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 o F heat CO 2, methane,...

Ice core data tell us that concentrations of greenhouse gases have increased over the last several hundred years. Main source of CO 2 : fossil fuel combustion Some sources of methane: wetlands, animals, natural gas leaks, landfills CO 2 methane

Data from temperature proxies show that the earth has warmed ~ 1-2 o F since 1000 AD. Models indicate that CO 2 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 o F. 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): CO 2, 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 = O 3

GOOD vs. BAD OZONE stratosphere 9-15 km troposphere Ozone profile ~10 ppm~10 ppb altitude “Natural ozone” Product of O 2 + sunlight Absorbs 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

Probability of ozone exceedance vs. daily max. temperature Lin et al 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 frontozone 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 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 { +2 o 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 ( ) and ( ). midwest California southeast northeast Cumulative probability plot shows the percentage of points below a certain concentration. Histogram of CO concentrations averaged over Northeast for 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/m 3 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 chem fields 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 probability of ozone exceedance vs. daily max. temperature Lin et al Future temperature change over Northeast , 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 chem fields 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 ozone was like leaves smoldering in another season, in the gutters.... A pressure rose then in the air and acquired direction: behind us and above, the air moved and cleaned until a bracing exhalation of clear air from the interior disturbed the water’s rim and 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 ~1.8 o F increase in surface temperatures across New England since Area-weighted annual average temperature across the Northeast since 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 CO 2 Back in time Sowers and Bender, 1995