Holm Tiessen, 2017

UNFCCC, ParisNovember 2015

The 2°C goal is not safe and 1.5°C has many benefits

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Key Messages from the UNFCCC Structured Expert Dialogue

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A long-term global goal defined by a temperature limit serves its purpose well

The ‘guardrail’ concept that a warming limit of 2° or 1.5° guarantees protection from dangerous anthropogenic interference no longer works

UNFCCC SED

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Assessing the adequacy of the long-term global CC goal implies risk assessments and value judgments not only at the global but also at regional and local levels

(Risk = probability x consequence)

We need benchmarks for sound climate policy in the light of national circumstances

UNFCCC SED

Holm Tiessen, 2017

We know how to measure progress on mitigation but challenges still exist in measuring progress on adaptation

The science on 1.5°C warming is less robust than for 2°C or more: is the difference really only a gradual increase in risks or does it include non-linear and threshold effects?

UNFCCC SED

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2°C warming should be a strict upper defence line

That defence line should be pushed as low as possible

The present 0.8°C warming already challenges the adaptive capacity of societies and ecosystems

Limiting warming to 1.5°C provides large benefitsin reduced damages, risks and adaptation needs

www.climateanalytics.org, 2015

Holm Tiessen, 2017

Countering the counter-argument:

mitigating for 1.5°C rather than 2°C does not pose greater risks to food security from biofuel competition

limiting warming to 1.5°C avoids large risks to food security

www.climateanalytics.org, 2015

Holm Tiessen, 2017

Recent science - policy discourse:

moved from 1.5° to significantly below 2°

assumes an overshoot is inevitable

wants to return to 1.5° by the end of the Century

whether to limit peak, end-of-century or long-term warmingis a political question

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Rising temperatures are not only an in situ phenomenonbut shift transitional zones and increase affected territory in- islands- mountains- high latitudes

Regional, national and international concerns needunderstanding of climate science in a societal context

Holm Tiessen, 2017

Questions on Mitigation and Adaptation

what is the relationship between changing means and extremes?

is CC reversible within "human" time scales (buffering)?

at what level of CC do irreversible changes occur?

what effects of CC are irreversible?

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To assess CC impacts and "desirable" limits

climate phenomena and their effectsmust be identified and quantified

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Drought types:

Meteorological drought is measured as the size and duration of a precipitation shortfall

Agricultural drought links meteorological drought to plant water demand, soil moisture deficits and agricultural impacts

Hydrological drought are effects of meteorological drought on water supply. they lag meteorological drought

Irrigation links agricultural and hydrological drought

Socio-economic drought are effects on the supply and demand of goods and services

American Meteorological Society

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There are direct effects of mean temperature change

zone of maximum freeze-thaw cycles shifts pole-ward and up-slopeaffecting:

- plants (trees)- cropping systems - soil C and N- technical structures (concrete)

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Alternating warm and freezing weather endangers vegetation, as early plant development may be cut by subsequent frosts

- freeze-thaw cycles reduce frost hardening and cause tree dieback- for winter crops this is agravated by lower snow pack- elevated CO2 increases frost sensitivity

Frost damage is an important issue as temperatures rise

Holm Tiessen, 2017Gu

Increased Cold Damage in a Warming World

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The University of Illinois warns that field working days are changing

the typical planting window for maize will be reduced and shifted bywarmer, wetter springs, and drier, hotter summers

April and May will be far too wet to work the fields, but a later planting window is risky because of summer droughts

new maize cultivars may be needed in the future:longer season (hoping for pollination before the drought) orshorter season (harvested before the drought, sacrificing yield)

Holm Tiessen, 2017

IPCC models and scenarios

fewer cold, and more warm days and nights arevery likely at the global scalelikely in North America, Europe, and Australia

for warming daily extremes there ismedium confidence for much of Asialow to medium confidence for Africa and South America- depending on the region

low confidence in predictions of El Niño or Monsoon regime changes- even in sign!

low confidence for the attribution of changes in tropical cyclone activity- because of incomplete understanding of the physical mechanisms

Holm Tiessen, 2017

Compare these model predictions to actual events:

From 2000 to 2008, Asia had the highest number of climate-related disasters

the Americas suffered the highest proportion (54.6%) economic losses,followed by Asia (27.5%) and Europe (15.9%)

Africa accounted for only 0.6% of global economic losses

- there are clearly problems with predicting but also with measuring climate events and impacts

Holm Tiessen, 2017

Current disaster impacts vary between regions:

Economic losses are higher in developed countriesFatalities and % GDP loss are higher in developing countries

but such statistics depend on highly variable data and are affected by few extreme extremes

impacts depend on the size of extremes and on return periods

Holm Tiessen, 2017

What is seen as extreme events depends on vulnerabilities:

location - heat wave in Sweden, rainfall on semiarid soils

adaptation - agriculture, disease control, urban design, infrastructure

extreme impact can be caused by less extreme events:for instance, at the geographical freeze-thaw boundary,freezing rain has brought down power grids

Holm Tiessen, 2017

discussion:

measurements, predictions, experiences,social perceptions and vulnerabilities

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Types of change

IPCC

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average summer temperatures around the 1900-2006 meanblue: observed 1900-2006red: projected 2090

The hottest summer on record in France (2003) was 3.6° above the meanThe average for 2090 is projected to be 3.7° above the meanThere is a small probability of summers 9.8° above the mean

Battisti et al

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How to quantify extremes?

count the number of record-breaking events and examine the count for any trenddistinguish hot extremes from cold extremes

combine indicators into a single Climate Extremes Index and measure the fraction of a region with high CEI

measure economic effects of extremes by an independentindex such as insurance payout

rarer, extremer events are naturally most difficult to quantify

Holm Tiessen, 2017

Predicting the incidence of extreme rainfall:

absolute humidity increases 7% per 1°C increase

absolute (but not relative) humidity increases are significant between 1973 and 2003 globally

increased atmospheric moisture content leads to increased precipitationoften as extreme rainfall

Holm Tiessen, 2017

Impacts of CC on agriculture a negative yield response to increased growing season temperatures explains one third of variations in global average yields of the six most widely grown crops.

between 1981 and 2002, high temperatures have resulted in annual combined losses for wheat, maize and barleyof 40 Mt or US$ 5 billion per year.

Lobell and Fields

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reduction in yield increases

wheat

maize

rice

temperature increase population increase

temperature increaseproductivity change food security risk

Global

Regional

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CO2 fertilization vs. CC

1 ppm of CO2 increase => ∼0.1% yield increase for C3 crops

35 ppm increase since 1981 should result in 3.5% yield increase

but there is a 3% decrease in wheat yield due to climate trends

effects of CO2 and climate have cancelled each other

CO2 benefits do not exceed temperature related losses - even below 2° warming

foregone global production of wheat (19 Mt yr-1), maize (12 Mt yr-1)and (barley 8 Mt yr-1)

Lobell and Fields

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Reanalysis of African maize trials:

each degree day above 30°C reduced the yield by 1% under optimal rain-fed conditions, and by 1.7% under drought conditions

Drought cannot be predicted with confidence under warming, but it will be more severe under higher temperatures

these are largely linear effects that have already started- confirming that there is no "guard rail" of 2° or 1.5°C

Lobell

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What are the mechanisms of CC effects on plants?

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growing degree days

"mean daily °C above a threshold that permits growth"

with its new variant:

"the time that foliage is inside the thermal kinetic window" (TKW)

Above the TKW (∼35°C), plant growth is reduced because- membrane phase changes (more saturated lipids produced)- RuBisCO enzyme kinetic are rates reduced- starch synthesis is reduced- heat shock proteins (HSP) are produced- heat stress increases N concentration, and quality- reproduction is curtailed

Holm Tiessen, 2017

In the thermal kinetic windowthe Michaelis-Menten constant for CO2 (Km) is minimal and stable

RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase)and other enzyme systems follow this relationship

Enzyme kinetics translate temperature effects into non-linear functions of reduced production

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Temperature dependence of biochemical reaction rate

30°C is a critical zone

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In addition to inhibition of photosynthesis, heat stress affects phytohormone levels

- increases abscisic acid, salicylic acid, and ethylene- decreases cytokinin, auxin and gibberellic acids

enzymatic changes cause premature plant senescenceabscission of reproductive organs in crops and fruit trees(even tropical trees)

heat stress reduces not only seed weight but also vigour andgermination, carrying the damage into future seasons

Holm Tiessen, 2017

All phenological stages are temperature sensitive:

development accelerates linarly with degree days,this reduces time for grain fillingabove 30 degrees the effect becomes non-linear

in addition, spikelet formation is most sensitive- damage at this stage reduces grain number

above the TKW, a 1°C rise depresses grain yield by 8 to 10%with 3 to 4% less grain weight and 5 to 6% fewer grains

Holm Tiessen, 2017Teixeira

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Holm Tiessen, 2017Lobell

Effect of changed temperature and rain on yields

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Effect of changed temperature and rain on yields (2)

Lobell

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In summary

Heat stress is determined by canopy temperature >30°Cwhich depends on weather, canopy properties, soil moisture

>34°C, both development and senescence acceleratereducing grain yields

Some responses are linear but at higher temperature (nearer 40°C)non linear and direct threshold effects occur

In agro-ecological zones whith wide diurnal temperature variationsmall increases in mean temperatures can markedly increasethe frequency of high temperature injury

canopy temperature can be reduced by 10 - 15°C under irrigation

Holm Tiessen, 2017

maxima do not behave like means:

in Europe, mean summer (growing period)maximum temperature change between 1880 - 2005 was+1.6 ± 0.4°C

models predict scaling factors of 2 in 90th percentile T maxfor Southern Europe: i.e. 4°C for 2°C mean change

The 2003 heat wave accelerated crop ripening by 2 weeks, reducedItalian maize yields by 36%, European fruit harvest by 25% andwheat harvests by 22% (mostly harvested before the peak heat)

markets compensated because it was only one season and onecontinent

Della-Marta et al.Battisti

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Effects of Extreme Events

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Average percentage share of damage by type of hazard

cropsforestry

livestock

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climate related disasters and deaths

WMO - Atlas of Losses

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North America & CaribbeanSouth America

Number of reported disasters by decade and hazard type (1971-2010)

WMO - Atlas of Losses

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Climate extremes occur even without anthropogenic climate change

In addition, there is high confidence that

heat waves, heavy precipitation, glacial retreat, permafrost degradation, mountain slope instabilities, mass movements, and glacial lake outbursts,will increase small islands will suffer rising sea levels, inundation, shoreline change, and saltwater intrusion into groundwater

Holm Tiessen, 2017

Extreme events have greatest impact in sectors with close links to climate:water, agriculture and food, forestry, health, transport, tourism

Settlement patterns, coastal development, urbanization, socioeconomic changes influence exposure and vulnerability to climate extremes (high confidence)

Ageing societies are vulnerable to climate extremes (heat waves)

Several Latin American countries score low in adaptation preparedness because of lack of "innovation" "social inequality" and "deficits in governance"

Holm Tiessen, 2017

Coping vs. adaptation

In post-Hurricane Mitch Nicaragua, poor households coped successfully, regaining most assets and avoiding extreme poverty

but their environmental, social, economic, and political vulnerabilitieskept them in a poverty trap missing development gains

too much coping will drain coping capacity

adaptation will reduce the need to cope in the future

adaption requires knowledge, learning and resources

Jakobsen (2009)

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Lempert and Groves, 2010

No regrets strategies

Risk management for climate change can benefit from the robustness of ‘no regrets’ adaptation.

A robust strategy prepares for both expected and surprising changes and may provide for broad stakeholder acceptance.

Low-regrets strategies should produce co-benefits: improve livelihoods, and ecosystem conservation

aim at sustainable pathways towards climate change mitigation, adaptation, disaster risk management,and sustainable development

Holm Tiessen, 2017

Holm Tiessen, 2017

Summary

there are physical-atmospherical reasons for non-linear changes in conditions and events, particularly at higher delta T

there are bio-physical reasons for linear responses at lower delta T,and non-linear responses and threshold effects at higher delta T

there are social and governance reasons for highly variable responsesat all delta T

is it posible to work towards a consensus to invest in a low delta T?