ES 1111

1
ES 1111

• Future Climates and the Consequences
• Chapters 9, 10, and 5

2
Determining Future Climates

• We attempt to foresee and predict future climates
  by using climate models
• Climate models are computer programs that use all
  the equations governing the weather and climate
• By inserting changes, like the amount of carbon
  dioxide in the atmosphere, we can see what the
  response in our climate will be (according to the
  model)
• Trying to create a model which accurately
  reflects the complexity of Earths climate is an
  immense challenge

3
Global Circulation Models

• Weather forecasting uses these models to predict
  short-term weather
• Weather observations are incorporated into the
  model, and new forecasts are generated every
  12-24 hours
• Over 20 trillion calculations are required
• The atmosphere is divided up into grids
  (horizontally and vertically), the amount to
  which depends on the model being used
• Weather forecasts produced by these models have a
  reasonable accuracy out to about 6 days

4
General Circulation Models

• Climate modelers use these GCMs to predict future
  climate
• Because of the length of time of the forecast
  period, the amount of calculations required are
  astronomical
• Because of this, the GCMs use a lower spatial and
  temporal resolution than models used for weather
  forecasting
• At best, the resolution is 2.5 degrees in
  latitude by 3.75 degrees of longitude, with 20
  vertical levels
• Therefore, the same detail is not possible

5
Atmospheric-Ocean Interactions

• Models for predicting weather treat the sea
  surface temperatures as a constant
• Climate models must include realistic
  representations of the oceans
• Currents and eddies are small features that play
  a big role in climate, but they are too small for
  our climate models grid
• Fluxes of heat between the ocean and atmosphere
  depend on such currents

6
Performance of GCMs

• There is about a 6 C scatter in temperature
  between different models
• Models have more difficulty in higher latitudes
  and over land
• Similar scatter results in precipitation
  forecasts
• Sea-level pressure is handled well
• Snow and ice cover is a problem
• Clouds are critical due to their potential to act
  as a positive or negative feedback to climate
  change, yet these models can not generate most
  clouds on their own (parameterization of the
  clouds must be done correctly)
• Models underestimate the clouds in low to
  mid-latitudes, and overestimate clouds in high
  latitudes

7
Other Difficulties

• GCMs have problems producing natural climate
  variability (only about 20-60 of the
  fluctuations are forecast)
• Some success has been observed in predicting
  consequences of specific perturbations (volcanic
  eruptions)
• Running the models to see how they simulate past
  climate is difficult because of our limitations
  in knowledge of that time

8
Improving GCMs

• Improving GCMs will require
• Bigger and faster computers
• Better physical representations of processes
• Clouds
• How much sunlight is absorbed/reflected from each
  type
• Spatial and temporal resolution must be better
• Precipitation processes must be better handled
• Moving away from parameterization
• Land-Surface Processes
• Changes in albedo (desertification, vegetation)
• Soil moisture variations
• Snow cover handled better
• Winds, Waves, and Currents
• Better heat, momentum, and moisture flux
  performance
• ENSO processes
• Ocean conveyor
• Changes in Greenhouse Gases and Ozone

9
Predicting Climate Change

• Our present climate has been fairly stable
• There is an estimate that, based on orbital
  factors, we will be headed into another ice age
  in about 23,000 years
• There is no way of knowing whether the climate
  will remain stable or flip into a new state
  accompanied by a radical change in climate
• With human activities predicted to have a big
  impact in the future, the chance of climate
  becoming more unstable will increase
• Whether natural climate variability or man-made
  change causes a climate shift is speculative

10
The Climate Forecast

• From GCMs, a doubling of carbon dioxide will
  result in an increase in mean global temperatures
  of between 1.5 and 4.5 C, with the best estimate
  of 2.5 C
• This change will happen by the year 2100
• Tropics are more stable than the high latitudes
• In spite of their uncertainties, the GCMs produce
  a world that resembles our current climate, and
  their behavior of increasing temperatures that
  mirror what happened lends them credibility
• Sea level change, due to mountain glaciers
  melting and thermal expansion, 27 cm higher
  (range from 17 to 49 cm) by 2100
• Further changes in sea level due to the Antarctic
  ice sheets melting could rise sea levels 60-120
  cm, but some models suggest increased snowfall
  and a growing ice sheet

11
Consequences of Global Warming

• Weather patterns may change on a regional scale
• Weather may become more extreme (more hurricanes,
  ENSO, lows weaker)
• Shifting of agricultural zones, famine, drought
• Migration and extinction of plants and animals
• Rising sea levels
• Rising sea levels yielding tectonic changes
• Changes in ocean circulation leaving Europe
  colder than it currently is
• Isostatic rebound of Scandinavia after retreat of
  ice sheets (10 mm per year of lifting)
• Spread of diseases and global pandemics
• Economic cost due to frequent extreme weather

12
Isostatic Rebound

• Figure 5.5, Page 126
• Figure showing the rebound of Scandinavia

13
Consequences for Illinois

• According to the National Assessment Synthesis
  Team of the US Global Change Research Program
• 3-6 C increase in mean annual temperature by
  2100
• Decrease of up to 50 in length of snow cover
• Increased precipitation (20-40) by 2100 due to
  greater rainfall events (more rain per storm)
• Increased evaporation would decrease lake levels
  (Lake Michigan by 4-5 feet)
• Longer growing season, increased agricultural
  yields
• Loss of boreal forests to more deciduous forests
• Loss of wetlands and associated birds and fish
• Increased number of invasive species (zebra
  mussels)
• Increased heavy precipitation events yielding
  increased water-borne disease outbreaks
  (cryptosporidiosis, encephalitis)

14
Illinois Summer Climate Shifts

• Figure from the National Assessment Synthesis
  Team of the US Global Change Research Programs
  book showing how Illinois summer climate will
  shift according to two climate models. One model
  suggests a summer climate more like the Carolinas
  by 2090, and another puts our summer climate more
  like eastern Oklahoma.

15
When Will We Know?

• When will we know if the observed warming is due
  to natural factors or man?
• The warmest year since 1860 was 1997
• The five warmest years have all been in the 1990s
• ENSO muddies the picture
• Confidence in GCMs will fall if the observed
  warming abruptly stops
• Linkage between economic growth and carbon
  dioxide emissions make reductions unpopular

16
Update!

• According to the National Oceanic and Atmospheric
  Administration and the World Meteorological
  Organization
• 2005 will be the warmest year (0.75 degrees
  Celsius above the 1950-1980 average)
• 1998 was 0.71 degrees C above
• 9 of the 10 hottest years on record since 1861
  occurred in 1995 or later (not counting 2005),
  with the last four years (2001-2004) being among
  the five hottest.

17
Gaia Hypothesis

• James Lovelock came up with this hypothesis
• Life and the global environment are two parts of
  a single system
• Natural selection drives adjustments in the
  biosphere that the Earths environment remains in
  a state optimum for life
• Phytoplankton (algae) produce dimethylsuphide
  (DMS). DMS converts into sulfate particles which
  are CCN. Therefore, warming of the sea would
  result in more algae, which would emit more
  sulfate particles, yielding more clouds, and
  serve as a negative feedback to the warming
  (climate thermostat)
• It is controversial, yet life and a narrow
  temperature range has been maintained despite
  changes in solar output (30 more), continents
  moving around, etc.