What if there were more greenhouse gases?

Greenhouse gases are like a blanket around Earth. They keep it warm.

What if we added more? Would Earth get warmer?

A natural amount of greenhouse gas keeps Earth about 33 degrees warmer than it would otherwise be. That is a good thing: without it, the planet would be frozen.

But people have been adding more of these gases to the air, mostly by burning coal, oil and gas. So what happens when the heat blanket gets a little thicker? In this lab you can make it harder for heat to escape in a simple model and watch what the planet's temperature does.

Greenhouse gases reduce the infrared that escapes to space at a given surface temperature. Adding more creates an imbalance: less heat leaves than sunlight brings in, so the planet gains energy until its temperature rises enough to restore balance.

This lab represents that with an effective emissivity, a teaching parameter, not a quantity derived from gas concentrations. How much warmer is the new balance, and how fast does the model get there?

Today, sunshine comes in and heat goes out. They balance.

That keeps Earth at about the same warmth from year to year.

Earth stays at a fairly steady temperature when the heat leaving it matches the sunlight it soaks up. In the model, that balance today is about 15 °C on average.

But the real air has been changing. NOAA measured a global average of 422.8 parts per million of carbon dioxide in 2024, about 50 percent more than before the Industrial Revolution. And NOAA reports that 2024 was the warmest year since global records began in 1850.

The model's baseline absorbs 238.2 W/m² and balances at 287.8 K with ε = 0.612. In the real climate, NOAA reports global mean CO₂ of 422.8 ppm in 2024, 50 percent above pre-industrial, and a 2024 global surface temperature about 1.46 °C above the 1850–1900 average, the warmest since records began in 1850.

The IPCC's Sixth Assessment Report (Working Group I, Summary for Policymakers, 2021) puts 2011–2020 at 1.09 °C warmer than 1850–1900.

In our pretend lab, Olly makes heat escape a little less easily.

Earth slowly gets warmer. Then it stops, at a new, warmer balance.

Lower 'how freely heat escapes' from 0.612 to 0.59, a small change that stands for adding greenhouse gases. Now a little less heat gets out than sunlight brings in, so the planet warms.

In the model Earth settles about 2.6 °C warmer, at about 17 °C on average. It doesn't jump there at once: the oceans soak up heat, so after 5 years it is about 16.9 °C and it creeps closer over the next years.

With ε = 0.59 the balance temperature is 290.5 K (17.3 °C), 2.6 K above baseline; the greenhouse warming readout rises from 33.3 to 35.9 K. Stepping from 288 K, the model reaches 16.2 °C at 2.5 years, 16.9 °C at 5 and 17.25 °C at 10, an e-folding time of about 2.8 years.

The size of the emissivity step is arbitrary: the model does not say how many ppm of CO₂ it represents. It is a picture of how a planet responds, not a calculation of Earth's future.

A thicker blanket keeps more warmth in.

The Earth has to get warmer before enough heat can escape again.

Greenhouse gases catch some of the heat Earth sends out. Add more, and less heat escapes. Now more energy is coming in than going out, so Earth warms up.

A warmer planet glows heat out more strongly, so eventually it sends out enough to match the sunlight again. That new balance is warmer than before. The ocean is the planet's giant heat store, which is why the warming takes time.

At balance S(1 − α)/4 = εσT⁴, so T ∝ ε^(−¼): (0.612/0.59)^¼ ≈ 1.0092, and 1.0092 × 287.8 K ≈ 290.5 K. The response time C/(4εσT³) is set by the 70 m mixed layer.

The model's limits: one global temperature, fixed albedo, no water-vapor, ice or cloud feedbacks, and no deep ocean, whose real response lasts centuries. The IPCC finds that ocean warming took up 91 percent of the extra heat in the climate system from 1971 to 2018, much of it below the mixed layer.

Scientists measure the air and the oceans all the time.

Many people are working on cleaner ways to make electricity and to travel. Caring for forests helps too, because trees store carbon.

Scientists watch the climate closely, with satellites, buoys and ocean robots. NASA explains that the extra greenhouse gases come mainly from burning fossil fuels, and the IPCC finds the planet was about 1.1 °C warmer in 2011–2020 than in 1850–1900.

NASA describes two kinds of response. Mitigation means adding fewer greenhouse gases, for example by making electricity, heat and transport cleaner, or helping forests, soils and oceans store more carbon. Adaptation means preparing for changes already happening. People around the world are working on both.

NASA frames responses as mitigation, reducing greenhouse gas sources such as fossil fuel use for electricity, heat and transport, or enhancing sinks such as oceans, forests and soil, and adaptation, reducing risks from changes such as sea-level rise and more intense extremes.

The IPCC (AR6 WG1 SPM, statement B.1, 2021) assesses that global warming of 1.5 °C and 2 °C will be exceeded during the 21st century unless deep reductions in CO₂ and other greenhouse gas emissions occur in the coming decades.