Natural increases in carbon dioxide concentrations have periodically warmed Earth’s temperature during ice age cycles over the past million years or more. Photos courtesy Nina Bednarsek, NOAA PMEL. ( right) A shell exposed to more acidic, corrosive waters is cloudy, ragged, and pockmarked with ‘kinks’ and weak spots. ( left) A healthy ocean snail has a transparent shell with smoothly contoured ridges. This drop in pH is called ocean acidification. Since the start of the Industrial Revolution, the pH of the ocean's surface waters has dropped from 8.21 to 8.10. It reacts with water molecules, producing carbonic acid and lowering the ocean's pH (raising its acidity). According to observations by the NOAA Global Monitoring Lab, in 2021 carbon dioxide alone was responsible for about two-thirds of the total heating influence of all human-produced greenhouse gases.Īnother reason carbon dioxide is important in the Earth system is that it dissolves into the ocean like the fizz in a can of soda. By adding more carbon dioxide to the atmosphere, people are supercharging the natural greenhouse effect, causing global temperature to rise. Without carbon dioxide, Earth’s natural greenhouse effect would be too weak to keep the average global surface temperature above freezing. Unlike oxygen or nitrogen (which make up most of our atmosphere), greenhouse gases absorb heat radiating from the Earth’s surface and re-release it in all directions-including back toward Earth’s surface. Why carbon dioxide mattersĬarbon dioxide is Earth’s most important greenhouse gas: a gas that absorbs and radiates heat. CO 2 emissions data from Our World in Data and the Global Carbon Project. Atmospheric CO 2 data from NOAA and ETHZ. NOAA graph, adapted from original by Dr. Emissions rose slowly to about 5 gigatons-one gigaton is a billion metric tons-per year in the mid-20 th century before skyrocketing to more than 35 billion tons per year by the end of the century. The amount of carbon dioxide in the atmosphere (blue line) has increased along with human emissions (gray line) since the start of the Industrial Revolution in 1750. 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. Over the next half century, the annual growth rate tripled, reaching 2.4 ppm per year during the 2010s.

In the 1960s, the global growth rate of atmospheric carbon dioxide was roughly 0.8± 0.1 ppm per year.

The more we overshoot what natural processes can remove in a given year, the faster the atmospheric concentration of carbon dioxide rises. Because we put more carbon dioxide into the atmosphere than natural sinks can remove, the total amount of carbon dioxide in the atmosphere increases every year. Since the middle of the 20 th century, annual emissions from burning fossil fuels have increased every decade, from close to 11 billion tons of carbon dioxide per year in the 1960s to an estimated 36.6 billion tons in 2022 according to the Global Carbon Budget 2022.Ĭarbon cycle experts estimate that natural “sinks”-processes that remove carbon from the atmosphere-on land and in the ocean absorbed the equivalent of about half of the carbon dioxide we emitted each year in the 2011-2020 decade. Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over many millions of years we are returning that carbon to the atmosphere in just a few hundred. NOAA image, based on Mauna Loa monthly mean data from NOAA Global Monitoring Lab.Ĭarbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy. In May 2023, carbon dioxide hit 424 ppm-a new record. At Mauna Loa, the highest monthly value each year occurs in May. The long-term trend of rising carbon dioxide levels is driven by human activities. The seasonal cycle of highs and lows (small peaks and valleys) is driven by Northern Hemisphere summer vegetation growth, which reduces atmospheric carbon dioxide, and winter decay, which increases it. This graph shows the station's monthly average carbon dioxide measurements since 1958 in parts per million (ppm).

The modern record of atmospheric carbon dioxide levels began with observations recorded at Mauna Loa Observatory in Hawaii.

Importance of carbon cycle