 is shown in Figure 1.2, together with the five-year average values. As can be seen there is an upward trend that is more serious from the 1970s onward.

Regionally, annual and monthly averaged temperatures were above normal across most of the world. Australia experienced its warmest year on record as well as its hottest April. For both Russia and Mexico, 2005 was the second warmest year on record.

1.4.2 carbon Dioxide

Carbon dioxide emitted from natural and anthropogenic (i.e., fossil fuel combustion) sources, is partitioned into three reservoirs: atmosphere, oceans, and the terrestrial biosphere. The result of increased fossil fuel combustion has been that atmospheric CO2 has increased from about 280 ppm (parts per million by dry air mole fraction) at the start of the industrial revolution to about 380 ppm today (see Figure 1.3). Roughly half the emitted CO2 remains in the

Co2 Levels Industrial Revolution

Year

FIGURE 1.3 CO2 levels in the last 1000 years.

Year

FIGURE 1.3 CO2 levels in the last 1000 years.

atmosphere and the remainder goes into the other two sinks: oceans and the land biosphere (which includes plants and soil carbon).

The present rate of anthropogenic carbon emission to the atmosphere is nearly 7 Pg/a (piga, P = 1015). During the 1990s, net uptake by the oceans was estimated at 1.7 ± 0.5 Pg/a, and by the land biosphere at 1.4 ± 0.7 Pg/a. The gross atmosphere-ocean and atmosphere-terrestrial biosphere (i.e., photosynthesis and respiration) fluxes are on the order of 100 Pg/a. Inter-annual variations in the atmospheric increase of CO2 are not attributed to variations in fossil fuel emissions but rather to small changes in these net fluxes. Most attempts to explain the inter-annual variability of the atmospheric CO2 increase have focused on short-term climate fluctuations (e.g., the El Niño/Southern Oscillation [ENSO] and post-mountain Pinatubo cooling), but the mechanisms, especially the role of the terrestrial biosphere, are poorly understood. To date, about 5% of conventional fossil fuels have been combusted. If combustion is stopped today, it is estimated that after a few hundred years, 15% of the total carbon emitted would remain in the atmosphere, and the remainder would be in the oceans.

In 2005, the globally averaged atmospheric CO2 mole fraction was 378.9 ppm, just over a 2 ppm increase from 2004. This record CO2 concentration in 2005 continues a trend toward increased atmospheric CO2 since before the industrial era values of around 280ppm. This continues the steady upward trend in this abundant and long-lasting greenhouse gas. Since 1900, atmospheric CO2 has increased by 84 ppm (22%), with an average annual increase of 1.6 ppm since 1980.

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