finding 21.1 : key-message-21-1

The Midwest is a major producer of a wide range of food and animal feed for national consumption and international trade. Increases in warm-season absolute humidity and precipitation have eroded soils, created favorable conditions for pests and pathogens, and degraded the quality of stored grain (very likely, very high confidence). Projected changes in precipitation, coupled with rising extreme temperatures before mid-century, will reduce Midwest agricultural productivity to levels of the 1980s without major technological advances (likely, medium confidence).

This finding is from chapter 21 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.

Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.

Note on regional modeling uncertainties

Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).fe83e7d3-3f29-4aef-81ae-28abd70dda2e,94a4d51e-96a4-4155-926d-31be60e2206a Globally recognized modeling efforts (i.e., the Coupled Model Intercomparison Project, or CMIP) do not include a realistic representation of the Great Lakes, simulating the influence of the lakes poorly or not at all.9db319af-7cec-440e-8dda-41526fed6cd0,5295673e-703b-42f8-9792-4ccf8e3cf747,03f91fdd-6d7d-431b-997b-91f63f52fe45,ee7f8311-bd00-4353-87a9-61ffb7813bf0,1cd8ac44-e9d5-4a2e-ab8e-e48c8988bbc2 Ongoing work to provide evaluation, analysis, and guidance for the Great Lakes region includes comparing this regional model data to commonly used global climate model data (CMIP) that are the basis of many products practitioners currently use (i.e., NCA, IPCC, NOAA State Climate Summaries). To address these challenges, a community of regional modeling experts are working to configure and utilize more sophisticated climate models that more accurately represent the Great Lakes’ lake–land–atmosphere system to enhance the understanding of uncertainty to inform better regional decision-making capacity (see for more information).

Description of evidence base:

Humidity is increasing. Feng et al. (2016)28675f8a-8858-40ac-b53a-710b489bca07 show plots of trends in surface and 850 hPa specific humidity of 0.4 and 0.2 g/kg/decade, respectively, from 1979–2014 for the April–May–June period across the Midwest. These represent increases of approximately 5% and 3% per decade, respectively. Automated Surface Observing Stations in Iowa9dc60b30-9bb1-46c8-aaea-9dba602c2d05 having dew point records of this length and season show dew point temperature increases of about 1°F per decade. Brown and DeGaetano (2013)83d23b83-2a04-4a6b-bdfa-caa8b54b1ccf show increasing dew points in all seasons throughout the Midwest. Observed changes in annual average maximum temperature for the Midwest over the 20th century (Vose et al. 2017,29960c69-6168-4fb0-9af0-d50bdd91acd3 Table 6.1) have been less than 1°F. However, future projected changes in annual average temperature (Vose et al. 2017,29960c69-6168-4fb0-9af0-d50bdd91acd3 Table 6.4), as well as in both warmest day of the year and warmest 5-day 1-in-10 year events (Vose et al. 2017,29960c69-6168-4fb0-9af0-d50bdd91acd3 Table 6.5), are higher for the Midwest than in any other region of the United States.

Garbrecht et al. (2007)232aa0b0-6c75-46f6-90df-85b58cfbb3b1 state that precipitation changes are sufficient to require U.S. policy changes for agricultural lands. The Soil Erosion Site ( describes the soil erosion process and provides links to soil erosion models.4baac62e-5892-4a0a-b435-e2cedc62f9a2 Nearing et al. (2004)43e7bfdb-30c7-407d-89ae-e94f7bff36a1 report that global climate models project increases in erosivity (the ability or power of rain to cause soil loss) across the northern states of the United States over the 21st century.

Spoilage in stored grain is caused by mold growth and insect activity, which are related to the moisture content and temperature of the stored grain.c65ba7e2-12f7-4a02-82c1-622c0aeb8711 The ability of fungi to produce mycotoxins, including aflatoxin and fumonisins, is largely influenced by temperature, relative humidity, insect attack, and stress conditions of the plants.1ca7e70d-66b3-42e1-9a68-31b976d2622f,2688cf64-d71f-4e21-84ad-f5cae499ed61 Humidity has a determining influence on the growth rate of these degradation agents.ca4947dc-278d-4b27-9c86-5a6a442575dc

Germination of wheat declined in storage facilities where moisture level increased with time.5c614c37-2c94-413e-85d1-28d44b88d452 Freshly harvested, high-moisture content grain must be dried to minimize (or prevent) excessive respiration and mold growth on grains.64513762-d666-447a-b19d-18bcd9cb0b80 The storage life of grain is shortened significantly when stored at warm temperatures. One day of holding warm, wet corn before drying can decrease storage life by 50%.858d3935-f2b4-46d1-8c20-4fdf50922067

Feng et al. (2016)28675f8a-8858-40ac-b53a-710b489bca07 show humidity is rising in the Midwest in the warm season. Cook et al. (2008)e6bbc070-a723-4341-be6e-09bbd3248a20 show that the factors leading to these humidity increases (warming Gulf of Mexico and strengthening of the Great Plains Low-Level Jet) will increase in a warming climate.

The ability of fungi to produce mycotoxins is largely influenced by temperature, relative humidity, insect attack, and stress conditions of the plants.2688cf64-d71f-4e21-84ad-f5cae499ed61 More extreme rainfall events would favor formation of Deoxynivalenol, also known as vomitoxin.1ca7e70d-66b3-42e1-9a68-31b976d2622f

Hatfield et al. (2011,a2704ef3-5be4-41ee-8dfa-4c82e416a292 Table 1) give the relationships between temperature and vegetative function as well as reproductive capacity. This work was expanded and updated in Walthall et al. (2012).3baf471f-751f-4d68-9227-4197fdbb6e5d

Mader et al. (2010)6a1bc03d-a204-4f8c-9779-73ee5c44e413 report a comprehensive climate index for describing the effect of ambient temperature, relative humidity, radiation, and wind speed on environmental stress in animals. St-Pierre et al. (2003)ef0e1901-7533-4af4-b3b8-840a78ca4a49 provide tables estimating economic losses in dairy due to reduced reproduction. The data show a strong gradient across the Midwest (with losses in Iowa, Illinois, and Indiana being three times the losses in Minnesota, Wisconsin, and Michigan under the current climate). Temperature and humidity increases projected for the Midwest will increase economic losses across the entire region. Lewis and Bunter (2010)5eace42f-0819-4bec-a799-23c78ad4b486 document heat stress effects of temperature on pig production and reproduction.

St-Pierre et al. (2003)ef0e1901-7533-4af4-b3b8-840a78ca4a49 provide tables estimating economic losses in dairy, beef, swine, and poultry, resulting in declines from both meat/milk/egg production. The data show a strong gradient across the Midwest (with losses in Iowa, Illinois, and Indiana being twice the losses in Minnesota, Wisconsin, and Michigan under the current climate). Temperature and humidity increases projected for the Midwest will increase losses across the entire region. Babinszky et al. (2011)3f7db557-5407-40cf-9078-d5be0f25ee0a identified temperature thresholds for meat/egg/milk production, beyond which performance declines. The adverse effects of heat stress include high mortality, decreased feed consumption, poor body weight gain and meat quality in broiler chickens, and poor laying rate, egg weight, and shell quality in laying hens.06f01e99-7afa-4be6-93ab-881cab8e56b8

Takle et al. (2013)6e8fbacd-aff6-48ab-a950-5a8df2799046 found that by mid-century, yields of corn and soybean are projected to fall well below projections based on extrapolation of trends since 1970 even under an optimistic economic scenario, with larger interannual variability in yield and total production. Liang et al. (2017)c5857041-2594-47cf-a6bc-3fab052fa903 report that the ratio of measured agricultural output to measured inputs would drop by an average 3% to 4% per year under medium to high emissions scenarios and could fall to pre-1980 levels by 2050 even when accounting for present rates of innovation. Schauberger et al. (2017)2967c8a9-063e-4118-92a4-71f266341e2f found that the impact of exposure to temperatures from 30°C to 36°C projected for the end of the century under RCP8.5 creates yield losses of 49% for maize and 40% for soybean.

According to Easterling et al. (2017),e8089a19-413e-4bc5-8c4a-7610399e268c evidence suggests that droughts have become less frequent in the Midwest as the region has become wetter. However, they note that “future higher temperatures will likely lead to greater frequencies and magnitudes of agricultural droughts throughout the continental United States as the resulting increases in evapotranspiration outpace projected precipitation increases.

New information and remaining uncertainties:

Global and regional climate models do not simulate well the dynamical structure of mesoscale convective systems in the Midwest, which are the critical “end processes” that create intense precipitation from increasing amounts of moisture evaporated over the Gulf of Mexico and transported by low-level jets (LLJs) into the Midwest. Secondly, the strengthening of future LLJs depends on strengthening of both the Bermuda surface high pressure and the lee surface low over the eastern Rocky Mountains. Confirming simulations of this in future climates are needed. Global and regional climate models do simulate future scenarios having increasing temperatures for the region with high confidence (a necessary ingredient for increased humidity). There is uncertainty of the temperature thresholds for crops because, as pointed out by Schauberger et al. (2017),2967c8a9-063e-4118-92a4-71f266341e2f some negative impacts of higher temperatures can be overcome through increased water availability. Agricultural yield models, productivity models, and integrated assessment models each provide different ways of looking at agricultural futures, and each of these three types of models has high levels of uncertainty. However, all point to agriculture futures that fail to maintain upward historical trends.

Assessment of confidence based on evidence:

There is very high confidence that increases in warm-season absolute humidity and precipitation very likely have eroded soils, created favorable conditions for pests and pathogens, and degraded quality of stored grain. There is medium confidence that projected increases in moisture, coupled with rising mid-summer temperatures, likely will be detrimental to crop and livestock production and put future gains in commodity grain production at risk by mid-century. Projected changes in precipitation, coupled with rising extreme temperatures, provide medium confidence that by mid-century Midwest agricultural productivity likely will decline to levels of the 1980s without major technological advances.

This finding was derived from scenario rcp_4_5
This finding was derived from scenario rcp_8_5

References :

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