Climate science essentials

Learn the basic science of climate change in 24 easy steps.

Video source: It's Okay To Be Smart / YouTube.

View Transcriptarrow

Let’s not beat around the rapidly melting iceberg here. Climate change is happening, and we are causing it. The evidence is overwhelming.

Scientists usually reserve this level of agreement for claims like, ‘Earth is a planet’ or, ‘Air is real’. Yet here we are. The climate-change ship has now left the dock, yet lots of people on shore are still debating whether boats can actually float. But maybe you’re a person who trusts and accept what climate scientists are telling us. It’s just … sometimes it’s hard to explain why. I mean, we’ve all been there.

[AT A PARTY] ‘I mean, I care about the environment. I figure with the polar bears and everything, we might as well try electric cars. What do we have to lose?’

And then they go CAPS LOCK SERIOUS saying they have proof that climate change is a hoax perpetuated by scientists paid off by the polar-bear lobby as part of a plan to install Al Gore as supreme world polar-bear emperor. Wake up sheeple!

To keep that from happening, we’ve put together this handy reference.

The science of climate change in 24 easy steps

#1: The sun is the source of warmth on Earth, so … thanks for that, sun. Ice and clouds reflect some of its light away, but the rest is absorbed by land and water and re-emitted as heat. Some of that heat escapes to space, and some is held in by the atmospheric greenhouse effect. 

#2: The insulating effect of Earth’s greenhouse gases are the reason that life exists as we know it …

#3: But human activities have increased the concentration of one of them, carbon dioxide, 40 per cent since the Industrial Revolution.

#4: We know the sun’s output has varied during history but, since the 1970s, the period when global temperatures increased the fastest, temperature and solar activity have moved in opposite directions.

#5: If the sun was to blame, it would cook the upper and lower layers of the atmosphere together. Instead we only see warming in the lower layers, the same place that human greenhouse gases, like carbon dioxide, are piling up. 

#6: Since 1870, with fossil fuels, cement production and land use combined, humans have put about 2,000 gigatons of CO2 into the atmosphere. That’s two million million tons, and about 40 per cent has stayed there. 

#7: Studying gases trapped in ice cores have let us see what Earth’s atmosphere was like in the past. At more than 400 parts per million, today’s carbon dioxide levels are the highest they’ve been for almost a million years. That’s before humans even existed. Totally uncharted territory for us. 

#8: More carbon dioxide in the atmosphere means average temperatures across the globe are increasing, and fast. Right now, Earth is warming about ten times faster than at the end of an ice age. 

OK, so CO2 is increasing. How do we know it’s our fault? The best evidence comes from looking at what isotopes, or different kinds of carbon, are in the atmosphere.

#9: Fossil fuels come mainly from old plants. Plants prefer to use the lighter isotope carbon-12 over the heavier carbon-13, so they contain a higher ratio of 12 to 13 than the atmosphere does. When more fossil fuels get burned, the percentage of carbon-12 in the atmosphere should go up, and that’s exactly what we see.

#10: And it’s not because of volcanic activity. Volcanoes only emit about 1 per cent as much CO2 as we do. 

#11: Normally that CO2 is balanced and exchanged between the atmosphere, plants, and animals, but eliminating carbon sinks has released centuries’ worth in just a few years.

#12: Other greenhouse gases are also increasing, like methane from farm animals and natural gas processing, or nitrous oxide from fertilisers.

#13: If we run simulations just using natural causes of climate change, they predict no change, or even cooling, in the 20th century. And that is not what’s happening.

#14: It’s still going to get colder in some places, but in the 2000s there were twice as many record highs as record lows. And each of the past three decades have been warmer than any other decade since we started measuring in 1850. 

#15: Since 1900, actual temperatures around the world have increased almost a full degree, and most of that has happened since the 1970s.

#16: Looking at data from tree rings and ice cores, the past 30 years is probably the warmest in eight centuries. Of course, not every place on Earth warms equally. 

#17: Oceans cover more than 70 per cent of Earth, and they absorb more than 90 per cent of the heat added to the planet. Naturally, that’s where we see the most extreme changes.

#18: Around the world, oceans are rising a tenth of an inch per year, and they’re up 8 inches since 1901. 

#19: This is because water expands as it warms.

#20: And when ice sheets and glaciers melt in Greenland and Antarctica, water that’s normally on frozen land gets put in the ocean.

#21: The oceans are Earth’s largest carbon sink. As more CO2 enters the atmosphere, more of it dissolves in the ocean, which makes the water more acidic. This doesn’t mean that the oceans will be made of acid, but …

#22: Animals with calcium shells are super-sensitive to pH. We’re on course for the oceans to hit pH 7.8 in 100 years, which could wipe out one third of species in the ocean.

#23: We also know that levels of summer sea ice in the Arctic have decreased 40 per cent since 1978, and they might be the lowest levels in 1,400 years.

#24: That white sea ice usually reflects the sun’s energy back into the atmosphere, but the dark ocean is soaking it up like a black shirt on a sunny day, which feeds the cycle forward.

If CO2 emissions continue on their current trends, Earth is on course to be 2.5 to 5 degrees warmer. The oceans could be up to a metre higher by the end of this century. Is that a big deal? Yeah! It’s the biggest deal. This is by far the greatest issue facing our species. The last time the Earth averaged a few degrees colder, most of North America was covered in a mile-thick sheet of ice. That many degrees warmer? We’re gonna have a bad time.

So now you’re armed with the facts. Why we know climate change is happening, and why we’re causing it. Please share this information with the people you know, then let me know: did it change any minds? Did it change your mind? Are facts enough? If not, then why do so many people continue to not believe in climate science? We’ll answer that question in our next video. Stay curious.

The enhanced greenhouse effect

Latest videos

Virtual Reef Diver

1:27
Video: Virtual Reef Diver

Sir David Attenborough: Civilisation at risk

1:17
Video: Sir David Attenborough: Civilisation at risk

Why fires burn

2:03
Video: Why fires burn