Climate changes and the local environment:
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.
How we know:
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.
Article author: Dr. Dagomar Degroot, Georgetown University