How We Know

Clear, simple evidence that shows climate change is real — and visible all around us.

How We Know

The Evidence (Explained Simply)

Climate change isn’t something you need a PhD to understand. You can see it in the world around us, and the measurements are as straightforward as checking a thermometer, taking a photo, or reading a ruler. These are the clearest, most universally understandable lines of evidence — the kind that make acceptance of the facts undeniable.

1. The planet is warming — and we’ve measured it directly

For more than 150 years, scientists around the world have taken temperature readings from land, ocean, and air. The pattern is unmistakable:

Temperatures today are much higher than they were 20, 30, or 50 years ago
The last decade was the warmest ever recorded
Every major scientific agency on Earth sees the same trend

This isn’t complicated. It’s a thermometer reading — and the thermometer keeps rising.

2. Ice is melting everywhere — and we have the photos

Satellites have been taking pictures of Earth’s ice sheets and glaciers for decades. The before-and-after images tell the story without needing a single word:

Glaciers that were massive in the 1980s are now dramatically smaller
Arctic sea ice is shrinking in both area and thickness
Greenland and Antarctica are losing ice at accelerating rates

You don’t need to interpret a graph. You can literally look at the pictures and see the change.

3. Sea levels are rising — because melting ice and warmer oceans take up more space

We measure sea level using:

Tide gauges (for over 100 years)
Satellites (for the last 30 years)

Both show the same thing:

Sea level is rising
The rate of rise is increasing
Coastal flooding is becoming more common

This is basic physics: warm water expands. Melting ice adds water. The ocean rises.

4. CO₂ levels are higher than at any time in human history

We’ve been measuring CO₂ in the atmosphere since 1958. We also know past levels from ice cores that trap ancient air. Here’s what the data shows:

CO₂ used to be about 280 ppm
Today it’s over 420 ppm
That’s a 50% increase in just 150 years
Nothing like this has happened in at least 800,000 years

And we know exactly where the extra CO₂ comes from: burning fossil fuels leaves a chemical fingerprint. This is not a guess — it’s a measurable, traceable signal.

5. Extreme weather is becoming more intense — exactly as predicted

A warmer planet doesn’t just get hotter. It gets more unstable. We’re seeing:

Stronger, longer heat waves
More intense rainfall and flooding
More severe droughts
Bigger wildfires
Stronger hurricanes in some regions

Weather has always varied — but the pattern of extremes matches exactly what physics predicts when the planet warms. This is not random. It’s the climate system responding to added heat.

6. Nature is shifting in ways that match a warming world

Plants, animals, and ecosystems are reacting in real time:

Spring arrives earlier
Growing seasons are longer
Species are moving north or uphill
Coral reefs are bleaching
Forests are stressed by heat and drought

Nature is telling the same story as the thermometers, satellites, and sea-level gauges. Everything points in the same direction.

Why this evidence matters

This page isn’t about politics. It’s not about ideology. It’s not about belief. It’s about observable reality — the kind anyone can understand:

A thermometer
A photograph
A ruler
A simple chemical measurement

When all of these independent lines of evidence point to the same conclusion, the picture becomes undeniable:

The planet is warming. We are the cause. And we can still choose what happens next.

Glossary of Helpful Terms

These simple definitions support the evidence above and make the science easier to understand.

ppm (parts per million)
A way to measure how much of a gas (like CO₂) is in the air. Example: 420 ppm means 420 molecules of CO₂ out of every million air molecules.
CO₂ (carbon dioxide)
A heat‑trapping gas released by burning coal, oil, and gas. It’s the main driver of today’s climate change.
Ice core
A long cylinder of ice drilled from glaciers or ice sheets. Tiny bubbles inside trap ancient air, letting scientists measure past CO₂ levels.
Baseline
The starting point scientists use to compare temperatures over time. It helps show how much warmer the planet is today.
Temperature anomaly
How much warmer or cooler something is compared to the baseline. It’s a clearer way to track long‑term warming.
Sea‑level rise
The increase in the height of the ocean caused by melting ice and expanding warm water.
Tide gauge
A device that measures sea level at the coast. We’ve used them for more than 100 years.
Satellite record
Measurements collected from space over time — like ice loss, sea level, and temperature.
Greenhouse gas
A gas that traps heat in the atmosphere, such as CO₂, methane, and water vapor.
Feedback loop
A change that reinforces itself. Example: warming melts ice → less ice reflects sunlight → more warming.
Coral bleaching
When ocean heat stresses corals, causing them to lose their color and weaken.
Ecosystem shift
When plants and animals move or change behavior because their environment is warming.
Extreme weather
Unusually intense events like heat waves, heavy rainfall, droughts, or wildfires.