the impacts of 1.5°c · 2016. 11. 16. · the impacts of climate change for the most vulnerable in...

A science briefing

REPORT

M-625 | 2016

The Impacts of 1.5°C

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COLOPHON

Executive institution

Climate Analytics

Project manager for the contractor Contact person in the Norwegian Environment Agency

Carl-Friedrich Schleussner Maria Malene Kvalevåg

M-no Year Pages Contract number

625 2016 19 16088182

Publisher The project is funded by

Norwegian Environment Agency/ Miljødirektoratet

Norwegian Environment Agency/ Miljødirektoratet

Author(s)

Carl-Friedrich Schleussner

Title – Norwegian and English

The impacts of 1.5C – a scientific briefing

Summary – sammendrag

This report reviews the current state of the literature on the differences in climate impact

projections between 1.5°C and 2°C. There are discernible differences for extreme weather events in

particular on the regional level, impacts on unique and threatened systems such as coral reefs, water

availability and tropical crop yields as well as abrupt shifts in the climate system and long-term sea-

level rise risks. Limiting warming to 1.5°C would substantially reduce the impacts of climate change

for the most vulnerable in particular in the Tropics, as well as in high-latitude regions. More science

is required to improve our understanding of the impacts of climate change at 1.5°C and the avoided

impacts when limiting warming to 1.5°C compared to 2°C or higher levels to provide a robust basis

for the IPCC special report. Coordinated efforts by the scientific community are underway to address

these issues and a wealth of new studies can be expected in time for the 1.5°C special report.

4 emneord 4 subject words

Effekter av klimaendringene, global oppvarming, 1.5 graders, Parisavtalen

Climate impacts, global warming, 1.5 degrees, Paris agreement

Front page photo

Jørgensen, Bjørn, Scanpix

The Impacts of 1.5°C | M-625

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Content

Executive Summary ............................................................................................ 3

1. Introduction ................................................................................................. 3

2. Climate Impact Projections at 1.5°C ................................................................... 4

2.1 Extreme Weather Events ............................................................................ 5

2.1.1 Extreme Temperatures ...................................................................... 5

2.1.2 Extreme Precipitation ....................................................................... 6

2.1.3 Droughts ........................................................................................ 6

2.1.4 Tropical Cyclones ............................................................................. 6

2.1.5 Quasi-resonant amplified mid-latitude planetary waves .............................. 6

2.1.6 El Niño Southern Oscillation ................................................................ 7

2.2 Impacts on Ecosystems .............................................................................. 7

2.3 Water Availability and Crop Yields ................................................................ 8

3. Climate Impacts Byond 2100 and Abrupt Shifts in the Climate System ........................... 9

3.1 Long-term Sea-level Rise ............................................................................ 9

3.2 Tipping elements and abrupt shifts in the Earth System .................................... 10

4. Vulnerability, livelihoods and sustainable development .......................................... 11

4.1 Impacts on health and labour productivity .................................................... 12

5. Scenario dependence of impacts at 1.5°C scenarios ............................................... 13

6. Key research questions and planned scientific activities for the 1.5°C Special Report ..... 14

7. References ................................................................................................. 15


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Executive Summary

International climate action is guided by and evaluated against targets to limit the

increase in global average temperature above preindustrial levels. The Paris

Agreement includes a long-term global temperature goal of “holding the increase in

the global average temperature to well below 2 °C… and pursuing efforts to limit the

temperature increase to 1.5 °C above pre-industrial levels, recognizing that this

would significantly reduce the risks and impacts of climate change.” Climate impacts

at 1.5°C, however, have not been a focus of the scientific community so far including

in the most recent fifth Assessment Report of the IPCC. The upcoming IPCC Special

Report on 1.5°C will aim to fill this gap. Here we review the current state of the

literature on the differences in climate impact projections between 1.5°C and 2°C.

We find discernible differences for extreme weather events in particular on the

regional level, impacts on unique and threatened systems such as coral reefs, water

availability and tropical crop yields as well as abrupt shifts in the climate system and

long-term sea-level rise risks. Limiting warming to 1.5°C would substantially reduce

the impacts of climate change for the most vulnerable in particular in the Tropics, as

well as in high-latitude regions. More science is required to improve our

understanding of the impacts of climate change at 1.5°C and the avoided impacts

when limiting warming to 1.5°C compared to 2°C or higher levels to provide a robust

basis for the IPCC special report. Coordinated efforts by the scientific community are

underway to address these issues and a wealth of new studies can be expected in

time for the 1.5°C special report.

1. Introduction

At its 43rd plenary, the IPCC decided “to accept the invitation from the UNFCCC to provide a

Special Report in 2018 on the impacts of global warming of 1.5°C above pre- industrial levels

and related global greenhouse gas emission pathways, and decides to prepare a Special

Report on this topic in the context of strengthening the global response to the threat of

climate change, sustainable development and efforts to eradicate poverty.”(IPCC, 2016).

By doing so, the IPCC followed an invitation by the UNFCCC spelled out in its decision

paragraph 21, 1/CP.21 on this matter. In addition to that, also decision 10/CP.21 on the 2013-

2015 Review of the long-term global goal and the overall progress made towards it addresses

these questions. Paragraph 8, 10/CP.21: “Encourages the scientific community to address

information and research gaps identified during the structured expert dialogue, including

scenarios that limit warming to below 1.5 °C relative to pre-industrial levels by 2100 and the

range of impacts at the regional and local scales associated with those scenarios.” (UNFCCC,

2015a).

It is important to note that when the IPCC 43rd plenary agreed to the 1.5°C special report,

many developing countries expressed their wish that this report should also include the

implications for sustainable development. There is therefore an expectation that the

assessment of impacts at 1.5°C will necessarily include an assessment of implications for a


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wide range of sustainable development parameters and metrics. The context for this is that

some developing countries are concerned that mitigation could interfere with their ability to

develop and to eradicate poverty, while for others the impacts of climate change are a main

obstacle for sustainable development. It is thus important that the design of the special

report includes assessment of these issues, including the effects of climate impacts on

poverty eradication and sustainable development, the co-benefits of mitigation and any

linkages to impacts, vulnerability and adaptation.

These decisions have been informed by the multi-year process of the 2013-2015 Review

including a structured expert science-policy dialogue (SED). The SED concluded its work in

2015 and published a comprehensive summary report that in particularly also assessed the

impacts at different levels of global mean temperature (GMT) increase such as 1.5°C and 2°C.

The report found that a ''concept in which up to 2°C of warming is considered safe, is

inadequate and would therefore be better seen as an upper limit''. On the other hand, it also

recognized substantial science-gaps in differentiation in impacts between a 1.5°C and a 2°C

warming limit (UNFCCC, 2015b). Such impact differentiation has not been at the focus of

scientific community in the IPCC AR5 and there is an expectation that the special report of

the IPCC will also address these issues.

In the following, the current state of the literature on the differences in climate impact

projections between 1.5°C and 2°C will be presented. In particular, results for different

impact and region specific findings will be outlined. This is followed by an analysis of risks at

multi-century time scales including abrupt shifts and large-scale so-called tipping elements in

the earth system. Implications for sustainable development will be analyzed. Finally, some

elements that require further research will be outlined including questions of scenario

dependence of impacts at 1.5°C and current research activities aiming at addressing these in

time for the 1.5°C special report.

2. Climate Impact Projections at 1.5°C

For the first time, an IPCC report focusses on a warming level rather than using a scenario

approach. Such GMT targets do not stand for themselves but rather serve as ‘focal points’ to

operationalise the ultimate objective of the United Nations Framework Convention on Climate

Change (UNFCCC) ‘avoiding dangerous interference’ with the climate system. They are

therefore primarily rooted in political risk assessments (Jaeger and Jaeger, 2011; Knutti et

al., 2015), which also means that the information on projected impacts of a greenhouse gas

(GHG) induced GMT increase (such as 1.5°C and 2°C above pre-industrial levels) provided the

basis for the adoption of different temperature limits.

To best assess the impacts at different levels of warming, translating global limits into

regional- and impact-related consequences as also requested in the respective UNFCCC

decisions is required. Feil! Fant ikke referansekilden. provides an overview of key

differences in climate impacts between 1.5°C and 2°C based on a recent literature

assessment.


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Figure 1 Projected impacts at 1.5 °C and 2 °C GMT increase above pre-industrial levels for a selection of indicators

and regions. a, Increase in global occurrence probability of pre-industrial 1-in-a-1000 day extreme temperature

events (Fischer and Knutti, 2015). b, Increase in extreme precipitation intensity (RX5Day) for the global land area

below 66° N/S and South Asia (Schleussner et al., 2016a). c, Reduction in annual water availability in the

Mediterranean (Schleussner et al., 2016a). d, Share of global tropical coral reefs at risk of long-term degradation

(Frieler et al., 2012). e, Global sea-level rise commitment for persistent warming of 1.5 °C and 2 °C over 2000 years

(Levermann et al., 2013). f, Changes in local crop yields for present-day tropical agricultural areas (Schleussner et

al., 2016a) (below 30° N/S, model dependent implementation of present day management). Dashed boxes: no

increase in CO2 fertilization (No CO2). Panels b, c and f display median changes that are exceeded for over 50% of the

respective land areas. From (Schleussner et al., 2016b), Copyright with Nature Climate Change.

Extreme Weather Events

Extreme weather events are among the most impact relevant climate hazards. Regional

assessments for extreme weather events including extreme temperatures and precipitation

are key to understand differences in the climate signals and to assess the differences

between different warming levels (Seneviratne et al., 2016). In the following, assessments for

different types of extreme weather events as well as large scale circulation systems affecting

the occurrence of such events are provided.

2.1.1 Extreme Temperatures

Changes in temperature extremes are found to be particularly pronounced (Figure 1a). Recent

assessments of the difference in the occurrence of heat extremes between 1.5°C and 2°C

found a robust difference between the warming levels indicating that the probability of

occurrence of a hot extreme almost doubles between 1.5°C and 2°C (Fischer and Knutti,

2015). Relative to a comparably smaller natural variability, a warming of 2°C would imply a

new climate regime in terms of heat extremes in tropical regions (Schleussner et al., 2016a)

and currently unusual heat waves are projected to become the new normal in Africa (Russo et

al., 2015). The world’s poorest people, that are dominantly located at low latitudes, will be

exposed to substantially more frequent daily temperature extremes at much lower levels of

warming then their wealthier counterparts (Harrington et al., 2016), with substantial

implications for human health as well as labor productivity (Dunne et al., 2013) or even

habitability of certain areas (Pal and Eltahir, 2015)


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2.1.2 Extreme Precipitation

Unlike trends in extreme temperature, patterns for precipitation related changes are

considerably more uncertain, although robust changes in the water cycle may be experienced

by half of the world's population under a 2°C warming (Sedláček and Knutti, 2014). A robust

increase in the intensity of heavy precipitation events (Absolute annual maximum of

consecutive 5-day precipitation, RX5Day, see Figure 1 b) of about 5% (66% uncertainty range:

[4,6%]) relative to the 1986-2005 reference period for 50% of the global land-area under a

1.5°C warming and 7% [5,7%] under a 2°C warming is projected globally (Schleussner et al.,

2016a). These changes are particularly pronounced in high northern latitudes and South Asia,

where an intensification of about 10% is projected under 2°C (Schleussner et al., 2016a).

However, extreme precipitation may also increase over the world’s dry regions, which

indicates that even regions experience an overall drying trend may at the same time see an

increase in extreme precipitation risk highly relevant for flooding (Donat et al., 2016). The

fraction of extreme precipitation events attributable to anthropogenic influence is estimated

as about 30% [20,40%] under 1.5°C and to increase to about 40% [30,50%] under 2°C (Fischer

and Knutti, 2015).

2.1.3 Droughts

With regard to dry extremes, the majority of the global land area may experience only minor

changes in dry spell length (Consecutive Dry Days, CDD) under a 1.5°C or 2°C warming

relative to the reference period. Robust changes are projected for about 25% of global land

area (Schleussner et al., 2016a) such as the subtropical regions and in particular in the

Mediterranean, where an extension of dry spell length of about 7% [4,10%] and 11% [6,15%]

for 1.5°C and 2°C is projected, respectively. It is, however, important to highlight that these

changes only relate to meteorological drought (precipitation induced only), rather than

including effects of temperature increase on evapotranspiration and soil moisture, which are

of key relevance to assess hydrological droughts. As increasing temperatures increase

evapotranspiration, drought conditions can also be elevated without necessarily decreasing

precipitation. If such effects are included, robust increases in drought occurrences are

projected for large areas globally (Dai, 2013; Prudhomme et al., 2013). In addition, also local

anthropogenic activity will interfere with the hydrological signal (Van Loon et al., 2016).

2.1.4 Tropical Cyclones

Studying the difference in storm activity such as tropical cyclones for 1.5°C and 2°C is

hampered so far by limited statistics of such events based on the current climate model

designs. However, with warming sea-surface temperatures and atmospheric adjustments, a

continuation of the poleward migration (Kossin et al., 2014) of such cyclones as well as

increases in intensity (Wing et al., 2015) are expected to increase with increasing warming

(Emanuel, 2013).

2.1.5 Quasi-resonant amplified mid-latitude planetary waves

Projections of extreme events are subject to substantial uncertainties related to the model

capabilities adequately reproducing such events, but also related to large-scale circulation


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adjustments related to climate change. One such phenomenon that present generation

climate models do not capture in full is related to quasi-resonant amplified mid-latitude

planetary waves (Coumou et al., 2014), which has been shown to increase probabilities of

specific norther latitude extreme weather events such as heat waves in western North

America and central Asia, cold outbreaks in eastern North America, droughts in central North

America, Europe and central Asia, and wet spells in western Asia (Screen and Simmonds,

2014). Although the processes driving these amplifications are not yet fully understood and

may differ between summer and winter events, sea-ice concentrations appear to be an

important driver at least of winter extremes (Kretschmer et al., 2016). As northern

hemisphere sea-ice is highly sensitive to levels of warming around 1.5°C, our understanding of

the atmospheric impacts of vanishing sea ice needs to be advanced to better assess the risks

posed by such wave amplifications for the mid-latitudes.

2.1.6 El Niño Southern Oscillation

Extreme event occurrences with multi-annual re-occurrence times will be strongly affected

by the El Niño Southern Oscillation (ENSO) in particular over tropical regions (Seneviratne et

al., 2012). Post-AR5 studies have shown that ongoing warming will lead to more extreme El

Niño as well as La Niña conditions (Cai et al., 2015a, 2015b; Latif et al., 2015). Enso related

extreme weather events such as extreme precipitation in South America or drying in Southern

Africa may thereby become more frequent. Changes in ENSO at 1.5°C, however, have not yet

been assessed and given substantial uncertainties in present generation models and the lack

of targeted 1.5°C and 2°C scenarios, it will hardly be possible to distinguish changes at 1.5°C

and 2°C warming in the near future.

Impacts on Ecosystems

Climate change has been recognized as one of the major threats to ecosystems (Oppenheimer

et al., 2014) and the velocity of climate change exceeds the mobility of many terrestrial

species for a warming exceeding 1.5°C (IPCC, 2014). In addition, ocean ecosystems appear to

be particularly threatened by climate change due to warming, deoxygenation as well as ocean

acidification (Gattuso et al., 2015). Risks for several coastal and marine organisms are found

to be high already for a warming around 1.5°C, which also comes with detrimental

consequences for ecosystem services such fisheries or coastal protection. In particular, global

coral reef systems are projected to be threatened by ocean acidification and thermal stress

(Frieler et al., 2012; Meissner et al., 2012). Projections accounting for warming as well as

ocean acidification indicate that virtually all global warm water coral reef systems will be at

risk of long-term degradation under a warming of 2°C and only under 1.5°C some of these

systems may survive (compare Figure 1 d). Similarly, polar ecosystems and traditional

livelihoods are under immense pressure as sea-ice vanishes and only a long-term warming of

well below 2°C may ensure significant summer sea-ice coverage in the Arctic (Hezel et al.,

2014). Taken together, these findings give additional justification to the assessment of

attributing high to very high risks for unique and threatened systems, one of the five key

reasons for concern in the IPCC AR5 (Oppenheimer et al., 2014).


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Water Availability and Crop Yields

Patterns of change in water availability emerge similarly to changes in water cycle extremes

(Schewe et al., 2014). While global changes are not yet significant, an increase in water

availability exceeding 5% and 10% is projected for high-latitudes regions, as well as the South-

Asian monsoon regions for a 1.5°C and 2°C warming (Schleussner et al., 2016a). At the same

time, water availability is projected to decrease in subtropical regions and most prominently

in the Mediterranean (see Figure 2 c). Total annual water availability in this region is

projected to reduce by about 9% at 1.5°C and by about 17 % at 2°C compared to the 1986-

2005 reference period. Risks also emerge for other, particularly subtropical regions such as

Central America, South Africa or Australia.

Crop yield projections are highly uncertain and differ substantially on the regional level.

While being sensitive to uncertainties arising from climate projections (in particular related

to changes in the water cycle), the dominant uncertainty arises from crop models that differ

substantially in the represented processes (Nelson et al., 2014). Most prominent processes

include CO2 fertilization (McGrath and Lobell, 2013), effects of other pollutants such as ozone

concentrations (Tai et al., 2014), or the impact of heat extremes (Deryng et al., 2014). In

addition, assumption about management changes and autonomous adaptation in agriculture

models differ considerably (Nelson et al., 2014).

Among these, CO2-fertilization also affecting the water use efficiency of the plants features

particularly prominent, as it would lead to increasing yields and thereby counterbalancing or

even overcompensating for detrimental effects of climate change. However, effects of CO2-

fertilization play out very differently between regions, with much higher gains in temperate

and higher latitudes than in tropical regions (Deryng et al., 2016). At the same time, it is

unclear to what extend such projected gains due to fertilization are realistic, as the

observational record indicates increased impacts of climate change on crop yields already in

the observational record mainly related to climate-related natural disasters (Moore and

Lobell, 2015). In an assessment of cereal production losses across the globe resulting from

extreme weather disasters during 1964–2007 it has been found that droughts and extreme

heat significantly reduced national cereal production by 9–10% (Lesk et al., 2016).

Figure 1 f shows projections of median yield changes at 1.5°C and 2°C warming for tropical

regions and different crop types based on (Schleussner et al., 2016a). Even when accounting

in full for the effects of CO2-fertilization, median tropical maize and wheat local yields are

projected to decrease at 1.5°C and this decrease is projected to double under 2°C.

Projections for soy and rice indicate a median increase in yields under 1.5°C, but little

additional gain for a warming of 2°C, indicating that positive effects of increased CO2 are

increasingly counterbalanced by detrimental climate effects.


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3. Climate Impacts Byond 2100 and

Abrupt Shifts in the Climate System

Many impacts of climate change will not materialize fully in this century, but rather over

centuries and millennia to come. This is particularly the case for the impacts on the ocean

and the cryosphere such as ocean acidification (Mathesius et al., 2015), glacier melt and sea-

level rise (Clark et al., 2016), and loss of permafrost (Schneider von Deimling et al., 2012).

Long-term Sea-level Rise

Even after temperatures stabilize or decline, sea-levels will continue to rise for centuries to

come with contributions from thermal expansion of the ocean, as well as glaciers and in

particular the Antarctic and Greenland ice-sheet. A peak warming within the range of current

iNDCs with a Carbon Budget of 1,250 GtC (after the year 2000) could be sufficient to trigger

substantially losses of the Greenland and Antarctic ice sheets eventually leading to about 20m

sea-level rise over 10, 000 years (Clark et al., 2016; Winkelmann et al., 2015). As displayed in

Figure 1 e, a persistent warming of 1.5°C over 2000 years would lead to a sea-level rise of

about 3 m, compared with nearly 5 m for 2°C. On average, 2000-year sea-level rise is

projected to increase by 2.3m per °C warming (Levermann et al., 2013), that could be

substantially higher on even longer time scales. However, the regional distributions of such

sea-level rise would differ decisively. As for future warming above pre-industrial levels, the

dominant contributions to sea-level rise would come from the polar ice-sheets, equatorial

sea-levels would rise above the global average.

Figure 2 An overview of selected tipping elements of the earth system and future temperature

trajectories. The exact location when such tipping points would be triggered is uncertain, and the ranges

indicated comprise data-driven assessments as well as expert elicitations. WAIS: West Antarctic ice-

sheet, THC: Atlantic thermohaline circulation, ENSO: El Nino Southern Oscillation. From (Schellnhuber,

H. J. Rahmstorf and Winkelmann, 2016), Copyright with Nature Climate Change .


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Tipping elements and abrupt shifts in the

Earth System

Key contributions of long-term future sea-level rise come from Greenland and parts of the

Antarctic ice sheet that are classified among the tipping elements of the earth system, which

means that they are projected to exhibit self-amplifying and strongly non-linear behavior

above a critical threshold. Once such dynamics are triggered, these ice-sheets would be in

unstable, irreversible retreat. For the Greenland ice sheet, the best estimate of such a

threshold is around 1.6°C GMT increase above pre-industrial levels (Robinson et al., 2012).

Recent findings from West Antarctica suggesting that an irreversible marine ice-sheet

instability might have already been triggered there for several basins (Favier et al., 2014;

Joughin et al., 2014), although a direct attribution of this tipping to an anthropogenic origin

cannot be made with sufficient confidence. At the same time, other potentially unstable

basins have been identified in East Antarctica (Mengel and Levermann, 2014). For the West

Antarctic ice sheet, some findings suggest that a full destabilization of the ice sheet, implying

at least 3 m of global sea-level rise, could be triggered following just another 60 years of

currently observed melt rates (Feldmann and Levermann, 2015). Although the underlying

time-scales of such a disintegration may reach up to several millennia, a thorough assessment

of a long-term global temperature limit requires to factor in such long-term effects. Evidence

from earth history indicates, that sea-levels during past warming periods not exceeding 2°C

above pre-industrial levels have been 6-13m higher than today (Dutton et al., 2015).

Figure 2 depicts a range of such tipping elements and an assessment of their respective

‘tipping points’. Several of these elements, including the West Antarctic and the Greenland

ice-sheet, Alpine Glaciers, Arctic summer sea-ice, but also tropical coral reefs fall within the

range of 1.5-2°C GMT increase above pre-industrial levels or even below.

These large scale identified tipping elements may, however, not be the only parts of the

climate system exhibiting abrupt or highly non-linear change with respect to increasing global

mean temperature. Recently, (Drijfhout et al., 2015) provide a catalogue of such abrupt

shifts in current generation climate models for warming scenarios exceeding 10°C. They

identified 37 such shifts including in in ocean circulation, sea ice, snow cover, permafrost,

and terrestrial biosphere and found that about 50% of all abrupt shifts identified already

occur at 2°C above pre-industrial levels, and only about 20% at a warming level of 1.5°C.

Their assessment, however, is based on occurrences of such abrupt shifts in individual climate

models, rather than ensembles, and from transient climate scenarios with contiguously

increasing temperatures. Thereby, abrupt shifts that occur with a certain time lag after the

forcing may not be adequately attributed.


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Figure 3 Poverty projections for 2030 for different policy choices and climate change scenarios. From (Hallegatte et

al., 2015).

4. Vulnerability, livelihoods and

sustainable development

The 1.5°C special report also speaks to requirements of poverty eradication and sustainable

development. Chapter 13 of the IPCC AR5 Working Group 2 report, assessed impacts on

livelihoods and poverty (Olsson et al., 2014). They found that:

“Climate change will create new poor between now and 2100, in developing and

developed countries, and jeopardize sustainable development. The majority of severe

impacts are projected for urban areas and some rural regions in sub-Saharan Africa and

Southeast Asia (medium confidence, based on medium evidence, medium agreement).

Future impacts of climate change, extending from the near term to the long term,

mostly expecting 2°C scenarios, will slow down economic growth and poverty reduction,

further erode food security, and trigger new poverty traps, the latter particularly in

urban areas and emerging hotspots of hunger. “

Similarly, the regional chapter on Africa (Niang et al., 2014) assesses that:

“Of nine climate-related key regional risks identified for Africa, eight pose medium or

higher risk even with highly adapted systems, while only one key risk assessed can be

potentially reduced with high adaptation to below a medium risk level, for the end of

the 21st century under 2°C global mean temperature increase above preindustrial levels

(medium confidence)”.

To what extent limiting warming to 1.5°C would reduce such risks remains an open question,

in particular as these impacts are to a large extent driven by vulnerabilities and exposure and

not just by an increase in climate hazards. The impacts of the 2015-2016 extreme El Nino

event in Africa underscore the vulnerability of these countries to climate hazards already at

current levels of warming.


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A recent comprehensive report of the World Bank addressed the impacts of impacts of

climate change on poverty (Hallegatte et al., 2015) and found clear evidence that climate

change is a threat to poverty eradication. In this report, different scenarios of climate change

impacts and socio-economic development until 2030 have been assessed (see Feil! Fant ikke

referansekilden.). Although socio-economic development clearly dominates, a high impact

climate change scenario is found to increase 2030 poverty levels by around 10% regardless of

the development scenario assumed. Under a low impact scenario, this increase will be

reduced to about 3%. Such findings are of great relevance for assessing near-term benefits of

stringent mitigation, as small differences in the climate hazard may be substantially amplified

by the extreme vulnerability of the global poor in the near term. The importance of this near-

term perspective is also underscored by assessments of risks for agricultural production. As

the bulk of growing food demand is expected in the next decades, impacts of smaller

magnitude in the near-term can be at least as consequential for food prices or food security

as larger magnitude impacts in the future (Lobell and Tebaldi, 2014). Such risks may be

further amplified by food supply shocks that arise from remote climate impacts in food

importing countries. It has been found that export bans in major producing regions, as a

result of for example climate disasters hitting such regions, would put up to 200 million

people below the poverty line at risk, 90% of which live in Sub-Saharan Africa (Bren d’Amour

et al., 2016).

Impacts on health and labour productivity

Health impacts of climate change may arise through a variety of factors also and in particular

also related to air quality and fossil fuel emissions. A direct health impact of climate change

is related to human mortality during extreme temperatures and a recent global cross-country

panel assessment (N=75 million deaths) showed that around 8% of observed mortality over the

1985 to 2012 was attributable to non-optimum temperatures, with the effect of cold

temperatures dominating the overall response (Gasparrini et al., 2015). Extreme hot and cold

events have been found to be responsible for about 1% of observed mortality in this panel.

Recently, first attempts to attribute excess deaths during heat waves have revealed that a

share of the fatalities during the 2003 heat wave in London and Paris can already be

attributed to anthropogenic climate change (Mitchell et al., 2016a). As projections of

extreme heat differ considerably between 1.5°C and 2°C, so may the effects on human

health.

Similarly, rising temperatures are projected to have detrimental consequences on labor

productivity (Zander et al., 2015). A global assessment of labor productivity indicated that a

warming of 2°C around 2050 could reduce global labor productivity by about 10% compared to

present day (Dunne et al., 2013).

As 1.5°C GMT increase above pre-industrial levels may already be reached in the 2030s,

establishing a direct connection between impacts at 1.5°C and the UN sustainable

development goals (SDGs) seems appropriate. In any case, integrated perspectives of SDGs

and warming targets should go beyond focusing on mitigation aspects only (Stechow et al.,

2016).


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5. Scenario dependence of impacts at

1.5°C scenarios

The preliminary findings of climate impacts at 1.5°C presented above are generally extracted

from existing scenario runs via approaches of pattern scaling or sub-selecting warming time

slices. A generalization of these findings is thereby based on the assumption of scenario

independence. While this assumption largely holds for temperature related signals, impacts

related to changes in the hydrological cycle as well as impacts including a socio-economic

component will show a clear scenario dependency. This is illustrated in Feil! Fant ikke

eferansekilden.Feil! Fant ikke referansekilden. that depicts the response of the global

annual precipitation for different RCP scenarios.

Figure 4 Illustration of scenario dependent changes in the global

precipitation response to different RCPs from (Mitchell et al., 2016b)

Displayed are changes in global mean precipitation annual-mean multi-

model-mean data from CMIP5 over the 2006-2100 period for RCP2.6 (blue)

and RCP8.5 (red). All anomalies are relative to pre-industrial levels.

Copyright with Nature Climate Change.

While precipitation changes under the continuous warming scenario RCP8.5 scale nearly linear

with GMT increase, the assessment of the RCP2.6 scenario reveals ongoing changes in the

hydrological cycle after GMT stabilization (Mitchell et al., 2016b). Such changes may be

related to dynamics of time lagged elements of the climate system, in particular the oceanic

response, (Herger et al., 2015) or regionally related to adjustments in large scale circulation

patterns such as the Atlantic Meridional Overturning Circulation (Schleussner et al., 2014).

Circulation related changes as e.g. the expansion of the Hadley Cell or movement of the

Intertropical Convergence Zone (ITCZ) may lead to highly non-linear regional changes or even

trend reversals under high emission scenarios (Hawkins et al., 2014).

Furthermore, most presently available emissions pathways that hold warming below 1.5°C in

2100 are characterized by a temporary overshoot above this warming level (Schleussner et

al., 2016b). Whether or not the impacts under such a 1.5°C scenario will be similar to non-

overshoot scenarios remains an open question.


14

6. Key research questions and planned

scientific activities for the 1.5°C

Special Report

Following the state of the current literature outlined above, a (non-exhaustive) list of key

research questions on the impacts of 1.5°C can be identified: 1. The consequences of peak warming and the duration of potential overshoot above 1.5°C

for associated climate impacts need to be assessed, as well as the longer term (multi-century and millennial) consequences of limiting warming to 1.5°C. This should include the assessment of tipping points and abrupt shifts.

2. Improved understanding of the consequences of ocean acidification and deoxygenation under 1.5°C pathways compared to higher levels of warming, and their implications for natural systems, livelihoods and marine living resources and related economic activities

3. The understanding of the potentials and limits of differentiating between different levels of warming in the light of model uncertainty and natural variability needs to be advanced.

4. The interlinkages between near-term warming and sustainable development trajectories need to be explored further. Given the substantial vulnerability to climate hazards in particular of the global poor over the next decades, near-term mitigation benefits arising from avoided impacts and the co-benefits of mitigation need to be reassessed.

5. Understanding the relationship between 1.5°C warming and achievement of the 17 recently adopted SDGs, in relation to high levels of warming and different socio-economic pathways.

A range of ongoing community research efforts are aiming at addressing impacts of 1.5°C

warming and to produce results in time for the 2018 special report. The following table

provides a (non-exhaustive) list of such activities and their main research aims.

Table 1 Ongoing research activities on 1.5°C impacts.


15

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Visiting address Trondheim: Brattørkaia 15, 7010 Trondheim

Visiting address Oslo: Grensesvingen 7, 0661 Oslo

the impacts of 1.5°c · 2016. 11. 16. · the impacts of climate change for the most vulnerable in...

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