Would the climate be warming without humans?
Image: Joseph Chan
Causes
- A brief history of climate change: who knew what, when
- What causes climate change?
- Would the climate be warming without humans?
- Is it just a cycle? (Earth’s wobbly orbit)
- Sunspots & solar activity
- Land use: agriculture & cities
- Volcanoes
- Ocean currents
- Black carbon & ash
- Blue hydrogen
- Greenhouse gases & how they work
- – Carbon dioxide & the carbon cycle
- – Methane (biogenic & ‘natural’ gas)
- – Nitrous oxide
- – Clouds & water vapour
- – Ozone
- – Man-made industrial chemicals
- – Aerosol pollution
- How to start an Ice Age!
- What’s in a name?
Other sections
Home > Climate wiki > What causes climate change? > Humans
Would the climate be warming without humans?
Summary
In the 4.54 billion years since Earth formed, natural climate factors or forcings have changed Earth’s climate, making it warmer or cooler many times, for different reasons outlined in the menu on this page.
The nice weather we’ve had for the last 4,500 years allowed us to build a global civilization. Ironically, burning fossil fuels and eradicating natural ecosystems that helped keep the carbon cycle in balance, has dangerously destabilised the climate. Today, when all of the 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 gases trap heat in the atmosphere, and why that changes the chemistry of the atmosphere, making it warmer. We also know we humans are emitting lots of these greenhouse gases (Video 2). No matter how much we might wish otherwise, there is no negotiating with the laws of physics and chemistry: we humans are entirely responsible for turning the heat nob on Earth’s thermostat to ‘high’.
Any opinion to the contrary would need to explain why global temperatures are rising instead of falling, and explain why fundamental laws of physics and chemistry have stopped working. The good news is that we can use nature to capture and store excess greenhouse gases back in the ground, so we can limit the impacts.
Causes
- A brief history of climate change: who knew what, when
- What causes climate change?
- Would the climate be warming without humans?
- Is it just a cycle? (Earth’s wobbly orbit)
- Sunspots & solar activity
- Land use: agriculture & cities
- Volcanoes
- Ocean currents
- Black carbon & ash
- Blue hydrogen
- Greenhouse gases & how they work
- – Carbon dioxide & the carbon cycle
- – Methane (biogenic & ‘natural’ gas)
- – Nitrous oxide
- – Clouds & water vapour
- – Ozone
- – Man-made industrial chemicals
- – Aerosol pollution
- How to start an Ice Age!
- What’s in a name?
Other sections
Home > Climate wiki > What causes climate change? > Humans
Summary
In the 4.54 billion years since Earth formed, natural climate factors or forcings have changed Earth’s climate, making it warmer or cooler many times, for different reasons outlined in the menu on this page.
The nice weather we’ve had for the last 4,500 years allowed us to build a global civilization. Ironically, burning fossil fuels and eradicating natural ecosystems that helped keep the carbon cycle in balance, has dangerously destabilised the climate. Today, when all of the 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 gases trap heat in the atmosphere, and why that changes the chemistry of the atmosphere, making it warmer. We also know we humans are emitting lots of these greenhouse gases (Video 2). No matter how much we might wish otherwise, there is no negotiating with the laws of physics and chemistry: we humans are entirely responsible for turning the heat nob on Earth’s thermostat to ‘high’.
Any opinion to the contrary would need to explain why global temperatures are rising instead of falling, and explain why fundamental laws of physics and chemistry have stopped working.
The good news is that we can use nature to capture and store excess greenhouse gases back in the ground, so we can limit the impacts.
More information
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Physicist and science educator Dr. Derek Muller explains the most common misconceptions about climate change:
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The Holcene Epoch—the geological epoch we are now living in—began at the end of the Pleistocene Glacial Epoch ~11,650 years ago after most of the glaciers and ice sheets had melted.
There were a few climate blips for the next 7,000 years, but from about 4,500 or so years ago until recently, the global climate was particularly stable. This was a period when agriculture became well-established and civilisation spread out across the globe.The amount of greenhouse gases in the atmosphere very slowly crept up because of agriculture, but the uneven orbit of the Earth around the sun was very very slowly leading is back into another Glacial Epoch. So, on balance, the global average temperature remained fairly constant.The so-called ‘Little Ice Age‘ and ‘Mediaeval Warm Period‘ were tiny 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.
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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).
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Radiative Forcing or 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) keep the Earth’s surface ~33°C warmer than it would be without them. Without them, we would be a frozen snowball. So, we do need greenhouse gases, but the balance needs to be just right.
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.
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In the following video, Professor Richard Alley explains how the chemistry of the atmosphere clearly points to humans burning fossils fuels.
Grass cuttings from around New Zealand are used to measure the proportion of carbon isotopes in New Zealand: Grass and the science of CO2 Radio NZ Podcast.
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“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
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- 2022: IPCC Sixth Assessment Report; Climate Change 2022: Impacts, Adaptation and Vulnerability
- 2021: IPCC Sixth Assessment Report; Climate Change 2021: The Physical Science
- 2021: UNEP; Emission Gap Report 2021
- New Zealand Climate Change Commission
- It’s time, Canterbury – our climate change conversation
- Carbon Brief Explainer: How the rise and fall of CO2 levels influenced the ice ages
- Carbon Brief: Why scientists think 100% of global warming is due to humans
- Carbon update: Global Action Tracker
- Science Direct: The Law of Conservation of Energy
- NOAA: Climate forcing
- NOAA: Ocean heat uptake
- IPPC: Chapter 8: Anthropogenic and Natural Radiative Forcing in: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
- NCIDSC (National Snow and Ice Data Centre): Climate change in the Arctic
- 2019: Diaz et al; Summary for policymakers of the global assessment report on biodiversity and ecosystem services, Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services.
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- 2022: IPCC Sixth Assessment Report; Climate Change 2022: Impacts, Adaptation and Vulnerability
- 2021: IPCC Sixth Assessment Report; Climate Change 2021: The Physical Science
- New Zealand Climate Change Commission
- It’s time, Canterbury – our climate change conversation
- Carbon Brief Explainer: How the rise and fall of CO2 levels influenced the ice ages
- Carbon Brief: Why scientists think 100% of global warming is due to humans
- Carbon update: Global Action Tracker
- Science Direct: The Law of Conservation of Energy
- NOAA: Climate forcing
- NOAA: Ocean heat uptake
- IPPC: Chapter 8: Anthropogenic and Natural Radiative Forcing in: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
- NCIDSC (National Snow and Ice Data Centre): Climate change in the Arctic
- 2019: Diaz et al; Summary for policymakers of the global assessment report on biodiversity and ecosystem services, Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services.