Can you think of some reasons why atmospheric CO2 may predictably rise and fall over the course of a year? The main reason is due to the seasonal signal of plant growth and decay in the Northern Hemisphere. What might account for the seasonal variation in CO2 concentration?
Seasonal Changes in Carbon Dioxide. This, combined with fewer trees and plants removing carbon dioxide from the atmosphere, allows concentrations to climb all winter, reaching a peak by early spring. During Northern Hemisphere spring and summer months, plants absorb a substantial amount of carbon dioxide through photosynthesis,...
This chart shows the levels of the heat-trapping gas carbon dioxide gradually rising and falling during the past 800,000 years, until recent decades when carbon dioxide levels shot up far higher than in the past. Scientists are still studying the reasons for that natural rise and fall.
After the leaves on the trees drop in the fall, the leaf litter and other dead plant material break down throughout the winter thanks to the hard work of microbes. During this decomposition, microbes respire and produce CO 2, contributing to atmospheric CO 2 levels in the process.
… comes in May… May is the turning point between all the decomposition throughout the winter months and the burst of photosynthesis that occurs with the return of leaves to the trees in spring. CO 2 measurements all over the globe reflect this pattern of peak CO 2 concentration occurring each May, regardless of the level of that peak.
In spring, plants in the Northern Hemisphere begin to grow and absorb CO2 from the atmosphere, so atmospheric CO2 concentration decreases—the line dives down. In fall, plants begin to decay and release their CO2 back into the atmosphere, so atmospheric CO2 concentration increases—the line shoots up.
During Northern Hemisphere fall and winter, when trees and plants begin to lose their leaves and decay, carbon dioxide is released in the atmosphere, mixing with emissions from human sources.
Because the northern hemisphere contains much more land than the southern hemisphere – which is mostly covered by ocean – the amount of carbon dioxide in the atmosphere increases overall during the northern winter [2].
(b) (ii) Explain why the concentration of CO2 varies with the seasons. CO2 is raw material for photosynthesis, there is an increase in the rate of photosynthesis in the summer, therefore less CO2 in the air during summer Increase in CO2 in winter because less photosynthesis due to trees losing leaves in autumn-winter.
There's more carbon dioxide in the winter and a bit less in the summer. That's the collective breathing of all the plants in the Northern Hemisphere. "Plants are accumulating carbon in the spring and summer when they're active, and they're releasing carbon back to the air in the fall and winter," Graven explains.
Because photosynthetic activity is the cause of seasonal CO2 swings, regions with more plants will experience larger fluctuations. Photosynthesis also occurs in the oceans, but little of this CO2 actually moves into the atmosphere, which is why only land photosynthesizes drive sea- sonal cycles.
As plants begin to photosynthesize in the spring and summer, they consume CO2 from the atmosphere and eventually use it as a carbon source for growth and reproduction. This causes the decrease in CO2 levels that begins every year in May.
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 many millions of years; we are returning that carbon to the atmosphere in just a few hundred.
For one thing, the mixing between the hemispheres is too slow for there to be much interaction between their two cycles. It takes roughly a year for the air to mix between the Northern and Southern hemispheres. The mixing within each hemisphere, in contrast is only weeks to months.
There is a much larger amount of land in the Northern Hemisphere, particularly with huge forested areas in Siberia, while the Southern Hemisphere is dominated by ocean, but because of the slow mixing, even if there were as much land in the south, the Mauna Loa cycle wouldn’t look very different.
While surface, aircraft, and satellite observations all provide valuable information about carbon dioxide, these measurements do not tell us the amount of carbon dioxide at specific heights throughout the atmosphere or how it is moving across countries and continents.
Carbon dioxide is the most important greenhouse gas released to the atmosphere through human activities. It is also influenced by natural exchange with the land and ocean. This visualization provides a high-resolution, three-dimensional view of global atmospheric carbon dioxide concentrations from September 1, 2014 to August 31, 2015. The visualization was created using output from the GEOS modeling system, developed and maintained by scientists at NASA. The height of Earth’s atmosphere and topography have been vertically exaggerated and appear approximately 400 times higher than normal to show the complexity of the atmospheric flow. Measurements of carbon dioxide from NASA’s second Orbiting Carbon Observatory (OCO-2) spacecraft are incorporated into the model every 6 hours to update, or “correct,” the model results, called data assimilation.
For example, dark red and orange shades represent regions where carbon dioxide concentrations are enhanced by carbon sources. During Northern Hemisphere fall and winter, when trees and plants begin to lose their leaves and decay, carbon dioxide is released in the atmosphere, mixing with emissions from human sources.
During Northern Hemisphere spring and summer months, plants absorb a substantial amount of carbon dioxide through photosynthesis, thus removing it from the atmosphere and change the color to blue (low carbon dioxide concentrations).
Near the top of the atmosphere, the blue color indicates air that last touched the Earth more than a year before. In this part of the atmosphere, called the stratosphere, carbon dioxide concentrations are lower because they haven’t been influenced by recent increases in emissions.
The OCO-2 mission represents an important advance in the ability to observe atmospheric carbon dioxide. OCO-2 collects high-precision, total column measurements of carbon dioxide (from the sensor to Earth’s surface) during daylight conditions.
Levels of carbon dioxide in the atmosphere rise and fall each year as plants, through photosynthesis and respiration, take up the gas in spring and summer, and release it in fall and winter. Now the range of that cycle is expanding as more carbon dioxide is emitted from burning fossil fuels and other human activities.
Specifically, the effect is more pronounced in the northern hemisphere, with
It takes about a year for changes in the northern hemisphere atmosphere to make their way into the southern hemisphere atmosphere (and vice versa), and even longer for those northern hemisphere changes to migrate to the South Pole. This slow mixing time means that seasonal variations are confined to the hemisphere in which they occur.
Note that all sites show a general increase in CO 2 concentrations over those 60 years. The sites in the Northern Hemisphere (Point Barrow, La Jolla, and Mauna Loa) also show seasonal variations, with the variations being the greatest at Point Barrow. The sites in the Southern Hemisphere (Christmas Island, Samoa, and the South Pole) show a much reduced seasonal variation, essentially vanishing at Samoa and the South Pole.
Overall, the measured amount of C O 2 increases, but in a cyclic pattern, as can be seen in observations shown below:
This chart shows the levels of the heat-trapping gas carbon dioxide gradually rising and falling during the past 800,000 years, until recent decades when carbon dioxide levels shot up far higher than in the past. Scientists are still studying the reasons for that natural rise and fall.
That in turn causes the oceans to release carbon dioxide to the atmosphere, much like a warm soda will bubble faster than a cold one. Because carbon dioxide traps heat, releasing it to the atmosphere causes the oceans to warm even more, which spurs the oceans to release additional carbon dioxide, and so on in a self-reinforcing cycle.
These tiny wobbles, caused by the gravitational tugs of the sun, moon, Saturn, and Jupiter, can slightly alter the amount of sunlight reaching our planet . A small alteration in the amount of energy reaching Earth’s surface can initiate changes to ...
For example, a small amount of additional sunlight reaching the Earth can cause a slight warming of the oceans.
As Texas Tech climate scientist Katharine Hayhoe explains in a video on this subject, “If we look at Earth’s history, we see that warming after the last ice age peaked about 6,000-8,000 years ago. Since then, the Earth’s temperature has been very slowly, gradually decreasing, on a long slide into the next ice age.”.
In addition, a 2019 study in the research journal Science Advances found evidence that as glaciers scraped the land, iron dust blown from the soil may have “fertilized” the ocean, boosting the growth of microscopic plants called phytoplankton, which then absorbed additional carbon dioxide.