Ag Weather Forum

As the very warm summer of 2020 continues, a report from the NOAA Climate division on global atmospheric greenhouse gas content, which was first published back in February 2020 is worth noting.

The following excerpted article from the NOAA Climate Science division summarizes the latest measurements in global atmospheric carbon dioxide content. Carbon dioxide is an important greenhouse gas which has been identified as contributing to global warming-induced climate change. The article author is NOAA Science Writer and Editor Rebecca Lindsey.

-- Bryce Anderson

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The global average atmospheric carbon dioxide (CO2) in 2018 was 407.4 parts per million (ppm for short), with a range of uncertainty of plus or minus 0.1 ppm. Carbon dioxide levels today are higher than at any point in at least the past 800,000 years.

In fact, the last time the atmospheric CO2 amounts were this high was more than 3 million years ago, when temperature was 2-3 degrees Celsius (3.6-5.4 degrees Fahrenheit) higher than during the pre-industrial era, and sea level was 15--25 meters (50--80 feet) higher than today.

Carbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy. Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over the span of many millions of years; we are returning that carbon to the atmosphere in just a few hundred years.

According to the State of the Climate in 2018 report from NOAA and the American Meteorological Society, global atmospheric carbon dioxide was 407.4 parts per million in 2018, a new record high. That is an increase of 2.5 ppm from 2017, similar to the increase of 2.2 ppm between 2016 and 2017.

In the 1960s, the global growth rate of atmospheric carbon dioxide was roughly 0.6 ppm per year. Over the past decade, however, the growth rate has been closer to 2.3 ppm per year. The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age 11,000-17,000 years ago.

Natural increases in carbon dioxide concentrations have periodically warmed Earth's temperature during ice age cycles over the past million years or more. The warm episodes (interglacials) began with a small increase in sunlight due to a tiny wobble in Earth's axis of rotation or in the path of its orbit around the Sun. That little bit of extra sunlight caused a little bit of warming. As the oceans warmed, they outgassed carbon dioxide -- like a can of soda going flat in the heat of a summer day. The extra carbon dioxide in the atmosphere amplified the initial warming.

Based on air bubbles trapped in mile-thick ice cores (and other paleoclimate evidence), we know that during the ice age cycles of the past million years or so, carbon dioxide never exceeded 300 ppm. Before the Industrial Revolution started in the mid-1700s, the global average amount of carbon dioxide was about 280 ppm.

The amount of carbon dioxide in the atmosphere has increased along with human emissions since the start of the Industrial Revolution in 1750. Emissions rose slowly to about 5 billion tons a year in the mid-20th century before skyrocketing to more than 35 billion tons per year by the end of the century.

By the time continuous observations began at Mauna Loa Volcanic Observatory in 1958, global atmospheric carbon dioxide was already 315 ppm. On May 9, 2013, the daily average carbon dioxide measured at Mauna Loa surpassed 400 ppm for the first time on record. Less than two years later, in 2015, the global amount went over 400 ppm for the first time. If global energy demand continues to grow and to be met mostly with fossil fuels, atmospheric carbon dioxide is projected to exceed 900 ppm by the end of this century.

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The full article along with additional graphics is at this link:

https://www.climate.gov/…

Bryce Anderson can be reached at bryce.anderson@dtn.com

Follow him on Twitter @BAndersonDTN

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