Long description

This figure consists of a pair of line graphs showing three possible scenarios for global carbon dioxide emissions from the year 2000 to 2100. Graph (a) on the left shows the emissions and graph (b) on the right shows the resulting atmospheric carbon dioxide concentrations. Both charts have x-axes labelled from 2000 to 2100 in intervals of 20 years. Graph (a) has a y-axis labelled ‘carbon dioxide emissions in gigatonnes per year’. This has a scale running from zero to 45 gigatonnes in 5 gigatonne steps. The zero point is also labelled ‘Net zero’. Historical emissions are shown by a black line which rises unevenly from just over 25 gigatonnes in 2000 to about 35 gigatonnes in 2010 and to 37 gigatonnes in 2022, with a pronounced dip in 2020. The first scenario is shown by a horizontal red line at 37 gigatonnes running from 2022 through to 2100. This is labelled ‘3.0 degrees Celsius’ at the right-hand side. The second scenario is shown by an orange line which descends from 37 gigatonnes in 2022 down to 33 gigatonnes in 2028 and to only 6 gigatonnes in 2055. This point is marked by a black dot on the line and labelled ‘2 degrees Celsius by 2100’. The orange line then descends further, reaching net zero in 2070, where there is a green dot on the line. The third scenario is shown by a green line which descends rapidly from 37 gigatonnes in 2022 down to 6 gigatonnes in 2040. This point is marked with a black dot on the line and is labelled ‘1.5 degrees Celsius by 2100’. The green line descends to net zero by 2050, where there is a green dot on the line. The black dots on the green and orange lines are linked by a horizontal dotted black line at 6 gigatonnes of emissions. A thick vertical grey line with an arrow head at the bottom descends from the red line at 37 gigatonnes down to the dotted black line. This grey line is labelled ‘Factor of six reduction’. Chart (b) has a y-axis labelled ‘carbon dioxide emissions in parts per million, ppm’. This has a scale running from 350 parts per million up to 650 parts per million. Historical data are shown as a black line rising from 370 parts per million in 2000 up to 420 parts per million in 2022. The projection for the first scenario is shown as a straight red line which continues rising to about 630 parts per million in 2100. This line is labelled ‘3 degrees Celsius’. The projection for the second scenario is shown by an orange line, starting at 420 parts per million in 2022, rising but flattening out to about 470 parts per million in 2100. This line is labelled ‘2 degrees Celsius’. The projection for the third scenario is shown by a green line starting at 420 parts per million in 2022, rising to about 435 parts per million in 2035 and then falling gently down to 205 parts per million in 2100. This line is labelled ‘1.5 degrees Celsius’.