Carbon Brief - Zeke Hausfather
Global emissions of CO2 need to decline precipitously over the next
few decades, if the world is to meet the Paris Agreement goals of
limiting global warming to “well below 2C” and, ideally, below 1.5C.
If these goals are to be met, young people would have to live the
greater part of their lives without contributing significantly to global
emissions. Essentially, they would have fewer “allowable” CO2 emissions
during their lifetime, compared with older generations.
To determine just how much smaller their personal CO2 limits would
be, Carbon Brief has combined historical data on emissions and
population with projections for the future. In a world where warming is
limited to 1.5C, the average person born today can emit only an eighth
of the lifetime emissions of someone born in 1950.
The interactive tool, below, shows the size of each person’s “carbon
budget” during their lifetime – based on when and where they were born.
It looks at two different scenarios: one where the world limits
warming to well below 2C above pre-industrial levels by 2100; and one
were warming is limited to 1.5C.
It also considers two different ways of sharing future allowable emissions: one where each country tracks “
optimal”
pathways taken from models; and another, focused on equality, where
each person can use the same portion of future emissions, no matter
where they live.
In all cases, younger generations will have to make do with
substantially smaller lifetime carbon budgets than older generations, if
the Paris limits are to be respected. This is because most of the
allowable emissions have already been used up, meaning young people will not have the luxury of unmitigated emissions enjoyed by older generations.
The idea for this analysis was first proposed to Carbon Brief by
Dr Ben Caldecott
at the University of Oxford. The methodology used – and its limitations
– are explained in detail at the end of this article. Carbon Brief is
now working to further develop the analysis with Dr Caldecott and his
colleagues.
The global picture
Global emissions must peak in the next decade and
quickly decline
for the world to stay below its Paris Agreement limits, according to
the UN. In the scenarios examined in this article (see methodology at
the end for details), global emissions peak around 2020, decline around
50% by 2045 and then fall below zero around 2075 in order to hold global
warming to below 2C.
Emissions have to fall even faster for warming to be kept below 1.5C –
falling around 50% by 2030 and to below zero by 2055. In the 1.5C
scenarios examined here, large amounts of
negative emissions are deployed by the end of the century, removing carbon from the atmosphere equivalent to roughly a third of today’s emissions.
These emissions pathways can be divided up into average “lifetime
carbon budgets” that depend on an individual’s year of birth. This
allocation is based on the changing global population and emissions
during each individual’s lifetime.
The figure below shows the global average lifetime carbon budget for
people born in each year between 1900 and 2017, in scenarios where
warming is kept below 1.5C (dark blue) or 2C (light blue).
Global average lifetime carbon budgets per-capita by birth year for 1.5C
and 2C scenarios, assuming a lifespan of 85 years. Based on historical
emissions data from the
Global Carbon Project, historical and future projected population from the
United Nations and global emission projections from
MESSAGE-GLOBIOM. Generation birth years shown at the bottom from the
Pew Research Center. See the methodology section for details. Chart by Carbon Brief using
Highcharts.
As the chart above shows, if warming is limited to well below 2C the
global average lifetime carbon budget for someone born in 2017 is 122
tonnes of CO2, only about a third as large as the budget for someone
born in 1950. If warming is to be limited to 1.5C, the remaining budget
is only 43 tonnes of CO2 and the difference is eight times as large.
Current per-capita global emissions are around 4.9 tonnes per person
per year. This means that the lifetime carbon budget of someone born
today is equal to 25 years of current emissions if warming is limited to
well below 2C – and only nine years of current emissions if warming is
limited to 1.5C.
Divvying up emissions
The analysis above uses a global average carbon budget. However, in
reality, there is no such thing as a “global average” person and each
country’s emissions will follow a slightly different trajectory in “well
below” 2C and 1.5C worlds.
In general, emission reductions will need to be proportionally larger
in developed, wealthier countries, such as the US, where per-capita
emissions are very high. Developing nations, such as India, already have
much lower per-capita emissions.
To put the difference into perspective, the average Indian had
emissions of 1.9 tonnes of CO2 in 2017, whereas the figure in the US was
16.9 tonnes of CO2.
Moreover, historical emissions vary greatly between countries, with
the likes of the US and UK responsible for a far larger share of
cumulative emissions since the industrial revolution. This poses an open
question as to how the fixed global carbon budgets set by the Paris
Agreement should be
divided between different countries.
IAMs are computer models that analyse a broad range of data – e.g. physical, economic and social – to produce information that can be used to help decision-making. For climate research, specifically,… Read More
|
There are lots of different ways to allocating future emissions between countries.
Integrated assessment models
(IAMs) – energy system models that examine what mix of different
technologies and choices are needed to meet climate targets – provide
one set of budget allocations, reporting future emissions for each
region of the world.
The figure below is based on the allocations in 1.5C scenarios from
IAMs. It shows how lifetime carbon budgets vary based on birth year, for
four major countries and regions that are responsible for the bulk of
global CO2 emissions. These are the US (light blue line), Europe (dark
blue), China (red), and India (yellow).
Lifetime carbon budgets by birth year based on historical emissions and
future IAM 1.5C scenarios, assuming a lifespan of 85 years. Based on
historical emissions data from the
Global Carbon Project, historical and future projected population from the
United Nations and regional emission projections from
MESSAGE-GLOBIOM. Generation birth years shown at the bottom from the
Pew Research Center. See the methodology section for details. Chart by Carbon Brief using
Highcharts.
If the remaining carbon budget is divided up in this way, based on
IAM pathways, then national allowable lifetime emissions are much more
similar for someone born in 2017 than in 1950 – but there are still
large differences between countries.
For example, someone born today in the US would still be allocated a
lifetime carbon budget some 15 times larger than someone born in India.
Their budget would be four times larger than someone born in China and
around twice as large as in Europe.
The table below shows the lifetime carbon budget in a 1.5C world (2C
world) both globally and by major country/region, broken down by
generation:
| Pre-Boomer
(pre-1946) | Boomers
(1946-1964) | Gen X
(1965-1980) | Millennials
(1981-1996) | Gen Z
(1997-2012) | Post-Gen Z
(post-2012) |
| Global | 275 | 325 (348) | 276 (322) | 202 (264) | 118 (191) | 56 (134) |
| US | 1494 | 1464 (1530) | 1191 (1342) | 846 (1052) | 472 (709) | 238 (489) |
| Europe | 686 | 698 (733) | 582 (668) | 398 (521) | 218 (363) | 105 (259) |
| China | 119 | 255 (291) | 256 (334) | 220 (326) | 151 (279) | 71 (213 |
| India | 38 | 64 (71) | 61 (74) | 52 (69) | 23 (54) | 18 (39) |
Lifetime
carbon budgets in tonnes of CO2 by birth year based on historical
emissions and future IAM 1.5C (and 2C) scenarios. Pre-Boomer generations
have identical 1.5C and 2C carbon budgets. Using generation periods
from the Pew Research Center and averaging the lifetime budget of all the birth years of each generation.
This approach raises obvious questions about equity, as it implies
that countries with high historical emissions will also receive a larger
share of the proverbial pie in the future. There are lots of different
ways to define equity – and
little agreement – regarding which approaches would be both possible and “fair” for allocating future emissions.
One alternative would be to allocate the remaining budget equally
between all people, wherever they live. This might be hard to achieve in
practice as, say, per-capita US emissions would need to fall rapidly
towards the global average while those in India would immediately rise.
But it provides a useful thought experiment that can be contrasted to
the lifetime carbon budget allocation set out above. Even this might
not be truly equal, is it neglects responsibility for historical
emissions.
The figure below shows the effect of this allocation on lifetime
carbon budgets by birth year for the same four major countries and
regions. It is based on historical per-capita emissions and equal
per-capita shares of the remaining carbon budget from 2018 onwards, in a
scenario where warming is limited to 1.5C.
Same as the prior figure, but using global emission projections from
MESSAGE-GLOBIOM to calculate future global per person emissions. See the methodology section for details. Chart by Carbon Brief using
Highcharts.
The chart above shows that lifetime carbon budgets converge much more
quickly when future emissions are divided equally, even though
historical differences between countries remain. As a result, someone
born in 2017 would have a similar lifetime carbon budget no matter where
they are born.
Some limitations
Calculating lifetime carbon budgets is necessarily imperfect and
relies on a series of unrealistic assumptions. Every person is different
and, in practice, individual emissions will be strongly affected by
income, behaviour and other factors.
While the average 1.5C lifetime carbon budget of someone, say, born
in the US around 1995 might be 696 tonnes of CO2, people in that
generation will, in practice, have widely varying individual emissions.
The approach taken here – dividing national emissions by population –
also glosses over the fact that a sizable portion of emissions for some
countries are the result of industrial and commercial activity
producing goods for trade that are not consumed at home. These
“consumption footprints” can differ significantly from national emission
estimates, as Carbon Brief has
previously examined.
For simplicity, a constant lifespan of 85 years is assumed when
calculating lifetime carbon footprints. This is higher than the current
average lifespan in most countries, but may be more realistic for
younger generations today given expected advances in medical science and
access to healthcare. However, in practice, lifespan differences
between countries will likely persist into the future and could impact
these calculations.
Finally, this approach assumes that emissions in a given year can be
assigned equally across the population regardless of age. In reality,
people are probably responsible for considerably lower emissions when
they are children than adults, as they are not, say, driving cars and
are often consuming less.
That said, this analysis provides a first look at how lifetime carbon
budgets vary by age. It suggests that the allowable lifetime emissions
for young people today is a fraction of that of previous generations, as
the global budget for avoiding warming of 1.5C or 2C has already been
mostly used up.
Methodology
Lifetime carbon budgets were calculated by adding the historical and projected future
per-capita
emissions for each year that an individual is expected to live
– assuming a constant lifespan of 85 years since a given birth year for
simplicity. This is higher than the current global average lifespan (it
is
typical of Japan today), but may be more typical for the lifespan of younger people today given continuing medical advances.
For example, if someone were born in the year 2000 in India, their
lifetime carbon footprint would be the sum of historical per-capita
emissions in India from 2000 to 2017, plus forecast per-capita emissions
in India between 2018 and 2085.
The end of 2017 serves as the demarcation between historical and
future emissions because 2018 emission and population values are not yet
available for all countries.
Carbon budgets were calculated for all possible birth years from 1900
to 2017 for major countries and each of the world regions where UN
population projections were available: Africa, Europe, Latin America and
the Caribbean, North America, Oceania and Asia.
Historical CO2 emission estimates for each country from 1751-2017 were obtained from the
Global Carbon Project.
Historical population data from 1950-2017 and future population
projections from 2018-2100 were obtained for each country from the UN
World Population Prospects 2017.
The “medium” scenario was chosen for future population projections, as
it matches reasonably well with the population assumptions in the Shared
Socioeconomic Pathway (
SSP2) world used for
IAM emission scenarios.
Future emissions by country for both 1.5C and 2C targets were based
on IAM runs from the International Institute for Applied Systems
Analysis (
IIASA)
MESSAGE-GLOBIOM
model using the SSP2 world. SSP2 is a world where current economic and
population trends broadly continue and MESSAGE-GLOBIOM was the model
chosen to represent SSP2. MESSAGE-GLOBIOM emissions by region – and globally – were taken from the
IAMC 1.5C Scenario Explorer.
As IAM runs in recent years lack country-specific values, regional
emission estimates were used to estimate country-specific trajectories
by scaling current country emissions by the percent reduction in
regional emissions from the IAM runs. For example, if the IAM runs
showed OECD countries reducing emissions by 50% by 2040 in a 1.5C
scenario, emissions in each OECD country were estimated to decrease by
50% by 2040.
Net future emissions were used for per-capita emission estimates.
This means that in many countries future per-capita emissions go
negative in the second half of the 21st century, particularly in 1.5C
scenarios. The distribution of negative emissions in MESSAGE-GLOBIOM
varies regionally, with a particularly high concentration of negative
emissions in Latin America and the Caribbean.
Finally, as both emission and population projections are only
available through to 2100, but people born after 2015 will still be
alive post-2100, per-capita emissions are assumed to remain constant at
2100 values in subsequent years.
Two future emission allocation scenarios are provided: one based on
the regional MESSAGE-GLOBIOM emission pathways and one where the global
MESSAGE-GLOBIOM projected emissions are distributed evenly to every
country on a per-capita basis after 2017. The latter shows how a more
equitable distribution of remaining emissions would affect lifetime
carbon budgets, compared to the allocation in IAMs.
The countries featured in the interactive tool are a subset of those
with the largest populations. However, major regions are also included,
so if there is a country not featured on the list its region should
provide a reasonable estimate. The “North America” region is not shown
as all member countries appear on the list.
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