Climate Change

🌡️ Climate Change

Part 1 of 7 — Weather vs. Climate & the Natural Greenhouse Effect

Topics in This Part

🔑 Key Concept: The greenhouse effect is natural and essential — it keeps Earth about $33\,^{\circ}\text{C}$ warmer than it would otherwise be. Human-caused climate change is the enhancement of this natural process by added greenhouse gases. The exam constantly rewards students who keep that distinction straight.

Weather vs. Climate

These two words are not interchangeable, and confusing them is the single most common error on this unit.

💡 Memory hook: Climate is what you expect; weather is what you get. A single cold winter day does not disprove a warming climate, because climate is a multi-decade statistical average, not a daily reading.

Climate scientists use a 30-year baseline (a "climate normal") so that short-term swings — a strong El Niño year, a big volcanic eruption — average out and the underlying trend becomes visible.

Concept Check 🎯

The Energy Balance: Shortwave In, Longwave Out

Earth's temperature is set by a balance between energy arriving from the Sun and energy radiating back to space.

1. Incoming solar radiation is mostly shortwave (visible light + UV). The Sun is hot (~$5500\,^{\circ}\text{C}$), so by Wien's Law it radiates short wavelengths.
2. About 30% of incoming sunlight is reflected straight back to space (by clouds, ice, light surfaces) — this fraction is the planet's albedo.
3. The remaining ~70% is absorbed by the surface and atmosphere, warming the planet.
4. The warmed Earth (a cool ~$15\,^{\circ}\text{C}$ object) re-radiates energy as .

Trace the Energy 🔽

Fill in each blank to describe Earth's energy balance.

The Natural Greenhouse Effect — and Why It Matters

Run the numbers without an atmosphere and Earth's average surface temperature would be about $-18\,^{\circ}\text{C}$ (well below freezing) — a frozen, lifeless rock. The actual average is about $+15\,^{\circ}\text{C}$.

Quantify the Natural Warming 🧮

Use Earth's effective (no-atmosphere) temperature of $-18\,^{\circ}\text{C}$ and its actual average surface temperature of $+15\,^{\circ}\text{C}$.

1) How many ${}^{}$ of warming does the natural greenhouse effect provide? Enter a number.

🌡️ Climate Change

Part 2 of 7 — The Greenhouse Gases & Global Warming Potential

🔑 The Idea: Not all greenhouse gases are equal. A molecule's impact depends on how strongly it absorbs IR, how long it stays in the atmosphere, and how much of it we emit. The metric that bundles strength and lifetime together is Global Warming Potential (GWP).

The Major Greenhouse Gases

🌡️ Climate Change

Part 3 of 7 — Evidence, the Carbon Cycle & Natural Drivers

🔑 Why it matters: To distinguish human-caused warming from natural variability, scientists rely on multiple independent lines of evidence and on understanding the natural cycles (the carbon cycle, Milankovitch cycles, the Sun) that have always shifted climate. The fingerprint of today's change points squarely at carbon we dug up.

The Lines of Evidence

No single graph proves climate change; the case rests on many datasets that agree.

🌡️ Climate Change

Part 4 of 7 — Feedback Loops & Tipping Points

🔑 The Idea: Climate isn't a simple thermostat. Feedback loops can amplify warming (positive feedback) or dampen it (negative feedback). The scariest part of the science is that several powerful positive feedbacks could push the system past tipping points that are hard to reverse.

Positive vs. Negative Feedback

⚠️ Don't moralize the words. In systems science, positive means amplifying (pushes change further) and negative means stabilizing (dampens change). A "positive feedback" is usually bad for the climate; a "negative feedback" is usually helpful.

Positive (amplifying) feedbacks:

🌡️ Climate Change

Part 5 of 7 — Impacts on Ecosystems, Oceans & People

🔑 The Idea: Warming isn't just "hotter days." It reshapes sea level, ocean chemistry, species ranges, weather extremes, and human health and security. The exam expects you to connect a cause to its downstream consequence.

Sea-Level Rise: Two Causes

Global sea level is rising for two distinct reasons — know both:

1. Thermal expansion — water expands as it warms. As the ocean absorbs heat, the same mass of water takes up more volume. This is currently a major contributor.
2. Melting land ice — glaciers and the Greenland/Antarctic ice sheets add new water to the ocean.

⚠️ Critical exam distinction: Melting sea ice (already floating, like Arctic pack ice) does NOT raise sea level — it already displaces its weight in water (Archimedes' principle). Only melting land-based ice adds water and raises sea level.

Consequences of sea-level rise: coastal flooding, saltwater intrusion into freshwater aquifers and farmland, loss of coastal wetlands, and displacement of people in low-lying areas and island nations.

Concept Check 🎯

Ocean Acidification: The "Other CO₂ Problem"

The ocean absorbs roughly a quarter of the CO₂ we emit. That's good for the atmosphere but bad for ocean chemistry:

🌡️ Climate Change

Part 6 of 7 — Solutions: Mitigation, Adaptation & Policy

🔑 The Idea: Responses fall into two big buckets. Mitigation reduces the cause (cut greenhouse-gas emissions or remove gases from the air). Adaptation reduces the harm from changes already underway. We need both.

Mitigation vs. Adaptation

💡 Quick test: If an action lowers emissions or pulls CO₂ out of the air, it's mitigation. If it helps people/ecosystems cope with warming that's already locked in, it's adaptation. Building a sea wall doesn't reduce CO₂ — it's adaptation. Switching a grid to solar is mitigation.

🌡️ Climate Change

Part 7 of 7 — Synthesis, Mixed Practice & Exit Quiz

You now understand the full arc: the energy balance and natural greenhouse effect (Part 1), the gases and their potency (Part 2), the evidence and carbon cycle (Part 3), feedbacks and tipping points (Part 4), impacts (Part 5), and solutions (Part 6). Let's tie it together and confirm mastery.

Quick Reference