Changes in Temperature and CO2 in the Atmosphere at Various Latitudes

doi:10.21203/rs.3.rs-3867321/v1

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Changes in Temperature and CO₂in the Atmosphere at Various Latitudes

https://doi.org/10.21203/rs.3.rs-3867321/v1

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The satellite-based Earth surface temperature, ENSO index, and change rate of the CO₂ concentration (ppm/year) were strongly correlated over the 40 years of observation, as reported in the previous paper. The temperature changed approximately one year after the ENSO index changed, and the change rate of the CO₂ concentration followed the temperature change by several months. CO₂ emission and absorption at the Earth’s surface respond to temperature changes. In this study, satellite-based Earth surface temperatures and change rates of CO₂ concentrations were further investigated at various latitudes. These two variables were correlated even at various latitudes. The change rate of the CO₂ concentration at northern latitudes responded to temperature changes more than that at southern latitudes. The change rates of CO₂ concentrations at various latitudes between 2008 and 2011 and between 2014 and 2017 during El Niño periods were compared, but the change rates of CO₂ concentrations at low latitudes were quite different between the two periods. Additionally, the change rate of the CO₂ concentration at the sine latitude of 0.75 (≒50 N) significantly responded to temperature changes regardless of ENSO occurrence. Furthermore, the temperature difference between the land and sea is greater in the north (20 N-90 N) than in the south (20S-90S). All these results support previous interpretations: (1) CO₂ emissions due to higher temperatures are related to plant respiration or decomposition processes, and (2) temperature changes first, after which the change in CO₂ concentration follows temperature changes by several months. These propositions are important for understanding today's warming period.

Atmospheric Sciences

Global temperature

Atmospheric CO2 concentration

Latitude

El Niño

Plant respiration

Plant distribution

Land-to-sea ratio

Carbon cycles

It is estimated that the global temperature has been 15±1°C for more than 2,000 years [1,2]. CO₂ concentrations in the atmosphere have changed during this period to some extent according to proxy records, and recent direct observations of CO₂ concentrations have shown that the CO₂ concentration steadily increases every year [3]. The change rate of the CO₂ concentration in the atmosphere is the change in the CO₂ concentration (rco₂) during a predetermined period and can be expressed as drco₂/dt, such as an annual change, for example, “ppm/year”. The major functions affecting drco₂/dt are (1) plant photosynthesis, (2) CO₂ solubilization into the ocean, and (3) plant decomposition or respiration [4]. For a small temperature range such as ±1°C, drco₂/dt may be considered to be approximately proportional to the temperature change, as shown in eq. (2) [5]:

drco₂/dt ≒ a rate of photosynthesis + a solubilization rate into sea + a decomposition rate　 (1)

≒ γ ΔT (γ: constant, ΔT: temperature change) (2)

Eq. (2) indicates that drco₂/dt is linearly dependent on ΔT in the small temperature range of 15±1°C.

Satellite-based temperature observations began in 1979, while direct CO₂ observations at the Mauna Loa Observatory, Hawaii, began in 1958. We compared satellite-based University of Alabama in Huntsville (UAH) Earth surface temperatures, the National Oceanic and Atmospheric Administration (NOAA) El Niño-Southern Oscillation (ENSO) index, and drco₂/dt data in the previous paper [6]. These three variables were strongly correlated over the 40 years of observation. Temperatures changed approximately one year after the ENSO index changed, and drco₂/dt followed ΔT by several months. CO₂ emission and absorption at the Earth’s surface respond to ΔT, as shown in the previous paper [6]. This finding supports eq. (2).

Eq. (2) was proposed by Murry Salby [7, 8] and can also be expressed with eq. (3). In other words, the CO₂ concentration may be approximately determined by the integral value of ΔT.

(3)

Since vegetation varies with global location and surface conditions such as moisture [7,8], the constant γ may change with global location and surface conditions. In this paper, we investigate the correlation between drco₂/dt and ΔT at various latitudes. This approach could help us better understand the process of global warming.

Atmospheric Data

Since 1979, NOAA satellites have been carrying instruments that measure natural microwave thermal emissions from oxygen in the atmosphere [9]. Every month, the UAH updates global temperature datasets that represent the piecing together of temperature data from a total of fifteen instruments flying on different satellites over the years. Further details are available [9]. Temperatures were obtained from the datasets, and the 13-month average of lower troposphere anomaly values was used.

The raw atmospheric CO₂ concentration data at different sine latitudes between 1979 and 2022 were obtained from NOAA, and other analytical data reported in this paper are available on the website [10].

Figure 1(a) shows a trend of ΔT in the tropics (20 S-20 N), north latitude (20 N-90 N), and south latitude (20 S-90 S) between 1984 and 2011. Figure 1(b) shows the drco₂/dt values across latitudes from north to south for the same duration [11]. Two variables are correlated even at the same latitudes during the observed 27 years. As shown in the previous paper, as temperatures change approximately one year after the ENSO index changes [6], the ΔT in the tropics strongly responds to El Niño, as shown in Figure 1(a). However, the drco₂/dt values at other latitudes are different, as shown in Figure 1(b). In general, drco₂/dt at higher northern latitudes more strongly responds to temperature changes.

To examine the response of drco₂/dt to ΔT at various latitudes, two variables were further compared between 1979 and 2022 in the tropics, at northern latitudes, and at southern latitudes. ΔT in the tropics again strongly responds to El Niño, as shown in Figure 2(a). The increasing trend in temperature is greater in the north (20 N-90 N) than in the south (20 S-90 S). It can be seen that drco₂/dt at a sine latitude of 0.75 (≒50 N) responds more strongly to ΔT than does that in the tropics, as shown in Figure 2(b).

Let us investigate three temperature points, α, β, and γ, in Figure 2(a) and α’, β’, and γ’ in Figure 2(b). The times (years) at which the two local maximum values, ΔT (α, β, and γ) and drco₂/dt (α’, β’, and γ’), are reached are almost the same. Figure 3 shows the CO₂ concentrations (ppm, left scale) at Barrow, AK (71 N, green), Mauna Loa, HI (19 N, red), and Tutuila, American Samoa (14S, purple) and the changes in temperature anomalies (℃, cyan, right scale) at northern latitudes (20 N-90 N) between 1979 and 2022. The timing of the CO₂ concentration response to ΔT (α and γ; see red arrows in Figure 3) is delayed by several months. Moreover, the CO₂ concentration at Barrow annually changes much more than that at Mauna Loa and Tutuila. The result is the same in that drco₂/dt at a sine latitude of 0.75 (≒50 N) significantly responds more strongly to ΔT than does that in the tropics, as shown in Figure 2(b).

The average annual increase rates of the CO₂ concentration between 1979 and 2022 (see Figure 2(b)) are 1.85, 1.90 and 1.83 (ppm/year) for the tropics (20 S-20 N), the northern latitudes (20 N-90 N), and the southern latitudes (20S-90S), respectively. The global CO₂ concentration increased at these rates during the study period, as shown in Figure 3. Although the CO₂ concentration steadily increased during the present warming period, it is not clear whether this change in CO₂ concentration caused an increase in the global temperature, as shown in Figures 1-3.

Figures 4(a) and 4(b) show the drco₂/dt (ppm/year) at sine latitudes of 0, 0.25, 0.50, 0.75, and 1.0) between 2008 and 2011 and between 2014 and 2017. These periods correspond to β and γ in Figure 2(a) and to β’ and γ’ in Figure 2(b), respectively. Both periods are El Niño events, but the drco₂/dt values at sine latitudes of 0 and 0.25 are quite different for both periods. Additionally, drco₂/dt at a sine latitude of 0.75 (≒50 N) significantly responds to ΔT regardless of ENSO occurrence.

CO₂ is emitted into the atmosphere from the Earth’s surface during El Niño, as shown in a previous paper [6]. One of the factors affecting CO₂ emissions includes plant respiration. Plant respiration occurs in plant cells, but the process mediated by bacteria is also another form of respiration by which plant-derived material such as fallen leaves decomposes. Overall, respiration (or decomposition) consumes O₂ and releases CO_2, as shown in the following equation.

C₆H₁₂O₆ + 6 O₂ = 6 CO₂ + 6 H₂O + energy (4)

C₆H₁₂O₆ denotes representative plant debris. Respiration increases with increasing temperature. Four lines of evidence to support this interpretation are shown in the paper. The difference in vegetation on Earth for plant respiration affecting CO₂ emissions was investigated between land and sea in this study. Figure 5 shows the temperature changes in the southern (20S-90S) and northern (20 N-90 N) regions for land and sea, respectively, between 1979 and 2022. The difference in temperature between the land and sea is greater in the north (20 N-90 N) than in the south (20 S-90 S). The larger difference in the north between land and sea may reflect the difference in vegetation.

Plant photosynthesis and respiration play critical roles in the carbon cycle, as discussed in a previous paper [6], and the CO₂ concentration changes seasonally. As shown in Figure 3, the change in seasonal CO₂ concentration becomes greater in the north. Figure 6 shows a forest biomass map [12], and Figure 7 shows the ratio of land to sea on Earth [13]. Land occupies approximately 30% of the Earth, and 30% of the land is forest. Approximately 10% of the Earth's surface is covered with forests. Subarctic forests extend to 50 N-70 N in the Northern Hemisphere. In the Southern Hemisphere, it can be detected only at the southern tip of South America. The Southern Hemisphere has a small land area and a small forest area. On the other hand, the Northern Hemisphere has a large land area and a large forest area. Furthermore, compared to that in the tropics, the annual temperature change in the tropics is greater at higher latitudes. Therefore, changes in the amount of decomposed plant matter throughout the year are thought to increase in the Northern Hemisphere and further north.

Finally, we summarize the following points (see Figure 6 and Table 1).

The global average ΔT was correlated with the global average drco₂/dt in CO₂ in previous work, while the same correlation was observed at the same latitudes from north to south in this study.
drco₂/dt followed ΔT for several months, and CO₂ emissions at the Earth’s surface responded to temperature fluctuations in previous work. Similarly, drco₂/dt followed ΔT at the same latitudes in this study.
However, the correlation between two variables differs depending on the latitude. In addition, the drco₂/dt at a sine latitude of 0.75 (≒50 N) responds to ΔT regardless of whether ENSO occurs and responds more strongly to ΔT than does that in the tropics.
The difference in ΔT between land and sea is greater in the north (20 N-90 N) than in the south (20 S-90 S). The temperature increase trend is greater in the north (20 N-90 N) than in the south (20 S-90 S).
All the results obtained in this study support previous interpretations: (1) CO₂ emissions due to higher temperatures are related to plant respiration or decomposition processes, and (2) temperature changes first and then drco₂/dt follows ΔT suggested by equation (2) drco₂/dt = γ ΔT (γ: constant, ΔT: temperature change).
The constant γ in eq. (2) may change depending on the vegetation type at different latitudes. The impact of plant respiration on carbon cycles may be much greater than expected. This proposition is important for understanding modern warm periods.

NOAA: The National Oceanic and Atmospheric Administration

ENSO Index: El Niño-Southern Oscillation Index

UAH: The University of Alabama in Huntsville

drco₂/dt: The change rate of the CO₂ concentration or CO₂ growth rate

ΔT: Temperature change

IPCC Assessment Report https://www.ipcc.ch/assessment-report/ar6/
https://www.drroyspencer.com/global-warming-background-articles/2000-years-of-global-temperatures/
NOAA database, https://gml.noaa.gov/ccgg/trends/gl_trend.html
IPCC Assessment Report https://www.ipcc.ch/site/assets/uploads/2018/02/Fig6-01-2.jpg
General information is available from https://www.encyclopedie-environnement.org/en/life/effects-temperature-on-photosynthesis/#Effects%20of%20Temperature%20on%20Photosynthesis:%20Summary%20Diagram; https://cid-inc.com/blog/plant-respiration-its-importance-and-applications/; https://pubs.acs.org/doi/epdf/10.1021/ja01861a033
Nishioka, M. Changes in Temperature and CO₂ Concentration Induced by El Niño, Sci Rep in press
Salby, M. Relationship Between Greenhouse Gases and Global Temperature. Video Presentation, April 18, 2013. Helmut-Schmidt-University Hamburg https://www.youtube.com/watch?v=2ROw_cDKwc0.
Salby, M. Atmospheric Carbon. Video Presentation, July 18, 2016. University College London https://www.youtube.com/watch?v=3q-M_uYkpT0.
https://www.drroyspencer.com/latest-global-temperatures/
NOAA database, https://doi.org/10.15138/9N0H-ZH07
NOAA database, https://gml.noaa.gov/ccgg/about.html
https://www.wur.nl/en/research-results/chair-groups/environmental-sciences/laboratory-of-geo-information-science-and-remote-sensing/research/integrated-land-monitoring/forest_biomass.htm
https://www.ecoclimax.com/2016/08/land-mass-at-each-longitude-and-latitude.html

Table 1. Summary of the results obtained in this study. The numbers correspond to those in Figure 6.

Number	Results	Data
①	Temperature change correlates with the change rate of CO₂ concentration across latitudes from north to south.	Fig. 1
②	Temperature change in the tropics strongly responds to El Niño.	Fig. 1(a) & 2(a)
③	A trend of the temperature increase is greater in the north (20 N-90 N) than in the south (20 S-90 S).	Fig. 2(a)
④	The change rate of CO₂ concentration at sine latitudes 0.75(≒50 N) responds to temperature change more than in the tropics.	Fig. 2 & 3
⑤	The change rate of CO₂ concentration at sine latitudes 0.75(≒50 N) significantly responds to temperature change regardless of ENSO occurrences.	Fig. 2 & 4
⑥	The difference of temperature change between land and ocean is larger in the south (20S-90S) than in the north (20 N-90 N).	Fig. 5

The authors declare no competing interests.

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Changes in Temperature and CO₂in the Atmosphere at Various Latitudes

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Abstract

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Introduction

Results And Discussion

Conclusions

Abbreviations

References

Tables

Additional Declarations

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