CO2: Endless warming

Carbon dioxide is the number one reason for man-made climate change. But what is carbon dioxide, and why is it harmful?
Protestors dressed in CO2 molecule costumes, demonstrate in Essen, Germany, as part of the .../ Credits: Reuters

Contribution to Human-Induced Climate Change: 70 percent
Global Warming Potency (100 years): 1 (benchmark to other gases

Carbon dioxide is the second most important greenhouse gas behind water vapor, but the most important contributor to anthropogenic climate change. Methane and ozone are more potent, but have less effect on climate change due to their smaller atmospheric concentrations.

The amount of carbon dioxide (CO2) in the atmosphere has been in flux throughout the Earth’s history, but the United Nations Intergovernmental Panel on Climate Change (IPCC) estimates that in pre-industrial times CO2 made up around 280 ppmv (parts per million volume) of the Earth’s atmosphere.

Since the beginning of the Industrial Revolution, however, the average amount of carbon dioxide in the atmosphere has increased by nearly 40 percent from an estimated 280 to more than 380 ppmv.

Carbon dioxide has always been with us. Scientists say Earth’s earliest atmosphere was made up mostly of steam, carbon dioxide, and ammonia from volcanic eruptions.

Today, carbon dioxide is naturally produced by the combustion of organic matter like coal, oil, and wood, and the fermentation or respiration processes of living organisms.

People are another source. The air we exhale is made up of about 4.5 percent CO2. Bacteria in the soil release CO2 when they digest leaves and carcasses. Even plants that usually absorb CO2 'exhale' it at night.

Role and Uses

CO2 is one of the most important substances on Earth. Besides providing warmth to the world, it is the world’s most important fertilizer.

Plants, phytoplankton, and algae need the gas for their photosynthesis to produce sugar and to grow. While doing so they absorb and bind carbon dioxide and produce oxygen. That is why forests are one of the world’s most important absorbers of CO2, otherwise known as 'carbon sinks'.

There are a number of artificial uses of carbon dioxide, in fire extinguishers, as dry ice and, as the food additive E290, CO2 adds the fizz to soft drinks and sparkling water.

The increase in CO2’s share of the atmosphere is mostly due to anthropogenic (man-induced) factors, such as burning fossil fuels, deforestation, and industrial production.

Most anthropogenic CO2 is produced by energy production and transport. Cement production is just one among many chemical processes that release the gas. Rotting organic materials release CO2, and so landfills are big CO2 contributors too.

In total, humans emit around 32 gigatons of carbon dioxide each year. Half of this stays in the atmosphere; the rest is absorbed by oceans and vegetation.

But with sharp increases in man-made CO2 emissions, the natural CO2 cycle has been thrown out of balance: vegetation can no longer transform the same proportion of CO2 into oxygen, and oceans are steadily reaching saturation level.

Theoretically, rising CO2 levels should be compensated for by plants and algae. Up to a certain concentration, more CO2 means more photosynthesis and more growth.

Unfortunately, under hot and dry conditions many plants close their pores to prevent the loss of water and switch to a process called photorespiration during which they consume oxygen and produce carbon dioxide. Only areas with enough precipitation and fertile soils will see increased growth as a result of rising CO2 levels.

The result is an enhanced greenhouse effect and, subsequently, climate change. While CO2 is only responsible for 20 percent of the natural greenhouse effect, it accounts for about 60 percent of the anthropogenic greenhouse effect that is causing the current global warming.

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