By Abigail Lin, Biological Sciences.
Rising temperatures due to global climate change cause several detrimental impacts on the world around us. This paper will analyze the consequences of climate change, specifically temperature changes, within California. Livelihoods of farmers and fishermen, distribution of disease, and fire intensity are examples of how California is affected by this crisis. Climate change in California is especially visible because California dominates the nation’s fruit and nut production, two water-intensive crops. The state’s reliance on large quantities of water to fuel its agricultural system makes it particularly susceptible to drought. Proliferation of detrimental disease vectors, loss of beneficial crops, and elevated levels of dryness imply a complex interaction between California ecosystems and climate change.
There are many farmers and agricultural workers in California impacted by changing climates, as the state is a major agricultural hotspot. Two-thirds of the nation’s fruits and over one-third of the nation’s vegetables are produced in California . Crops such as apricots, peaches, plums, and walnuts are projected to be unable to grow in 90% or more of the Central Valley by the end of the century because of the increase of disease, pests, and weeds that accompany rising temperatures .
Figure 1. Projection of crop failure by the end of the century. Heat increases diseases, pests, and weeds. Plum, apricot, peach and walnut crops will be unable to grow in 90% of Central Valley as a result.
Crop yields significantly decrease when heat sensitive plants are not grown in cool enough conditions. Fruits and nuts require chill hours, when the temperature is between 32 and 45 degrees Fahrenheit, to ensure adequate reproduction and development . However, with increasing temperatures, crops are receiving less chill hours during the winter. California grows 98% of the country’s pistachios, but changes in chill hours have affected fertilization . A study found that pistachios need 700 chill hours each winter, yet there have been less than 500 chill hours over the past four years combined . As a result, in 2015, 70% of pistachio shells were missing the kernel (the edible part of the nut) that should have been inside .
Repeated crop failures have also left farmers mentally taxed. Evidence suggests that suicide rates for farmers are already rising in response to farm debt that accumulates in response to poor crop yields . Not only is people’s financial well-being threatened by climate change, but so is their mental health. Mental stress threatens to rise as climates warm around the world, causing economic loss and upheaving agricultural careers.
Crab fisheries and fishers in California are also negatively impacted by the rise in temperatures. Warming oceans have led to an uncontrollable growth of algal blooms, which contaminates crab meat with domoic acid, a potent neurotoxin that causes seizures and memory loss . The spread of this toxin has forced many fisheries to close. California fishers lost over half the crabs they regularly catch per season, and qualified for more than 25 million dollars of federal disaster relief, during 2015 to 2016 . In response to financial loss, fishers adapted by catching seafood species other than crab, moved to locations where algal blooms have not contaminated their catch, or in the worst case, stopped fishing altogether . California crab fishers’ careers have already been dramatically altered by global warming, and the amount of algal blooms will only continue to increase if warming continues.
Temperature plays a major role in the prevalence of infectious diseases because it increases the activity, growth, development, and reproduction of disease vectors, living organisms that carry infectious agents and transmit them to other organisms. It is predicted that warm, humid climates will allow bacteria and viruses, mosquitoes, flies, and rats (all common disease vectors) to thrive . Most animal disease vectors are r-selected, meaning they put little parental investment into individual offspring, but produce many. Warm temperatures allow r-selected species to grow quickly and reproduce often. However, warm temperatures speed up biochemical reactions and are very energy demanding on organism metabolism . In response, disease vector ectotherms, organisms requiring external sources of heat for controlling body temperature, have successfully adapted to changing temperatures. These organisms thermoregulate, or carry out actions that maintain body temperature . Behavioral thermoregulation has shifted the geographical distribution of infectious diseases as disease vectors move to the warm environments that they favor .
Initial models about the distribution and prevalence of disease suggested a net increase of the geographical range of diseases, while more recent models suggest a shift in disease distribution . Recent models recognize that vector species have upper and lower temperature limits that affect disease distribution . It is estimated that by 2050, there will be 23 million more cases of malaria at higher latitudes, where previously infections were nonexistent, but 25 million less cases of malaria at lower latitudes, where previously malaria proliferated rapidly through populations, because the conditions necessary for malaria transmission will shift .
Figure 2. Shift of malaria disease distribution by 2050. Higher latitudes will have 23 million more cases of malaria while lower latitudes will have 25 million less cases. Although habitat suitability changed, there is little net change in malaria cases.
Cases of Coccidioidomycosis (Valley fever), an infectious disease spread from inhaling Coccidioides fungal spores, have recently reached record highs in California . Valley fever is especially prevalent in areas experiencing fluctuating climates, vacillating between extreme drought and high precipitation . After studying 81,000 cases collected over 20 years, researchers identified that major droughts have a causal relationship with increasing Coccidioidomycosis transmission rates . Initially, drought will suppress disease transmission because it prevents proliferation of the Coccidioides fungi. However, transmission rebounds in the years following drought because competing bacteria die off in high heat . Fungi have a number of traits that make them more tolerable to drought compared to bacteria including osmolytes for maintaining cell volume, thick cell walls to mitigate water loss, melanin which aids in thermoregulation, and hyphae that extend throughout the soil to forage for water . Disease spikes are seen after drought, such as the wet season between 2016 and 2017, which had about 2,500 more cases of Valley fever in comparison to the previous year. .
The role of rising temperatures in increasing Valley fever cases is evident in Kern County, one of the hottest and driest regions of California. Kern Country has the highest Valley fever incident rates in California; 3,390 cases occurred in a 47-month drought from 2012 to 2016 . Kern County has many cases of Valley fever because of its drought-like conditions. As climate change pushes areas throughout California that are usually cool and wet year-round into alternating dry and wet weather conditions, Valley fever cases are projected to increase.
Climate change is also associated with an increase in fire season intensity. The Western United States experienced three years of massive wildfires from 2020 to 2022, with each year burning more than 1.2 million acres . The ongoing drought has led to an accumulation of dry trees, shrubs, and grasses . A 2016 study found that this increase of dry organic plant material has more than doubled the number of large fires in the Western United States since 1984 . One of the ways that dry matter may ignite is by lightning. Projections show that by 2060, there will be a 30% increase of area burned by lightning-ignited wildfires compared to 2011 .
Residents in California are in danger of losing their lives and property to fire damage. A single fire can lead to massive destruction. In 2018, the Woolsey Fire burned 96,949 acres and hundreds of homes, and killed three people . Over one million buildings in California are within high-risk fire zones, and this number is projected to increase as temperatures continue to rise . With the amount of dry organic matter increasing and wildfire incidence surging, there will be more cases of property damage and loss of life in California. High temperatures and extreme weather events make it more likely that people will fall victim to these life-threatening disasters.
Increases in global temperature have a negative effect on human physical health and mental wellbeing. Climate change is making it more difficult to secure a livelihood, changing the spread of disease, and destroying lives and property. However, projections about rising temperatures allow farmers the chance to make informed decisions about which crops to grow, fishermen to relocate to areas that are less impacted by algal blooms, health experts to predict when and where outbreaks of certain diseases might occur, and fire protection services to increase their presence in high-risk areas. Projections help people predict where and when a climate change associated event is likely to occur, so that they may hopefully respond quicker and more efficiently. Consequences of climate change can be mitigated by using models as a guide for what to expect in California’s future.
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