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Extreme Events in a Warming World
April 2014Martin Hoerling, NOAA
1. What is Extreme Weather?
Extreme Weather is in the Fabric of Earth’s Atmospheric Circulation
Extreme Weather is not Necessarily the Same as Extreme Events
2. What is an Extreme Event?
N A T I O N A L O C E A N I C A N D A T M O S P H E R I C A D M I N I S T R A T I O N
NOAA uses a broad definition
“Extreme events are those that rarely occur at a given location or have significant impacts on society or ecosystems.”
What are ‘extreme events’?
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Meteorologically RareAND/OR
High Impact
Extreme Values (or Events)An extreme value (or event) can be thought of as the smallest or the largest
value in a sample of observations
There is great interest to know if, and by how much, the probabilityof extreme values (or events) is changing over time.
3. Why is it important to understand extreme events and their change?
N A T I O N A L O C E A N I C A N D A T M O S P H E R I C A D M I N I S T R A T I O N
The Nation Is Conscious of Extreme Events because of Impacts
Drought and Heatwaves
Hurricanes and Tropical Storms
Winter Storms and Crop Freezes
Flooding Wildfires Severe Local Storms
Figures: NOAA’s National Climatic Data Center
U.S. Billion‐Dollar Weather and Climate Disasters: 1980 – 2011
4. How Do We Know if Extremes are Changing?
N A T I O N A L O C E A N I C A N D A T M O S P H E R I C A D M I N I S T R A T I O N
• NOAA archives the nation’s climate data and information about observed extremes at the National Climatic Data Center. – http://www.ncdc.noaa.gov/climate‐information/extreme‐events
• Modeling can also tell us about changes we expect in the future.
Observational Record
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Extreme Values of Atmospheric Carbon Dioxide Concentration
Extreme Heat Content of the World Oceans
Extreme Values for Ocean Acidity~1/3 of emitted carbon dioxide dissolves in the oceans
(pH less than 7 is Considered “acidic”)
Extreme Values of the Global Mean Surface Temperature
An Extreme Value of Arctic Sea Ice Extent
5. How Do We Determine The Effect of Human Influences on Climate and Extremes?
Simulated Global Temperature with and without Anthropogenic Greenhouse Gas Forcing
6. Are extreme events changing over time, and if so why?
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IPCC AR5 WGI Chapter 2•“Overall, the most robust global changes in climate extremes are seen in measures of daily temperature, including to some extent, heat waves. Precipitation extremes also appear to be increasing, but there is large spatial variability”
•"There is limited evidence of changes in extremes associated with other climate variables since the mid‐20th century”
Extremes & Climate in Context
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2013 IPCC AR5: Synthesis on How Extreme Events Have Changed, and Will Change
7. Can Individual Events be Attributed to Climate Change?
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• Attribution studies can look at two questions:– Did climate change make this event more likely?– Did climate change make this event more intense?
• The answers to these questions can be different.
Intensity vs Frequency
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Climate change can influence an extreme event’s intensity and frequency.
N A T I O N A L O C E A N I C A N D A T M O S P H E R I C A D M I N I S T R A T I O N
In Response to Considerable Interest in the Topic
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NOAA (Herring, Hoerling and Peterson) and the UK Met Office (Peter Stott) co‐led the development of an annual BAMS report, Explaining Extremes from a Climate Perspective.
• IPCC SREX report: http://ipcc‐wg2.gov/SREX/• IPCC AR5: http://www.ipcc.ch/report/ar5/wg1/• NOAA State of the Science Fact Sheets (extreme events fact sheet coming soon):
http://nrc.noaa.gov/CouncilProducts/ScienceFactSheets.aspx• NOAA’s National Climatic Data Center: http://www.ncdc.noaa.gov/climate‐
information/extreme‐events• Explaining Extremes from a Climate Perspective:
• 2011: http://journals.ametsoc.org/doi/pdf/10.1175/BAMS‐D‐12‐00021.1• 2012: http://www.ametsoc.org/2012extremeeventsclimate.pdf
References
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