What impact will climate change have on air quality?

sammis power plant

The Sammis Power Plant near Steubenville, Ohio, which the PUCO agreed to allow FirstEnergy to continue operating through 2024 on the backs of ratepayers (courtesy of EarthJustice).

Though it’s hardly a secret that I view climate change as the preeminent issue of this generation, I usually try to bring some sobriety to the apocalyptic current that some of my fellow climate hawks bring to the table. Whether it’s casting a skeptical eye on the hype about climate change and conflict or challenging the use of the term “climate refugee,” I try to stay fairly level headed.

So it would seem reasonable that I would be somewhat wary of the hype surrounding the major new report from the U.S. Global Change Research Program on the public health impacts of climate change. I mean, as Kyle Feldscher of the Washington Examiner tweeted, somewhat snarkily,

But, here’s the thing, sometimes when Chicken Little screams that the sky is falling, you really do need to look up. And that’s the case with climate change. As this report lays out in tremendous detail, the public health implications of inaction are staggering, whether it’s the estimated 11,000 additional deaths per year from heat-related mortality, an increase in vector- and water-borne illnesses, or a spike in the frequency and intensity of disasters, things are going to suck unless we do something like yesterday.

Importantly, due to the lengthy atmospheric lifetimes of greenhouse gases (GHG), particularly CO2, some of these impacts are already baked into the cake. While the report makes it clear that we can stave off the worst effects on public health by taking immediate action to curb GHG emissions, the fact remains that we will inevitably have to adapt to that which we cannot mitigate and suffer that which we cannot adapt to. But since most of my focus is on air quality issues these days, I wanted to take a closer look at that chapter in the report.

Tracing improvements in air quality

First, it’s crucial that we note how much air quality has improved in the United States since the passage of the 1970 Clean Air Act Amendments (CAAA). According to the U.S. EPA, ambient levels of the six criteria air pollutants fell by a combined 63% from 1980 to 2014, including an astounding 99% for lead. All this occurred even as GDP grew by 147%.

This trend has paid significant dividends for Northeast Ohio. In Cleveland, for instance, the 3-year average for carbon monoxide (CO) from 1972-1974 was 17.3 parts per billion (ppb), well in excess of the 10 ppb standard. From 2012-2014, this value had fallen to just 4.3 ppb, a 75% decrease. Back in 1978, the 3-year average level of sulfur dioxide (SO2), which is generated largely from burning coal, stood at a mind boggling 497 ppb. In 2014, that level was down to 71 ppb, below the EPA’s 75 ppb standard.

The benefits of this dramatic improvement in air quality have been staggering. One study from the EPA found that, by 2020, the 1990 CAAA will prevent 230,000 premature deaths and generate benefits totalling $2 trillion. According to renowned University of Chicago economist Michael Greenstone, the 1970 CAAA extended the life expectancy of the average American by 1.6 years, totalling more than 336 million additional life-years. Here in Cleveland, we live, on average, 2.3 years longer because of this landmark piece of legislation.

But, as I’ve discussed before, a lot of people seem to think that these numbers mean we’ve moved beyond air pollution, that it’s something we’ve relegated to the past. That’s clearly not the case, given that a 2013 study estimated air pollution led to more than 200,000 premature deaths in 2005. In Cleveland, that number was 1,363, with the majority (62%) of deaths coming from electricity generation (466) and transportation (384). Clearly we have a long way to go, and incremental improvements in air quality will do a lot to winnow this number down further.

Will climate change affect this trend?

But that’s where climate change comes into play. The two primary bogeymen in the world of air quality are ground-level ozone and fine particulate matter (PM2.5). The formation of both of these pollutants depends heavily on meteorological conditions, particularly the former. When the conditions are right, ozone and PM2.5 levels can spike, with serious consequences for anyone who breathes air.

Now, obviously the most important thing that environmental officials can do is work to reduce emissions of ozone precursors, along with direct PM2.5 and its precursors. If there are simply fewer nitrogen oxide (NOx) and volatile organic compound (VOCs) molecules floating around, there will inevitably be less ozone in the air.

And this is true – to a point. That’s why the EPA estimates that, thanks to existing regulations like the controversial Mercury and Air Toxics Standard (MATS) and the Tier 3 Vehicle Emissions standard, ozone and PM2.5 levels will continue to decline. The agency projects, for instance, that ozone levels in Cuyahoga County will fall to 59 ppb in 2025 from 75 ppb currently.

Unfortunately, this fails to account for the impacts of climate change. Global warming is likely to make the types of meteorological conditions conducive to ozone formation – hot, still summer weather – considerably more common going forward. As the report’s authors note, “consequently, attaining national air quality standards for ground-level ozone will also be more difficult, as climate changes offset some of the improvements that would otherwise be expected from emissions reductions.”

To illustrate this effect, let’s look at recent history in Cleveland. From 2008 (when the EPA finalized its 75 ppb standard) through 2011, there were an average of 9.5 days each year when ozone levels exceeded the standard. This number plummeted further during the previous two mild summers, with 1 day and 3 days in 2014 and 2015, respectively. But then there’s 2012, the hottest year on record in the region. During that summer, we had 28 exceedance days, the highest number since 2002.

What will climate change’s impact be on air quality?

So what, exactly, does the report project? Well, it uses data from a 2015 paper by a group of EPA scientists that aims to “quantify and monetize the climate penalty” from higher ozone levels tied to climate change through 2030. Because the effects of climate change on PM2.5 are so difficult to suss out, the report focuses exclusively on ozone.

The authors use two global climate change scenarios, known as Representative Concentration Pathways (RCP) to estimate the effects. RCP 8.5 is a worst case scenario, while RCP 6.0 is slightly less pessimistic model that assumes we will take some action to curb emissions.

These models allow them to estimate the number of climate change-attributable, ozone-related premature deaths and illnesses in the US. While RCP 6.0 leads to somewhere between 37 and 170 premature deaths each year, RCP 8.5 could generate 420 to 1,900 additional early deaths. The authors find that “the economic value of these adverse outcomes ranges from $320 million to $1.4 billion for the RCP 6.0 scenario and from $3.6 to $15 billion for the RCP 8.5 scenario.”

climate change ozone impacts

The projected impacts of climate change on ozone levels and ozone-related mortality in the US for RCP 6.5 and RCP 8.0 (courtesy of Fann et al.)

These health impacts will not be distributed evenly, as the map above shows. Here the Midwest, particularly along the Great Lakes, significant global warming could drive ozone levels up by more than 5 ppb leading to tens or dozens of additional deaths. These findings are similar to those from a 2007 study (PDF) by Michelle Bell et al. in the journal Climatic Change. This study examined the impact of significant climate change on ambient ozone levels in 50 US cities by 2050. Bell et al. concluded that ambient summertime ozone levels would jump by 4.4 ppb, and every city studied would see an increase in the number of exceedance days by 2050. The average city would experience 5.5 more exceedance days per year, a 68% increase compared to the 1990s, while Cleveland could see a spike of 140%, from 7.5 to 18 days per year. The study uses the 1997 ozone standard of 85 ppb, meaning that the number of exceedances would likely be much higher for the current 2015 standard of 70 ppb. All told, ozone-related mortality was projected to increase 0.11-0.27%.

While this seems relatively insignificant, I should note that ozone is not a major cause of air pollution-related death here. If climate change was to have comparable impacts on particle pollution levels, these costs would increase by orders of magnitude. Unfortunately, this remains a real possibility. One study estimates that, while global PM2.5 concentrations may fall by up to 18%, they could increase by anywhere from 1 to 4 micrograms per cubic meter in the eastern US.

Ultimately, it’s not the projected number of additional deaths or asthma exacerbations that matters. What this report shows is that we have done an excellent job of cutting levels of harmful air pollutants, even as we increased emissions of a seemingly harmful one – CO2. But now, unless we take immediate action to slash the latter, all our great work on the former is at risk.

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