Dr. Rodrigo Caballero

Pushing the envelope:
Extreme weather and
extreme climate
Dr. Rodrigo Caballero
UCD School of Mathematical Sciences
23 rd January 2009

UCD Earth Systems Institute
Meeting the Challenge of Climate Change
Seminar Series
In collaboration with
Comhar Sustainable Development Council, Environmental
Protection Agency, Forfás, Geological Survey of Ireland,
Met Éireann, Sustainable Energy Ireland & Teagasc
Further details on the seminar series is available at www.ucd.ie/earth
A paper and podcast of this seminar will be available on the ESI website
soon, please join the online ESI mailing list for such notifications
ESI email: esi.admin@ucd.ie

The world is getting richer, faster
World per-capita GDP (1990 international dollars)
year
(Source: B. DeLong, www.j-bradford-delong.net/TCEH/1998_Draft/World_GDP/Estimating_World_GDP.html)

The poor are catching up
World per-capita GDP (1990 international dollars)
year
(Source: A. Maddison, www.ggdc.net/maddison)

9
World
Population
(billion)
The ‘Great Transition’
6
The present
7,000 21,000
World Income Per Capita ($)
The future?

All this growth has been powered by
fossil fuels
Atmospheric carbon dioxide concentration over time

The Challenge, part I
• Target future is unsustainable with current
technology
• Would burn through all known fossil fuel reserves
in about 100 years
• Achieving a globally wealthy long-term future
necessitates a fundamental change in the way we
produce and use energy

The Challenge, part II
• Elevated CO 2 levels may lead to dangerous
climate change
• But we need to continue emitting CO 2 while we
develop and adopt new technologies
• So how much CO 2 can we emit without running
significant risks?

Avoiding dangerous climate change
• This is a problem in risk assessment
• Need a tool that accurately determines the
climate impact of a given CO 2 level
• The only available tool are climate models
• But these remain a somewhat blunt tool, subject
to important uncertainties
(P. Raskin et al., Great Transition, 2002)

What is a climate model?
At heart, a climate model is a set of mathematical
equations the give the rate of change of wind,
temperature etc. For the atmosphere:

What is a climate model?
Need to solve the equations on a grid, using a computer

How good are the models?
Models are coming increasingly closer to
observations
LEVEL OF AGREEMENT WITH OBSERVATIONS:
perfect good
bad
1995
2001
2007
(Reichler & Kim, BAMS 2007)

Models reproduce recent climate change
only if anthropogenic CO 2 is included
(Anthropogenic = emitted by human activities)
Observed
Simulations with
anthropogenic
forcing
Same
simulations but
without
anthropogenic
forcing
(IPCC AR4, 2007)

Extreme climates

The Eocene
The Eocene (50 million years ago) was much warmer
than today
surface temperature ( o C)
Now
Eocene
(Greenwood&Wing, Geology 2001)

Northern Canada today

Northern Canada 50 million years ago

How did it get so hot?
CO 2 was a lot higher, for one thing
Eocene
Today
(Fletcher et al., Nature Geo 2007)

The ‘low-gradient paradox’
A major unsolved problem
Eocene simulations
using 500—2000 ppm CO 2
Eocene data
20 o C mismatch!
(Shellito et al. 2003)

Possible implications for future climate

What is wrong?
No-one really knows, but here’s the hypothesis we
are exploring in ongoing work:
• Poles kept warm by atmospheric heat transport
• Most transport associated with fronts
• Fronts not properly resolved
• Problem not noticeable in current climate, but is
exponentially amplified as temperature increases

The atmospheric circulation

Extreme storms

Simulating extreme storms
• Extreme storms highly sensitive to resolution
• Basic physics not fully understood
Observations
Lothar simulation
with 30 km resolution
(Wernli et al., QJRSM 2002)

How will extremes change in future?
• There is evidence that extremes may become
more frequent in a warmer climate
• But extremes are by definition rare
• To assess changes in once-a-century storms,
need to simulate several centuries
• Also need high resolution
• Very computationally demanding!

The 1000 year run
• We are currently conducting a 1000-year highresolution
run to assess changes in extreme
windstorms over Europe
• First of its kind
• Working with partners in the insurance industry
to assess how these changes may impact
property exposure

Extreme computing

The computational challenge
• With current technology, climate simulations
limited to about 30 km resolution
• Would like to run at 1 km resolution
• Requires 10,000-fold increase in computer power

The computational challenge
• By Moore’s law, this would
take 20 years — too long!
• Need to beat Moore’s Law
to adequately address
climate change uncertainty
• Requires much smarter use
of current technology /
changeover to new
technology

What role for Ireland?
• The ‘great transition’ to a wealthy and
sustainable future will be a knowledge-intensive
process
• It will be a fluid period of change and innovation
• Small players who take the initiative can punch
above their weight

What role for Ireland?
• Seizing these opportunities will require continued
investment in strategic areas, amongst which:
– Basic climate research (reducing uncertainty)
– Computer technology (beating Moore’s Law)
– Weather and climate risk assessment
– ‘Green finance’
– Alternative energy
• Ireland is well positioned to develop strong
capabilities in all these areas
• Facilitating such development is a key aim of the
UCD Earth Systems Institute