Climate and Climate Change

Remember: weather is what's happening today. Climate is the average weather of a place over a long time, usually 30 years or more. One freezing week in June doesn't change Idaho's climate, just like one bad test doesn't change your whole GPA.

• Latitude: places near the equator get direct sunlight all year and stay warm. Places near the poles get slanted, weaker sunlight and stay cold.
• Elevation: higher = colder. Idaho Falls at 4,700 feet is colder than Boise at about 2,700 feet.
• Distance from water: oceans heat and cool slowly, so coastal places have mild climates. Inland places like Idaho have bigger temperature swings, hot summers and cold winters. That's called a continental climate.
• Mountains: they block moisture, creating wet sides and dry rain shadows.
• Ocean currents and winds: warm currents warm nearby land; cold currents cool it.

Scientists group the world's climates into zones. The most common system, the Köppen system, uses temperature and precipitation:

• Tropical: hot and usually wet all year. Rain forests.
• Dry (arid and semi-arid): less rain than evaporation. Deserts and steppes. Much of southern Idaho is semi-arid high desert.
• Temperate: mild, with distinct seasons.
• Continental: big seasonal swings, cold snowy winters. Much of Idaho's mountains.
• Polar: cold all year. Ice caps and tundra.

Small areas can have their own microclimates, like a sunny south-facing slope or a city that stays warmer than the countryside (an urban heat island).

Here's a common myth: seasons happen because Earth gets closer to the Sun. Nope. Earth is actually closest to the Sun in early January.

Seasons happen because Earth's axis is tilted about 23.5°. In June, the Northern Hemisphere tilts toward the Sun. Sunlight hits more directly and days are longer, so it's summer. In December, we tilt away, and it's winter. That's why Australia has summer at Christmas.

Earth's climate has changed many times over its 4.6-billion-year history. There have been ice ages, when glaciers covered huge areas, and warm periods when there was no ice at the poles at all.

Natural causes of climate change include:

• Changes in Earth's orbit and tilt over tens of thousands of years, called Milankovitch cycles. These are the pacemakers of the ice ages.
• Volcanic eruptions: big ones blast particles into the stratosphere that block sunlight and cool the planet for a year or two.
• Changes in the Sun's energy output.
• Plate tectonics: moving continents change ocean currents over millions of years.

Scientists use clues called proxy data:

• Ice cores: long tubes of ice drilled from Antarctica and Greenland. Tiny air bubbles trapped in the ice are samples of ancient atmosphere, going back about 800,000 years.
• Tree rings: wide rings mean good growing years; thin rings mean dry or cold years.
• Ocean sediments, fossils, and coral that record temperatures of long ago.

Since 1958, scientists have measured carbon dioxide at the Mauna Loa Observatory in Hawaii. The graph of those measurements is called the Keeling Curve. According to NOAA data, CO₂ has risen every single year since 1959, from about 316 ppm (parts per million) to about 427 ppm in 2025. Before the Industrial Revolution, it was about 280 ppm. That means CO₂ is now about 50% higher than before industry began.

The main source of the extra CO₂ is burning fossil fuels (coal, oil, and natural gas) for electricity, heat, and transportation, along with cutting down forests. Scientists can tell the extra carbon comes from fossil fuels by its chemical fingerprint, a special mix of carbon types called isotopes.

At the same time, measurements show:

• Global average temperature has risen about 1.2 to 1.5 °C since the late 1800s, with the last ten years among the warmest on record.
• Most mountain glaciers are shrinking, and Arctic sea ice has decreased.
• Sea level is rising, as warming water expands and land ice melts.
• The ocean is absorbing much of the extra CO₂, which makes it more acidic. This is called ocean acidification, and it makes it harder for corals and shellfish to build shells.

The large majority of climate scientists and major science organizations, including NASA and NOAA, conclude that human activities are the main cause of recent warming. This is called anthropogenic (human-caused) climate change.

Climate has feedback loops that can speed up or slow down change:

• Ice-albedo feedback (speeds up): warming melts bright, reflective ice, exposing dark ocean or land that absorbs more heat, causing more warming.
• Water vapor feedback (speeds up): warmer air holds more water vapor, which is itself a greenhouse gas.
• Plant growth (can slow down): more CO₂ can help some plants grow faster and absorb more carbon.

Idaho depends on mountain snowpack for most of its water. Scientists track changes like earlier spring snowmelt, longer wildfire seasons, and shifts in river flow. These affect farmers, ski resorts, fish like salmon and trout, and city water supplies.

There are two main approaches:

• Mitigation: reducing greenhouse gas emissions, through things like renewable energy, nuclear power, more efficient cars and buildings, and planting forests.
• Adaptation: preparing for changes, like better wildfire management, water storage, and drought-resistant crops.

People disagree about the best policies: how fast to change, what it should cost, and who should pay. Those are questions of economics, values, and politics, and you'll be part of deciding them. Science's job is to give you the most accurate evidence possible.