From global carbon budgets
to food security
Highlights of research into our changing climate
The latest observations continue to show a changing climate;
not only increases in global temperatures, but also rising sealevels,
shrinking glaciers and reducing Arctic sea-ice. All these
are consistent with a warming world driven by increases in
atmospheric greenhouse gas concentrations.
The effects of these changes are already evident during
extreme events, impacting on people, infrastructure and
natural systems. For example, heatwaves that would occur
twice a century during the early 2000s in Europe are now
expected to occur twice a decade.
The latest climate model simulations reproduce many
features of the historical climate, giving confidence in their
predictions of future conditions. Using plausible greenhouse
gas emission pathways these models show that restricting
global average warming to less than 2 °C above pre-industrial
levels is achievable, but challenging given the need for
unprecedented changes in global emission rates and
Increased natural greenhouse gas emissions from wetlands
and permafrost regions may add to the cumulative emissions
into the atmosphere. These effects could further reduce the
allowable anthropogenic emissions compatible with keeping
below the 2 °C limit by around 100 gigatonnes of carbon (GtC)
in the most pessimistic simulation. This corresponds to about
ten years of anthropogenic emissions at the current rate.
By including short-timescale variability into climate model
simulations, the range of seasonal conditions under different
levels of climate change can be investigated. Comparing
the average seasonal conditions by 2100 for a world with
2 °C of warming to one with 4 °C shows that they follow
the global annual average. However, cold winters and cool
summers are still possible, though these are less likely under
4 °C than 2 °C of warming. Similarly, warm winters and
hot summers are more likely under a 4 °C world. Reducing
greenhouse emissions will reduce the rate and long-term
effects of anthropogenic climate change, with extreme
events showing the largest changes.
Food security and climate interact in a complex way.
Many parts of the world are projected to experience
increased vulnerability to food insecurity by the middle
of the 21st century because of global warming.
Under high levels of greenhouse gas mitigation, vulnerability
to food insecurity can be stabilised at mid-21st century
levels. However under a high greenhouse gas emissions
scenario large increases are possible through until the end
of the century. This highlights the requirement for both
mitigation and adaptation.
A glossary of frequently used terms and acronyms can be found inside the back cover.
Our climate is changing and humans are responsible for at
least half of the warming observed since the mid-20th century.
Limiting future climate change requires reducing atmospheric
concentrations of greenhouse gases, chief amongst these are
carbon dioxide (CO 2
) and methane. Reductions will lead to a
range of benefits for people and ecosystems across the globe.
OBSERVATIONS Weather and climate research centres,
including the Met Office Hadley Centre, analyse observations
of the Earth’s climate. Measurements show that surface
temperatures, sea-levels and ocean heat content are
rising; glaciers and Arctic sea-ice are decreasing in extent
and volume. These, amongst many other measurements,
demonstrate increasing energy in the climate system and a
warming world. Studies combining observations with climate
model simulations show that it is extremely likely that humans
are responsible for at least half of the measured surface
PREDICTIONS Climate models can also be used to simulate
and predict how the Earth’s climate is likely to respond
under continuing increases in atmospheric greenhouse gas
concentrations. Limiting global average temperature rise
to less than 2 °C above pre-industrial conditions is a goal of
the Conference of the Parties (COP) to the United Nations
Framework Convention on Climate Change (UNFCCC).
This will require global emissions of greenhouse gases to be
limited or eliminated, and would avoid many severe impacts
of climate change and lead to a wide range of benefits for the
natural world and human society.
IMPACTS Extreme events, for example heatwaves in Europe
and the Indian sub-continent, or Hurricane Patricia in Mexico
during 2015, demonstrate the vulnerability of society to the
impacts of the current climate. Our present understanding
of the effects of climate change on regional climate extremes
and their subsequent impacts on human systems are
presented in this brochure.
MITIGATION Climate models indicate that it will be a
challenge to restrict climate change to a global average
temperature rise of less than 2 °C. Furthermore, alongside
human activities, natural processes release and absorb
greenhouse gases from the atmosphere, and the rate at which
they do so is linked to global temperature. We show how
these processes further restrict the amount of man-made
greenhouse gases that can be emitted if we are to avoid severe
impacts of climate change.
VULNERABILITY Food security is of concern to many people
in large parts of the world. Rising global temperatures along
with other aspects of climate change are projected to reduce
food security during the course of this century. Only with
large and sustained reductions in net emissions together
with adaptation to moderate levels of climate change can the
outlook be improved by the end of the century.
Here we present an update of recent research carried out by
the Met Office Hadley Centre in collaboration with partner
institutes across the globe.
The Met Office Hadley Centre Climate Programme is
funded by the UK Government through a three-year
focussed research programme, currently spanning
2015-2018. We work in collaboration with leading
academic and research organisations worldwide, as
well as governments and stakeholders across the globe,
to advance our understanding of climate science. We
also build capacity and enable knowledge transfer, for
example PRECIS (Providing Regional Climate for Impacts
Studies), and play a key role in many EU-funded projects,
including EUCLEIA (European Climate and weather
Events: Interpretation and Attribution) and EUSTACE (EU
Surface Temperature over All Corners of Earth).
Continuing evidence for a changing climate
Observations continue to
show a warming world
The Met Office Hadley Centre is one of a number of centres
around the world which monitor changes in the climate.
Land ice (in ice sheets and glaciers), sea-ice, sea-level,
ocean-heat content as well as global near-surface temperature
are among the observations which show long-term changes
consistent with a warming world.
A key result from the Intergovernmental Panel on
Climate Change Fifth Assessment Report (IPCC AR5)is
that most of the recent warming of the Earth’s surface
since the mid-20th century is likely to have been driven
by increasing concentrations of greenhouse gases
in the atmosphere. Measurements from the Mauna
Loa Observatory in Hawaii show this rise, with CO 2
concentrations reaching greater than 400 parts per
million (ppm) for the six months between February
and July 2015. This is around 120ppm (40%) above the
values in 1800 as determined from ice-core records.
Atmospheric CO 2
at Mauna Loa Observatory
Temperature difference (°C)
Met Office Hadley Centre and Climatic Research Unit
NOAA National Centers for Environmental Information
NASA Goddard Institute for Space Studies
Crosses for 2015 show January-September averages.
Whiskers show uncertainty in using the year-to-date
as an indicator of the full year average.
1850 1900 1950 2000
FIGURE 2: Average global near-surface temperature relative
to 1850-1900, including uncertainties (grey shading). Source:
HadCRUT4, NOAA-GlobalTemp, NASA-GISS.
In 2014 the global average temperature was
0.56±0.1 °C above the 1961-90 average. This was nominally
the joint-warmest year (with 2010) in records dating back to
1850. Uncertainties in the data, such as a lack of complete
coverage in the Arctic, mean it is not possible to say which of
several recent years was categorically the warmest.
Parts per million
Scripps Institute of Oceanography
NOAA Earth System Research Laboratory
1960 1970 1980 1990 2000 2010
Currently 2015 looks set to be warmer again, with the global
average temperature running 0.70±0.1 °C above the 1961-
90 average up to September. Estimates of the 2015 annual
global temperature anomaly are that it will be very close to
1 °C above pre-industrial levels. This is close to the half-way
point of the 2 °C limit set by the UNFCCC. This year’s record
temperature is partly due to the influence of a strong El Niño
event taking place in the Pacific, but the long-term warming
trend due to human influence is by far the dominant cause.
A recent new analysis show that the much-discussed “slowdown”
in the rate of global temperature rise is no longer as
prominent in the observations 1 .
FIGURE 1: Monthly atmospheric CO 2
concentration at Mauna Loa
Observatory since 1958. Source: Scripps Institute of Oceanography
and NOAA Earth System Research Laboratory.
Karl, Thomas R., et al., 2015, Possible artifacts of data biases in
the recent global surface warming hiatus, Science 348.6242.
180 120W 60W 0 60E 120E 180
-10 -5 -3 -2 -1 -0.5 0 0.5 1 2 3 5 10
Anomaly (°C) relative to 1961-1990
FIGURE 3: Observed annual near-surface temperatures for 2014
relative to 1961-90. White boxes indicate areas with insufficient
data. Source: HadCRUT4.
The 2014 average European temperature was the warmest
on record, at around 0.3 °C above the previous record set
in 2007. There were no large-scale heatwaves; instead these
record values were the result of temperatures remaining
consistently above average for most of the year; 25% of
days were in the warmest 10% of the normal range.
So far during 2015 there have been heatwaves in Europe,
India, Pakistan, and around the Persian Gulf.
Warm days (% days per year)
Europe Australia Globe
1950 1960 1970 1980 1990 2000 2010 2020
FIGURE 4: Regionally averaged annual number of warm days (when
the maximum temperature exceeds the 90th percentile calculated
over the 1961-90 base period), for Europe, Australia and the globe;
the expected amount is shown by the dashed line. Source: GHCNDEX.
million km 2
1990 2000 2010
FIGURE 5: Change in monthly Arctic sea-ice extent from the
average over 1981-2010. Source: NSIDC.
FIGURE 6: Global sea-level rise (actual values) since 1993 from the
TOPEX (1993-2001), Jason-1 (2002-08) and Jason-2 (2008-13)
satellite altimeter experiments. Source: University of Colorado.
Maximum and minimum Arctic sea-ice extent and
global average sea-level rise show continued changes
consistent with increasing energy in the climate system.
During 2015 the tropical cyclone season in the
eastern and central North Pacific has been exceptionally
active. There have been 24 named storms so far this
year (to 27 October), which, joint with 1985, is the
largest number of storms recorded in a season.
The region has seen an Accumulated Cyclone Energy
(ACE) more than twice its usual level. It also saw the
development of Hurricane Patricia in October, which
became the strongest hurricane on record in the
western hemisphere. In contrast, the North Atlantic
has been relatively quiet with an ACE index 40% lower
Human influence on climate extremes
Recent seasons and extremes fit into the picture of ongoing
human influence on the climate
Understanding how human influences on the climate are
affecting extremes helps inform decisions on how to adapt
to future conditions and highlights the potential benefits
In 2013, the IPCC concluded that it is extremely likely that
human emissions and other activities have caused more
than half of the observed increase in global average surface
temperature from 1951 to 2010. Further to this assessment
of large scale global averages, it is also extremely likely
that human influence on the climate has contributed to
observed changes in the frequency and intensity of daily
temperature extremes across the globe since the middle
of the 20th century.
The number and intensity of climate extremes are very
sensitive to changes in the average conditions, and are also
the events which have the greatest impacts on society. In
many cases human influence can be shown to have affected
their severity or frequency. The relative differences in
probability of extreme events can be assessed by comparing
climate simulations of worlds with only natural influences to
those which also include human ones. These experiments
will allow the detection of any change in the characteristics of
extreme events and then attribute these changes to human
or natural causes. The Met Office Hadley Centre is leading on
a project to attribute extreme events shortly after they have
UK winter of 2013/14
The winter of 2013/14 in the UK was dominated by an
exceptional clustering of intense low-pressure storms,
driven by a particularly strong North Atlantic jet stream.
These depressions caused tidal surge and wave damage
across coastal regions, and their rainfall led to saturated
ground and eventual flooding of river valleys and plains.
This resulted in damage to transport infrastructure, as well
as business and residential properties.
Climate simulations were used to model UK winter rainfall.
They show that the extreme level of total seasonal rainfall
experienced during the 2013/14 winter is about eight times
more likely when the large-scale atmospheric patterns
resemble those observed during that period. A human
influence can be identified in extreme rainfall events with
shorter durations. Anthropogenic climate change has made
extreme rainfall over 10 consecutive winter days around
seven times more likely. This new analysis is in agreement
with emerging evidence which suggests an increase in
the frequency and intensity of extreme UK rainfall. It is
also consistent with the detection of human influence on
changes in extreme rainfall over larger spatial scales.
Chinese spring 2014
In northern China, the spring of 2014 was the third
warmest since reliable records began in the late 1950s;
2.2 °C higher than the 1961-90 average. During late
May, 12 stations recorded temperatures over 40 °C,
breaking historical records. The number of hot spring
days (maximum temperature > 25 °C) is linked to the
mean spring-time temperature, and both these quantities
have increased over the last half-century. The likelihood
of hot spring mean temperatures as observed in 2014
has increased by around 11-fold as the result of human
influences on the climate system.
0 2 4 6 8 10
of the average
to 1961-90 for the
end of the 21st
two different CO 2
heatwave of 2003
is shown by the
vertical line. RCP2.6
results in a global
change of around
2 °C by 2100, and
RCP8.5 by over 4 °C.
Increasing chances of hot European summers
A study in 2004 on the severe heatwave in western and
central Europe in summer 2003 showed that human
influence at least doubled the odds of such an event.
By accounting for the 0.81 °C rise in average summer
temperatures in Europe between the 1990s and 2003-12,
an updated study shows that moderate heatwaves that
would occur twice a century in the early 2000s are now
expected to occur twice every decade. Furthermore, in
little over a decade, the chances of more severe heatwaves
occurring, like that experienced in 2003, have increased
from less than once in a millennium in the late 1990s to
around once in a century. Observations of the summer
temperature across Europe over the years since 2003
suggest that we are continuing along a track where, by
the 2040s, more than half of summers are projected to be
warmer than that seen in 2003 if emissions of greenhouse
gases continue on their current rising path. The range of
summer European temperatures expected by 2100 under
two emissions futures are shown in Figure 7.
Carbon budgets and the link to global temperatures
Models indicate that limiting
global warming to 2 °C will require
large and rapid reductions of
near-term emissions sustained
well into the future
The amount of future warming depends not only on
current levels of greenhouse gas emissions, but also on
past emissions; in other words, the cumulative emissions
of greenhouse gases in the atmosphere. To have a 66%
chance of staying below a 2 °C rise in global average
temperature; compared to pre-industrial levels, total
cumulative emissions must remain less than 1000
gigatonnes of carbon (GtC). If not just CO 2
other greenhouse gases and aerosols are included in this
calculation, the amount that can still be emitted (the
global carbon budget) becomes even smaller at 790 GtC
(equivalent to 2900 GtCO 2
). Total anthropogenic emissions
to date since 1870 have reached just over 545 GtC
(2000 GtCO 2
Different climate models, using the same pathways of
concentrations, project a range of possible emissions
because they have different and plausible ways of
representing natural carbon sinks. However, not all natural
greenhouse-gas releasing mechanisms have been included
in these models. The possible effects of such a mechanism
are presented opposite.
Figure 8 shows the increase in global average temperatures
expected in two representative CO 2
pathways (RCPs), and Figure 9 the emissions which
correspond to these pathways. By mid century, despite
large and rapid near-term emission reductions in RCP2.6,
the global average temperatures are similar to the highemissions
in RCP8.5 because of inertia in the climate system.
Temperature difference relative to 1850-1899 (°C)
Global average surface temperature change
1850 1900 1950 2000 2050 2100
FIGURE 8: Globally averaged surface temperature increases over the 20th
and 21st century from historical observations and under two different CO 2
concentration pathways. Around half of the RCP2.6 models exceed 2 °C of
global warming even with sustained emission reductions, highlighted by
the dark blue shading. Following IPCC SPM Figure 7.
However, by 2100, emissions from RCP8.5 result in a global
average temperature rise of over 4 °C over pre-industrial
levels. Only with the sustained, significant emission
reductions through to the end of the century, captured
by the RCP2.6 scenario, is the global average temperature
rise restricted to around 2 °C. But some models indicate
temperature rises of over 2 °C by 2100 even under
RCP2.6. With RCP2.6, net global emissions of CO 2
to approximately zero by 2100 (Figure 9). Some models
simulate greater weakening of natural carbon sinks than
others meaning an increased requirement for emissions
reductions or even active CO 2
Feedback from natural carbon-releasing processes
Carbon emissions (GtCO 2
Fossil fuel emissions
1850 1900 1950 2000 2050 2100
FIGURE 9: Average and 5th-95th range of compatible emissions profiles
over the 20th and 21st century for the two different CO 2
pathways. Around half of the RCP2.6 models include net negative
emissions in the final years of the 21st century, highlighted by the dark
Additional emissions from wetlands
and permafrost regions reduce the
carbon budgets allowed to attain
global temperature thresholds
There are many processes, known as feedback mechanisms,
in the Earth system that both influence and are influenced
by the climate and atmospheric CO 2
of the recent generation of climate models did not include
these effects from wetlands and permafrost regions,
because they are difficult to incorporate in an interactive
manner. The results of independent, offline experiments
show that these feedback mechanisms can have a
significant impact on the total amount of greenhouse
gases released over the 21st century.
Together, wetlands worldwide and permafrost regions
(Arctic and Antarctic tundra and high-altitude areas)
currently store vast quantities of carbon which could
be released as CO 2
and methane (CH 4
) if these regions
warm further. Any extra greenhouse gases emitted by
these natural sources will reduce the net anthropogenic
emissions allowable if global average temperature rise is
to be restricted to below 2 °C.
Including these natural greenhouse gas emission
mechanisms into projections from a high-emissions
scenario (RCP8.5) increase the annual amount of CH 4
and CO 2
emitted over time by an additional 20% of CO 2
and 4% CH 4
. Combining all these influences gives rise to
around an additional 100ppm of CO 2
in the atmosphere by
the end of the century, resulting in up to an extra degree
of warming by 2100.
The feedbacks from wetlands and permafrost regions can
be combined with other known processes to determine
their greenhouse gas input into the atmosphere. For a
global average temperature rise of 2 °C this reduces the
cumulative emissions that can be released by human
actions by around 100GtC (360 GtCO 2
) in the most
pessimistic simulation. This corresponds to about ten
years of anthropogenic emissions at the current rate.
Many benefits of emission reductions
Avoiding impacts from extreme seasonal temperatures and rainfall
Reducing greenhouse gas emissions will reduce the rate and
long-term effects of anthropogenic climate change. This
would result in smaller changes in the average conditions and
less severe extreme events. There are many benefits across a
wide range of sectors, from improvements in air quality and
human health to food and energy security. By comparing
impacts between greater or lesser amounts of global
temperature rise, the benefits of limiting anthropogenic
climate change can be demonstrated.
Adding simulated short-timescale variability into longterm
projections, illustrates the range of seasonal average
temperature and rainfall that regions might experience
under climate change. They can be expressed in terms of the
extreme hot, cold, wet or dry seasons which are associated
with the heatwaves, cold spells, floods, and droughts that
Using these simulations, the natural variability of future
climates can be compared by selecting those with global
average temperature rises of 2 °C or 4 °C by 2100. In the test
region of England and Wales, changes in average seasonal
temperature still follow the global patterns. However, the
inclusion of year-to-year variability shows that although
the chances of cold winters or wet summers reduce as the
world warms under climate change, they are still possible in
individual years, even with 4 °C of warming. An increasing
chance of dry summers with only a modest reduction in the
chances of very wet summers is expected. Hence, despite the
chance of cold winters and wet summers becoming less with
climate change, they do not vanish entirely; hence we still
have to be prepared for them.
By including the uncertainties derived from a wide range
of natural processes, these future projections can be used
to estimate the range of extreme weather events that could
be experienced. The average maximum daily temperatures
experienced in London during a 1-in-50 year event increase
from 35.7 °C over 1961-90 to 38.8 °C by the 2050s. And the
average autumnal 5-day rainfall event totals increase from
78.4 mm to 87.0 mm.
The chances of a colder than average winter
(according to 1961-90 long-term averages) are
about 20% by 2020, but they drop to 4% by 2100.
The chance of the very cold winter temperatures
seen in 2009/10 was about 6%, but by 2100 the
chance drops to less than 1%.
No strong change in winter average rainfall
amounts was found. However significant increases
in extreme rainfall events in autumn are expected.
The chances of a summer considered very hot
historically (happening once every 20 years) rises to
occurring 9 times out of 10 by 2100 (i.e. happening
much more often than not).
For the next 20 years there is still a 35-40% chance
of getting a wetter than average summer. The
chance drops to about 20% by 2100.
The chances of a very wet summer (defined as 20%
more rain than the 1961-90 average) are expected to
fall from 18% in 2020 to 10% by 2100.
TABLE 1: Changes to England and Wales summer and winter temperature and rainfall during the 21st century under a medium-high emissions scenario.
-4 -2 0 2 4 6 8 10
Temperature anomaly (°C)
-4 -2 0 2 4 6 8 10 12
Temperature anomaly (°C)
-100 -50 0 50 100 150 200
Precipitation anomaly (%)
-100 -50 0 50 100 150 200 250
Precipitation anomaly (%)
2 °C of global average temperature rise 4 °C of global average temperature rise
FIGURE 10: Distributions of summer and winter temperature and rainfall under global average warming of 2 °C and 4 °C for England
and Wales. A clear shift to warmer temperatures is seen for both cases, but with more extreme summer and winter warm periods
more likely under 4°C. There is little change in average winter rainfall, but drier summers are more likely in a warmer world.
Climate change and food insecurity
A warming climate increases vulnerability to food insecurity across the globe,
but mitigation can limit this trend
Among the most significant impacts of climate change is
the potential increase of food insecurity and malnutrition.
Understanding the specific impacts of climate change on
food security is challenging because the relationship
between climate and the dimensions of food
security is complex. Food security itself
is more than a simple measure of
production; it also includes not
only availability of food, but
also access, utilisation and
stability. Climate change
will affect all aspects
of food security,
and threatens to
Here we show
a measure of
countries. This is
a measure of how
vulnerable to disruption
a country’s food security
system is as a result of flood
and drought events. The presentday
measure of vulnerability to food
insecurity is shown in Figure
11. Figures 12-15 show future
projections under two scenarios
of greenhouse gas emissions,
RCP2.6 and RCP8.5, for the 2050s
Vulnerability to food insecurity
The index shows vulnerability to food insecurity increasing
by the 2050s under both RCP scenarios. However there are
marked differences between the two by the 2080s. The
scenario with rapid and sustained reductions in future
global emissions (RCP2.6) changes little from
the 2050s to the 2080s. However, the
high global emissions scenario
(RCP8.5) shows further
substantial increases in
vulnerability by the 2080s,
as climate change
continues unabated in
FIGURE 11: Vulnerability is comprised of an index that measures
the exposure of national food systems to climate-related hazards,
their sensitivity to impacts of the climate hazards, and their
ability to respond in the face of these impacts. The index has
been designed so that it is best suited to measuring vulnerability
in developing and least developed countries.
of vulnerability to
show that in the
next few decades,
warming as a
result of the inertia
in the climate
system will threaten
food security in
developing and least
regardless of emissions
over that timeframe.
However, beyond the 2050s
the benefits of mitigation are
clear. Under RCP8.5 the levels of
vulnerability to food insecurity continue
to rise, but under RCP2.6 they
remain stable at approximately
the same levels as in the 2050s.
RCP2.6 – 2050s
RCP2.6 – 2080s
Vulnerability to food insecurity
FIGURE 12: Vulnerability to food insecurity under RCP2.6 in the 2050s.
Vulnerability to food insecurity is projected to increase from the present
day. Even with rapid and sustained reductions in greenhouse gas
emissions, the climate will continue to change in the next few decades,
with negative consequences for food security.
FIGURE 13: Vulnerability to food insecurity under RCP2.6s in the 2080s.
Vulnerability to food insecurity is projected to remain steady after
the 2050s. With rapid and sustained reductions in greenhouse gas
emissions, the climate stabilises over time and, although the situation is
worse than the present day, it does not continue to deteriorate.
RCP8.5 – 2050s
RCP8.5 – 2080s
Vulnerability to food insecurity
FIGURE 14: Vulnerability to food insecurity under RCP8.5 in the 2050s:
Vulnerability to food insecurity is projected to increase from the present
day, as a result of the impacts of climate change.
FIGURE 15: Vulnerability to food insecurity under RCP8.5 in the 2080s.
Levels of vulnerability to food insecurity across the developing world are
projected to increase further still, as a result of climate change.
For further information on these results and to explore how climate change compares against scenarios of adaptation
please visit www.metoffice.gov.uk/food-insecurity-index
The focus of the work by the Met Office Hadley Centre is driven by the Hadley Centre Climate Programme (HCCP).
Related work from other projects benefits from underpinning science from the HCCP. Here we highlight an example of a
project we are leading.
The Met Office Hadley Centre is working in partnership with
the Grantham Institute, Tyndall Centre and Walker Institute
on the AVOID2 programme, which is providing answers
to questions around the issue of “preventing dangerous
anthropogenic interference with the climate system”.
The top-level, policy-relevant result from the programme is
that keeping warming to less than 2 °C is still within reach.
However, this would involve global emissions peaking
before 2030 or sooner, and a significant and sustained global
decarbonisation with removal of atmospheric CO 2
Recent results describe some cost-optimal pathways to
achieving less than 2 °C with the following characteristics:
electricity highly decarbonised by 2050; sectors such as
industry, transport and buildings shift to electricity and other
low-carbon fuels; and, a substantial deployment of carboncapture
and storage (CCS). The sooner global mitigation
action begins and emissions peak, and the sooner CCS is
scaled-up, the lower costs will be. For example, meeting less
than 2 °C but waiting until 2030 for global mitigation action
to start would cost two-thirds more in GDP compared with
global action starting in 2020. Similarly, the necessary rates of
decarbonisation to meet less than 2 °C would be two to three
times greater when starting in 2030 compared with action
starting in 2020.
If reductions in CO 2
emissions occur later in the century,
then to keep within the 2 °C limit there will be a greater
requirement for BECCS (BioEnergy with CCS), which may hit
planetary limitations. Changing land-use to bio energy crops
can give rise to extra CO 2
emissions (e.g. from deforestation),
which need to be included when assessing the net effect of
BECCS on future global CO 2
emissions. Therefore CO 2
is not a substitute for near-term emissions reductions.
Investigation of the Intended Nationally Determined
Contributions (INDCs) show a long term global average
surface temperature change of likely less than 2.7 °C by 2100,
compared with over 5 °C with no mitigation. The proportion
of impacts avoided by following the INDC pledge pathway
compared to a no mitigation scenario is of the order of 75%
(e.g. for heatwave exposure) to 50% reduction of people
affected by flooding per year, to 25% reduction in area of
cropland experiencing a decline in suitability for crop growth.
The avoided impacts depend strongly on what happens to
emissions after 2030.
millions of people
exposed to heatwaves/year
Emissions capped at INDC level
Strong further action to meet 2°C target
thousand km 2
millions of people
FIGURE 16: Global impacts of mitigation at INDC and higher levels
compared to no action.
millions of people exposed
to increased water stress
Accumulated Cyclone Energy – a measure used to quantify
the intensity of individual tropical cyclones and also entire
seasons. For the seasonal measure it accounts for the number,
duration and intensity of all the storms that occurred during
Adaptation – Actions taken to adapt to a future, changing
climate to cope with, for example, rising sea-levels, changes
in rainfall amounts or intensity and increases in heatwave
duration and severity.
Earth-system – Used to describe situations where all physical,
chemical and biological processes occurring on, in and
around the Earth are considered.
Mitigation – Actions taken to prevent given levels of climate
change occurring. This is usually achieved by decreasing
the amount of greenhouse gases present in the atmosphere
through reducing emission rates or enhancing processes
which remove these gases.
HadCRUT4 – Met Office and the Climate Research Unit,
University of East Anglia (www.metoffice.gov.uk/hadobs/
NOAA-GlobalTemp – NOAA-National Centers for
Environmental Information Merged Land Ocean Surface
NASA-GISS – NASA Goddard Institute for Space Studies
GHCNDEX – Global Historical Climate Network – Daily –
NSIDC – National Snow and Ice Data Center
University of Colorado – Sea Level Research Group
Projections – Climate model experiments run using plausible
estimates for future greenhouse gas emissions and other
processes that affect the climate to provide best possible
information for future conditions. Different scenarios can
be created by using different emission models. See RCP.
RCP – Representative Concentration Pathway. These indicate
possible trajectories of greenhouse gas (and aerosol)
concentrations over the 21st Century. They do not prescribe
the emissions that lead to these concentrations. Four standard
RCPs are used, and are identified by the equivalent increase
in radiative heating that the greenhouse gas concentrations
result in by 2100. RCP2.6 has concentrations of greenhouse
gases peaking early in the 21st century, before falling
rapidly by 2100, whereas RCP8.5 has continued increases
in atmospheric greenhouse gas concentrations throughout
the 21st century. A further two, RCP4.5 and RCP6.0, are
Paul van der Linden
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