Projections of Future Atlantic Hurricane Activity Hurricane Katrina, Aug. 2005 GFDL model simulation...
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Projections of Future Atlantic Hurricane Activity Hurricane Katrina, Aug. 2005 GFDL model simulation of Atlantic hurricane activity Tom Knutson NOAA / Geophysical Fluid Dynamics Lab Princeton, New Jersey http:// www.gfdl.noaa.gov/~tk 1
Projections of Future Atlantic Hurricane Activity Hurricane Katrina, Aug. 2005 GFDL model simulation of Atlantic hurricane activity Tom Knutson NOAA
Projections of Future Atlantic Hurricane Activity Hurricane
Katrina, Aug. 2005 GFDL model simulation of Atlantic hurricane
activity Tom Knutson NOAA / Geophysical Fluid Dynamics Lab
Princeton, New Jersey http://www.gfdl.noaa.gov/~tk 1
Slide 2
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Slide 3
Climate Change Attribution are observed changes consistent with
expected responses to forcings inconsistent with alternative
explanations Observations All forcing Solar+volcanic Source: IPCC
4th Assessment Report. Used with permission.
Slide 4
IPCC Projections of Future Changes in Climate IPCC best
estimate for low scenario (B1) is 1.8C (likely range is 1.1C to
2.9C), and for high scenario (A1FI) is 4.0C (likely range is 2.4C
to 6.4C). Broadly consistent with span quoted for SRES in TAR, but
not directly comparable Source: IPCC 4th Assessment Report. Used
with permission.
Slide 5
There is some evidence that overall Atlantic hurricane activity
may have increased since in the 1950s and 60s in association with
increasing sea surface temperatures Source: Kerry Emanuel, J.
Climate (2007). PDI is proportional to the time integral of the
cube of the surface wind speeds accumulated across all storms over
their entire life cycles. 5 Increasing data uncertainty
Slide 6
6 Source: Vecchi et al. Science (2008) Projection 1: Absolute
SST ~300% projected increase in Power Dissipation Indirect
attribution: CO2 SST Hurricanes Projection 2: Relative SST
Projected change: sign uncertain, +/- 80% No Attribution Supported
by dynamical models. Two future projections of Atlantic tropical
cyclone power dissipation
Slide 7
Example of a regional model that reproduces the interannual
variability and trend of Atlantic hurricane counts (1980-2006)
18-km grid model nudged toward large-scale (wave 0-2) NCEP
Reanalyses 7 Source: Knutson et al., 2007, Bull. Amer. Meteor.
Soc.
Slide 8
Late 21 st century projected Atlantic region climate changes:
18-Model CMIP3 ensemble Higher shear Higher potential
intensity
Slide 9
The 26.5 o C threshhold temperature for Atlantic tropical storm
formation: a climate dependent threshhold, which may increase to
~28.5 o C by the late 21st century with climate warming. Source:
Knutson et al., 2008, Nature Geoscience. 9 Note the decrease in
overall number of storms in the warmer climate
Slide 10
The regional model simulates increased hurricane rainfall rates
in the warmer climate (late 21 st century, A1B scenario) consistent
with previous studies Present Climate Warm Climate Warm Climate
Present Climate Rainfall Rates (mm/day) Avg. Rainfall Rate
Increases: 50 km radius: +37% 100 km radius: +23% 150 km radius:
+17% 400 km radius: +10% Average Warming: 1.72 o C Source: Knutson
et al., 2008, Nature Geoscience. 10
Slide 11
Example of a double-downscaling method used to explore
frequencies and intensities of Atlantic hurricanes at high
resolution Geophysical Fluid Dynamics Laboratory/NOAA
Slide 12
Late 21 st Century Climate Warming Projection-- Average of 18
CMIP3 Models (27 Simulated Hurricane Seasons) Source: Bender et
al., Science, 2010
Slide 13
Conclusions: What can climate science tell us about late 21 st
century climate and Atlantic hurricanes? i)Climate science provides
a compelling case that human emissions of greenhouse gases have
caused much of the long- term global warming over the past 50 yr
and 140 yr (IPCC AR4). ii)Climate models project substantial
further global warming over the 21 st century, including in the
tropical Atlantic. iii)Sea level rise has already begun and further
sea level rise is expected to exacerbate storm surge impacts, even
if the storms themselves do not change. iv)There is no consensus
among current models on future changes in Atlantic tropical storm
frequency (+/- 60%). Globally there is a general consensus on a
decrease (or little change) in global frequency of tropical storms.
v)Most high-resolution models agree that hurricane intensities will
increase (range +2 to 11% by 2100) and that hurricanes will have
higher rainfall rates (~+20%). In one study, the number of very
intense category 4 and 5 Atlantic hurricanes doubles by 2100,
though not for all of the climate models used in the study. vi)
However, we cannot yet conclude that humans have already caused a
detectable change in Atlantic hurricane activity. Note that humans
may have already caused changes that are either below the
'detection threshold' or are not yet confidently modeled (e.g.,
aerosol effects). 13 Decreasing Confidence