http://co2.cms.udel.edu/Increasing_Atmospheric_CO2.htm
Increasing Atmospheric Carbon Dioxide
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There is good evidence that the level of atmospheric carbon dioxide (CO2) today is more than 25% higher than at any time in the past 420,000 years. The recent increase in atmospheric CO2 has occurred since the beginning of the “industrial” era (defined as since 1750) and most of that increase has occurred over the past 50 years. The increase in atmospheric CO2 is primarily from burning of fossil fuels (land-use changes and cement manufacturing also contribute) with half of this increase having occurred since the mid 1970s.
Direct Measurements of Carbon Dioxide
Scientists from the Scripps Institution of Oceanography have been measuring the level of CO2 in the atmosphere at the Mauna Loa Observatory in Hawaii since the late 1950s. They have found an increase from 316 parts per million (ppm) in 1959 to 382 ppm in 2006. The unit ppm represents 1 part CO2 per 1 million parts air. Figure 1 shows this record.
please see graph at:
http://co2.cms.udel.edu/Increasing_Atmospheric_CO2.htm
Figure 1. Record of atmospheric carbon dioxide from the Mauna Loa Observatory; atmospheric CO2 concentrations in parts per million (ppm) are shown on the y-axis against time for almost 50 years. Monthly average values are given as individual points. Plotted using data from CDIAC website (see References section for information).
In Figure 1 the overall trend upward from the late 1950s through the present shows the “sawtooth” pattern of the annual cycle caused by the growth and decay of plants. These seasons correspond to those in the Northern Hemisphere for the Mauna Loa record.
This increase is seen worldwide, with a slightly different seasonal pattern depending on the location, but with the same total increase. CO2 measuring stations have been established from the tropics to polar regions and many have been making measurements for decades. Since the atmosphere mixes relatively rapidly, the average concentration is fairly similar everywhere in the world. Many of these data sets can be found at the US Department of Energy CDIAC (Carbon Dioxide Information Analysis Center) website at the Oak Ridge National Laboratory (see References section for information).
Information from Ice Cores - Digging into the Past
With mounting evidence of rising CO2 levels, scientists have tried to determine whether our planet had previously experienced similar CO2 increases. The answer has been found in the frozen ice in Greenland and Antarctica.
Air bubbles frozen in glacial ice tell about the concentration of atmospheric gases at the time the ice was formed. It is possible to drill into glaciers and collect ice samples, or cores; younger ice is at the top of the core while older ice is found deeper. This method has been used to learn about atmospheric conditions several hundreds of thousands of years ago.
Through analysis of the ice cores, scientists have learned that atmospheric CO2 levels and temperatures varied over the past 420 thousand years; CO2 and temperature followed similar patterns. During the coldest periods, marked by maximum glacial coverage, CO2 concentrations hovered near 190 parts per million (ppm). When temperatures warmed and glaciers retreated, CO2 concentrations were much higher but never exceeded 300 ppm until recently. This pattern is illustrated in Figure 2.
please see graph at:
http://co2.cms.udel.edu/Increasing_Atmospheric_CO2.htm
Figure 2. Historic atmospheric CO2 levels and air temperatures over the past 420,000 years reconstructed from ice cores taken at the Vostock ice station in Antarctica. Time is shown on the x-axis (horizontal) as years before present (BP); atmospheric concentration of CO2 is shown on the y-axis (vertical) as parts per million (by volume " ppmv). Figure derived from Petit et al, 1999 (see References section for information).
Figure 2 has been interpreted with the background knowledge that glacial events over the past one to two million years show periods of about 100 thousand years. This longer record has been supplemented with shorter cores from Antarctica and Greenland which show that between about 1000 AD and the mid-1800s, atmospheric CO2 was fairly constant at about 290 ppm. Since the mid-1800s (within the industrial era), CO2 levels have climbed to levels not reached at any time in the past half million years. Scientists link this finding to a simultaneous increase in CO2 emissions caused by human activities.
Emissions of Carbon From Human Activities
Several human activities release CO2 into the atmosphere (called anthropogenic, human-origin, emissions). Fossil-fuel burning is the predominant anthropogenic source of CO2, but cement production and other activities also contribute (including the “land-use” activity of deforestation). Using a combination of modern and historic data, scientists estimate that humans have sent a total of 305 billion metric tons of carbon into the atmosphere since 1751; half of these emissions have occurred since the mid-1970s (Figure 3).
please see graph at:
http://co2.cms.udel.edu/Increasing_Atmospheric_CO2.htm
Figure 3. Annual emissions of carbon to the atmosphere from 1751 to 2003 due to anthropogenic (human-caused) sources, primarily from fossil-fuel burning. Plotted using data from CDIAC website (see References section for information).
Today, atmospheric CO2 levels are 25% greater than at any time in the past 420,000 years. Human activities, primarily the burning of fossil fuels, but also including land-use activities, are responsible for the increase.
There has been considerable research and analysis of increased atmospheric CO2 and global warming; see section on “Climate Change”. About half of the recent emissions are not accumulating in the atmosphere, but are going into the ocean and, to a lesser extent, into soils. These are considered “sinks” in the global carbon budget because they take up atmospheric CO2. The chemistry of the ocean changes as a result of increased CO2 concentrations; this subject is further examined in the section on “Ocean Acidification”.
