5.3 Climate & Climate Change

Weather vs. Climate

Weather is the state of the atmosphere at a specific time and place; climate is the long-term average of weather conditions (temperature and precipitation) for a region over many years. A single cold day does not contradict a warming climate, and the Regents repeatedly tests whether students can separate short-term variation from long-term trends in data. When you read a graph, a year-to-year zigzag is weather-scale variability, but a steady slope sustained over decades is a climate trend.

Climate is most simply described by two long-term averages - average temperature and average precipitation - which together place a region into broad zones such as tropical, arid, temperate, or polar.

Factors That Control Climate

Several controls determine a region's climate. Knowing them lets you explain temperature and precipitation patterns on any map.

Latitude

Latitude is the most important control. Near the equator, the Sun's rays strike at a high angle and concentrate energy, so insolation and temperature are high year-round. Toward the poles, the same energy spreads over a larger, angled surface, so it is colder. This single factor explains the broad bands of tropical, temperate, and polar climates.

Proximity to Water and Ocean Currents

Water has a high specific heat, so it warms and cools more slowly than land. Regions near large lakes or oceans therefore have smaller temperature ranges - milder winters and cooler summers - than inland regions at the same latitude. Ocean currents transport heat: a warm current (like the Gulf Stream) raises coastal temperatures, while a cold current lowers them and can reduce coastal precipitation.

Mountains and the Orographic Effect

When moving air meets a mountain, it is forced upward on the windward side. The rising air cools adiabatically, condenses, and drops heavy precipitation on that slope. After crossing the summit, the now-dry air sinks down the leeward side, warming and creating a dry rain shadow. This orographic effect explains why one side of a mountain range is lush while the other is desert.

Prevailing Winds

Prevailing winds are the dominant surface winds of a latitude belt - for the mid-latitudes (including New York), the prevailing westerlies that blow from west to east. They deliver the temperature and moisture of upwind regions, which is why U.S. weather systems generally track eastward. Winds are named for the direction they come from, so a westerly blows toward the east. These global wind belts arise from large convection cells driven by the uneven heating between equator and poles, tying climate back to the insolation ideas in Section 5.1.

Evidence and Causes of Climate Change

The Regents asks students to interpret data as evidence of long-term change. Key lines of evidence include:

• Rising atmospheric CO2, recorded directly since 1958 and reconstructed from ice cores and air bubbles trapped in glacial ice.
• Increasing global average temperature over the past century.
• Retreating glaciers and shrinking sea ice.
• Rising sea level, from thermal expansion of seawater and melting land ice.

The leading cause of recent warming is the enhanced greenhouse effect: human activities - chiefly burning fossil fuels (coal, oil, natural gas) and deforestation - release greenhouse gases that trap more outgoing infrared energy. The Regents expects students to connect this human input to the carbon cycle rather than to natural cycles alone, and to recognize feedback loops that amplify change. For example, as ice and snow melt, they expose darker land and ocean with lower albedo, which absorb more insolation and cause further warming and melting - a positive feedback. Melting permafrost releasing methane is another.

Natural drivers such as Milankovitch cycles (variations in Earth's orbit and tilt) operate over tens of thousands of years and cannot explain the rapid warming measured over the past century, which closely tracks rising emissions.

The Carbon Cycle and Human Impact

The carbon cycle is the movement of carbon among four reservoirs: the atmosphere (as CO2), the oceans (dissolved CO2 and carbonate), living organisms (through photosynthesis and respiration), and rock/sediment (limestone and fossil fuels). Natural sinks - oceans absorbing CO2 and plants performing photosynthesis - normally balance the carbon that respiration and volcanism release.

Burning fossil fuels transfers carbon that was locked in rock for millions of years into the atmosphere faster than these sinks can remove it, so atmospheric CO2 rises. Excess oceanic CO2 also causes ocean acidification, harming shell-forming organisms. Understanding this imbalance is the foundation for the Human Sustainability strand, where students weigh mitigation strategies such as renewable energy, reforestation, and reduced emissions.