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Chicago by the Numbers

Chicago by the Numbers

THE CITY OF CHICAGO, with a population of 2.7 million people, is the financial, industrial and cultural capital of the Midwest. While that fact makes Chicagoans proud, they may be less proud to know that Chicago is responsible for roughly 34.6 million metric tons of heat-trapping (greenhouse) gases, in CO2-equivalent terms, according to “Climate Change and Chicago,” a 2008 report. Adding in the six surrounding counties in the Chicago area increases this to about 103 million metric tons per year. This region accounts for nearly half the total emissions of the state of Illinois, with emissions greater than the state totals of more than 30 individual states.

According to the report, Chicago’s temperatures have risen by 2.6°F since 1980. Winters have warmed by almost 4°F since then as well. Winter ice coverage on Lake Michigan has decreased, several major heat waves—particularly those in 1995 and 1999—have occurred and the frequency of heavy rainfall events has doubled over the last hundred years.

Predicting the Future
Although it is extremely likely that temperatures, both globally and in Chicago, will continue to rise over the coming decades, it is unpredictable just how much they will rise. Much of that depends on what is done globally to slow the progression of climate change. To that end, the authors of the report discuss two possible scenarios. In the higher emission scenario, Chicago and the rest of the world continues to depend on fossil fuels as their primary energy source, and atmospheric carbon dioxide levels rise from their present-day levels of 385 parts per million (ppm) to almost 1000 ppm by the end of the century. Under the lower emission scenario, a focus on sustainability and conservation results in atmospheric carbon dioxide levels rising to about 550 ppm by the end of the century.

So what does that mean for Chicago? When it comes to temperature, the report claims that Chicago could see substantial increases in annual and seasonal temperatures and extreme heat events, particularly under the higher emissions scenario. For example, by the end of the century, under lower emissions, temperature could increase by 3-4°F; under higher emissions, 7-8°F, with the greatest increases (up to 10°F) during sum
mer.  The number of very hot days (over 90°F) is very likely to increase as well, the report states. By the end of the century, very hot days are projected to increase from the present-day level of about 15 days per year to 5 weeks under the lower emissions scenario and 8 weeks under the higher. Proportionally, an even larger percentage increase is projected in  extremely hot days (over 100°F), with more than 30 of these days projected to occur each year by end-of-century under the higher emissions scenario.

The projected increases in extreme temperatures over the coming century could have a number of adverse impacts on human health. Extreme temperatures and resulting decreases in air quality can lead to increases in both morbidity as well as mortality. Currently, just under 100 deaths in Chicago are attributed to extreme heat each year. An “analog city” analysis, which transposes the weather conditions from the European Heat Wave of 2003 (responsible for 40,000 deaths across Europe) to the city of Chicago, estimates that if a similar heat wave were to occur over Chicago, given its present-day infrastructure, demographics, and emergency preparedness, more than ten times the annual average number of heat-related deaths would occur in just a few weeks.

According to the report, shifting climate zones can also affect the frequency of vector-borne and water-borne disease outbreaks. Vector-borne disease in the Chicago area is currently at a low level but it is an on-going health concern that has increased over recent decades. For example, since 2002, the Cook and DuPage Counties have reported almost 1100 cases of human illness from West Nile virus. The bacteria that causes Lyme disease, carried by the deer tick, has emerged in the region recently.

Waterborne disease outbreaks from all causes in the U.S. are distinctly seasonal, clustered in key watersheds, and associated with heavy precipitation. Heavy precipitation events have already increased in frequency over the last century and are likely to continue to increase in the future, raising concern about the potential for future waterborne disease outbreaks. In Chicago, increases in winter and spring precipitation are likely, with projected increases of about 10% by mid-century and 20-30% by the end of the century under both the higher and lower emissions scenarios, according to the report.

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