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Climate Change in Libya 1957-2057

Rachel McDonald Oxford University Centre for the Environment

& Dáithí Stone & Myles Allen

Department of Physics, University of Oxford

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Why climate change is particularly important for Libya

n  Libya has a stake in every aspect of the climate change issue: –  As a major fossil fuel producer. –  As fossil fuel consumer with high per capita emissions. –  Potentially sensitive to small shifts in climate regimes.

n  This talk will focus on the impact of climate change on Libyan climate: –  The evidence for human influence on global climate. –  The implications for climate over the African continent. –  New studies linking weather and climate. –  Implications for water scarcity and drought risk.

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Libya at the nexus of the climate change issue

Fossil fuel consumers

At risk from climate change

Fossil fuel producers

Libya

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Warming of the climate system is now “unequivocal” (IPCC, 2007)

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Khadijateri cave paintings

But climate has changed before: how can we be sure this is not a natural cycle?

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We cannot explain the past century without both human and natural influence on climate

Colours: Simulations with human and natural influences

Observations

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We cannot explain the past century without both human and natural influence on climate

Colours: Simulations with natural influences alone

Observations

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Observed and modelled regional temperature changes

n  Simulations that include human influence (orange bands) agree with observed changes (black lines)

n  Simulations that exclude human influence (blue bands) do not agree with observed changes.

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Observed and modelled temperature change in Libya (10-25E, 20-33N)

n  Warming of ~0.5oC since the 1970s, with superimposed internal variability.

n  Consistent with models driven with combination of human and natural influence (orange band).

n  Less consistent with models driven with natural influences alone (blue band).

n  Source: global climate models used in IPCC 4th Assessment.

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All scientists agree that this warming will continue if GHG levels continue to rise

Pat Michaels (2000, 2004)

Climate response to the IS92a emissions scenario, predicted by IPCC models and by Patrick Michaels, a prominent critic of the IPCC

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Long-term warming depends on future emissions, but some further warming is inevitable

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So what do the models project for the Saharan region?

n  Warming relative to early 20th century (1901-1950) –  3-5oC under A1B (medium)

emissions scenario (orange) –  4-7oC under A2 (high)

emissions scenario (red) –  2-4oC under B1 (low)

emissions scenario (blue) Source: IPCC 4th Assessment.

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Changes in rainfall and drought risk may be more important than changes in temperature

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Changes in rainfall and drought risk may be more important than changes in temperature

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Surface temperature departures from normal in early August 2003, from NASA’s Moderate Resolution Imaging Spectrometer, courtesy of Reto Stöckli, ETHZ

The most significant impacts of climate change are changing risks of extreme weather

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Many people think there is no way of linking climate change to individual weather events

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In fact, we can establish a causal link between individual weather events and climate change

n  The drivers of climate change (greenhouse gases, volcanic eruptions…) affect weather in the way that the loading on a dice helps the dice to come up six.

n  Edward Lorenz’s definition of climate: –  “Climate is what you expect, weather is what you get”

n  Updated for the 21st century… –  “Climate is what you affect, weather is what gets you”

n  But we cannot roll the weather dice many times to work out how the loading is changing, so we have to use computer simulation.

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The climateprediction.net seasonal attribution experiment (Pall et al, 2007)

n  Aim: to quantify the role of increased greenhouse gases in precipitation responsible for recent extreme weather events.

n  Challenge: we are interested in unlikely events, even given present climate drivers (loading on the dice).

n  Approach: large (multi-thousand-member) ensemble simulation of April 2000 – March 2001 using forecast-resolution model.

n  Identical “non-industrial” ensemble removing the influence of increased greenhouse gases, including attributable SST change.

n  Use several coupled models for SST pattern.

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Standard climate models may be good enough for large-scale temperature, but not for precipitation

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Precipitation in a higher-resolution (1.25x0.8o) version of HadAM3

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Simulating the climate that might have been on your desktop: http://attribution.cpdn.org

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The world’s largest climate modelling facility: www.climateprediction.net

~260,000 volunteers, 170 countries

Thank you!

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Autumn 2000 as observed (ERA-40 reanalysis)… …and in one of the wetter members of our ensemble.

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Model resolution over Libya

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Changing “risk” of high rainfall in Tripoli due to greenhouse gas increase 1900-2000

Increased return-time = ~3x reduced chance of >240mm rainfall in any given year

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Changing risk of low rainfall in Tripoli due to greenhouse gas increase 1900-2000

Reduced return-time = double chance of <70mm rainfall in any given year

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Conclusions from climate modelling

n  Strong evidence from global models for human influence on regional temperatures and precipitation.

n  More detailed modelling required to understand changing drought risk.

n  Initial results suggest a 15% reduction in median (“normal”) rainfall but doubling of drought risk.

n  More work required to assess the detailed prospects for the future.

n  Modelling tools and expertise are available through collaboration with University of Oxford and UK Met Office.

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How Oxford could help

n  Strong interdisciplinary program on climate change. n  Independent of UK government. n  Established links with Arab nations (including Libya

and the Gulf States) on water scarcity issues. n  New project enabling regional climate modeling on

personal computers with UK Met Office & Microsoft. n  One of the UK’s principle centres for Islamic

Studies.

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Myth: observed temperature changes can be explained by solar variability