What causes climate change?

What causes climate change?

Menu: The causes

(Image: Joseph Chan)

Would the climate be getting warmer without humans?

Summary

  • In the 4.54 billion years since Earth formed, natural climate factors or forcings have changed Earth’s climate many times.
  • Today, when all natural forcings are added together, Earth should be cooling. Instead, we’re warming rapidly (Figs. 1 & 2).
  • We know from fundamental laws of physics that greenhouse gasses trap heat in the atmosphere. We know we’re emitting lots of them (Video 2) and that’s changing the chemistry of the atmosphere and making it warmer. 
  • Any alternative opinion would need to explain not only why global temperatures are rising instead of falling (Figs. 1 & 2), but also why the laws of physics and chemistry have stopped working.
  • The good news is that we can use nature to store excess greenhouse gasses in the ground, so we we can limit the impacts.

Maybe the weather is a little erratic, but that’s happened before, right? The truth is, we’ve just enjoyed ~11,000 years of a pretty good climate. The last 4,500 years or so has been particularly pleasant, and that’s allowed us to build a global civilization.

We’ve had it so good for so long that it’s hard to imagine why we can’t continue.

But ironically, our modern lifestyle was fuelled by taking as much carbon out of the ground and throwing the burnt remains into the atmosphere as fast as possible, that we’ve turned the heat nob on Earth’s thermostat to ‘high’.

That and eradicating most of the natural ecosystems that once helped keep the carbon budget in balance, has thrown us into a very deep and unstable carbon ‘debt’: far too much is in the atmosphere and oceans. And every year we’re not just adding more, we’re doing it faster…in spite of Covid-19.

So here we are. Our climate is changing. Wild weather and rising sea levels are forcing us to change as well, because no matter how much we might wish otherwise, we can’t negotiate with the laws of physics and chemistry. Ignoringor worse denyingthe problem is like jumping off a tall building (without a parachute) and denying gravity.

Fig. 1: This composite graph from Carbon Brief shows that an increase in temperature from greenhouses gases (red line) matches the warming we’ve observed (light grey line). Each of the natural and anthropogenic cooling and warming ‘forcings’ are explained in WHAT CAUSES CLIMATE CHANGE (menu at the top left).
Fig. 2: The blue line shows that with all the natural climate forcings combined, the planet should be slightly cooling. The red line shows that human factors far outweigh this cooling, even when volcanic eruptions lead to short drops in temperature. NOTE: not all areas of the planet are warming equally. The Arctic and Antarctic are warming much faster that the tropics. (Image: Carbon Brief)

No time to explore the website?  This short video answers common questions.

Explainers

Climate over the past 11,000 years:

The Holcene Epochthe geological epoch we are now living inbegan at the end of the Pleistocene Glacial Epoch ~11,650 years ago. By ~11,000 years ago the wild swings in climate that began when the glaciers started to retreat ~20,000 years ago, had settled down. There ere a few climate blips along the way, but the last 4,500 or so years have been particularly stable. The coastline along Pegasus Bay off Christchurch, for example, began to accumulate sand and grow out into the bay, evidence that sea levels were stable.

The so-called ‘Little Ice Age‘ and ‘Mediaeval Warm Period‘ were even briefer climate blips that didn’t last long (geologically speaking). The first was triggered by volcanic eruptions and was largely felt in the Northern Hemisphere. Climate proxy records show that it didn’t have the same impact across the globe.


Loss of natural ecosystems:

“Nature across most of the globe has now been significantly altered by multiple human drivers, with the great majority of indicators of ecosystems and biodiversity showing rapid decline. Seventy-five per cent of the land surface is significantly altered, 66 per cent of the ocean area is experiencing increasing cumulative impacts, and over 85 per cent of wetlands (area) has been lost.”                          Diaz et al, 2019 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services


Laws of chemisty:

Professor Richard Alley explains how the chemistry of the atmosphere clearly points to humans burning fossils fuels.

Forcing:

The term ‘climate forcing’ comes from ‘radiative forcing’ or RF, which is the difference between the amount of solar energy reaching Earth’s atmosphere and the amount that escapes. If more solar energy escapes than arrives, the planet cools. Conversely, if less energy escapes than gets in, the planet warms.

Click here to learn about the main forcings and how they work (links to a page on this site).


Laws of Physics:

RF is due to the Law of Conservation of Energy, a basic law of thermodynamics, which states that: ‘Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.’

The Stefan-Boltzmann Law explains how natural greenhouse gasses (natural forcings) keeps the Earth’s surface ~33°C warmer than it would be without them.

Different climate forcings each determine how much solar energy arrives and escapes.

  • Natural Forcings are those that happen through natural changes.
  • Anthropogenic Forcings are those due to human activities.

The Clausius-Clapeyron Equation describes a discontinuous phase transition between the different states (gas, liquid, solid) of water.

References and further reading