Flooding impacts and climate change


An Uncertain Future
The outlook for Iowa communities and flooding as our climate changes

September 5, 2019
This Full report
Executive summary (3 pg)
News release

By James E. Boulter

I-29 flooding across highwayFloodwater makes Interstate 29 impassable between Crescent and Loveland during the 2019 Iowa floods. Source: Iowa Flood Recovery Advisory Board.

Iowa’s Floods of 2019 — a sign of things to come?

Scenes like the one above replayed across Iowa this past spring. On the eastern part of the state, the Mississippi River reached flood-stage for 38 days, resulting in a levee breach in Davenport, and on the western side of the state, the Missouri River basin took on more runoff in three months than it typically gets in a year. A total of 47 levee breaches on the Missouri were reported by the U.S. Army Corp of Engineers with every Iowa levee south of Council Bluffs being affected.[1] Early estimates put total statewide damages at $1.6 billion, a number that can only grow as additional damages are discovered.

Across the Midwest, May of 2018 to April of 2019 experienced record-setting amounts of precipitation for this 12-month period, with an average of 45 inches. This beat the previous record, set in 2010-11 by a full inch. Iowa exceeded this with over 50 inches and shattered its May to April precipitation record by over 2.5 inches — a record first set in 1902-03. Iowa experienced February snow accumulations 3½ times its recent average and upstream, Minnesota and Wisconsin vastly exceeded snowfall norms, some locations seeing up to 40 inches above normal.[2][3] This historically wet period caused the extensive and persistent flooding seen throughout the region this spring, but there was a difference in the response from the leaders of affected communities across the state even though most recognized that flooding was getting worse. Following the floods in Davenport, in the east, and Hamburg, in the west, their respective mayors chose divergent approaches to describing their dire circumstances: Davenport’s two-term mayor was concerned that relating the floods to climate change might be divisive, “We know there’s something going on, so how do we come together and deal with that? … Let’s not try to label it. Let’s not try to politicize it. It’s just a matter of something is changing.”[4] Conversely, Hamburg’s mayor approached it quite differently: “I’m looking at global warming — I don’t need to see the graphs… I’m living it and everybody else here is living it.”[5]

The sum total of current scientific understanding backs up the Mayor of Hamburg's sentiment. As discussed later in the paper, there are studies that show that Iowa’s average temperature is slowly increasing. The least-favorable projections show that there may be as many as 43 days of extreme heat (as classified as days of 105 °F or higher) in Des Moines by 2050.[6]

These slow and steady increases in temperature have led to increases in precipitation. Since the mid-1970s, the average annual rainfall in the Upper Mississippi River basin has been steadily rising at almost one inch per decade, and there has been a 42 percent increase in the amount of rain falling in the top 1 percent of days with precipitation across the Midwest.[7] Simply put, this is because warmer temperatures increase the rate at which water evaporates, and as air heats up it is able to hold more water. Thus, when clouds form and later drop rain, there is more of it: 6-7 percent more for every degree Celsius (or 1.8 °F) of air temperature increase.

This paper will put these observations and trends in the context of the latest understanding from climate science. It will examine the more recent and robust predictions of future climates and the effects of climate change that are projected for the region, and it will seek to answer these vital questions: in the face of our changing climate, will Iowa’s flooding worsen as the world grows warmer and, what is the outlook for the next 10-30 years if only limited action is taken to address the problem? It is hoped that this paper will inform meaningful discussions about how Iowans should respond to the threat of climate change — and in the ways we seek to mitigate its impacts.

Predicting future climates: the basics

Before considering how climate change might further affect Iowa’s and the region’s future, it is crucial to understand the nature of the various computer models and scenarios that generate such predictions and what they can tell us.

Can climate models make predictions for the Midwest?

Climate models have advanced tremendously since their earliest computerized ancestors in the 1980s as they grew to simulate a far greater range of processes in the Earth system. Initially, the models were only able to calculate outputs such as ground temperature, cloud cover, simple hydrology, and snow depth. Now these global climate models (GCMs) incorporate all the latest scientific understanding from the range of disciplines that inform our knowledge of planetary systems: atmospheric physics and chemistry, geology, plant biology and ecology, oceanography, and meteorology, to name a handful. Early models operated on a coarse geographical scale, meaning that the entire planet was divided into 864 squares, approximately 600 miles on a side.[8] Since then, computing power has increased by more than 10 million times and these spatial scales are now fewer than 50 miles on a side. More recently, a new class of models may focus on specific regions such as the continental U.S. These “downscaled” models are sometimes referred to as Regional Climate Models (RCMs). They enable predictions on scales as small as a few miles which has been crucial for projecting changes at the state level. (See the appendix for additional background information.)

Can models tell us anything about individual events?

Only a decade ago, claiming attribution of any single extreme weather event to global warming was still considered to be questionable. More recently, “attribution of extreme weather events under a changing climate is now an important and highly visible aspect of climate science.” Further, “…the science of event attribution is rapidly advancing, including the understanding of the mechanisms that produce extreme events and the rapid progress in development of methods used for event attribution.”[9]

Nonetheless, deterministic or causal questions: “whether climate change caused a particular extreme event” are more fruitfully phrased in statistical language: “how much more likely was such an extreme event in the context of a human-altered climate?” Attribution studies are certainly appealing for addressing public curiosity about the possible relationship between climate change and a recent disaster. But they are perhaps better used to inform risk management decisions when predicting recurring or novel extreme events.[10] (See the appendix for more discussion.)

Is the scientific basis of climate change well understood?

Climate models are all based on the fundamental physics that describes Earth’s atmosphere. Our robust understanding of the relationship between the amount of human-influenced greenhouse gases (GHGs) in Earth’s atmosphere and the state of the global climate dates back to the middle of the 19th century. What they knew then, and what we still recognize to be true, is that the composition of the atmosphere — the gases and the clouds that form above us — determines how much of the sun’s energy is stored as heat at the surface and how much is reflected out to space. Even small changes in this balance have significant consequences for the global average temperature and for regional processes such as cloud formation and precipitation.

Furthermore, an overwhelming majority — 97 percent of scientists across many disciplines studying a wide variety of topics related to the climate, agree that the changes in Earth’s climate that we have observed and that are predicted are directly attributable to human actions.[11] Stated another way, there is a clear consensus that climate change is primarily caused by changes in the concentration of GHGs in the atmosphere: carbon dioxide from the burning of fossil fuels and from changing land-use practices, methane from oil and gas extraction and livestock production, nitrous oxide from agricultural practices, synthetic fluorine-containing gases like Freon, and changes in atmospheric particles including carbon soot and other pollutants. (See the appendix to learn more.)

How do models incorporate human responses?

When modeling future climates, what goes into the models — the inputs — are just as important as the actual computer code. While some uncertainties remain even as GCMs increase in complexity, the factor most responsible for late-century climate outcomes remains the decisions humanity makes: How much will global GHG emissions continue to increase before stabilizing? How quickly will we reduce carbon dioxide and other GHG emissions? Will we discover and implement “carbon negative” strategies to reduce atmospheric concentrations of carbon dioxide?

Models have clearly demonstrated that the timing and rate of changes in emissions (or "pathways" to reach reduction targets) matter as much as the high watermark of human GHG emissions or when they cease entirely. Various narratives of possible climate and energy choices for the remainder of the century can be summarized as “emissions scenarios” for use in climate models. Significantly, these facilitate comparisons between different climate modeling studies by having a limited number of possible scenarios as inputs to the models. The Intergovernmental Panel on Climate Change (IPCC) adopted this small number of scenarios in its fourth report and they have entered wide-scale use.[12]

Our report will compare the IPCC future scenarios in which human society makes a range of choices to mitigate its impacts on the global climate. The least ambitious response (RCP8.5) is also consistent with some of the most alarming potential climate outcomes. Conversely, future climate impacts are greatly reduced in the more robust RCP2.6 scenario — a response that exceeds what the U.S. has previousy committed to in the 2015 Paris Accord in emissions reductions. Obviously, this scenario will be the most challenging to achieve. The middle scenario, RCP4.5, is unlikely to result in global average temperatures remaining below the accepted “safe limit” of a 2 °C global temperature increase[13] and even RCP2.6 is unlikely to meet the goal of 1.5 °C set out in the Paris agreement.[14] Whenever possible, we will compare the moderate emissions scenario (RCP4.5) to RCP8.5 (the higher emission scenario). (See the appendix for more details.)

Upper Midwest climate impacts over the next 10-30 years

Throughout the Midwest, changes in climate expected to have the greatest impacts are increased temperatures including incidents of extreme heat, and greater variability in precipitation including extreme rain events, droughts, and flooding. These physical changes drive a range of secondary effects including threats to human health — particularly to vulnerable populations, economic impacts due to damages to infrastructure such as roads, bridges and wastewater treatment systems, lost labor productivity resulting from extreme temperatures, and reduced agricultural productivity resulting both from changes in precipitation and increased temperatures.

Temperatures — and their extremes — are increasing

The climate trend with the highest level of confidence is the increase in average temperatures. This is illustrated for the past approximately 70 years of statewide temperature data (as a four-year average). There has been an overall increasing trend of 0.4 °F per decade over the past four decades (Figure 1).

Figure 1. Temperatures in Iowa are already increasing

Figure 1: Temperatures rising
Source: National Climate Data Center, Climate at a Glance, 2019

Across the contiguous U.S., most of this historical warming has occurred during the winter months. However, the largest warm-season temperature increases are projected to occur here in the Midwest (in both the RCP4.5 and RCP8.5 scenarios).

Toward the middle of the century (between 2036-2065), a group of 32 climate models predicts an increase in average annual temperatures relative to the period of 1976-2005, including warm season increases. This warming is either 4.2 °F for RCP4.5 or 5.3 °F for RCP8.5 and exceeds the warming we’ve already seen by a factor of 3-4. (The average temperature from 1986-2016 is currently only 1.3°F warmer than that of the first half of the last century, 1901-1960). To summarize, not only do both the moderate and high-end scenarios predict increases in temperature, but they also project a higher rate of increase in temperature, a trend that — if continued — will make the hottest summer days even hotter.

By 2030, 29 RCMs using RCP8.5 predicted an average of 30 days with a heat index over 105 °F in Des Moines, increasing to 43 days by 2050. For comparison, there were only 6 days that hot in 2000.[15] Under that scenario, extreme heat alone is projected to result in nationwide losses in labor and associated losses in economic revenue up to $9.8 billion per year in 2050 (in 2015 dollars).[16]

Economic and health impacts


Nationwide economic damage also results from decreases in agricultural efficiency, primarily driven by increased summertime heat in the Midwest. This measure of efficiency (based on the ratio of outputs of crop and livestock relative to resource inputs such as land, labor, and capital) has been increasing since 1948, but has recently exhibited greater variability and is projected to decrease back to 1980 levels sometime between 2040 and 2030 under RCP4.5 and RCP8.5 scenarios, respectively.[17] In effect, these increasing temperatures are projected to cancel out the most recent 40 years of agricultural efficiency advancements — even under a moderate emissions scenario.

Projected climate change impacts on human health are mostly related to increases in extreme summertime temperatures, and disproportionately affect the elderly, expecting mothers, and children. There is also a strong connection to socioeconomic status, with low-income communities and urban residents being particularly vulnerable. Elevated temperatures are statistically associated with increased hospital admissions for cardiovascular and respiratory complications, kidney failure, electrolyte imbalance, negative impacts on fetal health, and preterm birth.[18] In urban areas such as Des Moines, heat island effects yield still higher temperatures, on average 3 °F greater than neighboring rural regions.

Extreme heat also uniquely affects rural populations where many work in outdoor occupations, where some are economically vulnerable, and where healthcare access may be limited.[19] Finally, longer growing seasons resulting from warmer average temperatures also produce greater amounts of pollen, especially from trees in springtime and noxious plants like ragweed in the fall, exacerbating allergies for many. For some this may result in more hay fever symptoms; for others it may result in worsened asthma attacks and even emergency room admissions.

Statistical estimates of deaths due to extreme heat currently exceed 1,300 deaths per year in the U.S., and direct attribution studies estimate over 65,000 hospital admissions during the summer months. Hospital death records tend to underreport this as the cited cause, with an average of 670 deaths reported annually between 2006-2010.[20] Cities throughout the Midwest region are projected to have the greatest increases in premature deaths from climate change, reaching up to 2,000 annually by 2090 under RCP8.5. These additional deaths may be reduced to 840 by reductions in global emissions to achieve the RCP4.5 scenario. They may be further reduced by adaptations such as increased availability of air conditioning. Risk of death from extremely cold temperatures will also decrease under most climate projection scenarios.[21]

Increases in average temperatures may also lead to the spread of serious diseases. Reduced frequency of very cold periods is resulting in the northward spread of mosquitoes carrying viruses like West Nile and ticks infected with Lyme disease and co-infections that have not historically been a hazard in the region. Warmer summers increase the prevalence of freshwater algal blooms, and can expose people to cyanobacteria through drinking water supply contamination or through recreational use of affected lakes and streams, resulting in skin and eye irritation, respiratory illness, gastrointestinal illness, and liver and kidney damage. For example, in 2014 in Toledo, Ohio, half a million people were warned to avoid drinking the water due to toxins overwhelming a water treatment plant in Lake Erie’s western basin as a result of a harmful algal bloom. In 2018, Greenfield, Iowa, experienced the same loss of drinking water for nearly a week.[22] These outbreaks of cyanotoxins from increased temperatures are made much worse when compounded with excess nutrients (nitrogen and phosphorous) in agricultural runoff, as well as contaminated water supplies from flooding and overwhelmed water infrastructure in extreme rain events.[23]

Precipitation is also increasing — and growing more intense

Iowa and the Upper Midwest have a much clearer trend in annual precipitation than the whole of the contiguous U.S., as increases in precipitation in some regions are offset by droughts in other parts of the country. Because of Iowa’s location downstream of the Upper Mississippi and Upper Missouri River basins, the regional trend for the Upper Mississippi River basin (Figure 2) is, in many ways, as relevant as Iowa’s own record. This region’s average annual rainfall has been steadily rising at almost one inch per decade — a total increase of over 12 percent since the mid-1970s. Iowa’s statewide trend over the same period is still higher at 1.25 inches per decade — the largest increase across the U.S.

Figure 2. Precipitation in the Upper Mississippi River Basin has steadily increased
Figure 2 Precipitation in MW steadily increased
Source: National Climate Data Center, Climate at a Glance, 2019

Looking forward, average rainfall amounts in Iowa are predicted by a group of 23 models to increase by 10-20 percent over the 1976-2005 average by 2080 under the RCP8.5 emission scenario, but rainfall increases due to climate change exceed natural variability only in the springtime with significant confidence.[24] Thus, it’s better to explore the frequencies of extreme rainfall events in order to get a fuller understanding of the effects of climate change.

Nationally, a larger fraction of total annual rainfall is falling during extreme events.[25] There has been a 40 percent increase since 1970 in the number of two-day precipitation events whose rainfall totals set a five-year record, with the largest increases in frequency and intensity in the Midwest and Northeast regions.[26] Projecting forward, a group of 30 models predicts that by 2041-2050, there will be another 30 percent more of these events in the Midwest under both RCP4.5 and RCP8.5 scenarios. When predicting the frequency of these events for the latter half of the century the projections diverge, with the lower emission scenario resulting in an 50-60 percent increase by 2100 and more than double that for the higher emission scenario.[27]

Focusing on the Midwest, there has been a 42 percent increase in the amount of rain falling in the top 1 percent of days with precipitation. This analysis compared the most recent three decades (1986-2016) to the first six decades of the 20th century. Another analysis observed a recent increase of around 30 percent in one-day rainfall totals during the months of April through September (Figure 3).

Figure 3. Upper Midwest Extreme Rainfall Events Becoming More Widespread
Fig 3 extreme rainfall graph
Source: National Climate Data Center, Climate Extremes Index, 2019

Temperature is one crucial determining factor in the frequency of extreme rainfall events, but increased temperature can also produce drought. Many factors influence rainfall trends, making quantitative predictions of future events somewhat less confident. Their relatively short duration and small geographical scale also represent a challenge for model projections. Climate-induced changes in atmospheric circulation patterns heavily impact the frequency and duration of extreme rainfall events as both atmospheric water vapor and clouds are transported by atmospheric circulation patterns.

To give an example, a summer rainstorm in Iowa can start with evaporation over the Gulf of Mexico. If the surface of the Gulf is warmer, more water will evaporate, and if the air is warmer, it will hold more water. The storm also relies on the transport of that water by wind and subsequent cloud formation. As the system moves northward, clouds are formed by convection during the daytime heat in the central states. This can generate massive storm clouds and the potential for catastrophic amounts of rainfall if the local temperatures and climate conditions are right — something that’s happening much more frequently due to climate change. Despite challenges, downscaled models have projected increases in both frequency and intensity of severe thunderstorms, especially during the spring, in the Midwest and Southern Great Plains of the U.S.[28]

Economic and health impacts

Impacts of extreme rainfall may lead to flooding, but also a variety of other economic losses and expenses, especially transportation infrastructure and water management systems. Such events may overwhelm designed capacity of stormwater systems. “The U.S. Environmental Protection Agency (EPA) estimates that the cost of adapting urban storm water systems to handle more intense and frequent storms in the Midwest could exceed $480 million per year (in 2015 dollars) by the end of the century under either the lower or higher scenario (RCP4.5 or RCP8.5).”[29] Data collected by the Federal Emergency Management Administration (FEMA) on the number and cause of federal disaster declarations indicate a sharp increase in extreme weather events. Of 26 severe storm declarations in Iowa since 1953, all but five have occurred since 2000 and 14 have already occurred in the current decade.[30] (See appendix for more analysis of disaster frequency.)

Bridges are subject to substantial wear, both in the form of erosion of their footings (or “scour”), and of the roadways when the bridges are overrun with water (called “overtopping”) following heavy rainfall events. According to the Iowa State Institute for Transportation, climate model projections show that six bridges in the Cedar and Skunk River basin would be exposed to streamflow conditions that exceed current design standards. “Each location is projected to have increased vulnerability from more frequent episodes of highway overtopping and potential bridge scour.”[31] Further, “the EPA estimates that the annual cost of maintaining current levels of service on Midwestern bridges in the face of increased scour damage from climate change could reach approximately $400 million in the year 2050 under either the lower or higher scenario (RCP4.5 or RCP8.5).” [32]

Extreme rainfall events and storms may have significant impacts to human health, but primarily through flooding as described below. Many community wastewater systems are affected by extreme rainfall and flooding events. The Iowa Department of Natural Resources records the number of discharges of raw sewage, an obvious health hazard. While no formal study using the data of the 10 years of discharges has yet been made, of the 903 release events from April 2018 to March 2019, 612 were rain/flooding induced events.[33] Furthermore, Iowa has at least 10,000 concentrated animal feeding operations. Lagoons can be overtopped and newly applied manure to land can contaminate streams during rainfall events. Other direct injuries or even premature deaths may result from structural failures, or being struck by objects (debris, trees, power lines) propelled by high winds. Additionally, power outages may limit access to electricity for crucial medical equipment and may lead people to use gas or charcoal grills indoors leading to carbon monoxide poisoning. Finally, interruptions to vital transportation and communication systems may provide an additional hazard to vulnerable populations, especially the ill and disabled.[34] Surveys of patients after Hurricane Katrina showed that those with cancer, hypertension, kidney disease requiring dialysis, cardiovascular disease, and respiratory illnesses were particularly affected.[35]

The Fourth National Climate Assessment summarized the impact of these trends:

“An increase in localized extreme precipitation and storm events can lead to an increase in flooding. River flooding in large rivers like the Mississippi … and Missouri Rivers and their tributaries can flood surface streets and low-lying areas, resulting in drinking water contamination, evacuations, damage to buildings, injury, and death.” “By mid-century, the region is projected to experience substantial, yet avoidable, loss of life, worsened health conditions, and economic impacts estimated in the billions of dollars as a result of these changes.” [36]

Flooding is the greatest concern — but trends are harder to quantify

The highest profile and most costly outcomes of this year’s historic precipitation events are the floods that devastated households, businesses, municipal and transportation infrastructure in communities across the state. In addition to the dramatic images of flooded roads, homes and downtown businesses, another form of flooding caused substantial harm to many of Iowa’s farmers: field flooding. Inundation of farm fields has led to late planting in some cases — and none at all in many others, spoilage of stored grain, deaths of livestock, and substantial damage to costly farm capital infrastructure. As a result of the March 2019 floods, 80 Iowa counties (81 percent of the state) received Presidential Major Disaster Declarations. For many Iowans, this year’s floods appear to be a repeat of other recent “100-year flood” events such as 1993, 2008, and 2011, leaving them to wonder if this the way of the future in a changing climate.

Predictions of flood frequency and severity are generally less confident than those of increased temperatures and more frequent extreme rainfall events. Individual floods are determined by a complex set of processes stemming from a variety of phenomena including climate change. Although it might seem intuitive that heavy rains would lead directly to flooding, this link is subject to an even wider variety of factors including local variations in topography, hydrology, land use and urbanization, and other effects that varies with season such as snowfall accumulation, degree of soil saturation and the timing of thaw events.[38] Consequently, some regions in the U.S. will experience increases while others may see decreases in both the frequency and/or severity of river flooding events. Although projections for flooding are complicated, compelling studies offer sobering assessments of future hazards of inland flooding and potential costs related to flood damages in the Midwest.

One detailed analysis of 18 downscaled GCMs concluded that springtime conditions in the later third of this century may be consistent with those during the devastating 1993 floods of the Mississippi River valley. During May and June of that year, over 17 million acres were flooded over a nine-state region (including every county in Iowa), resulting in at least $2 billion (in 1993 dollars) in crop losses alone.[39] The study examined atmospheric phenomena that are conducive to forming large quantities of airborne moisture contained in particular air circulation patterns (termed “atmospheric rivers”). This paper predicted increases of 20 to 40 percent in springtime precipitation in the Upper Mississippi River Valley, consistent with other model predictions for the mid-century. In short, this study makes a compelling argument that a changing climate may produce more historic-level floods in the region and that the anomalous atmospheric conditions that led to the 1993 floods may become a new normal; this prediction should be of great concern to policymakers as well as citizens of Iowa.[40]

As discussed above, flood predictions are made more difficult by the complex interplay among the many factors that determine their severity. But this also means that, when a variety of contributing factors come together in the right way, they can lead to extreme flooding events that may not be easily predicted. The U.S. Global Change Research Program reported with high confidence as recently as 2017 that multiple effects of climate change may combine with a range of other human factors and natural variability to generate climate disasters: “The physical and socioeconomic impacts of compound extreme events (such as… flooding associated with high precipitation on top of snow or waterlogged ground) can be greater than the sum of the parts. Few analyses consider the spatial or temporal correlation between extreme events.”[41] It is extraordinary that just two years after this statement, this exact compounding of events produced the devastating 2019 Missouri River floods from which so many are still recovering. No studies attributing the cause of these floods is possible at this early date, yet the overwhelming frequency of these events must be alarming to Iowans.

Economic and health impacts

In Iowa, the costs continue to increase from this year’s floods. “Iowa Farm Bureau Federation’s (IFBF) economists say the state may see upward of $2 billion in damages from recent flooding, noting that there have been multiple breaches in levees with roads and bridges rendered unsafe or impassable.”[42] Nationwide claims to the National Flood Insurance Program (NFIP) have recently escalated, with the six costliest years of all-time occurring since 2005. Most of these were related to the severe hurricanes Katrina (2005), Sandy (2012), Harvey, Irma, and Maria (2017), but even without considering those events, the upward trend is clearly discernable in the national data. [43]

In response to current and anticipated impacts of climate change, the State of Iowa recently added $15 million to a fund designed to help local governments repair infrastructure damaged by the recent flood and prepare for the next one. Instituted in 2011 after several major floods, this program allows local governments to retain some portion of sales taxes to finance flood protection structures such as levees and floodwalls. However, the $600 million in revenue had already been committed — allocated to 10 cities. [44]

Despite the magnitude of these economic projections, the damages from flooding are still greater when considering human health impacts, both those directly caused and those due to indirect effects of social disruption. Different populations are exposed to varying levels of risk and it is understood that children, older adults, low-income communities, and some communities of color are disproportionately affected by the health impacts of climate change. Public health implications of increased flood frequencies include the northward spread of insect-borne diseases such as dengue, Zika, chikungunya, and yellow fever due to increasing temperatures and the presence of flooded conditions that benefit the reproduction of mosquitos. Other less obvious but significant human impacts include reduced food security, especially for those most vulnerable: these include threats to food safety, disruptions to food availability, decreasing access to food, and higher food prices. Another critical health impact just beginning to be recognized is the increased levels of depression and anxiety for flood victims that may persist for years after an event (for example, farmers who have experienced significant economic losses), and mental health impacts on children who are displaced from their homes and lose the stability of their community.

Climate Change in Iowa: an imperative to act

“Our atmosphere and Earth’s surface are warming at an unprecedented rate. Globally, the five warmest years on record were each of the last five years, and extreme weather disasters are increasing in frequency and severity. In the Midwest states, we have seen changes in the form of dramatic variability in rainfall, higher humidity, and warmer nights.”
— Iowa Climate Statement 2019: Dangerous Heat Events Will Be More Frequent and Severe

We are not on track to meet climate goals

Meeting the emission reduction targets consistent with the goals of the U.N. Paris Climate Agreement will require a significant change to the world’s current emissions trajectory, which currently is on track to a global increase of 7.6 °F. Even the full set of member nations’ emission reduction commitments fail to bring the planetary average temperature increase to less than 6 °F — and that’s if they all met them, which is not currently happening.

The global commitment to remain within what some consider to be “safe” climate space of 3.6 °F (2 °C), and the U.N. goal of 2.8 °F (1.5 °C) remain far out of reach at this time. The nations of the world must make significant progress to meet this challenge, starting in the first round of negotiations to “ratchet up their ambition” in 2020. Finally, it has become quite clear in the past few years that we must make crucial changes within years — not decades — if we are to avoid the most catastrophic projected outcomes of climate change.[45]

These may not seem like a particularly large temperature increases, but in comparison to the amount of warming that has already taken place (approximately 1.8 °F, or 1 °C), and considering the climate impacts we are already experiencing, contemplation of a 7.6 °F warmer world almost defies the imagination. Fortunately, we have computer models to suggest to us what the consequences of this would be — and the potential losses are staggering.[46]

Climate choices have economic costs

For example, looking only at U.S. projections of the costs of inland flooding by 2090, economic damages may total $8 billion per year under the RCP8.5 emissions scenario (compared to the period between 1980 and 2010). But under RCP4.5, 47 percent of these losses may be avoided. Related damages to roads are still greater with costs estimated at $20 billion annually (in the absence of adaptation measures) and savings of 59 percent under the reduced emission scenario (RCP4.5). Additional annual costs related to flooding under RCP8.5 include bridges ($1.0B), municipal and industrial water supplies ($0.32B), and algal blooms ($0.20B). Similarly mitigating climate change to achieve the RCP4.5 emissions scenario is projected to result in savings between 33-48 percent for these damages. In short, the nationwide costs of inaction add up: the difference between these scenarios is over $16 billion annually by the end of the century.

Damages to crops, roadways, and bridges are certainly significant — as confirmed by this spring’s human and economic costs. However, these expenses pale in comparison to the total costs of climate change under the moderate and high emission scenarios. Losses occurring on coastal properties are estimated at $118 billion per year, with only 22 percent savings at the moderate emission scenario. Still larger is the economic burden of premature deaths due to extreme temperatures. This is estimated to exceed $140 billion under RCP8.5 — but the RCP4.5 pathway may reduce the cost of those mortalities to less than $60 billion.[48]

Estimates of total damage to the U.S. economy reach 4 percent of U.S. GDP under current emissions (corresponding to an increase of 7.6 °F) but remain close to 1 percent if we are to attain the most ambitious goal of 2.8 °F temperature increase (1.5 °C).[49] At current U.S. GDP levels of $19.4 trillion, this corresponds to annual economic costs of climate change decreasing from almost $380 billion down to less than $100 billion per year. Both costs are very high, but their difference suggests that rapid investment will yield significant long-term dividends.

Emission scenarios have implications

Finally, when considering the magnitude of societal changes illustrated in various RCPs or emission scenarios, the challenges may seem daunting. However, it’s crucial to understand that global GDPs increase for all scenarios presented — and more rapidly for the more ambitious emission reductions. This indicates that the models describing policies and actions to mitigate climate change do not assume a downturn in the global economy — they may instead generate economic growth.

Under RCP8.5, world oil consumption continues to rise until peaking in 2075 followed by a sharp decrease. By comparison, RCP2.6, requires technology to remove carbon dioxide from the atmosphere to offset continued fossil fuel consumption by the middle of the century. Under all scenarios, primary energy consumption also increases continuously, but more slowly for all those other than RCP8.5. One difference is that, under the more ambitious emission scenario (RCP2.6), primary energy sources are dominated by bio-energy and natural gas — petroleum use is nearly eliminated. For RCP8.5, coal grows to almost 50 percent of primary energy production, with oil and gas comprising almost half of the remainder.[50] So none of these four RCPs assume the elimination of fossil fuels, but new research is suggesting that we need to reach net zero carbon emissions by around 2050 to meet the 1.5 °C goal.[51]

Climate Change in Iowa: ongoing and future responses

As the state of Iowa works to respond to the immediate and proximate threats of climate change described above, it is crucial to consider a broad range of actions to mitigate Iowa’s role in the production of greenhouse gases. It is equally important to invest in a broad range of adaptation strategies such as the development of resilient infrastructure and socioeconomic systems. However, those priorities will not be discussed in this paper as there are many other excellent resources for such guidance.[52]

There are co-benefits to mitigation of climate change impacts

Because Iowa currently produces no fossil fuels, all purchases of coal, oil, propane and natural gas represent a net loss to the state GDP. Transitioning to domestic, renewable energy would bring billions of dollars back to the state, along with thousands of high-paying jobs. Further, with fully half of its power plants still burning Wyoming coal, the potential for air pollution reductions, with accompanying economic and health benefits, is enormous. In neighboring Wisconsin, a study from the Center on Wisconsin Strategy estimated a state GDP increase of $14 billion, tax revenues of $110 million (plus income tax on newly created jobs), and healthcare savings of greater than $20 billion, along with the creation of 162,000 jobs in the green energy sector, a 10 percent increase over the current number of energy-related jobs.[53]

In 2018, Iowa ranked fifth in total energy consumption per capita — the highest of any non-fossil fuel producing states. This is partly because Iowa was the fourth-largest consumer in 2016 of liquid fossil fuels. Propane consumption is a large component of this, used both for drying the state's large corn harvest and for residential heating. However, when it comes to transportation fuel the state has already become a leader in biofuels. The state’s 42 ethanol and two cellulosic plants as well as 12 biodiesel plants produce more fuel than the state uses, producing a large export market.[55]

For electricity, Iowa is a leader in wind production. In 2018, 34 percent of the state's electricity came from wind turbines, and 37 percent in 2017, either the highest or second-highest share for any state. Currently there are nearly 9,000 megawatts of wind capacity, the equivalent of nine large nuclear power plants.[56] MidAmerican Energy Company, an Iowa utility, recently reached a milestone of more than 50 percent of its native Iowa load covered by wind generation on the way to providing 100 percent renewable electricity by 2021.[57] This is largely due to Iowa’s excellent wind production potential, but also the proactive establishment of a renewable energy portfolio dating back to 1983. This state’s large availability of wind power was a factor in recently attracting cloud data centers from Microsoft, Apple, Google and Facebook — all to be in central Iowa.[58]

Some actions are already underway in Iowa

Forty-five percent of Iowa’s electricity is still generated by coal combustion, making it one of the more coal-dependent states.[54] Much progress has been made, as coal comprised 75 percent of electricity as recently as 2008. Solar production remains less than one-fourth of a percent of total electricity generation. This share mostly consists of distributed solar photovoltaics with utility-scale solar lagging behind.[59] However, there are some hotspots in the state, including the Farmers’ Electric Cooperative in Washington County, where members have access to community solar arrays to purchase their own electricity.[60] Electricity-intensive agricultural industries such as a dairy operation and an egg processing facility have also “gone solar” throughout the state.

Following the Trump administration’s announcement of their intent to withdraw from the United Nations Paris Climate agreement, thousands of states, cities, counties, universities, and corporations pledged to uphold the spirit of that accord by creating voluntary carbon reduction targets. In Iowa, five city and two county governments have signed “We Are Still In” and/or “Climate Mayors” commitments: Des Moines, Fairfield, Iowa City, Dubuque, Windsor Heights, Johnson County, and Linn County[61]. The State of Iowa has not yet followed the examples of its Midwest neighbors (Illinois, Michigan, Minnesota and Wisconsin) to join the U.S. Climate Alliance.[62]

Policies are needed to speed implementation

One effective way to broaden these admirable (but still too rare) efforts is through market forces — to mobilize the power of national economies at scale. Carbon pricing schemes ranging from traditional “cap and trade” to more recent revenue-neutral “carbon fee and dividend” approaches are quickly spreading to incentivize the rapid shift to a decarbonized economy. The World Bank counts a total of 57 carbon pricing initiatives already implemented or scheduled for implementation in nations or states around the world. Together, these represent over 20 percent of global GHG emissions.[63] In the 116th U.S. Congress, over half a dozen bills have been introduced with a few receiving bipartisan co-sponsorship — a prospect that would have been unimaginable only a few years ago.[64] There is an increasing basis for hope that this may be the most likely path to comprehensive climate legislation in a divided U.S. government.[65]

While crucial, reductions of fossil fuel emissions are not the only means for Iowa to mitigate. According to the IPCC, agriculture, forestry and other land-use choices contribute approximately 23 percent of net human greenhouse gas emissions.[66] In addition to ensuring food security for the U.S. and the world, Iowa’s land-use choices can have a significant impact on its net GHG emissions. Examples of this include reestablishing historic wetland margins and the implementation of regenerative farming practices to increase carbon storage in the ground through federal initiatives such as the Conservation Stewardship Program (CSP). Climate Smart Agriculture, a USDA program initiated by former Agriculture Secretary Tom Vilsack, would move farmers in the direction of being part of the solution to increased carbon dioxide in the atmosphere.[67] An advantage of land conservation approaches is that they simultaneously mitigate the impacts of excess nutrients (i.e. nitrogen and phosphorous) in U.S. waterways and coastal areas, yielding additional co-benefits of improved human and environmental health.

As a national and world leader in agricultural productivity with a huge fraction of its land dedicated to crop and livestock production, Iowa can provide a compelling example of climate leadership in the agriculture sector. Using effective incentives, Iowans can implement practices to reduce greenhouse gas emissions and sequester carbon, as well as make the landscape more resilient to the more extreme weather that has become the norm. This will become ever more important to sustain our food and agricultural system and protect the financial security of rural communities in a climate-changed world. To succeed at scale, we will need to think beyond existing programs like CSP to create innovative financial incentives. Examples include crop insurance that recognizes and rewards farming practices that reduce yield risk, farm lending programs that consider the value of conservation management in loan decisions, and tax incentives that encourage climate-smart agriculture. The Leopold Center for Sustainable Agriculture at Iowa State University performed research on agriculture in a changing climate for nearly 30 years. Restoring its funding, largely discontinued by the Iowa General Assembly in 2017, would be another means to achieve climate-smart agriculture.[68]

Conclusion

Americans’ perceptions are finally undergoing a rapid shift toward acceptance of the realities of climate change and a growing level of concern for the harmful impacts it will have — and indeed is already having — on families, communities and businesses. Iowans are seeing this during the early presidential campaign for 2020, with at least half of the remaining Democratic Party candidates advancing policy proposals or statements about climate change impacts and policy strategies. Many candidates have tuned their policies to address the challenges of — and opportunities for — climate change mitigation in a strongly agricultural economy.[69]

The effects of climate change, in both rural and urban Iowa, are becoming increasingly clear. However, these impacts are still small compared with what is projected over the next few decades under moderate and higher emission scenarios, and almost insignificant compared to those projected to the latter part of the century. It is especially true that younger generations around the world are vocally advocating — sometimes forcefully and stridently — for their own futures, which feel terrifyingly beyond their control.[70]

It is incumbent on those who have the ability and responsibility to take immediate actions and overcome the narratives of doubt and conflict illustrated by the two mayors in the middle of last spring’s catastrophic flooding. Now, as national politics begin to inundate Iowa’s media landscape — much as the floodwaters overran the physical landscape — it is crucial that science-informed discussions of policy responses to climate change be prominent in our personal conversations, candidates' political statements and debates, and our community discussions across all forms of media.



Appendix: Q&A on climate models and predictions

Where can I find out more information on climate change?

Start with the Climate Science Special Report and the National Climate Assessment, both products of the U.S. Global Change Research Program: https://www.globalchange.gov/.

One of the best, easy-to-follow introductions is published by the British scientific academy, The Royal Society: https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/.

For direct access to a wide range of data, both processed for understanding and in its raw form: https://www.climate.gov/, https://climate.nasa.gov/ and https://www.noaa.gov/climate/.

For regionally specific information from journalists, go to https://www.climatecentral.org/ and for award-winning, up-to-date climate reporting, read https://insideclimatenews.org/.

To hear about climate change directly from scientists in a bit more depth — explaining common misconceptions, check out: https://skepticalscience.com/ or http://www.realclimate.org/.

Finally, to examine the most thoroughly considered, definitive, global consensus, look at the reports available from the Intergovernmental Panel on Climate Change, https://www.ipcc.ch/.

What are climate models and how do they work?

The most important technique for making climate predictions uses global climate models (GCMs, formerly known as “general circulation models”). There are dozens of independent versions of these with varying levels of sophistication and complexity, some running on some of the most powerful computers on the planet. In practice, because all the aspects of the planet depend on each other — the cryosphere (ice) reacts to changes greenhouse gas (GHG) concentrations in the atmosphere; the hydrosphere (ocean and bodies of freshwater) interacts with the lithosphere (hard rock), and the biosphere (life) depends on them all — humankind’s knowledge of these relationships is represented by equations that fit our scientific understanding of each factor bounded by reasonable limits. Each equation describes just one element of the Earth system, but they are combined into a computer program as millions of lines of code to form a GCM.

As they interact during a model run, familiar patterns begin to emerge which represent and follow the climate patterns of the real world. For instance, these models are complete with clouds and precipitation, winds, storm systems, oceanic circulation, and multi-year climate cycles as well as rising temperatures, increasing sea levels, changing seasons, and receding ice sheets.

Why can we trust models in policymaking?

It’s important to recognize that models are neither “right” nor “wrong.” They are all approximations. But because we cannot run a controlled experiment to determine the future outcomes of dramatic increases in greenhouse gas concentrations, we must rely on computer models instead. (Actually, we are currently running an uncontrolled experiment on ourselves and only subsequent generations will know the outcome.) But we do not trust models blindly. They are routinely evaluated for their “skill” in reproducing past climatic conditions. By inputting historic conditions and events (GHG concentrations, solar activity, volcanic eruptions, etc.) we can run them retrospectively to see how well they match the observed record (temperatures, sea levels, etc.) GCMs are both tuned and validated by comparing specific elements of model behavior to physical processes that can be independently measured, ranging from energy balances, to cloudiness, to large-scale circulation patterns. Other factors considered include variations in the sun’s activity, volcanic activity, and air pollution levels.

For models with demonstrated “skill” we can then input possible greenhouse gas emissions and allow them to predict future climates. Finally, the output of dozens of competing models from around the world are routinely evaluated and compared to generate a range of predicted outcomes. We are just now reaching the point where we can compare the earliest climate model predictions to ongoing climate changes, and observed globally averaged temperature and sea-level increases have been within the range of prior predictions.[71] Some of the latest developments focus on attribution of climate events: they use a downscaled models to compare the strength of an event in the current climate to that of the same event in a fictitious climate not altered by human activities. Such analyses are also supported by physical reasoning based on knowledge of the climate system and/or by statistical analyses of similar events in the region over time.

Why did we select the scenarios for this report?

“Emissions scenarios for climate change research are not forecasts or predictions, but reflect expert judgments regarding plausible future emissions based on research into socioeconomic, environmental, and technological trends…”[72] In 2010, the IPCC (Intergovernmental Panel on Climate Change) implemented a set of four climate scenarios called Representative Concentration Pathways (RCPs). This third-generation approach to represent future human choices began with a range of plausible GHG concentration outcomes. Each of the four RCPs was drawn from a set of five storylines, which combined different detailed accounts of climate choices and policies, population and demographic projections, economic growth, technology development, and land use changes.

The result is a set of emissions scenarios (top frame) ranging from continued increases in GHG emissions to ones incorporating “net-negative” emissions before the end of the century. Each climate simulation discussed below references a specific RCP so that the reader can understand what set of societal choices determined the particular model climate outcome illustrated.[73] Similarly, for a desired outcome (such as preventing global warming in excess of 2 °C or 3.6 °F), it’s crucial to fully comprehend the emission scenario or pathway required to achieve it.

RCPs are numbered 2.6, 4.5, 6.0, and 8.5, with lower numbers corresponding to more done to address climate change (Figure 4). In the short-term (i.e. before about 2040), there is little difference between scenarios RCP4.5 & RCP6.0 (blue and orange lines, middle frame). But in that time period, the emission rates and resulting atmospheric CO2 concentrations found in RCP4.5 are substantially lower than those of RCP8.5 (red line) and higher than those of RCP2.6 (green line).

RCP8.5 represents net GHG emissions in 2050 that are 52 to 95 percent higher than 2010, and RCP4.5 illustrates a range of emissions scenarios from 38 percent lower than 2010 emissions up to 17 percent higher.[74] In terms of global climate implications, RCP8.5 results in an average global temperature increase of 3-5 °F by 2050 and 5-10 °F by 2100, while RCP4.5 yields an average global temperature increase of 2-3 °F by 2050 and 2-5 °F by 2100 — only half that of the higher emission scenario (bottom frame). RCP2.6 is also referred to as a “peak and decline” scenario because of the timescale in which emission reductions begin, resulting in stable GHG concentrations before the end of the century.

Whenever possible, this paper focuses on differentiating short-term climate projections between RCP8.5 as a high emission scenario, RCP4.5 as a moderate emission scenario, and RCP2.6 as a low-emission scenario. None of these modeled scenarios follow a so-called “business-as-usual” pathway in which humanity entirely fails to respond to climate change. Even RCP8.5 scenario cuts emissions by the end of the century. However, the climate impacts of this pathway would be catastrophic by 2100, despite any late actions taken.

Is there a discernable trend in Iowa’s climate-influenced disasters?

Iowa’s location between the largest rivers that drain the central United States makes it particularly prone to flooding; this is observed throughout the state’s history. In Iowa, the Federal Emergency Management Administration (FEMA) has declared a total of 27 flood declarations since 1953. These have taken place at a rate of one to seven events per decade with no obvious increase, and only six of these have occurred since 2000.[75] In contrast to the clear trends in temperature and precipitation discussed above, there isn’t yet a strong trend indicated in Iowa or in the continental U.S. for this specific measure.

In contrast, the record of severe storms occurring in Iowa increases sharply. Of 26 severe storm declarations since 1953, all but five have occurred since 2000. Iowa’s FEMA-declared severe storm count has jumped from only one single event in the 1980s to 14 already in the current decade.[76] This is consistent with the number of billion-dollar disasters per year across the continental U.S., tracked by the Department of Commerce.[77] While the frequency of billion-dollar floods has remained relatively flat, the number of billion-dollar severe storms has increased dramatically. (Figure 5)

Figure 5. Billion-dollar severe storms and floods are more frequent across U.S.*
Figure 5: Billion-dollar storms more frequent
* Note All values are in 2019 dollars, with a 95 percent Confidence Interval, or CI. Source: National Oceanographic and Atmospheric Administration, National Center for Environmental Information

Dr. James Boulter photo Dr. James Boulter is a professor of Chemistry in the Watershed Institute for Collaborative Environmental Studies at the University of Wisconsin—Eau Claire. He received a Ph.D. in analytical chemistry with an emphasis in atmospheric sciences from the University of Colorado, Boulder. His current research activities with undergraduates are split between laboratory studies of atmospheric particulate matter related to climate and human health, and surveys in the China and the U.S. assessing public perceptions of and responses to climate change. He teaches classes in introductory, analytical and environmental chemistry, the environmental health impacts of radiation and air pollution, and various aspects of climate change and sustainability. He has significantly contributed to efforts at the University and with the City of Eau Claire to inventory and monitor their total greenhouse gas emissions and to develop climate actions plans with a goal to achieve carbon neutrality by 2050.



The author would like to acknowledge the significant editorial contributions of David Osterberg and Nathan Vinehout Kane.

This research was supported by a grant from the Environmental Defense Fund. The conclusions are those of the author and the Iowa Policy Project.

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