Transcript Chapter 1.1 The Science of Climate Change

CLIMATE CHANGE AND DEVELOPMENT: A SUMMARY
OF FINDINGS FROM STUDIES AND PROJECTIONS
A Brown Bag Presentation
By
Samson WASAO
African Institute for Development Policy
Nairobi, Kenya
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DEFINITION OF TERMS
• Weather: Atmospheric conditions at a
particular place (air temperature, pressure,
humidity, wind speed, and precipitation
• Climate: weather averaged over time(typically
30 years)
• Climate Variability: Mean state of climate on
all temporal and spatial scale beyond
individual weather events
DEFINITIONS
• Climate Change: Shifts in the mean state of the
climate or its variability persisting for an
extended period of time (decades or more)
• Vulnerability: Exposure to climate conditions,
sensitivity to the conditions and capacity to adapt
to the conditions
• Adaptation: Actions taken to help communities or
ecosystems to moderate, cope with or take
advantage of actual or expected changes in
climate conditions
DEFINITIONS
• Resilience: Capacity of a system to absorb
disturbance and reorganize while undergoing
change so as to still retain essentially the same
function
• Risk: A Function of Harzard and vulnerability
• Mitigation: Actions to reduce human
forcing(activities) on the climate system,
including reducing greenhouse gas emissions
What is Climate Change?
• The Basic Science……and general
observations
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Long-term climate variability
The Earth’s climate changes on timescales of days to many millennia
Past ~2.5 million years:
• Ice age cycle every ~100,000 years, driven by changes in Earth’s orbit
• Temp. change of up to ~6-7º C globally between cold ice age & warm interglacial
• Human beings evolved against backdrop of glacial-interglacial oscillations
• Humans have experienced a world up to ~6º C cooler than at present
• Humans have experienced a world up to ~1.5º C warmer than at present
Pillar of Lake sediment, Libyan Sahara
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REFERENCES: Brooks, 2005; IPCC (2007 - WGI Ch.
African climate today
• Today’s climatic pattern
Adams: http://www.esd.ornl.gov/projects/qen/nercAFRICA.html
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implies Africa’s long history of
climatic variation and change
• African climate is highly
variable, esp. in marginal
areas such as dry lands, where
monsoon zones oscillate on
timescales of years to
millennia
• The climate of Africa will
change in the future, with or
without human intervention
The Science of Climate
Change: Anthropogenic
Impacts
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Greenhouse gas concentrations are rising
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Increase since ~1750 due to industrial activity
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Rapid rise over past 50 years
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Atmospheric CO2 concentration has remained below
300 ppm for at least past 600,000 years
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Now at 380 ppm and rising
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Temperatures are rising
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Source: IPCC (2007)
Global temperatures over the past 1,200 years
Source: Science, 10 February 2005
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Attributing climate change to human activity
Natural + anthropogenic forcing
Natural forcing only
Global mean surface temperature anomalies from observations (black) as as
simulated by a variety of global climate models.
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Source: IPCC (2007)
Future emissions and warming scenarios
A2 SRES Scenario
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Strong regional economic growth and no
capping of greenhouse gas emissions:
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By 2100
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Doubling
- GHG concentrations of 700-1,000 ppm
- Temperature rise of 2°-6° C
EU Guardrail
Doubling
EU Guardrail
EU proposes keeping global temperature increase
below 2º C to avoid “dangerous” climate change
- Almost certain to exceed this “guardrail” value
- Stabilisation below 550 ppm unlikely
- Likely 2°C by 2050 and 3°C by 2100
Last time global temperature was 3°C above
pre-industrial value: 3 million years ago
For higher temperatures, must go back tens of millions
of years – no past analogue of future
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Source: IPCC (2007)
Projected temperature and precipitation changes
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Source: IPCC (2007)
Past, present and future sea level
Conservative estimate?
• 1990s: fastest recorded rise at 4mm per year
• Future increases likely to be similar or greater
• Longer term: ≥ 1m per century very plausible
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Source: IPCC (2007)
Climate Change: Potential
Impacts on Development in
Africa
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Temperature response: Africa
Top: Projected temperature changes over Africa from the MMD-A1B simulations. Annual mean, DJF and
JJA change between 1980-1999 and 2080-2099, averaged over 21 models. Bottom: observed trends &
projected changes for A1B scenario (orange envelope), & B1, A1B & A2 scenarios (blue, orange & red bars
respectively).
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Source: IPCC (2007)
Precipitation response: Africa
Annual
DJF
JJA
Precipitation changes over Africa from the MMD-A1B simulations. Top row: Fractional change in
precipitation between 1980-1999 and 2080-2099, averaged over 21 models. Bottom row: number
of models out of 21 that project increases in precipitation.
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Source: IPCC (2007)
Regional rainfall projections
North Africa
 Decrease in mean annual rainfall (by ~20%) along Mediterranean coast & northern Sahara,
extending along West African coast to ~15° N.
Sahel
 Regional & global models project increased rainfall in of much of Sahel

However, uncertainty over sign of change in western Sahel (W of 20° E)

More variability from year to year & uncertainty in timing of rains likely
Tropical & Eastern Africa
 Increase in mean annual rainfall likely (~7% according to models used in IPCC AR4)
Southern Africa
 Regions N of 10° S & E of 20° E: summer rainfall projected to increase

Regions S of 10° S: decrease in rainfall (fewer rain days, reduction in average intensity)

June-August rainfall likely to decrease in much of southern Africa:
~30% decrease under A2 scenario; up to ~40% in extreme west

Possible increased summer rainfall over convective region of central & eastern S. Africa &
Drakensberg Mountains
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Source: IPCC (2007)
Water stress
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Increases in temperature alone will have significant
impacts on water stress.
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High uncertainty in precipitation & runoff projections
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Water stress will increase in many areas even in
absence of climate change
PROJECTIONS TO
BE TREATED WITH
CAUTION!
Number of people (millions) with an increase in
water
stress (Arnell, 2006b). Scenarios are all derived
from HadCM3 and the red, green and blue lines
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relate to different population projections.
Change in annual runoff by 2041-60 relative to
1900-70, in percent, under the SRES A1B
emissions scenario and based on an ensemble
of 12 climate models (Milly et al., 2005).
Source: IPCC (2007)
Potential impacts on agriculture
• W & Central Africa: losses of 2-4% of GDP
• N & southern Africa: losses of 0.4-1.3% of GDP
• Adverse impacts on mixed rain-fed semi-arid systems in Sahel, & mixed rain-fed & highland
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perennial systems in Great Lakes region & elsewhere in E. Africa.
B1 world - marginal areas (e.g. semi arid regions) become more marginal
By 2080s
 decrease in extent of rain-fed land & production potential for cereals
 area of arid & semi-arid land expands by 5-8% (60-90 million hectares)
 Wheat production likely to disappear from Africa
 Possible significant reductions in maize production in southern Africa if ENSO conditions
become more dominant
Crop net revenues in S Africa could fall by up to 90%, affecting small-scale farmers most severely
(without considering adaptation)
Growing season could lengthen in parts of Ethiopian highlands & parts of southern Africa such
as Mozambique due to higher temperatures & rainfall changes
Low warming could increase productivity in some areas
•
• Impacts are uncertain: depend on uncertain rainfall projections, management regimes, extent
and nature of adaptation, interactions between temperature, rainfall, runoff, rainfall onset, CO 2
fertilisation, erosion, changes in distribution of pests & diseases
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Source: IPCC (2007)
Potential impacts on livestock
• Warmer temperatures may favour small farms and systems based on goats & sheep, which are
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more heat tolerant, and have adverse impacts on larger farms which depend more on cattle,
which are less heat tolerant (IPCC, 2007, WGII, Ch. 9)
Increased rainfall may increase pasture in areas such as the Sahel & Sahara if pasture expands
into desert regions, and decrease it where pasture is replaced by woodland
Decreased rainfall may increase pasture where it replaces woodland, or decrease pasture where
vegetation systems collapse completely (e.g. Kalahari region)
• In some areas, expansion of mobile pastoralism might represent a means of coping with &
adapting to reductions in rainfall and greater rainfall variability, particularly where water stress
limits the potential for irrigation (Brooks, 2006b)
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Potential impacts on ecosystems
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Distributions of woodlands, grasslands, scrub and desert are likely to change
Species likely to shift in ranges, particularly in highland & marginal areas (e.g. drylands)
Mangroves likely to be affected - may migrate inland if not prevented by settlement
Coral reefs threatened by higher ocean temperatures, more extreme events (heat
extremes, tropical storms), ocean acidification, human impacts - threats to marine
ecosystems, fish populations, food resources, tourism
10-15% of mammals in 141 national parks “Critically Endangered or Extinct” by 2050
assuming no migration (25-40% by 2080, falling to 10-20% with unlimited migration)
 Westward range shift in central Africa; eastward shift in southern Africa
• Of 5197 plant species examined, substantial reductions in suitable area for 81-97%, 25•
42% lose all area by 2085
For global mean temperature increase of 2-3º C (reviewed in Warren, 2006)
 Potential threat of ecosystem collapse in African Great Lakes
 Five South African parks lose 40 % of animals
 Fynbos ecosystem lost
 Up to 80% of Karoo lost threatening 2800 plant species with extinction
 All Kalahari dunefields mobile.
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Source: IPCC (2007)
Sea-level rise & extreme events
Rainfall-related hazards
 Drought likely to increase in frequency, severity, duration in many areas
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Flash floods likely to increase in parts of Sahel & Sahara as rainfall increases
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Increase rainfall or rainfall event intensity may exacerbate erosion
Tropical storms
 May become more intense, increasing risk in SE Africa, Madagascar, Mauritius
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Flood risk associated with storms and storm surges likely to be exacerbated where coastal
systems such as coral, mangroves, wetlands lost as a result of climate change or other stress
Sea-level rise
 Threatens much of the densely populated coast of West Africa
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Banjul threatened for SLR of 0.5 m
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Will exacerbate erosion & impacts of storms & storm surges
Fires
 Already affect large areas - some 50% of recorded fires are in Africa. Increased temperatures
and more frequent or protracted dry spells will increase fire risk
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Source: IPCC (2007)
Adapting to climate change in Africa
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Recent development has ignored longer-term (multi-decadal) climatic variability

Development based largely on European and North American assumptions of a static climate has
acknowledged seasonal and year-to-year variations in climate, but fails to address reality of
longer-term variations
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Failure to plan for historically familiar multi-year & decadal variability has resulted in catastrophes
such as the Sahel drought and famine of the 1970s (and beyond)
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Development that assumes a static climate increases vulnerability to “shocks” associated with
longer-term climatic variability, particularly in marginal environments
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Highly variable & often marginal African environments require flexible, responsive systems
Climate change is likely to increase climatic variability
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High uncertainty in climate projections means that, in many instances, adaptation cannot simply be
based on planning for a specific, predicted future (exceptions may be sea-level rise)
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The need for flexible and responsive systems, already crucial but often not recognised, will increase in
the future
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Traditional African livelihoods such as pastoralism and mixed agro-pastoral systems developed as means
of coping with often severe climatic variability and change
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These systems will be invaluable in securing adaptation & development in future
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Development in the face of climate change is not a choice between modernity and tradition - traditional
methods and modern technology must both play a role in adaptation
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END of PRESENTATION
Thank You!