U-235, 435

U-238, 433

ultraviolet (UV) radiation, 26

atmosphere and, 27

effect of, 33

temperature and, 27

unconventional reserves of oil and natural gas, 365, 369–372

environmental cost of, 372–374

in U.S. and Canada, 373f

UNFCCC. See United Nations Framework

Convention on Climate Change uniform distribution, 162, 163, 163f

United Nations Framework Convention on Climate Change (UNFCCC), 480–481

United Nations’ Millennium Ecosystem Assessment, 10

United Nations Population Division, 79

United States (U.S.)

age structure diagram, 73

agricultural policies, 303

air pollution in, 394–395

electricity generation by fuel in, 343f

energy consumption by, 375–376

environmental history, 18–19

environmental policy in, 473, 476t, 478f

expansion, 18

fracking in, 371–372

greenhouse gas emissions in, 484

international efforts, 19

MSW stream, 123f

Nuclear Waste Policy Act, 440

oil imported to, 379

per capita footprint, 102

pollution concerns, 19

resource consumption by, 117f

resource management, 18

shale formations in, 362–364

solid waste produced by, 122

species protection laws in, 249t

unconventional reserves of oil and natural gas in, 373f

water usage, 272

West Nile virus in, 88

wind energy in, 454

United States Department of Agriculture (USDA), 417

units of measure, A–3

uranium, 432–433

uranium ore, 434, 436

urban areas

carbon footprint in, 496f

ecological footprint in, 496f

I-20

environmental justice in, 497

parks in, 501–502

population of, 492–497

sustainable, 502–507

upgrading, 504

urban flight, 498

redlining and, 499

suburban sprawl and, 498f

urban heat island, 496

urbanization, 490–509

trade-offs of, 496–497, 497t

urban planners, 498–499, 502

U.S. See United States

USDA. See United States Department of Agriculture

UV-A, 26–27

UV-B, 26–27, 31f

increased levels of, 36

photosynthesis and, 36

skin cancer and, 33, 36

UV-C, 26–27

UV radiation. See ultraviolet radiation