Climate Change Consequences - Often Unexpected

An increasingly common fallback position once climate change "skeptics" accept that the planet is warming and humans are the dominant cause is the myth that climate change won't be bad.  In fact, this particular myth comes in at #3 on our list of most used climate myths.  It's an ideal fallback position because it allows those who reject the body of scientific evidence to believe that if they are wrong on the science, it's okay, because the consequences won't be dire anyway.

One of my colleagues, Molly Henderson recently completed a Masters Degree program class on scientific research which focused on climate change, which she aced (way to go, Molly!).  For her final research paper, she examined the consequences of climate change on the prevalence of water-borne diseases in the US Great Lakes region.

This is obviously a very focused topic on a specific region and predicted consequence of climate change, but I think it also provides a perfect example as to why this notion that the effects of climate change will somehow be benign or good is fundamentally flawed.  As a general rule, climate change is not a good thing, because all species are adapted to the current climate in the region in which they reside.  There is a certain amount of climate change to which species can adapt and survive, but adaptation can be a difficult and ugly process.

As Molly's paper makes clear, while humans are a very adaptable species, at the same time we've built a lot of infrastructure whose specifications are based on the current climate.  We have large agricultural farms which depend on a relatively constant climate in order to successfully grow crops, for example.  As Molly's paper shows, there are some other climate change consequences on our infrastructure which we might not even normally think about.

The Problem

Molly states the problem as follows.

"Many cities that surround the Great Lakes are equipped with sewer systems that capture and combine sanitary sewage and stormwater as they are conveyed to wastewater treatment plants (McLellan et al., 2007).  The EPA estimates that 150 communities within the Great Lakes drainage basin are serviced by combined sewer systems (CSS) (U.S. EPA, 2012).   Extreme precipitation events can overcome the conveyance capacity of CSS and cause overflows, known as combined sewer overflows (CSO).  These overflow events result in untreated sanitary sewage and stormwater discharges into receiving waters (i.e, rivers, streams, lakes, etc.).  

Urban stormwater and sewage overflow water contains human pathogens including viruses, protozoans, and pathogenic bacteria that can cause adverse health effects if ingested.   The Great Lakes provide drinking water for an estimated 40 million people and there are more than 500 recreational beaches along lake shores (Great Lakes Legislative Caucus, 2012).  Waterborne disease outbreaks result when water supplies are contaminated with pathogens that infect humans.

It is well known that extreme precipitation events that cause CSO in the Great Lakes Region can lead to waterborne disease outbreaks, as seen in the 1993 outbreak of intestinal illness in Milwaukee, Wisconsin which affected an estimated 403,000 people (Curriero et al., 2001).   Observed and projected climate changes due to global warming infer that more frequent extreme precipitation events are on the horizon for this region, thus potentially leading to a higher incidence of waterborne disease outbreaks if mitigation measures are not taken to improve existing CSS infrastructure and reduce greenhouse gas emissions."

Personally when I think about the consequences of climate change, the possibility that increased heavy precipitation events could cause combined sewer systems to overflow, thus introducing pathogens into drinking water sources has never previously crossed my mind. 

Climate Literature Investigating this Problem

In retrospect this is a perfectly logical climate change consequence in regions which will receive increased precipitation, and indeed Molly shows that a great deal of research has been done on this specific concern in the specific region of the Great Lakes.  Sousounis & Grover (2002) used the  the Canadian Coupled Climate Model and the Hadley Coupled Climate Model to show that an increase in heavy precipitation events is among the expected climatic changes in the Great Lakes region.  A paper led by Katharine Hayhoe (who we've previously seen here and here responding to the wave of hate directed her way when she was asked to write a climate chapter for a Newt Gingrich book) also examined some of the expected climatic changes in the Great Lakes region, as described by Molly:

"Some positive impacts such as a decrease in energy use in the winter and risk of cold-related illnesses may result; however, a higher demand for energy in the summer and higher rates of heat-related mortality is likely to offset this positive impact.  This study also highlights the economic impacts on the Great Lakes due to projected lake level reductions and the article places emphasis on reducing greenhouse gas emissions."

Patz et al. (2008) hypothesized that extreme precipitation events may overwhelm the common combined sewer systems in the Great Lakes region, causing potentially dangerous overflows into sources of drinking water and recreational waterways, and recommended upgrading sewage/stormwater infrastructure and greater protection of watersheds.

A National Resource Defense Council (NRDC) fact sheet highlights the fact that that more than half of the waterborne disease outbreaks in the United States over the past 50 years are linked to heavy rain events, lending additional credibility to this potential problem.  Curriero et al. (2001) examined the association between extreme rainfall and waterborne disease outbreaks in the United States between 1948 and 1994, and their conclusions were consistent with the NRDC fact sheet, finding that 51% of outbreaks in their study sample were preceded within a 2-month lag by an extreme level of precipitation.

Adaptation Has a Cost

The good news is that while most of us probably haven't considered this particular climate change consequence, obviously a number of scientists have investigated it.   While it may seem on the surface like a relatively minor regional concern, Molly notes that 40 million people rely on the Great Lakes Region as a water supply, and the recreational beaches along the shores of the Great Lakes are an important economic contributor to the region. Additionally, combined sewer systems serve roughly 772 communities containing about 40 million people in the USA.  It's also a larger region - over 30 million people live within the Great Lakes basin area; that's 10% of the US population plus 25% of Canada's. 

However, since we are aware of the problem, the Great Lakes region can adapt to it.  The bad news is of course that upgrading sewage and stormwater infrastructure is not a cheap undertaking.  As another example we recently discussed, adjusting to a rising frequency of heat waves resulting from continued climate change will be another costly adaptation, as will shifting the geography of our agricultural production.

There are alternatives to facing these types of climate change costs.  We can try to prevent the problems from occurring by addressing the source (greenhouse gas emissions), which is likely the cheapest option, or we can simply allow them to happen and face the consequences.  As renowned paleoclimatologist Lonnie Thompson put it:

"Three options remain for dealing with the crisis: mitigate, adapt, and suffer...Sooner or later, we will all deal with global warming. The only question is how much we will mitigate, adapt, and suffer."

Molly's research provides one specific example of this choice.  If we fail to mitigate these types of consequences, we will either have to pay the cost to adapt to them, or suffer the consequences of failing to act.  The good news is that we are aware of the problem both on a global and local scale.  Now we just have to decide how we want to address it.


McLellan, Sandra L., Hollis, Erica J., Depas, Morgan M., VanDyke, Meredith, Harris, Josh, and Scopel, Caitlin O. (2007).  Distribution and Fate of Escherichia coli in Lake Michegan Following Contamination with Urban Stormwater and Combined Sewer Overflows.  Journal of Great Lakes Research, (33), 566-580.

U.S. Environmental Protection Agency (2012).  National Pollutant Discharge Elimination System (NPDES).  Retrieved April 27, 2012 from

Great Lakes Legislative Caucus (2012).  Great Lakes Facts and Figures.  Retrieved on April 27, 2012 from

Curriero, Frank C., Patz, Jonathan A., Rose, Joan B., Lele, Subhash (2001).  The Association Between Extreme Precipitation and Waterborne Disease Outbreaks in the United States, 1948-1994.  American Journal of Public Health, 91(8), 1194-1199.

Sousounis, Peter J. and Grover, Emily K. (2002).  Potential Future Weather Patters over the Great Lakes Region.  Journal of Great Lakes Research. 28(4), 496-520.

Hayhoe, Katharine, VanDorn, Jeff, Croley, Thomas II, Schlegal, Nicole, and Wuebbles, Donald (2010).  Regional Climate Change Projections for Chicago and the U.S. Great Lakes.  Journal of Great Lakes Research, 36, 7-21.

Patz, Jonathan A., Vavrus, Stephen J., Uejio, Christopher K., McLellan, Sandra L. (2008). Climate Change and Waterborne Disease Risk in the Great Lakes Region of the U.S. American Journal of Preventative Medicine, 35(5), 451-458. doi:10.1016/j.amepre.2008.08.026.

National Resources Defense Council (2010).  Rising Tide of Illness:  How Global Warming Could Increase the Threat of Waterborne Diseases.  Retrieved March 12, 2012 from

Posted by dana1981 on Wednesday, 16 May, 2012

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