Carbon dioxide in Earth's atmosphere

Although carbon dioxide in the atmosphere occurs only in a very low concentration of less than one per thousand, it is very important for life on Earth in many ways. Plants "breathe" a carbon dioxide ( CO2), it is vital for them. In breathing of animals and other natural processes of carbon dioxide is released and free to the atmosphere. CO2 the Earth's climate and by its solubility in water affected despite its low concentration on the strength of the greenhouse effect the pH of the oceans significantly.

• 4.1 control mechanism of the Earth
• 4.2 Precambrian ( Erdfrühzeit )
• 4.3 Phanerozoic
• 4.4 Ordovician to Carboniferous
• 4.5 Permian - Triassic boundary
• 4.6 Paleogene
• 4.7 Neogene and Quaternary 4.7.1 Measurement error

• 5.1 issuers
• 5.2 relative to the concentration in the oceans
• 5.3 irreversibility and uniqueness

Carbon cycle

The total amount of carbon on earth is 65.5 billion gigatons. More than 99.9 % of which are bound in the rock. In the Earth's atmosphere are, however, only 800 gigatons of carbon, equivalent to 3,000 gigatons of CO2.

In the carbon cycle, a very large amount of carbon is constantly exchanged between the atmosphere and other depots such as oceans, living things and soil. Most CO2 sources have a natural origin and are compensated by natural CO2 sinks. The atmospheric carbon dioxide concentration is influenced by the metabolism of living beings on the earth, but also of reactions that occur independently of any life, and have their origin in physical and chemical processes. The time constant, i.e. the speed of these operations varies widely, ranging from a few hours to several millennia.

The carbon dioxide concentration of the young Earth had released their origin in volcanic activity, which until now feeds the atmosphere of carbon dioxide and up to date about 130-230 megatons of carbon dioxide annually. Since the existence of the earth the trace gas is removed by weathering of rocks from the atmosphere. One part is also deposited by biogenic sedimentation and removed from the circulation so.

This abiotic processes are faced with much larger material flows, resulting from the respiration of living organisms. It is produced by a number of microorganisms from the fermentation and aerobic respiration. The natural carbon dioxide sources include the combustion of organic material by forest fires.

As CO2 dissolves well in water, changed a change in concentration of this trace gas in the air and the content of carbon dioxide and thus the pH of the oceans and seas of the earth. The increase in the atmospheric concentration of carbon dioxide since the industrial revolution has therefore led to an acidification of the oceans; almost half of the introduced by man into the atmosphere the carbon dioxide went into the oceans in solution.

Interaction with plants

Plants convert carbon dioxide through photosynthesis into sugars, especially glucose to. The required energy for this reaction they win on the absorption of sunlight by chlorophyll. The process is called photosynthesis, oxygen is produced as a waste product. This gas is discharged from the plant into the atmosphere, where it is subsequently used for the breathing of heterotrophic organisms and other plants; thus creating a cycle. Through these material flows the carbon dioxide of the atmosphere is completely replaced every 3-5 years on average. Land plants take in this case preferably on the lighter carbon isotope 12C. This effect can be measured by means of isotopic studies.

The natural decay of organic material in forests and grasslands as well as reoccurring in nature fires result in an annual release of about 439 gigatons of carbon dioxide. New plant growth compensates for this effect completely, because are thus annually about 450 gigatons absorbed.

The pre-industrial concentration of 280 ppm, as well as the current (2011) already significantly increased concentration of 390 ppm for C3 plants below the optimum for an ideal growth value. In greenhouses, the carbon dioxide content of the air is therefore artificially raised to values ​​of 600 ppm and more. By this carbon dioxide fertilization plant growth can be increased under otherwise ideal conditions, up to 40 %. In nature, such a high growth enhancement by CO2 fertilization is not to be expected, since usually limit the availability of nutrients and / or water, but not the concentration of CO2 in the air growth. Over the period 1982-2010 still a significant global effect detectable by CO2 fertilization has been found. In addition was also twice as much carbon dioxide absorbed by the biosphere as in 1960 in 2010; However, the man-made emissions have quadrupled over the period. Although 90 % of all plant species C3 plants, but 40 % of the earth's surface of C4 plants are colonized, their ecological and economic importance, therefore, is high. These respond to a CO2 fertilization only with a growth increase of a few percent, as they can absorb very well in the pre-industrial atmospheric concentration of the trace gas already.

The performance of the responsible for the photosynthesis of plants Rubisco molecule depends on its temperature, as well as the CO2 concentration in the ambient air. Although the tolerance to higher temperatures with increasing CO2 concentration also increases, is to be expected, however, that associated with the increase of CO2 concentration in the atmosphere global warming in many regions will in the future lead to a decreasing Photsynteserate and thus decreasing primary production.

The effect of elevated carbon dioxide concentration on the biosphere is being investigated as part of the FACE experiment.

Spatial and temporal variations in the atmospheric concentration

Because the metabolism of plants is directly dependent on light, near-surface CO2 concentrations fluctuate in the diurnal cycle. With adequate plant cover shows up in the night, a maximum and a minimum on the day. In and around urban centers, the CO2 concentration is high, but significantly reduced in forests compared to the surrounding area. If started indoors, the concentration increase in the wild up to ten times the average value of the mean concentration.

Looking at the profile of the concentration over several years an annual variation in the amount of 3-9 ppmv is evident in the growing season in the northern hemisphere has its cause. The influence of the Northern Hemisphere dominates the annual cycle of variation of carbon dioxide concentration, because there are far more land and thus a larger biomass than in the southern hemisphere. The concentration is highest in May in the northern hemisphere, because that takes place in the spring greening starts at that time; it reaches its minimum in October, when the photosynthetic biomass is greatest.

Due to the temperature dependence of plant metabolism, there is also a difference between equatorial CO2 concentrations with the data obtained in Arctic latitudes; these show the seasonal influence of the growth period: During the annual course of the curves äquatornah is only about 3 ppm, it lies in Arctic latitudes at 20 ppm.

In researching the carbon dioxide concentration of the atmosphere Charles Keeling pioneered. This described in the late 1950s, not only the first time the above-mentioned oscillations, but could help with the created by him Keeling curve for the first time show that the man increased the concentration of this trace gas.

Importance as a greenhouse gas

CO2 is a major greenhouse gas. It absorbs and emits infrared radiation at wavelengths of 4.26 microns ( mode shape of the asymmetric stretching) and 14.99 microns ( shear wave) and is therefore important for the strength of the greenhouse effect. In a clear sky, the share of CO2 in total greenhouse effect is 26 %.

60 % of the greenhouse effect is indeed due to water vapor, but the concentration of water vapor suspended in the atmosphere from about the Clausius -Clapeyron equation alone of the average global temperature of the Earth, so the vapor pressure and can be just about permanently altering. Water vapor acts in this way only reinforcing to global temperature changes. Thus, carbon dioxide is the main greenhouse gas whose concentration can be changed for good immediately. Since the mid 19th century, its concentration increases by human activities.

A doubling of the atmospheric CO2 concentration from pre-industrial value of 280 ppm to 560 ppm would likely result in the present state of science in global warming of 3 ° C. This value is called the climate sensitivity.

Course in Earth

Life, but also abiotic processes had always been a great influence on the carbon dioxide concentration in the atmosphere, but these were also shaped by it. Thus, there is a reciprocal relationship.

Control mechanism of the Earth

Geologically, the greenhouse effect (usually) caused by carbon dioxide in the first place was crucial. On Earth, it was very early on water in liquid form. The paradox of the weak young sun describes how it came to the young Earth despite a weak sun at elevated temperatures. The luminosity of the sun has risen by over 30% since its formation 4.6 billion years ago. This is to be seen against the background that a doubling or halving of pre-industrial CO2 concentration of 280 ppm of the same change in radiative forcing caused such a change in the solar constant by 2%. The concentration of greenhouse gases - especially carbon dioxide and methane - has significantly decreased over a self-regulating mechanism in the course of history. Increased temperature caused increased weathering of the earth's surface and precipitation of carbon dioxide in the sea in the form of lime. This decreased the carbon dioxide content, whereby the temperature dropped and weathering and precipitation decreased and the temperature leveled off in the sequence back to the old value at a lower carbon dioxide content in the atmosphere. With the large oxygen catastrophe, the change in the strength of the greenhouse effect was very rapid, as the powerful greenhouse gas methane rapidly disappeared from the atmosphere. It was followed by the Huron ice age, probably the longest piece Snowball Earth event of earth history. The earth was covered with ice to a large extent.

Volcanoes came from still greenhouse gases such as carbon dioxide, that accumulated due to the no longer held weathering and precipitation in the sea in the atmosphere. The carbon dioxide content increased as a result in a period of about 10 million years ago to extremely high values ​​increases until the greenhouse effect was strong enough to melt the ice. As a result, absorbed the now re-excavated earth's surface much more sunlight, and it was followed by some 10,000 years with a sauna global climate. Due to the now strong weathering and precipitation of the carbon dioxide content was greatly reduced and deposited huge quantities of lime in a very short time, which ultimately led them to return as before to a temperate climate, but with a significantly reduced methane and CO2 content of the atmosphere. Ultimately, that is, two abiotic climate regulators of these are responsible for ensuring that the climate in geological periods has stabilized again and again despite changing radiation power of the sun and by life itself to changes in environmental conditions at moderate temperatures: the volcanism and plate tectonics as a recycler of calcification and thus as Kohlenstoffdioxidproduzenten and weathering and precipitation as Kohlenstoffdioxidsenke.

Precambrian ( Erdfrühzeit )

Today it is believed that early after the formation of the earth 4.58 billion years existed first life forms. Cyanobacteria and algae to produce oxygen began in the Precambrian, around 3.5 billion years ago - for which they received CO2.

To determine the atmospheric carbon dioxide concentration prior to hundreds of millions of years, proxy measurements were carried out. In the context of isotope studies borates are analyzed in the shells of foraminifera. In an acidic medium 11B is increased incorporated into boric acid, which is necessary for the structure of the shell of the living beings. Thus, conclusions about the prevailing pH, including the carbon dioxide content of more water are possible. The CO2 concentration can be even with the help of Δ13C, another isotope investigation determined. In the development of the earth's atmosphere, it is assumed that the " first atmosphere " a carbon dioxide content of about 10% had.

Phanerozoic

In the wake of the great catastrophe oxygen, the oxygen concentration 543 million years before present rose in the time of the Cambrian explosion sharply. The associated transition from anaerobic to aerobic ie a metabolism that is not based on oxygen conversion of oxidative oxygen -based metabolism indeed had probably one of the first mass extinction result, but the evolution opened up new paths, since by oxidation far more energy metabolic processes is available, can use as anaerobic life forms. At the time of the Cambrian explosion of atmospheric CO2 content was (6000 ppm =) at about 0.6%.

Ordovician to Carboniferous

The appearance of the first land plants at the end of the Ordovician period 444 million years ago, the weathering of the soil increased greatly, which the atmosphere withdrew large amounts of CO2. The result was a series of ice ages. In Devon, before about 400 million years ago was the proliferation of land plants. This carbon could accumulate to a greater extent not only on the sea floor, but also on land. The CO2 content of the air was in Devon in the range of about 6000 ppm. The world's widespread coal deposits developed since that time, but mainly in the age of the eponymous carbon, ie in the period between about 360 and 300 million years ago. Since that time, the deposited plant fossils allow by analyzing the number of stomata, so the stoma to estimate the then prevailing atmospheric CO2 concentration. The diversification and the evolution of their leaves may have been partly influenced by the slowly decreasing CO2 concentration. The appearance of the white rot towards the end of the Carboniferous is probably the reason for since that time lower formation rate of coal.

Permian - Triassic boundary

250 million years ago, it came at the Permian - Triassic boundary to a 600,000 -year-long, reinforced volcanic activity, which was the cause for the formation of the Siberian Traps. It is estimated that this came about 170,000 gigatons of carbon dioxide in the atmosphere and oceans. Although alternative explanations can not be excluded, it is nowadays preferred assume that the concomitant acidification of the oceans and the massive warming of the atmosphere in conjunction with the release of an estimated 18,000 gigatons of hydrogen chloride was responsible for the greatest mass extinction in Earth's history. For comparison: since the beginning of industrialization around 2000 gigatons of CO2 emitted by mankind.

The past 200 million years include periods of extreme heat; sea ​​levels were so high that a 200 -meter-deep shallow seas trained on the continental land masses ( eg, before 100 million years ago during the warm phase of the Cretaceous period ). With the proliferation of land plants biogenic sedimentation gained increasing importance and helped to reduce over many millions of years, the atmospheric CO2 content. Between 200 million and 150 million years ago today, the CO2 content was approximately 3000 ppm.

Paleogene

Between 60 and 50 million years BP, the CO2 concentration increased. The reason was probably the very fast drift of contemporary India in the north, large amounts of the greenhouse gas arrived in the carbonate-rich in the subduction seafloor into the atmosphere. This increase took place 50 million years BP with the collision of India today with the Asian continent to an end. The subsequent unfolding of the Himalayas was the cause of the then incipient drop, which was caused by the erosion of itself auffaltenden Mountains. Shortly thereafter, 49 million BP is the Azolla event dates, which further reduced the atmospheric concentration of the greenhouse gas.

However, 55 million years ago, at the boundary between the Paleocene and Eocene, there came several times in between to large entries carbon into the atmosphere. In the Paleocene / Eocene Thermal Maximum ( PETM ) were released over a period of about 20,000 years estimated 2500-6800 gigatons of carbon. We still do not know where this carbon came; the associated global warming by about 6 ° C, however, was so great that it seems unlikely today that the greenhouse effect of carbon dioxide alone is sufficient for this. As with the occurring two million years later Eocene Thermal Maximum 2, it is nowadays mostly assume that methane for the observed strong temperature rise was the cause. Methane in the atmosphere has only a very short retention time of twelve years; it is degraded to CO2. For a methane entry is ultimately a carbon dioxide - entry. The heating phase of the PETM had a period 120000-170000 years.

34 million years ago, the CO2 content of the air reached a value of 760 ppm. The Antarctic ice sheet began to take shape its present. The associated global cooling led to a further Massenaussterbeereignis, the Grande Coupure.

There is geological evidence that about 20 million years ago CO2 concentrations fell below a value of 300 ppm and at 600 ppm, a tipping point exists, which was the main cause for the onset of Antarctic glaciation.

Neogene and Quaternary

Low carbon dioxide concentrations could have been the trigger for the evolution of C4 plants, their number increased in the period between seven and five million years before present strong. These are able to fix CO2 efficiently than C3 plants, which means an evolutionary advantage at low atmospheric CO2 concentrations.

In the Neogene ( 23 to 2.6 million years ago ) the global climate cooled further. With the formation of the Antarctic and Arctic ice sheets is another way to reconstruct the CO2 content of the atmosphere of bygone days was long. This method is considerably more accurate than the methods based on the analysis of rock samples. The longest, obtained in the Antarctic ice cores ranging to 800,000 years in the past. In these tiny air bubbles are trapped, their CO2 content has been preserved. The vast number of studies comes from a variety of Antarctic ice cores.

During the 800,000 year CO2 concentrations between 180-210 ppm varied during the ice ages and rose to values ​​280-300 ppm during the warmer interglacial to. The results of the analysis of ice cores indicate that atmospheric CO2 levels were ppmv in the range 260-280 before the start of industrial emissions. The concentration did not vary greatly over the last 10,000 years. In 1832 the concentration was in the Antarctic ice cores at 284 ppmv.

The beginning of human agriculture during the current Holocene could be closely linked to the increase in atmospheric carbon dioxide concentrations, which was observed at the end of the last ice age. This carbon dioxide fertilization could increase plant growth and reduced the need for a high permeability of the stoma for effective CO2 uptake, which in turn reduced the water loss through evaporation and water use of the plants made ​​more efficient.

Measurement error

A study presented the assertion stable CO2 concentrations during the current interglacial the last 10,000 years in question. Based on an analysis of fossil leaves argued Wagner et al., That the concentration of CO2 in the period 7000-10000 years before present siginifikant higher ( ~ 300 ppm) were and there were substantial changes that have been accompanied by changes in climate. From third parties that claim is disputed and noted that it is much more likely to calibration problems is acting as to actual changes in carbon dioxide concentration. Greenland ice cores often indicate higher and more varying CO2 concentrations, which is caused by in-situ decomposition of calcium carbonate dust, which was found in the ice. Whenever the concentration of dust in Greenland was low - as is almost always the case in Antarctic ice cores - which is reported good agreement between Arctic and Antarctic measurements.

Anthropogenic increase in CO2 concentration

The anthropogenic input of CO2 equals just 3 % of the annual natural emissions, but 97% of natural emissions of natural sinks are again completely absorbed. The man-made entry in the carbon cycle has been taken so far, however, only about half of oceans, soils and plants, which has led since the mid-19th century to a steady increase in concentration in the atmosphere. In comparison, the released amount of CO2 from volcanoes is less than 1% of the released from the crowd.

The atmospheric CO2 concentration exceeded already in 1850 for the first time values ​​that were not observed in ice cores of previous millennia. The rate of increase has accelerated since then steadily. In 2011, a concentration of 390 ppm ( parts per million) was achieved; they had risen between 2000 and 2009 at an annual 2.0 ppm. This current concentration is about 39% above the pre-industrial value of 280 ppm, as it existed in pre-industrial times, higher than at any time during the past 800,000 years and likely to be higher than they ever had in the course of the last 20 million years.

The recent dramatic rise in CO2 concentration is due entirely to human activities. Researchers know this for three reasons: On the one hand you can see the liberated carbon dioxide amount calculated on the basis of different national statistics; on the other hand one can examine the ratio of carbon isotopes in the atmosphere, since the combustion of long time buried carbon release from fossil fuel CO2, which has a different isotope ratio than live plants. This enables researchers to distinguish between natural and man-made contributions to the CO2 concentration. And third, a combustion leads not only to an increase in CO2 concentration, but to the same extent also to a decrease in the O2 concentration in the atmosphere. In contrast, a volcanic CO2 release is not associated with a decrease in oxygen concentration. Through measurements of atmospheric O2 content it was clearly demonstrated that the CO2 released for the most part comes from burns and is not of volcanic origin.

The burning of fossil fuels like coal and petroleum is the main reason for the anthropogenic increase of CO2 concentration; Deforestation is the second most important cause. In 2012, 9.7 gigatons of carbon, or 35.6 gigatons of CO2 released from the burning of fossil fuels and cement production. In 1990, there were 6.15 gigatons of carbon or 22.57 gigatons of CO2; it is this, an increase of 58 % in 23 years. Changes in land use in 2012 led to a release of 0.9 gigatonnes in 1990, there were 1.45 gigatons. Estimated to be between 13 % and 40 % of the average world released by the burning of fossil fuels amount of carbon were emitted alone In the large-scale Asian Smogereignis of 1997. In the period 1751-1900 about 12 gigatons of carbon in the form of carbon dioxide released by the burning of fossil fuels. This means that the emitted globally in 2012 alone carbon dioxide corresponding to 80 % of the 1750-1900 global liberated in the 150 years amount of substance.

The energy stored in the global terrestrial vegetation carbon amount grew from about 740 billion tons in 1910 to 780 billion tons in 1990.

Issuers

The five largest emitters of carbon dioxide are tabulated below.

The five countries with the highest CO2 emissions per capita are:

There have been proposed several techniques to remove this excess CO2 from the atmosphere and spend in carbon sinks.

Relative to the concentration in the oceans

The Earth's oceans contain in the form of bicarbonate and carbonate ions, a large amount of carbon dioxide. It is about 50 times the quantity which is in the atmosphere. Bicarbonate is formed by reactions between water, rock and carbon dioxide. An example is the solution of calcium carbonate:

Changes in the concentration of atmospheric CO2 concentrations are attenuated by reactions such as these. Since the right side of the reaction produces an acid component, the supply of the CO2 leads to the left hand side to a lowering of the pH of seawater. This process is known as ocean acidification known ( the pH of the ocean becomes more acidic, even when the pH in the alkaline range remains ). Reactions between carbon dioxide and non- carbonate rocks next to lead to a rise in concentration of bicarbonate in the oceans. This reaction can be reversed later and leads to the formation of carbonate rocks. This produced large amounts of carbonate rock over the course of hundreds of millions of years.

Currently, about 57 % of the CO2 emitted by man of the biosphere and the oceans are removed from the atmosphere. The ratio between remaining in the atmosphere for a total emitted carbon dioxide quantity is named after Charles Keeling airborne fraction; The proportion varies around a short-term agents, but is typically about 45 % over a long period of five years. One third to one half of the captured carbon dioxide by the oceans went into the ocean areas south of the 30th parallel in solution.

Ultimately, most of the carbon dioxide released by human activities will go into the seas in solution, an equilibrium between the air concentration and the concentration of carbonic acid in the oceans is achieved after about 300 years. Even if a balance will be achieved, including carbonate minerals dissolve in the oceans, there is the increased concentration of bicarbonate and the decreasing or unchanged concentration of carbonate ions to a rise in concentration of non- ionized carbonic acid, and above all an increased concentration of dissolved carbon dioxide lead. This will, in addition to higher average global temperatures, even higher equilibrium concentrations of CO2 mean in the air.

Due to the temperature dependence of the Henry's constant, solubility of carbon dioxide in water increases with increasing temperature.

Irreversibility and uniqueness

The combustion of the resources of all currently known fossil fuels would make it possible to let the CO2 content of the atmosphere rise to approximately 1600 ppm. This would make the earth - warm between 4 ° C and 10 ° C, which would lead to unimaginable consequences - depending on the true value of the climate sensitivity, the one currently knows only approximately.

To stop the increase in the concentration in the air at present about 2 ppm per year, CO2 emissions would be abruptly reduced by 55%. In this case, there would be for a short time, a balance between the human and the natural emissions, the CO2 receiving reservoir. As they are, however, increasingly saturated need emissions by the year 2060 to be reduced in order to prevent a further increase to be 20% of the current rate.

As a border with an exceedingly dangerous global warming 2 ° C were fixed, it is the so-called two -degree target. To achieve this objective, global emissions would need in 2050 by 48% to 72 % be less than the emissions of the year 2000.

In one study, it was assumed that the CO2 input is completely stopped at a certain point and is calculated for a long time einstellenen concentrations. Regardless of whether the maximum concentration at which the emissions completely stopped, stood at 450 ppmV ppmV or at 1200, remained on the course of the third millenium, a relatively constant share of 40 % of the applied amount in the atmosphere. Judging from pre-industrial 280 ppmV and currently (2011) 390 ppmv atmospheric Kohlenstoffxioxid concentration off, this means that 40 % of the applied amount of ( 390 ppmV - 280 ppmv ) * 40 % = 110 ppmV * 40 = 44 ppmV without measures of geoengineering remained until the end of the third millennium in the atmosphere. But only if the end of 2011 any, derived from fossil fuels, emissions would have been stopped. The concentration in the air would then be 324 ppmv at the end of the third millennium.

After has formed a balance between the concentration between oceans and atmosphere, CO2 is then, so bound via the much slower running CaCO3 weathering the carbonate weathering. Computed David Archer of the University of Chicago, that even after 10,000 years, about 10% of the originally additionally introduced carbon dioxide amount are thus located in the atmosphere. This period is so long, that this very slow-acting feedback mechanisms such as the melting of Antarctic ice sheets or the decay can be significantly affected by methane hydrates. So it could be that the next ice age cycle could be greatly reduced or even suppressed, which is expected in the next year tens of thousands. Archer and other authors point out that in the public perception of the longevity of the carbon dioxide - is rarely addressed, however, is a non -setting of the hand to the fact - as opposed to the much-discussed waste radioactive fission products. During the Paleocene / Eocene temperature maximum large amounts of carbon were placed in the atmosphere. Investigations have shown that the duration of the heating, caused by good agreement with the model.

View

It is assumed that the Karbonatverwitterung will be saturated in about 30,000 years, and thus can not cause any further reduction in the concentration of CO2 in the atmosphere and oceans. Since then acting silicate weathering proceeds more slowly again, in 100 000 years ago for about 5% of the people brought in by the amount of carbon will be found in the atmosphere. In about 400,000 years the amount of carbon will assume the value back in the atmosphere and oceans, which had stock before human intervention in the carbon cycle.

On time scales of billions of years, the trend of decreasing CO2 concentration seems inexorably converge, as the occasional massive historical releases of carbon buried by volcanic activity are increasingly rare (as the mantle cools and the geothermal gradient is slowly deteriorate ). The speed of these processes, however, is extremely small; so they have no relevance to the atmospheric carbon dioxide concentration of the next hundred, thousand or million years.

Assuming that the influence of humanity to release the deposited carbon, will be avoided in future, the long-term trend looks like this: Plant life on land will die completely, as the majority of the remaining carbon in the atmosphere over a period of billions of years in the soil will be deposited, because the natural release of carbon dioxide by tectonic activity is expected to weaken by further decreasing radioactivity in the Earth's interior as well. Some microbes can carry out photosynthesis at CO2 concentrations of a few ppm on. Last life forms would probably die because of rising temperatures and loss of atmosphere when the sun is to the red giant in about 4 billion years ago. The loss of plant life is next to lead to the eventual loss of oxygen.