The carbon budget and the impact of the carbon cycle upon land, ocean and atmosphere, including global climate.
The Carbon Budget
A budget takes into account what goes into a system and what goes out. In terms of a carbon budget this would include how much carbon is emitted by various processes (such as combusting fossil fuels) compared to what can be absorbed by nature or captured by people. This can be calculated using a carbon footprint calculator, as found at https://www.carbonfootprint.com/calculator.aspx . Your carbon footprint is defined as the total amount of greenhouse gases produced to directly and indirectly support human activities, usually expressed in equivalent tons of carbon dioxide (CO2).
We could consider the carbon budget at various scales;
1. Individually – how much carbon is produced by our activities such as heating our home, the food we eat, how we get around, less how much carbon is absorbed by the plants in our gardens, our use of renewable energy like solar etc.
2. Businesses – how much carbon is produced to run the business, is it offset in any way? The cool Geography website is hosted by Ecohosting, who “Provide Carbon Neutral Web Hosting Based Entirely In The UK, Powered By Renewable Energy” 1
3. Nations – as part of international agreements countries must consider how much carbon is produced in their country compared to how much is absorbed in biological and geologic sequestration, or captured using technology.
4. Globally – this is the scale we need to address, as the carbon system is interconnected and global, so changes to the budget in one part of the world will have impacts upon other parts of the world. Since many of the carbon emissions have occurred in wealthier countries they have a bigger impact on other countries.
A summary of the size of these changes to the Carbon Budget can be seen in the table below. Many of these are human induced or Anthropogenic changes resulting from human activity since the industrial revolution.
n.b. not all fluxes considered, figures are to illustrate changes. Source – IPCC3
The diagram below shows some of these exchanges (n.b. not all fluxes are shown on the diagram and the 2 sources are different hence some of the differences in figures). It is clear from the diagram that it is land use changes like deforestation and the burning of fossil fuels that is increasing the amount of carbon in the atmosphere, at rates faster than the oceans, rocks and vegetation of the Earth can absorb.
The global carbon budget and climate change.
In 2015, the countries that signed the UN Framework Convention on Climate Change adopted a target to stop the average global temperature from rising before it reaches 2°C above pre-industrial levels.
This goal can be met if cumulative emissions of carbon do not exceed 1 trillion tonnes of carbon (GtC) 2
However, of that 1 trillion tonnes of carbon 535 GtC have already been emitted during industrial times. This leaves only 465 GtC to stay within the agreed limits.
Many developing countries also support a reduction in the target to keep global average temperature increases below 1.5°C above pre-industrial levels.
Impact of the changing carbon budget on THE LAND
The changing carbon budget can have significant impacts upon the land.
It is thought that plants on land have taken up approximately 25 percent of the carbon dioxide that humans have put into the atmosphere. 3
Overall, the world’s plants have increased the amount of carbon dioxide they absorb since 1960 although the amount they absorb varies from year to year. Only some of this increase occurred as a direct result of fossil fuel emissions.
NASA have found that increased amounts of atmospheric carbon dioxide means more carbon is available to convert to plant matter in photosynthesis. This means that plants were able to grow more. This extra growth is referred to as carbon fertilization. This extra growth is not boundless however, as plants also need water, sunlight, and nutrients, especially nitrogen. If a plant doesn’t have one of these things, it won’t grow regardless of how abundant the other necessities are. This means that the amount of extra carbon taken in from place to place on earth varies according not just to how much extra carbon there is but also factors such as water and nitrogen availability. You can see how much extra carbon fertilization is taking place on the map below.
Source: Boston University/R. Myneni
Land use decisions.
Agriculture has become much more intensive, so we can grow more food on less land.
In high and mid-latitudes, some abandoned farmland is reverting to forest, and these forests store much more carbon, both in wood and soil, than crops would.
In many places, we prevent plant carbon from entering the atmosphere by extinguishing wildfires. This allows leaf litter and woody material (which stores carbon) to build up. All of these land use decisions are helping plants absorb human-released carbon in the Northern Hemisphere.
However, this balance could be changing as more forest fires appear to be occurring releasing this stored carbon. According to NASA “In the far north, where an increase in temperature has the greatest impact, the forests have already started to burn more, releasing carbon from the plants and the soil into the atmosphere. Tropical forests may also be extremely susceptible to drying. With less water, tropical trees slow their growth and take up less carbon, or die and release their stored carbon to the atmosphere.” 3
In the tropics forests are being removed, often through fire via slash and burn, and this releases carbon dioxide.
Global warming and the land
Other impacts of the global warming element of changing carbon budgets can occur and impact upon the terrestrial environment.
1. Carbon dioxide increases temperatures, extending the growing season and increasing humidity. This has led to some additional plant growth. However, warmer temperatures also stress plants. With a longer, warmer growing season, plants need more water to survive. Scientists are already seeing evidence that plants in the Northern Hemisphere slow their growth in the summer because of warm temperatures and water shortages. 3
2. Higher temperatures can “bake” the soil, this allows the rate at which carbon seeps out to increase in some places.
3. The permanently frozen soil, the permafrost—is thawing. Permafrost contains rich deposits of carbon from plant matter that has accumulated for thousands of years because the cold slows decay. When the soil warms, the organic matter decays and carbon—in the form of methane and carbon dioxide—seeps into the atmosphere. 3
4. There is increasing evidence of complex feedback loops emerging too, an example of cattail plants can be seen in the diagram.
Impact of changes to the carbon budget in THE OCEANS
The oceans are a very important sink and source of carbon, and changes to the carbon budget can have profound impacts upon the oceans. NASA calculate that about 30 percent of the carbon dioxide that people have put into the atmosphere has diffused into the ocean through the direct chemical exchange (recall the physical carbon pump). 3
As carbon dioxide dissolves into the ocean it creates carbonic acid, and this increases the acidity of the water. This is a slight change and the ocean remains alkaline (the pH has dropped from 8.2 to 8.14), NASA state that “Since 1750, the pH of the ocean’s surface has dropped by 0.1, a 30 percent change in acidity.”
This ocean acidification is bad for many marine organisms as the carbonic acid reacts with carbonate ions that shell building creatures use to create calcium carbonate shells. This is bad for shell-based creatures making their shells thinner and more fragile, and damaging things like coral. An effect called coral bleaching can be seen on the Great Barrier Reef in Australia, where ocean acidification’s effects are already taking place. Coral bleaching is when unicellular organisms that help make up the coral begin to die off and leave the coral giving it a white appearance. 5
A benefit of this acidification of the oceans are that in the long term because the more acidic seawater will dissolve calcium carbonate rocks more which will release more carbonate ions and increase the ocean's capacity to absorb CO2.
Phytoplankton grown better in cooler nutrient rich waters, an increase in ocean temperatures could also decrease the abundance of phytoplankton. This would reduce the amount of carbon held in the oceans. A few species of phytoplankton and ocean plants might benefit from more carbon in the oceans, but most are not.
A study by Roxy (2016)6 shows that marine ecosystems are suffering because of increasing ocean temperatures. The study on phytoplankton changes in the Indian Ocean shows a decline of up to 20% in marine phytoplankton during the past six decades.
Warmer ocean water also absorbs less carbon dioxide from the atmosphere than cooler water.
Changes in sea level
Long-term measurements of tide gauges and recent satellite data show that global sea level is rising, with best estimates of the global-average rise over the last two decades centred on 3.2 mm per year. The overall observed rise since 1901 is about 20 cm. 8
The graph below derived from the IPCC shows that sea levels are predicted to continue to rise;
3. Increased temperatures in the atmosphere and ocean is causing the massive ice sheets that cover Greenland and Antarctica to melt at an accelerated pace. Scientists also believe meltwater from above and seawater from below is seeping beneath Greenland's and West Antarctica's ice sheets, effectively lubricating ice streams and causing them to move more quickly into the sea. Higher sea temperatures are causing the massive ice shelves that extend out from Antarctica to melt from below, weaken, and break off. 7 In 2002 the Larsen B Ice Shelf covering 3,250 square kilometers splintered and collapsed in just over one month.
Ocean salinity and the thermohaline conveyor
The Earth has ocean currents and wind systems that move heat from the equator northwards towards the poles then transport the cold water back towards the equator. The oceanic part of this is known as the thermohaline circulation. “Thermo” refers to temperature, “haline” refers to the salt content of the water. It works like this;
1. As ocean water moves northwards towards the higher latitudes it both cools and increases in salt content at the surface as some water evaporates and/or salt is ejected in the forming of sea ice.
2. The saltier colder water is denser and thus heavier, it drops deep into the ocean a
3. This water moves along the depths until it can rise to the surface near the equator, often in the Indian or Pacific Ocean
4. Heat from the sun then warms the cold water at the surface, and evaporation leaves the water saltier.
5. The warm salty water is then carried northwards; it joins the Gulf Stream, a large powerful ocean current that is also driven by winds.
6. The warm salty water travels up the U.S. east coast, then crosses into the North Atlantic region where it releases heat and warms Western Europe. 9
With Global warming, it is a concern that large amounts of melting ice in Greenland could dilute the salty water and weaken or even shut down this circulation. This would cool large parts of western Europe.
Impact of the carbon cycle upon THE ATMOSPHERE, with particular reference to global climate
Radiative forcing - also known as climate forcing and is the difference between insolation (sunlight) absorbed by the Earth and energy radiated back to space.
Climate forcing – the influences that cause changes to the Earth's climate system altering Earth's radiative equilibrium, forcing temperatures to rise or fall.
Enhanced greenhouse effect – The impact on global climate of additional heat retained in the atmosphere due to the additional greenhouse gasses such as Carbon dioxide that humans have emitted into the atmosphere.
The greenhouse effect describes the natural balance between incoming and outgoing solar radiation in our atmosphere. The various greenhouse gasses in our atmosphere such as carbon dioxide, methane, and halocarbons absorb a wide range of energy—including infrared energy (heat) emitted by the Earth—and then re-emit it. The re-emitted energy travels out in all directions, but some returns to Earth, where it heats the surface. Without these greenhouse gases, Earth would be a frozen planet with an average temperature of around -18 degrees Celsius. With too many greenhouse gases, Earth would be like Venus, where the greenhouse atmosphere keeps temperatures around 400 degrees Celcius. 3
The enhanced greenhouse effect includes the impact of people. Indeed, it is the impact on global climate of additional heat retained in the atmosphere due to the additional greenhouse gasses such as Carbon dioxide that humans have emitted into the atmosphere. The extra greenhouse gasses cause what is known as radiative forcing, changes to the Earth's climate system altering Earth's radiative equilibrium, forcing temperatures to rise or fall.
Energy is constantly flowing into the atmosphere in the form of sunlight that always shines on half of the Earth’s surface. Some of this sunlight (about 30 percent) is reflected back to space and the rest is absorbed by the planet. And like any warm object sitting in cold surroundings — and space is a very cold place — some energy is always radiating back out into space as invisible infrared light. Subtract the energy flowing out from the energy flowing in, and if the number is anything other than zero, there has to be some warming (or cooling, if the number is negative) going on.
There are a couple of theories that relate to climate change and why it happens, but the finger points overwhelmingly towards human enhanced global warming given the current evidence collected by scientists. The International Panel for Climate Change (IPCC) is an independent body of thousands of scientists from all over the globe and they agree that human industrial activity is to blame for the current upward trend in temperatures. This is because more of the incoming solar energy is trapped and retained by the extra greenhouse gasses.
These extra greenhouse gasses pose a long term problem, as according to NASA, to date “land plants and the ocean have taken up about 55 percent of the extra carbon people have put into the atmosphere while about 45 percent has stayed in the atmosphere. Eventually, the land and oceans will take up most of the extra carbon dioxide, but as much as 20 percent may remain in the atmosphere for many thousands of years.”3
The current level of radiative forcing, according to the IPCC AR4, is 1.6 watts per square meter (with a range of uncertainty from 0.6 to 2.4). That gives a total warming effect of about 800 terawatts — more than 50 times the world’s average rate of energy consumption, which is currently about 15 terawatts. 10
The changes in the carbon cycle can impact upon each reservoir of carbon. Excess carbon in the atmosphere warms the planet and helps plants on land grow more. Excess carbon in the ocean makes the water more acidic, putting marine life in danger.
The cause of changes to the Earth’s climate are extra greenhouse gasses. The Keeling Curve (named after scientist Charles David Keeling) is a graph of the accumulation of carbon dioxide in the Earth's atmosphere based on continuous measurements taken at the Mauna Loa Observatory on the island of Hawaii from 1958 to the present day. The graph shows rapidly increasing carbon dioxide levels in the atmosphere.
Image credit: Delorme [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Mauna_Loa_CO2_monthly_mean_concentration.svg
Over longer periods of time scientists have had to use other data sources. Scientists have drilled out a huge core of ice in Antarctica. The air trapped in bubbles in the ice can be analysed and this has shown that the Earth is normally cooler than it is now and that Ice ages are common. It also shows a very strong link between CO2 concentrations and temperature. Consider now that the graph never shows Carbon dioxide levels above 300ppm. The current level is now over 400ppm and is rising.
This has resulted in rising temperatures. We have already seen temperatures rise 1°C above preindustrial levels by 2015. Even if greenhouse gas concentrations stabilized today, the planet would continue to warm by about 0.6°C over the next century because of greenhouses gases already in the atmosphere. 11
Predictions by the IPCC show continued warming over a range of scenarios, from a low amount of carbon emissions to higher amounts. This is shown on the graph below. Model simulations by the Intergovernmental Panel on Climate Change estimate that Earth will warm between two and six degrees Celsius over the next century, depending on how fast carbon dioxide emissions grow. Scenarios that assume that people will burn more and more fossil fuel provide the estimates in the top end of the temperature range, while scenarios that assume that greenhouse gas emissions will grow slowly give lower temperature predictions. The orange line provides an estimate of global temperatures if greenhouse gases stayed at year 2000 levels.
(©2007 IPCC WG1 AR-4.)
NEXT TOPIC - Carbon & water cycles - Life on Earth
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4 - National Geographic, 2017. Ocean Acidification. Accessed the 30th December 2018 retrieved from https://www.nationalgeographic.com/environment/oceans/critical-issues-ocean-acidification/
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8 - Shum, C.K. & Kuo, C.Y. (2011). Observation and Geophysical Causes of Present-Day Sea-Level Rise. 10.1007/978-90-481-9516-9_7.
9 - Renee Cho, 2017. Could climate change shut down the Gulf Stream? Earth Institute, Columbia University. Accessed 1st of January 2019 retrieved from https://phys.org/news/2017-06-climate-gulf-stream.html
10 - David L. Chandle, 2010. Explained: Radiative forcing. MIT News. Accessed 2nd of January 2019 retrieved from http://news.mit.edu/2010/explained-radforce-0309
11 – NASA Earth bservatory, 2010. How Much More Will Earth Warm? Accessed 2nd of January 2019 retrieved from https://earthobservatory.nasa.gov/features/GlobalWarming/page5.php
Written by Rob Gamesby