Climate Change, Smog, and the Lilac Bush
Loretta Mickley, Harvard University
Main current collaborators: Daniel Jacob, Cynthia Lin, David Rind, Shiliang Wu
Smog layer covering New York and Lake Erie. View looks toward the southwest from Canada at sunset.
Greenhouse gases act as a kind of blanket to slow the escape of heat from earth.
ice
earth
visible light
Without any greenhouse gases, the earth would be very cold, around 0 oF
heat
CO2, methane, . . .
Ice core data tell us that concentrations of greenhouse gases have increased over the last several hundred years.
Main source of CO2: fossil fuel combustion
Some sources of methane: wetlands, animals, natural gas leaks, landfills
CO2 methane
Data from temperature proxies show that the earth has warmed ~ 1-2 oF since 1000 AD. Models indicate that CO2 is the likely reason.
Mann et al., 1999
Large uncertainty far back in time!
thermometer data
Historical records
Hockey stick plot
proxy data
In the last 25 years, temperature changes have varied greatly over the globe.
insufficient data
Large increases in temperature
At high latitudes, higher temperatures melt ice, less sunlight gets reflected back to space, and temperatures climb still higher.
Models of the earth-atmosphere system tell us that temperatures are likely to increase over the next 100 years.
Predictions depend on scenario of future energy use and on the model used.
Globally averaged temperatures predicted to increase 1-5 o C, or 2-10 oF.
But increases could vary a lot from region to region.
Observations suggest that climate may have changed in recent decades in New England.
Ice-in and ice-out dates for lakes show warming trend.
no ice
Lilacs in New England are blooming about 1 day earlier per decade.
ice out earlier?
ice in later?
What does climate change have to do with the ozone hole? Is there a connection between smog and climate?
Climate change (a.k.a. global warming): CO2, methane, . . .
Ozone hole = loss of ozone over the Antarctic and Arctic:
ozone column amounts over Antarctica, October 2001
Air pollution (smog) = bad air at the earth’s surface, damages crops and people’s health.
+ ozone
ozone, particulate matter (PM)ozone = O3
GOOD vs. BAD OZONE
stratosphere
9-15 km
troposphere
Ozone profile
~10 ppm~10 ppb
altit
ude
“Natural ozone”Product of O2 + sunlightAbsorbs ultraviolet sunlight
Smog ozone is formed in the soup of chemicals in the troposphere, some natural and some manmade. Needs sunlight.
Precursors: NOx, volatile organic compounds (cars, power plants, vegetation. . .)
Ozone layer
smog
Probabilityof ozone exceedancevs. daily max. temperature
Lin et al. 2001
Number of summer days with ozone levels > 84 ppb, averaged over Northeast
1988, hottest on record
Day-to-day weather affects the severity and duration of pollution episodes. Will climate change affect smog?
New England
The probability of having an ozone episode increases with increasing temperature due to faster chemical reactions, increased biogenic emissions, and stagnation.
days
Stagnation conditions often lead to high ozone days.
Day 1
Stalled high pressure system, high ozone.
cold front ozone levels
Day 4
Cold front is beginning to push away smog.
cold front Unhealthy for “sensitive people”
High ozone levels can affect even remote rural areas
Number of summer days with ozone levels > 84 ppb, averaged over 8 hours, at the top of Mt. Washington.
Nighttime trajectories of air masses that correspond to high ozone levels on Mt. Washington
80 ppb
85 ppb
High ozone air over New England often comes from Midwest.
very hot summer
Compare present-day model results against observations for validation.
For future climate, increase greenhouse gas content of the atmosphere.
1950 spin-up (ocean adjusts) 2000 increasing greenhouse gas 2050
Timeline
We used a global climate model to see how changes in future circulation patterns would affect smog.
Use equations to describe air motions, transit of sunlight through the atmosphere, and chemical reactions.
Grid structure of global climate model
1950 spin-up (ocean adjusts) 2000 increasing greenhouse gases 2050
Timeline
spin up
1995-2002
2045-2052
{+2o C Temp change
model global mean temperatures
We implemented two tracers of pollution – carbon monoxide (CO) and black carbon particles (soot) – into the model.
We applied manmade sources and simple sinks to the CO and soot.
CO, soot ~ proxies of ozone
Our approach: Look at daily mean concentrations averaged over specific regions for two 8-year intervals (1995-2002) and (2045-2052).
midwest
Californiasoutheast
northeast
Cumulative probability plot shows the percentage of points below a certain concentration.
Histogram of CO concentrations averaged over Northeast for 1995-2002 summers (July-Aug)
Cumulative probability plots for surface both tracers show significantly higher extremes in 2050s compared to present-day.
Increased concentrations of these pollutants at extremes indicate more severe pollution events in the future.
July - August
2050s
1990s We found that the frequency of summertime cold fronts in the future decreased by 10-20% across the Midwest and Northeast.
That meant that pollution episodes lasted longer and pollutants could accumulate.
1. Climate change could cause a slowdown in the number of cold fronts coming through in future summers, which would lengthen smog episodes.
100 x g/m3
Evolution of a smog episode over 6 days in summer (model output)
weak winds
cold front from Canada
low pressure system
Traditional approach for calculating the full effect of climate change on air quality (smog) is very time-consuming.
Global model
Regional climate model
met fields
met fields
Chemical transport model
Regional chemistry model
downscaled met
chemfields
FUTURE AIR QUALITY
Work involves an array of models to go from global scale to regional scale.
We devise a simpler method to look at effects of climate on smog.
Idea: Use probability of ozone exceedance + daily GCM maximum temperatures to predict number of exceedance days each summer in future.
Step 1. find probability for each model day’s maximum temperature
Step 2. likely number of exceedances = sum of probabilities for each summer
Observed probabilityof ozone exceedancevs. daily max. temperature
Lin et al. 2001
-4
-2
0
2
4
6
8
10
1900 1950 2000 2050 2100
Sum
mer
Tem
pera
ture
Ano
mal
y (o
C)
CCSM 1 PCM 1CCSM 2 PCM 2CCSM 3 PCM 3CCSM 4 HadCM3ECHAM 1 GFDL 0ECHAM 2 GFDL 1ECHAM 3 GISS
Future temperature change over Northeast 1900-2100, calculated by many global climate models
+
= future smog episodes
1. 2.
New approach for calculating the effect of climate change on air quality is very quick!
Global model
Regional climate model
met fields
met fields
Chemical transport model
Regional chemistry model
downscaled met
chemfields
FUTURE AIR QUALITY
Global model
Statistically downscale temperatures and apply ozone probabilities
daily max temperature
2. Higher future temperatures could increase the number of bad air days over the Northeast by a factor of 2-6, depending on what
energy paths we follow.
Assumptions, caveats: for these calculations, we assumed that the emissions of ozone precursors remain constant over time, but the emissions of greenhouse gases like carbon dioxide increase according to different scenarios.
Plots show number of summer days with ozone levels > 84 ppb, averaged over Northeast
1988, hottest on record
Observed smog days
Calculated future smog days
SMOG (excerpts from T’s poem)
. . . The smell of too much ozonewas like leaves smolderingin another season,in the gutters. . . .
A pressure rose thenin the airand acquired direction:behind us and above,the air moved and cleaneduntil a bracing exhalationof clear airfrom the interiordisturbed the water’s rimand purged the atmosphere. . .
Many thanks to T. Wilson, Bob Engel, and my husband Michael Charney
Funding sources: NASA, EPA, NOAA, Bunting Institute
Extra slides
Observations show a ~1.8oF increase in surface temperatures across New England since 1899.
Area-weighted annual average temperature across the Northeast since 1900.
Trends in temperature at different sites across the Northeast.
But it’s important to keep in mind that New England is just a tiny part of the world!
Temperature changes going back 400,000 years
Series of ice ages.
Reasons for temperature swings
= changes in earth’s orbit or tilt ??, sea ice mechanism ??
Temperature changes are probably amplified by changes in CO2
Back in time
Sowers and Bender, 1995
