Genesee County, Michigan has warmed steadily for more than a century. Although average annual temperatures in the state have climbed more slowly than the global trend, they have still risen by around 0.6° C (1.1° F) relative to twentieth-century averages. 

Michigan is known for its long and snowy winter seasons. Rising temperatures, however, have sharply shortened the length of winter across the state. The total number of days in the winter season with at least 2.5 cm (1 inch) of snow cover has declined sharply since 1920, with most of the decline happening since 1980. As winter grows shorter, snow falls less frequently. 

Yet that does not necessarily mean that winters have become less snowy across the state. Snowfall trends from county to county vary widely, in large part because water in the nearby Great Lakes cools more slowly than air. If the lakes are largely ice-free, warm water can heat up otherwise cool air blowing into Michigan. The air then absorbs moisture and deposits it as "lake-effect" snow in some, but not all of, Michigan. 

Now that the Great Lakes are ice-free for much longer than they were, on average, in the twentieth century, blizzards have grown more common in Michigan even as winters have grown shorter. Overall, precipitation in all seasons has increased across Michigan, at a rate of roughly 1.5 mm/year since the 1930s. Much of the increase has come not through extreme events, but a steady rise in wet days that follow wet days. There are signs that cloudiness is now more frequent than it was in the twentieth century. 

In this context, Genesee County in Michigan has recently endured particularly extreme and destructive weather. In March 2012, for example, temperatures in a normally cold month soared to a record-shattering 31° C (88° F). In January 2014, a severe snowstorm dropped 18 inches of snow on the county, the second-heaviest fall since 1975. 

These reconstructions rely on the National Oceanic and Atmospheric Administration (NOAA) State Annual and Seasonal Time Series and a freely available report, "Historical Climate Trends in Michigan and the Great Lakes Region," by Dr. Jeffrey Andresen of the Department of Geography at Michigan State University. 

NOAA's State Annual and Seasonal Time Series relies largely on weather station measurements. Adresen's report largely draws on data collected by weather instruments but also includes information from other sources, such as observations from aircraft. 

Heat waves and blizzards brought about by rising temperature trends have imposed high costs on Michigan, including Genesee county. Nation-wide statistics suggest that the elderly, especially those with limited mobility and insufficiently insulated or air conditioned houses, are in great danger during both extreme heat and blizzards. Heat waves can also damage roads and train tracks, impose strains on energy and water resources, and lower crop yields if they arrive in key development stages. 

Yet in Michigan, a trend towards wetter weather may also have had beneficial impacts for regional agriculture. Computer simulations show that increases in soil moisture available to corn at mid-season, and a rise in plant-available water in the soil profile over the whole season, have both increased corn yields across Michigan. Until now, global warming has therefore had a complex mix of beneficial and destructive impacts on Michigan, and therefore on Genesee county.

Average annual temperatures across California have been rising since the nineteenth century, a trend that has sharply accelerated since around 1970. Average temperatures across all seasons in Tulare County in south central California have mirrored that statewide pattern. As the county warmed, it suffered a series of severe droughts, which are usually defined as long-lasting moisture deficits that have environmental and social consequences. Droughts in the county involve three sources of water: surface water at low elevations, snow at high elevations, and groundwater buried below the surface. 

Precipitation in much of California has long varied by as much as 50% from year to year. Hotter temperatures, however, are increasing the rate of evaporation across California, including in Santa Barbara County. That has affected both mountain snow and lowland liquid water, and has made local droughts even longer and drier than they once were. One of the most severe droughts in the county's history recently began in February 2012 and lasted into 2017. The driest stretch of the drought started in February 2014 and endured until January 2017. It was part of a broader Californian drought that started in coastal areas several years earlier, and was up to 27% more likely to occur in our warmer climate. 
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Longer, drier summers and an earlier snowmelt have caused drier forest conditions in southwest California, which has increased the amount of available kindling for wildfires to consume. These conditions have increased the size and duration of wildfires in California, and dramatically lengthened the wildfire season in Santa Barbara county. 

These reconstructions rely on several easy to use tools that are available online: the National Oceanic and Atmospheric Administration (NOAA) State Annual and Seasonal Time Series, the NOAA Weekly Palmer Drought Indices, the National Drought Mitigation Center's United States Drought Monitor, and the United States Geological Survey (USGS) interactive website. 

NOAA's State Annual and Seasonal Time Series relies largely on weather station measurements. NOAA's Palmer Drought Indices use a standard way of measuring drought that considers both water supply and demand in a soil moisture model. Negative values represent droughts, and positive values represent wet conditions. The United States Drought Monitor uses a number of drought indicators, including the Palmer Drought Indices, that consider both environmental and social manifestations of water shortages. The interactive tools made available by the USGS draw on open data provided by a range of United States government agencies, including the Army Corps of Engineers and the Bureau of Reclamation. 

Droughts can sharply reduce the quantity of water in reservoirs and aquifers across California, which often supply water to local residents. Reservoirs, which collect precipitation, and aquifers, which are the groundwater storage spaces, both contribute to Santa Barbara’s water supply. This supply is crucial for both commercial and industrial use.

If global warming continues, Santa Barbara’s premium wine industry could be significantly affected. This is because distinct grape species can only thrive in specific temperature ranges. If Santa Barbara fails to produce grapes that can tolerate higher temperatures, then the decline in suitable land could be up to 20%. Wine is currently the third-most produced commodity in Santa Barbara county, and wine sales comprise nearly a tenth of the county's economy. 

One of the main water sources that supplies residents in Santa Barbara county is the Lake Cachuma reservoir. The reservoir supplies 85 percent of the water supply for over 250,000 residents of Goleta district in Santa Barbara county. Its available water supply plummeted during the California drought. As of October 1st 2017, it is still only 43% full. 

The lack of water in the Cachuma reservoir, in conjunction with the drought, will force Santa Barbara county to search for alternative water sources. Just recently, the county decided to reopen its desalination plant to supply more water to their residents. The reactivation of this plant cost the county an estimated $71 million, not including the cost of maintaining the plant. It will supply 3 million gallons of water per day to residents to cover 30% of the city’s water usage. In a warmer and drier future, such desperate measures may well be necessary across California. 

The Paris Agreement on Climate aims to limit the increase in Earth's average temperature to 2° C, relative to pre-industrial levels. That will require dramatic cuts to human-caused greenhouse gas emissions, and in all likelihood new technology to draw carbon dioxide out of the atmosphere. Even if successful, however, these steps will still leave us with enough warming to greatly raise sea levels around the world.

​There are two reasons for this: first, warm liquids take up more volume than cold liquids, and second, water will flood into the oceans from ice caps on Greenland, West Antarctica, and other polar regions. Low-lying coastal regions, including much of Washington, DC, will eventually be flooded unless they are defended with extensive dikes and levees. If global temperatures rise by 4° C relative to pre-industrial averages - which they would if current long-term trends continue - then much of Washington, DC would ultimately be well below sea level. 

Climate projections based on continuing high greenhouse gas emissions - known as "high emissions scenarios" - predict that average water levels around Washington, DC would reach 3 feet above present levels by 2110. The city will be particularly vulnerable to flooding because it will be periodically threatened by hurricanes that could have higher sustained winds and higher storm surges than they do today. Under high emissions scenarios, there is a near certain chance by the end of the 21st century that the city will endure flooding more than 10 feet above the current high tide line.

Climate projections based on continuing high greenhouse gas emissions estimate that the mean daily maximum temperature of Washington, DC will rise from roughly 20°C (68°F) to nearly 26°C (78°F) by 2100. Days with extreme heat (above 35°C, or 95°F) would increase by a factor of 9, from roughly 10 today to approximately 90 in 2100. Even if countries adhere to the Paris Agreement and sharply reduce their emissions, extreme heat days will probably still rise by a factor of 3, to roughly 30, by 2100. Precipitation patterns are unlikely to change as dramatically. 

These projections primarily rely on two tools that are freely accessible online: the National Oceanic and Atmospheric Administration (NOAA) Climate Explorer app, and the Climate Central Surging Seas, Mapping Choices app.

The Climate Explorer tool uses weather information recorded by meteorological instruments at weather stations to reconstruct past climate changes. It uses supercomputer simulations of future climate changes under both high and low emissions scenarios. 

The Surging Seas tool combines historic flood statistics and local sea level trends with global scenarios of sea level increases, which were compiled in the 2014 U.S. National Climate Assessment. 

Nearly 5,000 people live in nearly 2,000 homes on roughly 2,500 acres of land in parts of Washington that are currently under 10 feet above the high tide line. That territory is home to property worth $9 billion, and it includes 26 EPA-listed sites (including hazardous waste dumps and sewage sites). Under high emissions scenarios, all will be flooded by the year 2100. Even under low emissions scenarios, all will be permanently underwater, although that could take hundreds of years. Much of Washington, DC will eventually need to be evacuated or else protected by extensive and very expensive defenses against the sea, if these prove to be feasible.  

​Under high emissions scenarios, extreme heat will severely tax transportation and electrical infrastructure in Washington, DC. Higher temperatures could increase the presence and transmission rate of disease, especially those that spread through mosquito vectors, such as Zika and malaria. Extreme heat days could well lead to increased mortality among the poor, sick, and elderly. 

The local human consequences of rising sea levels and temperatures will depend greatly on technological and social developments that are hard to foresee. Nevertheless, climate change should impact Washington, DC with particular force.