2.2 Global Carbon Emissions
Global CO 2 concentrations in the atmosphere follow the balance between emissions, released through human activities such as deforestation and burning fossil
fuels, as well as natural processes such as respiration and volcanic eruptions, and
uptake by the biosphere and ocean. During the last 7000 years, prior to 1750,
atmospheric CO 2 from ice cores shows only very slow changes (increase) from
260 ppm to 280 ppm, in contrast to the human-caused increase of CO 2 since
pre-industrial times. The contribution of CO 2 emissions from early anthropogenic
land use is unlikely sufficient to explain the CO 2 increase prior to 1750 [10]. Further
back in time, during the past 800,000 years prior to 1750, atmospheric CO 2 varied
from 180 ppm during glacial (cold) up to 300 ppm during interglacial (warm)
periods.
The levels of heat-trapping GHG in the atmosphere have reached successive new
records along the years with no sign of a reversal in this trend. Since 1990, there has
been a 41% increase in total radiative forcing—the warming effect on the climate—
by long-lived GHG, with CO 2 accounting for about 82% of the increase in radiative
forcing over the past decade [11]. In 2018, GHG concentration in the atmosphere
reached new maximum values, with globally averaged of CO 2 at 407.8 ± 0.1 ppm,
CH 4 at 1869 ± 2 ppb and N 2 O at 331.1 ± 0.1 ppb [11], larger than the increases in
the ten-year averaged growth rates. The global averaged concentration registered in
2018 represented, 147%, 259% and 123% of pre-industrial (1750) levels for CO 2 ,
CH 4 and N 2 O, respectively [11]. The most recent data available, measured at
Mauna Loa Observatory, Hawaii, with average seasonal cycle removed, pointed out
to 413.03 ppm, at March 17, 2020.
CO 2 remains in the atmosphere for centuries and in the oceans for even longer,
meaning future generations will be challenged with increasingly severe impacts of
climate change, including rising temperatures, more extreme weather, water stress,
sea level rise and disruption to marine and land ecosystems. The increase of
atmospheric CO 2 above pre-industrial levels was, initially, primarily caused by the
release of carbon to the atmosphere from deforestation and other land use change
activities [10], while emissions from fossil fuels, started before the Industrial Era,
became the dominant source of anthropogenic emissions to the atmosphere from
around 1950, and their relative share has continued to increase until present, as
Fig. 2 illustrates for the decade 2009–2018. Anthropogenic emissions occur on top
of an active natural carbon cycle that circulates carbon between the reservoirs of the
atmosphere, ocean and terrestrial biosphere on timescales from sub-daily to millennia, while exchanges with geologic reservoirs occur at longer timescales. Archer
[12] showed that 20–35% of the CO 2 remains in the atmosphere after equilibration
with the ocean (2–20 centuries).
The global carbon budget averaged over the last half-century (1959–2018),
revealed 82% of the total emissions were caused by fossil CO 2 emissions and 18%
by land use change [13]. The total CO 2 emissions were partitioned among the
atmosphere, ocean and land, meaning that 24% were absorbed by the oceans, 29%
by the terrestrial biosphere and 45% remained in the atmosphere, while 2% of the
Carbon Economy and Carbon Footprint
9
Global CO 2 concentrations in the atmosphere follow the balance between emissions, released through human activities such as deforestation and burning fossil
fuels, as well as natural processes such as respiration and volcanic eruptions, and
uptake by the biosphere and ocean. During the last 7000 years, prior to 1750,
atmospheric CO 2 from ice cores shows only very slow changes (increase) from
260 ppm to 280 ppm, in contrast to the human-caused increase of CO 2 since
pre-industrial times. The contribution of CO 2 emissions from early anthropogenic
land use is unlikely sufficient to explain the CO 2 increase prior to 1750 [10]. Further
back in time, during the past 800,000 years prior to 1750, atmospheric CO 2 varied
from 180 ppm during glacial (cold) up to 300 ppm during interglacial (warm)
periods.
The levels of heat-trapping GHG in the atmosphere have reached successive new
records along the years with no sign of a reversal in this trend. Since 1990, there has
been a 41% increase in total radiative forcing—the warming effect on the climate—
by long-lived GHG, with CO 2 accounting for about 82% of the increase in radiative
forcing over the past decade [11]. In 2018, GHG concentration in the atmosphere
reached new maximum values, with globally averaged of CO 2 at 407.8 ± 0.1 ppm,
CH 4 at 1869 ± 2 ppb and N 2 O at 331.1 ± 0.1 ppb [11], larger than the increases in
the ten-year averaged growth rates. The global averaged concentration registered in
2018 represented, 147%, 259% and 123% of pre-industrial (1750) levels for CO 2 ,
CH 4 and N 2 O, respectively [11]. The most recent data available, measured at
Mauna Loa Observatory, Hawaii, with average seasonal cycle removed, pointed out
to 413.03 ppm, at March 17, 2020.
CO 2 remains in the atmosphere for centuries and in the oceans for even longer,
meaning future generations will be challenged with increasingly severe impacts of
climate change, including rising temperatures, more extreme weather, water stress,
sea level rise and disruption to marine and land ecosystems. The increase of
atmospheric CO 2 above pre-industrial levels was, initially, primarily caused by the
release of carbon to the atmosphere from deforestation and other land use change
activities [10], while emissions from fossil fuels, started before the Industrial Era,
became the dominant source of anthropogenic emissions to the atmosphere from
around 1950, and their relative share has continued to increase until present, as
Fig. 2 illustrates for the decade 2009–2018. Anthropogenic emissions occur on top
of an active natural carbon cycle that circulates carbon between the reservoirs of the
atmosphere, ocean and terrestrial biosphere on timescales from sub-daily to millennia, while exchanges with geologic reservoirs occur at longer timescales. Archer
[12] showed that 20–35% of the CO 2 remains in the atmosphere after equilibration
with the ocean (2–20 centuries).
The global carbon budget averaged over the last half-century (1959–2018),
revealed 82% of the total emissions were caused by fossil CO 2 emissions and 18%
by land use change [13]. The total CO 2 emissions were partitioned among the
atmosphere, ocean and land, meaning that 24% were absorbed by the oceans, 29%
by the terrestrial biosphere and 45% remained in the atmosphere, while 2% of the
Carbon Economy and Carbon Footprint
9