3.1. MK trend test
We included the carbon emissions per capita from 190 countries in out study. The per-capita emissions from 128 of these countries had a positive growth rate, and these emissions accounted for 67.37% of the total per-capita emissions. The per-capita emissions from 61 countries had a negative growth rate, and accounted for 32.11% of total per-capita emissions, and only one country, South Sudan, had a zero growth rate in emissions. Figure 1 shows the trends for the per-capita emissions from each continent.
Figure 1 shows that the net trend for per-capita carbon emissions for all continents is positive growth. 91.67% of countries in South America and 82.6% of countries in North America had positive growth trends. Countries with a positive growth trend accounted for 78.57%, 77.78% and 76.08% of the per-capita emissions from Oceania, Africa and Asia, respectively. Europe had the smallest increase in per-capita carbon emissions of all the continents, and countries with a positive growth trend accounted for 24.39% of the total per-capita emissions from Europe.
Figure 2 shows the density distributions for the growth rate of per-capita carbon emissions from all continents. It can be seen from the figure that the growth rate for most of Europe is negative, while the peak for other continents corresponds to slight positive growth. The distribution is particularly narrow for South America and Africa, and the peak is slightly higher for South America than for Africa. The density distribution for the growth rate in Asia is the broadest, showing the growth rate here to be more decentralized than for the other continents. Compared with other continents, the frequency of high growth rates in Asia is higher. There is a secondary peak in the distribution for Oceania at around a growth rate of -0.3 mts/yr.
Table 1 lists the countries with the twenty highest positive and negative growth rates. Twelve of the strongest twenty countries for growth are in Asia, accounting for 60% of the top twenty growth countries. The area around 30° N is the most concentrated area of countries with high growth rates. This area includes four countries in Africa; two countries in Europe; and one country each in North and South America. Europe has the greatest number of countries with negative growth rates in the top twenty. These twelve European countries account for 60% of all countries in the top twenty list for strong negative growth, which also includes five countries in Asia; and one country each in North America, Africa, and Oceania.
Table 1
Twenty countries with the strongest rates of increase and decrease.
Country Code | Increase Rate | Country Code | Decrease Rate |
OMN | 0.438733 | ARE | -0.46155 |
GNQ | 0.272753 | LUX | -0.37608 |
TKM | 0.266631 | NRU | -0.28774 |
SAU | 0.261462 | DNK | -0.26567 |
TTO | 0.25524 | USA | -0.20121 |
CHN | 0.244688 | BHR | -0.16523 |
BIH | 0.209024 | BEL | -0.16132 |
KOR | 0.185939 | GBR | -0.15022 |
MNE | 0.176898 | FIN | -0.14466 |
IRN | 0.176237 | PRK | -0.13669 |
MYS | 0.175769 | SWE | -0.13565 |
KAZ | 0.148168 | UKR | -0.12939 |
BRN | 0.123302 | SGP | -0.12824 |
MNG | 0.120517 | CZE | -0.12356 |
SYC | 0.120106 | AZE | -0.12325 |
MDV | 0.110251 | LIE | -0.12103 |
CHL | 0.093517 | SVK | -0.10171 |
TUR | 0.08693 | DEU | -0.08428 |
ZAF | 0.086919 | GAB | -0.08306 |
MUS | 0.084493 | ISL | -0.07974 |
3.2. Future trends in per-capita carbon emissions
We calculated the Hurst index for the per-capita carbon emissions from every country in the world. We found 165 countries, 86.84% of all countries, to have a Hurst index greater than 0.5 and 25 countries, 13.16% of all countries, to have a Hurst index less than 0.5. No countries have a Hurst Index of 0.5. This indicates that the future per-capita carbon emissions from most countries will continue to follow the current trend.
We combined the Hurst index with the current growth rate to estimate future per-capita carbon emissions from each country. We divided the future trends into 5 types: persistent decrease (increase rate < 0, H > 0.5, decrease expected to continue into the future), persistent increase (increase rate > 0, H > 0.5, increase expected to continue into the future), anti-persistent decrease (increase rate < 0, H < 0.5, current trend in per-capita carbon emissions expected to reverse and become an increasing trend in the future), anti-persistent increase (increase rate > 0, H < 0.5, current trend in per-capita carbon emissions expected to reverse and become a decreasing trend in the future), and unidentified (H = 0.5, random changes in future trends expected).
As shown in Fig. 3, the emissions trends from most countries are likely to persist into the future. A persistent decrease is anticipated for 57 countries, accounting for 30.00% of all countries, and these are mainly concentrated in Europe (except Central Europe), in areas near 0 ° in Africa, and in the border area between Asia and Europe. There are 37 countries in Europe, 11 countries in Asia, 11 countries in Africa, 4 countries in North America, 3 countries in Oceania and 1 country in South America for which a persistent decrease is expected. A persistent increase is expected for 108 countries, accounting for 56.84% of all countries, and most of these countries, 36, are in Africa. Africa is followed by Asia and North America, where persistent increases are expected for 31 and 15 countries, respectively, and then by North America, Oceana and Europe, in which a persistent increase is expected for 9, 9 and 8 countries, respectively. An anti-persistent decrease is expected for only 5 countries, accounting for 2.63% of all countries: 4 in Europe and 1 in Africa. An anti-persistent increase is expected for 20 countries, accounting for 10.53% of all countries, and Africa accounts for the greatest number of these, 6. Africa is followed by Asia and North America, each of which include 4 countries for which an anti-persistent increase is expected. Two countries in each of North America, Oceania and Europe are also associated with an expected anti-persistent increase.
3.3. MK change test
Figure 4 shows the years when MK change occurred for the first time for each country. During 1992 to 2018, 77 out of 190 countries experienced a change-point: Europe accounted for the greatest number of countries, 21 (27.27%), followed by Africa and Asia, which accounted for 18 and 17 countries (23.38% and 22.08%), respectively. North America, Oceania and South America accounted for 11 (14.29%), 6 (7.80%) and 4 (5.19%) countries that experienced a change-point, respectively. The proportion of countries in Europe where the trend is likely to mutate is 52.5%, the highest proportion for any continent, followed by North America at 47.8% and Oceania at 42.9%. Asia, Africa and South America have the lowest proportions of mutation countries, at 36.9%, 33.9% and 33.3% respectively.
The number of change-points was greatest in 1994 and smallest in 1999. From 2009 to 2013, the number of change-points increased year by year, and the distribution of change-points over the remaining years was relatively uniform. Changes to increasing trends were more concentrated before 1998 and changes to decreasing trends became clearer after 2011. The distribution of ascending and descending trend mutations was more random in other periods and the number of changes to increasing trends was 42, slightly higher than the number of changes to decreasing trends, which was 35. Changes occurred simultaneously in two countries in Asia in 1994 and 2015. When changes occurred in Asia in other years, they only occurred in one country and were generally a change to an increasing trend. In Europe, changes occurred in different years in different countries, with a gap between those where the change occurred earliest and those countries where the change followed after a lag. Change points in Europe are mainly concentrated after 2003, and most changes were to decreasing trends. In North America, change-points were mainly concentrated at the beginning and the end of the study period. At the start of the study period, most changes were to increasing trends, while all changes at the end of the study period were towards decreasing trends. South America had the smallest number of countries with change points, only 4. Two countries experienced change points in 1994, one to an increasing trend and one to a decreasing trend, one country experienced an change to an increasing trend in 1997 and one country experienced a change to an increasing trend in 2004. There were two countries with change points in Africa in 1994, 2001, 2011 and 2014. In other years, there was only one country in Africa with a change point. Before 2002, the number of changes to increasing and to decreasing trends was similar. After 2002, most changes were to increasing trends. The times for the changes in Oceania countries are discrete and all changes are to increasing trends. The timing of change points is different for the different continents. The changes in America and Oceania mainly occurred near the start of the study period while most changes in Europe were concentrated in later stages of the study period. There were more slightly changes in Africa towards the end of the study period than at the start, and changes in Asia occurred throughout the study period.
3.4. The gravity center shift for per-capita carbon emissions
Figure 5 shows the annual shift of the gravity center for per-capita carbon emissions from 1992 to 2018, and shows that there was a longitudinal shift in three stages. From 1992 to 1998, the gravity center moved westward relatively quickly. From 1999 to 2006, center of gravity fluctuated longitudinally, moving alternately eastward and westward relatively slowly, eventually moving slightly eastward. From 2007 to 2018, the gravity center moved quickly eastwards. Over the whole study period, the gravity center for per-capita carbon emissions moved 1.95° eastwards. In the latitude direction, the center generally kept moving southward. From 1992 to 1998, the southward movement was relatively fast; from 1999 to 2006, the rate of southward movement was relatively slow and occasionally small northwards movements occurred. From 2006 to 2018, the gravity center continued to move steadily to the south, but the speed gradually slowed down, becoming almost stagnant after 2014. At this same time, the speed of eastward movement accelerated significantly. Over the whole study period, the center of gravity for per-capita carbon emissions moved to the south by 4.51°. The distance moved in the second stage is not great, in terms of longitude or latitude, and there are some fluctuations in the direction during this stage. We therefore simplified our description of the shift in the center of gravity into two stages. From 1992 to 2004, the gravity center for per-capita carbon emissions gradually shifted to the southwest, and, after 2004, it gradually shifted to the southeast until 2018. With the exception of 2009 and 2012, there was a clear shift in the gravity center location.
3.5. The drivers for the gravity center shift
The trend in the shift for the center of gravity for per-capita carbon emissions changed in 2004. Before 2004, the center of gravity moved to the southwest and, after 2004, it moved to the southeast. Therefore, we describe the shift in longitude in 2004 and earlier as a positive contribution to the west and a negative contribution to the east; after 2004, there is a longitudinal shift to the east, and so a positive contribution to the east, and a negative contribution to the west. The near-constant southward movement can be described as a positive contribution to the south and a negative contribution to the north. Figure 6 shows the top twenty positive and negative contributors to the shift in the gravity center for per-capita carbon emissions each year from 1993 to 2018.
Figure 6 (a) shows that Palau (PLW) and Canada (CAN) were the most frequent positive contributors to the longitudinal shift before 2004, both contributed positively eight times; followed by Trinidad and Toba Colombia (TTO), Chile( CHL), Kazakhstan (KAZ), Nauru (NRU), North Korea (PRK), Saint Kitts and Nevis (KNA), each of which contributed positively to the longitudinal shift seven times. Mexico (MEX), Dominica (DMA), Antigua and Barbuda (ATG), United Arab Emirates (ARE), Singapore (SGP), Tonga (TON), Equatorial Guinea (GNQ), Barbados (BRB), and Luxembourg (LUX) all made positive contributions six times before 2004. After 2004, Mongolia (MNG), China (CHN), the United States (USA), and Luxembourg (LUX) were the most frequent positive-contributing countries for the longitudinal shift, all of these countries contributed positively 9 times; followed by the Bahamas (BHS), Kazakhstan (KAZ), Malaysia (MYS), and Mongolia (LUX). Trinidad and Tobago (TTO) contributed positively to the longitudinal shift eight times, and Palau (PLW) and South Korea (KOR) each contributed positively to the longitudinal shift seven times. Figure 6 (b) shows that Malaysia (MYS) contributed negatively to the longitudinal shift ten times before 2004, which is more than any other country; Bahamas (BHS), South Korea (KOR) and Qatar (QAT) each contributed negatively nine times, and China (CHN) contributed negatively eight times. After 2004, Qatar (QAT), St. Kitts and Nevis (KNA), North Korea (PRK), New Zealand (NZL), and Australia (AUS) were the most frequent negative-contributing countries for the longitudinal shift, and each of these countries contributed negatively eight times, followed by the United Arab Emirates (ARE), Canada (CAN), Barbados (BRB), Grenada (GRD), Japan (JPN), and Chile (CHL), each of which contributed negatively seven times. Suriname (SUR), Brunei Darussalam (BRN), Antigua and Barbuda (ATG), Guyana (GUY), and Bahrain (BHR) contributed negatively to the longitudinal shift six 6 times.
As shown in Fig. 6 (c), Seychelles (SYC) was the most frequent positive-contributor to shifts in latitude for the gravity center, and contributed positively 16 times, followed by Denmark (DNK), Chile (CHL), Estonia (EST), Finland (FIN), and Luxembourg (LUX), each of which contributed positively 14 times. Malaysia (MYS) and Brunei Darussalam (BRN) each contributed positively to the latitudinal shift for the gravity center 12 times. Figure 6 (d) shows that New Zealand (NZL) made the most frequent negative contribution to the latitudinal shift, at 14 times through the study period, followed by Palau (PLW), Canada (CAN), Ireland (IRL), and Kazakhstan (KAZ), each of which contributed negatively 12 times, and Singapore (SGP), which contributed negatively 11 times.
The three countries that made the greatest cumulative contribution to longitude shifts in the gravity center before 2004 were Nauru (NRU), Trinidad and Tobago (TTO) and Kazakhstan (KAZ), which contributed 0.886°, 0.307°, and 0.299° respectively to the westward shift in the center of gravity. The three countries that made the greatest cumulative negative contributions before 2004 were Korea (KOR), Qatar (QAT) and Australia (AUS), which respectively contributed 0.437°, 0.417°, and 0.394° to the eastward shift of the center of gravity. After 2004, the three countries with the greatest cumulative positive contributions were the United States (USA), Palau (PLW), and China (CHN), which contributed 0.715°, 0.630° and 0.322° respectively to the eastward shift of gravity center; The top three countries with cumulative negative contributions were Australia (AUS), Qatar (QAT) and North Korea (PRK), which contributed 0.361°, 0.325°, and 0.304°, respectively, to the westward shift of the center of gravity.
The three countries with the greatest positive cumulative contributions to the latitude shift for the gravity center were Luxembourg (LUX), Chile (CHL) and Seychelles (SYC), which contributed 0.351°, 0.199°, and 0.198° to the southward shift of the center of gravity, respectively. The three countries with the greatest negative cumulative contribution were Nauru (NRU), Gabon (GAB), and Montenegro (MNE), which contributed 0.213°, 0.093°, and 0.063° to the northward shift of the center of gravity, respectively.
Taking 1992 and 2004 as base points for the shift of the gravity center for per-capita carbon emissions, the total contribution of countries to the left of the base point is the total contribution of western countries, and the total contribution of countries to the right of the base point is the total contribution of eastern countries. Before 2004, the total contribution of western countries is a westward shift of 2.33°, and the total contribution of eastern countries is an eastward shift of 1.03°. This indicates that the overall growth in per-capita carbon emissions was greater in western countries than in eastern countries before 2004. After 2004, the total contribution of western countries was an eastward shift of 1.92° and that of eastern countries was an eastward shift of 1.81°, indicating that per-capita carbon emissions from western countries entered a generally declining stage, while the per-capita carbon emissions from eastern countries continued to increase.