Climate Change Science and Projected Impacts on Western North America

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Climate Change Science and Projected Impacts on
Western North America

• Dr. Nathan Mantua
• University of Washington
• Climate Impacts Group

Carpe Diem Western Water and Climate Change
Project November 30, 2007
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Main points

• The natural greenhouse effect is a crucial part
  of earths climate
• the natural greenhouse effect is intensifying and
  global climate is warming under human influence
• the American Southwest is projected to experience
  significant drying, while snow pack and snowmelt
  runoff in summer is projected to decline westwide

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Intergovernmental Panel on Climate Change
Governments require information on climate change
for negotiations The IPCC formed in 1988 under
auspices of the United Nations Function is to
provide assessments of the science of climate
change Scientific community contributes widely
and on a voluntary basis 75 of the authors in
WG1 IPCC (2007) did not work on WG1 IPCC
(2001) Substance of IPCC WG1 report in the hands
of scientists. Major reports issued in 1990,
1995, 2001, and 2007. Nobel Peace Prize - 2007!
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The Greenhouse Effect

• There is a natural greenhouse effect that warms
  the earths average surface temperature by 33 C
  (about 60 deg. F)

Pierce
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Industrial revolution and the atmosphere
The current concentrations of key greenhouse
gases, and their rates of change, are
unprecedented.
Nitrous Oxide
Carbon dioxide
Methane
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The World Has Warmed
Globally averaged, the planet is about 0.75C
warmer than it was in 1860, based upon dozens of
high-quality long records using thermometers
worldwide, including land and ocean. Eleven of
the last 12 years are among 12 warmest since 1850
in the global average. (IPCC 2007)
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Warming is Unequivocal
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A different world in the Arctic present and
future
The Arctic was also warm in the period 1925-1940,
but the extent of warmth was not global at that
time.
Clear decreases in Arctic sea ice extent.
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Paleoclimate New and Independent Evidence From
Many Types of Past Data
eg., changes in glaciers, indicating a global
average temperature change in the 20th century
consistent with the thermometers. And the
corals. And the tree rings. And the boreholes.
And the ice cores.
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Human and Natural Drivers of Climate Change
Carbon dioxide is causing the bulk of the
forcing. On average, it lives more than a
hundred years in the atmosphere and therefore
affects climate over long time scales.
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Attribution

• are observed changes consistent with
• expected responses to forcings
• inconsistent with alternative explanations
• Most of the observed increase in globally
  averaged temperatures since the mid-20th century
  is very likely (gt90 certainty) due to the
  observed increase in anthropogenic greenhouse gas
  concentrations

TS-23
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Observed Impacts of 20th Century Climate Warming
in the West

• Retreating glaciers
• Declines in low elevation snowpack
• Timing shifts to earlier snowmelt runoff
• Earlier flowering dates for plants, extended fire
  seasons, bark beetle outbreaks in western forests
  

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1948 to 2000 saw trends to earlier (snowmelt)
runoff in western snowfed rivers
Spring-pulse dates
Figure by Iris Stewart, Scripps Inst. of Oceanog.
(UC San Diego)
Center time
Spring pulse
Centers of Mass
Stewart et al., 2005
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What about the future?
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Whats in the pipeline and what could come?

• Warming will increase if GHGs increase. If GHGs
  were kept fixed at current levels, a committed
  0.6C of further warming would be expected by
  2100. More warming would accompany more
  emission.

CO2 Eq
3.4oC - 6.1oF
850
2.8oC - 5.0oF
600
1.8oC - 3.2oF
0.6oC - 1.0oF
400
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A1B is a typical business as usual (2090-2099)
scenario Global mean warming 2.8oCMuch of land
area warms by 3.5oCArctic warms by 7oC get
less warming for lower emissions
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• Large regions of the dry subtropics become dryer,
  while wetter high latitude regions become wetter
  still

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Dust Bowl era -0.9mm/day 1950s drought -1.3
mm/day

• there is a broad consensus among climate models
  that this region will dry significantly in the
  21st century if these models are correct, the
  levels of aridity of the recent drought, or the
  Dust bowl and 1950s droughts, will, within the
  coming years to decades, become the new
  climatology of the American Southwest

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Projections of Future Changes in Climate