The USA's climate and environment

The Northeast and upper Midwest have humid continental climates — hot summers, genuinely cold winters, precipitation year-round, and lake-effect snow downwind of the Great Lakes that can bury cities in a day.

The Southeast is humid subtropical: hot, very humid summers, mild winters, and afternoon thunderstorms most summer days. Air conditioning is not optional. This is also hurricane country.

The Great Plains have a continental climate with extreme temperature swings and the world's most active severe thunderstorm environment, where cold dry air from Canada meets warm moist air from the Gulf.

The Southwest is arid and semi-arid desert — Phoenix, Las Vegas, Tucson — with summer temperatures routinely above 40 °C and a monsoon season bringing brief violent storms. Water supply is the region's binding long-term constraint.

The West Coast splits sharply. Southern and central California have a Mediterranean climate with dry summers and wet winters. The Pacific Northwest is mild and wet, with a genuine temperate rainforest on the Olympic Peninsula.

Alaska ranges from subarctic to arctic, and Hawaii is tropical with microclimates that change within kilometers. Both are outliers on every metric.

Hurricanes affect the Atlantic and Gulf coasts, with a season running June 1 to November 30 and peak activity around September. Florida, Louisiana, Texas and the Carolinas carry the most exposure. Storm surge, not wind, causes most hurricane deaths.

Tornadoes occur in every state but concentrate in the central plains and the Southeast. The US records roughly 1,200 a year — vastly more than anywhere else — with peak season in spring and early summer. A tornado warning means one has been detected and you should shelter immediately; a watch means conditions are favorable.

Wildfire risk is highest across the West and increasingly in the Southeast and Great Plains. Fire season has lengthened measurably, and the wildland-urban interface — where housing meets vegetation — is where most structures are lost.

Earthquake risk concentrates along the Pacific rim, particularly California, the Pacific Northwest and Alaska, but the New Madrid zone in the central Mississippi valley and parts of the intermountain west also carry real exposure. Standard homeowners insurance does not cover earthquake damage anywhere.

Flooding is the most widespread hazard and affects every state. Standard homeowners insurance does not cover flood damage — that requires separate coverage, usually through the National Flood Insurance Program. This is the single most common insurance gap in American homeownership.

Extreme heat kills more Americans in a typical year than hurricanes, tornadoes and floods combined, and the deaths concentrate among older people and outdoor workers.

The 100th meridian, running roughly through the middle of the Dakotas down to Texas, has historically marked the dividing line between the humid east and the arid west. Almost everything about western settlement, agriculture and law follows from what is on each side of it.

Western water law operates on prior appropriation — first in time, first in right — rather than the riparian rights used in the east. Water rights are property, senior rights are served before junior ones regardless of use, and this shapes agriculture and urban growth across the region.

The Colorado River supplies water to around 40 million people across seven states and Mexico. Sustained drought and structural over-allocation have driven reservoir levels at Lake Mead and Lake Powell to historic lows, and negotiations over allocation cuts are among the most consequential ongoing environmental disputes in the country.

Groundwater depletion is a parallel problem. The Ogallala Aquifer, which underlies much of the Great Plains and supports a substantial share of US agriculture, is being drawn down far faster than it recharges in its southern portions.

For anyone moving west, water availability and cost are worth checking as seriously as property tax — several rapidly growing areas have begun restricting new development on water supply grounds.

The United States is the second-largest annual greenhouse gas emitter after China and the largest cumulative historical emitter. Emissions per person remain among the highest of any large economy.

The energy mix has shifted substantially. Coal generation has declined sharply, displaced mainly by natural gas from shale and increasingly by wind and solar. Renewables plus nuclear now generate roughly 40 percent of US electricity, and solar and battery storage account for the large majority of new generating capacity being built.

There is no comprehensive federal climate statute equivalent to the UK's Climate Change Act. Policy operates through EPA regulation under the Clean Air Act, tax credits including those in the Inflation Reduction Act, and state-level action — California and several northeastern states operate their own carbon markets and vehicle standards.

Federal land is a defining feature of the American West: the federal government owns roughly 28 percent of US land, including over 60 percent of Utah, Nevada and Idaho. This land is managed by the Bureau of Land Management, Forest Service, Fish and Wildlife Service and National Park Service.

The National Park System covers 63 designated national parks within more than 400 units. The America the Beautiful annual pass covers entrance to all federal recreation sites and pays for itself in about three park visits.